formation mechanism of polycyclic aromatic hydrocarbons and fullerenes in premixed benzene flames

Formation Mechanism of Polycyclic Aromatic Hydrocarbonsand Fullerenes in Premixed Benzene Flames

HENNING RICHTER, WILLIAM J. GRIECO, and JACK B. HOWARD*Department of Chemical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue,

Cambridge, MA 02139-4307, USA

A better understanding of the formation of polycyclic aromatic hydrocarbons (PAH) and fullerenes is ofpractical interest due to the apparent environmental health effects of many PAH and potential industrialapplications of fullerenes. In the present work, a kinetic model describing the growth of PAH up to coronene(C24H12) and of C60 and C70 fullerenes is developed. Comparison of the model predictions with concentrationprofiles in a nearly sooting low-pressure premixed, laminar, one-dimensional benzene/oxygen/argon flame(equivalence ratio f 5 1.8, pressure 5 2.67 kPa) measured by Bittner using a molecular beam system coupledto mass spectrometry shows reasonably good predictive capability for stable and radical intermediates and growthspecies up to C16H10 isomers. Cyclopentadienyl is found to be a key species for naphthalene formation. The furthergrowth process is based on H abstraction and acetylene addition but also the contribution of small PAH isconsidered. Good to fair agreement between model predictions and experimental data for larger PAH including thedifferent C16H10 isomers obtained by gas chromatography coupled to mass spectrometry and high performanceliquid chromatography could be achieved for PAH in a sooting low-pressure premixed, laminar, one-dimensionalbenzene/oxygen/argon flame (f 5 2.4, 5.33 kPa). C60 and C70 fullerenes are underpredicted, and possible reasonssuch as uncertainties in rate coefficients or the existence of other formation pathways are discussed. PAHdepletion in the burnt gas is not reproduced by the model and is believed to involve supplementary sinks suchas reactions involving PAH and growing soot particles. © 1999 by The Combustion Institute

NOMENCLATURE

Abbreviations Used in the Mechanism

C10H7S secondary naphthyl (1-naphthyl)

C10H7O 1-naphthoxy, 2-naphthoxyC10H7P primary naphthyl (2-naphthyl)C7H7 benzylC10H7OH 1-naphthol, 2-naphtholC10H7CH3 methylnaphthaleneC10H8 naphthaleneA2R5 acenaphthaleneA2R5CH3 methylacenaphthaleneC12H10 biphenylA3 phenanthreneA2YNEP primary naphthylacetylene (2-

naphthylacetylene)A2YNEP*S secondary A2YNEP radical

(H-abstraction at the position2 of naphthalene)

A3S*1 1-, 8-, 9- and 10-phenanthrylA2YNEP*P primary A2YNEP radical (H-

abstraction at the position 3 ofnaphthalene)

A3L anthraceneA3L*S secondary anthracylA3L*P primary anthracylA3LYNE anthracylacetyleneA3LYNE*P primary anthracylacetylene

radicalA4L benz[a]anthraceneA4L*S secondary benz[a]anthracylA3*P primary phenanthrylA3YNE phenanthrylacetyleneA3YNE*S secondary

phenanthrylacetylene radicalCHRYSEN chryseneCHRYSEN*S secondary chrysene radicalC6H6 benzeneC7H7 benzyl (C6H5CH2)BENZYLB benzylbenzeneC6H5 phenylFLUORENE fluoreneBENZNAP benzylnaphthaleneBENZNAP*P primary benzylnaphthalene

radicalC17H12 benzo[a]fluoreneFLTHN fluorantheneACEPHA acephenanthryleneFLTHN2 fluoranthene radical

(fluoranthyl)*Corresponding author: E-mail: [email protected]

COMBUSTION AND FLAME 119:1–22 (1999)© 1999 by The Combustion Institute 0010-2180/99/$–see front matterPublished by Elsevier Science Inc. PII S0010-2180(99)00032-2

FLTHNCH3 methylfluorantheneBKFLUOR benzo[k]fluorantheneA3*S2 4- and 5-phenanthrylA3CH3 methylphenanthreneA3CH2R cyclopenta[def]phenanthrenePYRENE*P primary pyrene radicalPYRENECH3 methylpyrenePYRENE*S1 4- and 9-pyrenylPYRENE*S2 5- and 10-pyrenylBBFLUOR benzo[b]fluoranthenePYRYNEP primary pyrenylacetylenePYRYNEP*S secondary radical of primary

pyrenylacetyleneBAPYR benzo[a]pyreneBAPYR*S secondary benzo[a]pyrenylANTHAN anthanthraceneANTHAN*S secondary anthanthracylCPCDPYR cyclopenta[cd]pyreneCPCDPYR*S secondary

cyclopenta[cd]pyrenylDCPP dicylcopenta[cd]pyrene (all

isomers)PYRYNE secondary pyrenylacetylenePYRYNE*S secondary radical of PYRYNEBEPYREN benzo[e]pyreneBEPYREN*S secondary benzo[e]pyrenylINPYR indeno[1,2,3cd]pyreneBGHIPER benzo[ghi]peryleneBGHIPE*S1 1-, 2-, 3-, 8-, 9-, 10-, 11- and

12-benzo[ghi]perylenylCPBPER cylcopentabenzo[ghi]perylene

(all isomers)BGHIPE*S2 5- and 6-benzo[ghi]perylenylCORONEN coroneneFLTHNC2H fluoranthylacetylene (all

isomers)BGHIF benzo[ghi]fluorantheneBGHIF2 benzo[ghi]fluoranthylBGHIFCH3 methylbenzo[ghi]fluoranthene

(all isomers)BGHIFC2H benzo[ghi]fluoranthylacetylene

(all isomers)FLTHNR cyclopenta[cd]fluorantheneFLTHNR*S secondary

cyclopenta[cd]fluoranthylBGHIFR cyclopenta[cd]benzo[ghi]

fluorantheneCOR corannuleneCORCH3 methylcorannulene (all

isomers)

BGHIFR*S secondary cyclopenta[cd]benzo[ghi]fluoranthyl

COR2 corannulene radicalCOR1 cylcopenta[cd]corannuleneC5H5 cyclopentadienylC8H6 phenylacetyleneA1YNE* phenylacetylene radical (H-

abstraction at phenyl)

Intermediates leading to C60 and C70: see Popeet al. [40]

INTRODUCTION

The investigation of the chemical mechanism ofparticle growth in flames is motivated by agrowing body of data revealing health effects ofcombustion generated compounds and parti-cles. Many of the polycyclic aromatic hydrocar-bons (PAH) found to be mutagenic or tumori-genic [1–6] are present in atmospheric aerosols[7]. An association between air pollution andmortality was found in a study conducted in sixU.S. cities [8]. The development of reactionmechanisms for complex combustion systemsusually involves the comparison of experimentaldata such as concentration profiles with modelpredictions using an initial reaction networkwhich can then be improved based on observeddeficiencies. After the investigation of simplesystems such as H2/O2 or H2/F2 [9] the increaseof both computational power and experimentaldata allowed the description of larger and largersystems [10].

Data suitable for testing chemical modelspertinent to PAH formation in flames are avail-able from measurements in a nearly sootingpremixed low-pressure benzene flame using mo-lecular beam sampling coupled to mass spec-trometry (MBMS) [11]. The data consist ofprofiles of temperature and concentration ofstable species up to 202 amu and radicals up to91 amu. The data on radicals have been ex-tended to 201 amu species using nozzle beamsampling followed by radical scavenging andsubsequent analysis by gas chromatography cou-pled to mass spectrometry (GC-MS) [12, 13].Concentration profiles for stable species up tocoronene (C24H12) in premixed propane, acety-

2 H. RICHTER ET AL.

lene, and benzene flames at reduced pressure[14], and up to pyrene (C16H10) in premixedmethane, ethane, and propane flames at atmo-spheric pressure [15] were obtained by probesampling and GC-MS. PAH concentrationshave been measured also for the high-tempera-ture pyrolysis of toluene in shock tubes [16].Global soot yields in shock tubes were deter-mined under oxidative [17] and nonoxidativeconditions [18–20] following the pioneeringwork of Graham et al. [21] who studied sootformation investigating the pyrolysis of a largerange of aromatic but also nonaromatic species.Detailed kinetic models for PAH formationhave been developed, first for the growth offused-ring species in acetylene pyrolysis [22] andlater for growth up to benzo[ghi]fluorantheneand cyclopenta[cd]pyrene (C18H10) in premixedflames of methane [23], ethane [23], acetylene[24], and ethylene [24, 25], as well as up topyrene in toluene pyrolysis [16].

The formation of fullerenes in flames also in-volves PAH intermediates and therefore is an-other source of interest in PAH formation.Fullerenes are a new form of carbon with consid-erable potential for industrial applications.Charged fullerenes were observed in premixedlow-pressure acetylene and benzene flames [26,27] and macroscopic quantities of C60 and C70were isolated from flame-generated condensablematerial [28–32]. Also other fullerene-relatedmolecules such as oxygen- and hydrogen-con-taining compounds [33, 34] and fullerenic nano-structures [35–37] have been identified in flamesamples. Fullerene formation mechanismshave been discussed qualitatively [27, 38, 39]and a kinetic model for C60 and C70 has beentested in a simplified system [40, 41].

The objective of the present work is to extendand assess the modeling of PAH and fullereneformation. To that end a network of chemicalreactions describing the formation of PAH upto coronene (C24H12) and of C60 and C70fullerenes was developed and critically testedagainst experimental flame data [11, 42].

APPROACH

The growth of PAH and fullerenes being themain focus of the present work, the developed

mechanism was applied to a sooting low-pres-sure premixed, laminar, one-dimensional ben-zene/oxygen/argon flame (equivalence ratio f 52.4, 10% argon, gas velocity at burner at 298K 5 25 cm s21, pressure 5 5.33 kPa) firststudied by McKinnon [43] and known to pro-duce substantial yields of fullerenes [29, 31].Soot volume fractions, the temperature profileand mole fraction profiles for H2, O2, CO, CO2,CH4, H2O, Ar, C2H2, and C6H6 measured bymass spectrometry are reported for this flame[43]. Recently, concentration profiles for PAHup to ovalene (C32H14) and fullerenes in thisflame were measured by Grieco [42] usingGC-MS and high-performance liquid chroma-tography (HPLC) analysis of flame samples. Inthe following text, this flame will be calledFlame I. In order to ensure the correct descrip-tion of the flame propagation chemistry and ofthe first growth steps, the model was also testedagainst MBMS data of Bittner and Howard [11]from a nearly sooting low-pressure premixed,laminar, one-dimensional benzene/oxygen/ar-gon flame (f 5 1.8, 30% argon, 50 cm s21, 2.67kPa), here called Flame II. Modeling the growthof higher PAH requires reasonably good pre-dictions for smaller intermediates and for keyradical species such as H and OH. Such capa-bility was achieved as shown in Figs. 1a and 1bby model predictions for H, OH, C5H5, phenyl,acetylene, and phenylacetylene in Flame IIcompared to experimental data. Experimentaldata [43] and predictions obtained for H2, H2O,C2H2, and CO in Flame I are shown in Fig. 2.The successful testing of the model for smallerstable and radical species is essential for theconfident application of the model to largerspecies and the assessment of potential errorsand uncertainties.

Kinetic models describing the high-tempera-ture oxidation or combustion of aromatic com-pounds include the model of Emdee et al. [44]for toluene which was tested against flow reac-tor data and the models of Lindstedt and Skevis[45] and Zhang and McKinnon [46] for benzenewhich were tested against Bittner’s Flame IIdata [11]. The present development began withthe benzene destruction chemistry of Zhangand McKinnon [46] with improvements byShandross et al. [47]. Rate coefficients werechosen after a careful check of the literature

3FORMATION OF PAH AND FULLERENES

and experimental data measured at high tem-perature were used whenever available. Twotypes of reactions, H abstraction from aromaticspecies and acetylene addition to their radicalsare crucial for PAH growth as was found in theearly computer modeling of this process byFrenklach et al. [22], and has been widelysupported in many subsequent studies. Pub-lished experimentally determined rate coeffi-cient expressions for H abstraction from ben-zene [48, 49] and acetylene addition to phenyl[50] were used without modification. No unam-biguous trend in the reactivity of PAH andPAH-radicals with an increasing number ofrings was seen in the few available studies[51–53], so the rate coefficients were approxi-mated as being independent of molecular

weight over the whole growth process. Thecomputations were performed with PREMIX[54] using experimental temperature profilesshown in Fig. 1b [11] and 2 [43]. The uncertaintyof the temperature measurements is estimatedto be 650 K. Thermochemical and transportparameters were taken from the literature forbenzene destruction [47] and fullerene growth[55] or were calculated using group additivity[56]. All reactions are treated as reversible.

The PAH and fullerene growth model devel-oped in this work and the testing of the modelagainst experimental results are described be-low. Some aspects of the benzene destructionchemistry important for the growth process arediscussed briefly. A complete listing of thereactions including the rate coefficients startingwith naphthalene formation and some minorchanges relative to the Shandross mechanism[47] are given in Table 1. Abbreviations used forcertain species are given in the text in bracketstogether with the molecular formula and thespecies name. The nomenclature of radicalsfollows a convention different from that nor-mally used in organic chemistry and distin-guishes between primary and secondary radi-cals, e.g., 1-naphthyl, a secondary radical, iscalled C10H7S while 2-naphthyl, the corre-sponding primary radical, is designatedC10H7P. An example for a tertiary radical—notused in the present model—is 9-anthryl, ob-

Fig. 1. (a) Comparison between experimental mole fractionprofiles [11] and model predictions in a nearly sootingbenzene/oxygen flame (f 5 1.8, 30% argon, v258C 5 50 cms21, 2.67 kPa); Flame II. H: F (experiment, left scale),(prediction, left scale). OH: } (experiment, left scale), ----(prediction, left scale). C5H5: ■ (experiment, right scale), zzzz

(prediction, right scale). (b) Comparison between experi-mental mole fraction profiles [11] and model predictions ina nearly sooting benzene/oxygen flame (f 5 1.8, 30% argon,v258C 5 50 cm s21, 2.67 kPa); Flame II. Temperature:(experimental). C6H5: F (experiment, left scale), (pre-diction, left scale). C2H2: } (experiment, right scale), ----(prediction, right scale). Phenylacetylene: ■ (experiment,left scale), zzzz (prediction, left scale).

Fig. 2. Comparison between experimental mole fractionprofiles [43] and model predictions in a sooting premixedbenzene/oxygen flame (f 5 2.4, 10% argon, v258C 5 25 cms21, 5.33 kPa); Flame I. Temperature: (experimental).H2: F (experiment, left scale), (prediction, left scale).H2O: } (experiment, left scale), ---- (prediction, left scale).C2H2: ■ (experiment, left scale), zzzz (prediction, left scale).CO: Œ (experiment, right scale), z-z-z (prediction, rightscale).

4 H. RICHTER ET AL.

TABLE 1.

Growth Process of PAH and Fullerenes

k 5 ATn exp (2Ea/RT) A: cm3 mole21 s21 Ea: cal A n Ea Ref.

Formation of indene1. C10H7S 1 O2 5 C10H7O 1 O 1.00E13 0.0 0.0 Marinov et al. [23]2. C10H7S 1 OH 5 C10H7O 1 H 5.00E13 0.0 0.0 "3. C10H7P 1 O2 5 C10H7O 1 O 1.00E13 0.0 0.0 "4. C10H7P 1 OH 5 C10H7O 1 H 5.00E13 0.0 0.0 "5. C10H7O 5 INDENYL 1 CO 7.40E11 0.0 43850.0 "6. INDENE 1 H 5 INDENYL 1 H2 2.19E08 1.77 3000.0 "7. INDENE 1 OH 5 INDENYL 1 H2O 3.43E09 1.18 2447.0 "8. INDENE 1 O 5 INDENYL 1 OH 1.81E13 0.0 3080.0 "9. INDENYL 1 H 5 INDENE 2.00E14 0.0 0.0 "

10. C7H7 1 C2H2 5 INDENE 1 H 3.20E11 0.0 7000.0 "Formation of naphthol

11. C10H7O 1 H 5 C10H7OH 2.53E14 0.0 0.0 Baulch et al. [58]12. C10H7OH 1 H 5 C10H7O 1 H2 1.15E14 0.0 12400.0 "13. C10H7OH 1 H 5 C10H8 1 OH 2.23E13 0.0 7929.0 "14. C10H7OH 1 OH 5 C10H7O 1 H2O 6.00E12 0.0 0.0 He et al. [59]

Formation of methylnaphthalene15. C10H7S 1 CH3 5 C10H7CH2 1 H 5.00E13 0.0 0.0 Marinov et al. [23]16. C10H7P 1 CH3 5 C10H7CH2 1 H 5.00E13 0.0 0.0 "17. C10H7CH2 1 H 5 C10H7CH3 1.00E14 0.0 0.0 "18. C10H7CH3 1 H 5 C10H8 1 CH3 1.20E13 0.0 5148.0 "

Formation of acenaphthalene19. C10H7S 1 C2H2 5 A2R5 1 H 3.98E13 0.0 10100.0 Fahr and Stein [50]

Formation of methylacenaphthalene20. A2R5 1 H 5 A2R5*S 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]21. A2R5 1 OH 5 A2R5*S 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]22. A2R5*S 1 CH3 5 A2R5CH2 1 H 5.00E13 0.0 0.0 Rxn. 16.23. A2R5CH2 1 H 5 A2R5CH3 1.00E14 0.0 0.0 Rxn. 17.24. A2R5CH3 1 H 5 A2R5 1 CH3 1.20E13 0.0 5148.0 Rxn. 18.

Formation of phenanthrene25. C12H10 1 H 5 C12H9 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]26. C12H10 1 OH 5 C12H9 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]27. C12H9 1 C2H2 5 A3 1 H 3.98E13 0.0 10100.0 Fahr and Stein [50]28. A2YNEP 1 H 5 A2YNEP*S 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]29. A2YNEP 1 OH 5 A2YNEP*S 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]30. A2YNEP*S 1 C2H2 5 A3*S1 3.98E13 0.0 10100.0 Fahr and Stein [50]31. A3*S1 1 H 5 A3 5.00E13 0.0 0.0 estimate, this work

Formation of anthracene32. C10H7P 1 C2H2 5 A2YNEP 1 H 3.98E13 0.0 10100.0 Fahr and Stein [50]33. A2YNEP 1 H 5 A2YNEP*P 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]34. A2YNEP 1 OH 5 A2YNEP*P 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]35. A2YNEP*P 1 C2H2 5 A3L*S 3.98E13 0.0 10100.0 Fahr and Stein [50]36. A3L*S 1 H 5 A3L 5.00E13 0.0 0.0 estimate, this work37. A3L 1 H 5 A3L*S 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]38. A3L 1 OH 5 A3L*S 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]39. A3L 1 H 5 A3L*P 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]40. A3L 1 OH 5 A3L*P 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]41. A3L*P 1 H 5 A3L 5.00E13 0.0 0.0 estimate, this work42. A3L 5 A3 8.00E12 0.0 65000.0 Colket and Seery [16]

Benz[a]anthracene formation43. A3L*P 1 C2H2 5 A3LYNE 1 H 3.98E13 0.0 10100.0 Fahr and Stein [50]44. A3LYNE 1 H 5 A3LYNE*P 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]45. A3LYNE 1 OH 5 A3LYNE*P 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]46. A3LYNE*P 1 C2H2 5 A4L*S 3.98E13 0.0 10100.0 Fahr and Stein [50]47. A4L*S 1 H 5 A4L 5.00E13 0.0 0.0 estimate, this work


TABLE 1

continued


Chrysene formation48. A3 1 H 5 A3*P 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]49. A3 1 OH 5 A3*P 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]50. A3*P 1 C2H2 5 A3YNE 1 H 3.98E13 0.0 10100.0 Fahr and Stein [50]51. A3YNE 1 H 5 A3YNE*S 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]52. A3YNE 1 OH 5 A3YNE*S 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]53. A3YNE*S 1 C2H2 5 CHRYSEN*S 2.50E14 0.0 16000.0 Kiefer et al. [48]54. CHRYSEN*S 1 H 5 CHRYSEN 5.00E13 0.0 0.0 estimate, this work

Formation of fluorene55. C6H6 1 C7H7 5 BENZYLB 1 H 1.20E12 0.0 15940.0 estimate based on [60]56. C6H5 1 C7H7 5 BENZYLB 2.00E22 23.045 2304.0 estimate based on [47]57. BENZYLB 1 H 5 BENZYLB* 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]58. BENZYLB 1 OH 5 BENZYLB* 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]59. BENZYLB* 5 FLUORENE 1 H 4.00E11 0.0 4000.0 Rxn. 66.

Formation of benzo[a]fluorene60. C10H8 1 C7H7 5 BENZNAP 1 H 1.20E12 0.0 15940.0 Rxn. 55.61. C10H7P 1 C7H7 5 BENZNAP 2.00E22 23.045 2304.0 Rxn. 56.62. BENZNAP 1 H 5 BENZNAP*P 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]63. BENZNAP 1 OH 5 BENZNAP*P 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]64. BENZNAP*P 5 C17H12 1 H 4.00E11 0.0 4000.0 Rxn. 59.

Formation of fluoranthene65. C10H7S 1 C6H5 5 FLTHN 1 H 1 H 5.00E12 0.0 0.0 Marinov et al. [23]66. C10H7S 1 C6H6 5 FLTHN 1 H2 1 H 4.00E11 0.0 4000.0 "67. ACEPHA 5 FLTHN 8.51E12 0.0 62860.0 Brouwer and Troe [61]

Methylation of fluoranthene68. FLTHN2 1 CH3 5 FLTHNCH2 1 H 5.00E13 0.0 0.0 Rxn. 16.69. FLTHNCH2 1 H 5 FLTHNCH3 1.00E14 0.0 0.0 Rxn. 17.70. FLTHNCH3 1 H 5 FLTHN 1 CH3 1.20E13 0.0 5148.0 Rxn. 18.

Formation of benzo[k]fluoranthene71. C10H7P 1 C10H7S 5 BKFLUOR 1 H 1 H 5.00E12 0.0 0.0 Rxn. 65.72. C10H8 1 C10H7S 5 BKFLUOR 1 H2 1 H 4.00E11 0.0 4000.0 Rxn. 66.73. C10H8 1 C10H7P 5 BKFLUOR 1 H2 1 H 4.00E11 0.0 4000.0 Rxn. 66.

Formation of cyclopenta[def]phenanthrene74. A3 1 H 5 A3*S2 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]75. A3 1 OH 5 A3*S2 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]76. A3*S2 1 CH3 5 A3CH2 1 H 5.00E13 0.0 0.0 Rxn. 16.77. A3CH2 1 H 5 A3CH3 1.00E14 0.0 0.0 Rxn. 17.78. A3CH3 1 H 5 A3CH2 1 H2 1.20E14 0.0 8235.0 estimate based on [44]79. A3CH3 1 H 5 A3 1 CH3 1.20E13 0.0 5148.0 Rxn. 18.80. A3CH3 1 OH 5 A3CH2 1 H2O 1.26E13 0.0 2583.0 estimate based on [44]81. A3CH2 5 A3CH2R 1 H 1.20E12 0.0 15940.0 estimate based on [60]

Formation of acephenanthrylene82. A3 1 H 5 A3*S1 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]83. A3 1 OH 5 A3*S1 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]84. A3*S1 1 C2H2 5 ACEPHA 1 H 3.98E13 0.0 10100.0 Fahr and Stein [50]

Formation of pyrene85. A3*S2 1 C2H2 5 PYRENE 1 H 3.98E13 0.0 10100.0 Fahr and Stein [50]

Formation of methylpyrene86. PYRENE 1 H 5 PYRENE*P 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]87. PYRENE 1 OH 5 PYRENE*P 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]88. PYRENE*P 1 CH3 5 PYRENECH2 1 H 5.00E13 0.0 0.0 Rxn. 16.89. PYRENECH2 1 H 5 PYRENECH3 1.00E14 0.0 0.0 Rxn. 17.90. PYRENECH3 1 H 5 PYRENE 1 CH3 1.20E13 0.0 5148.0 Rxn. 18.

Pyrene-oxidation91. PYRENE 1 OH 5 A3*S1 1 CH2CO 1.30E13 0.0 10600.0 Wang and Frenklach [24]92. PYRENE 1 OH 5 A3*S2 1 CH2CO 1.30E13 0.0 10600.0 "

6 H. RICHTER ET AL.

TABLE 1

continued


93. PYRENE 1 O 5 A3*S1 1 HCCO 2.20E13 0.0 4530.0 "94. PYRENE 1 O 5 A3*S2 1 HCCO 2.20E13 0.0 4530.0 "95. PYRENE*S1 1 O2 5 A3*S2 1 2CO 2.10E12 0.0 7470.0 "96. PYRENE*S2 1 O2 5 A3*S2 1 2CO 2.10E12 0.0 7470.0 "

Formation of benzo[b]fluoranthene97. A3*S1 1 C6H5 5 BBFLUOR 1 H 1 H 5.00E12 0.0 0.0 Rxn. 65.98. A3*S1 1 C6H6 5 BBFLUOR 1 H2 1 H 4.00E11 0.0 4000.0 Rxn. 66.

Formation of benzo[a]pyrene99. PYRENE*P 1 C2H2 5 PYRYNEP 1 H 3.98E13 0.0 10100.0 Fahr and Stein [50]

100. PYRYNEP 1 H 5 PYRYNEP*S 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]101. PYRYNEP 1 OH 5 PYRYNEP*S 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]102. PYRYNEP*S 1 C2H2 5 BAPYR*S 3.98E13 0.0 10100.0 Fahr and Stein [50]103. BAPYR*S 1 H 5 BAPYR 5.00E13 0.0 0.0 estimate, this work

Benzo[a]pyrene-oxidation104. BAPYR 1 OH 5 PYRYNEP 1 CH2CO 1 H 6.50E12 0.0 10600.0 Wang and Frenklach [24]105. BAPYR 1 O 5 PYRYNEP 1 CH2CO 1.10E13 0.0 4530.0 "106. BAPYR*S 1 O2 5 PYRYNEP 1 HCO 1 CO 2.10E12 0.0 7470.0 "107. PYRYNEP 1 OH 5 PYRENE*P 1 CH2CO 2.18E-4 4.5 21000.0 "108. PYRENEP 1 O 5 PYRENE*P 1 HCCO 2.04E07 2.0 1900.0 "

Formation of anthanthracene109. BAPYR 1 H 5 BAPYR*S 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]110. BAPYR 1 OH 5 BAPYR*S 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]111. BAPYR*S 1 C2H2 5 ANTHAN 1 H 3.98E13 0.0 10100.0 Fahr and Stein [50]

Anthanthracene-oxidation112. ANTHAN 1 H 5 ANTHAN*S 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]113. ANTHAN 1 OH 5 ANTHAN*S 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]114. ANTHAN 1 OH 5 BAPYR*S 1 CH2CO 1.30E13 0.0 10600.0 Wang and Frenklach [24]115. ANTHAN 1 O 5 BAPYR*S 1 HCCO 2.20E13 0.0 4530.0 "116. ANTHAN*S 1 O2 5 BAPYR*S 1 2CO 2.10E12 0.0 7470.0 "

Formation of cyclopenta[cd]pyrene117. PYRENE 1 H 5 PYRENE*S1 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]118. PYRENE 1 OH 5 PYRENE*S1 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]119. PYRENE*S1 1 C2H2 5 CPCDPYR 1 H 3.98E13 0.0 10100.0 Fahr and Stein [50]

Formation of dicylcopentapyrene120. CPCDPYR 1 H 5 CPCDPYR*S 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]121. CPCDPYR 1 OH 5 CPCDPYR*S 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]122. CPCDPYR*S 1 C2H2 5 DCPP 1 H 3.98E13 0.0 10100.0 Fahr and Stein [50]

Formation of benzo[e]pyrene123. PYRENE 1 H 5 PYRENE*S2 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]124. PYRENE 1 OH 5 PYRENE*S2 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]125. PYRENE*S2 1 C2H2 5 PYRYNE 1 H 3.98E13 0.0 10100.0 Fahr and Stein [50]126. PYRYNE 1 H 5 PYRYNE*S 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]127. PYRYNE 1 OH 5 PYRYNE*S 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]128. PYRYNE*S 1 C2H2 5 BEPYREN*S 3.98E13 0.0 10100.0 Fahr and Stein [50]129. BEPYREN*S 1 H 5 BEPYREN 5.00E13 0.0 0.0 estimate, this work

Formation of indeno[1,2,3-cd]pyrene130. PYRENE*S1 1 C6H5 5 INPYR 1 H 1 H 5.00E12 0.0 0.0 Rxn. 65.131. PYRENE*S1 1 C6H6 5 INPYR 1 H2 1 H 4.00E11 0.0 4000.0 Rxn. 66.

Formation of benzo[ghi]perylene132. BEPYREN 1 H 5 BEPYREN*S 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]133. BEPYREN 1 OH 5 BEPYREN*S 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]134. BEPYREN*S 1 C2H2 5 BGHIPER 1 H 3.98E13 0.0 10100.0 Fahr and Stein [50]

Formation of cyclopentabenzo[ghi]perylene135. BGHIPER 1 H 5 BGHIPE*S1 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]136. BGHIPER 1 OH 5 BGHIPE*S1 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]137. BGHIPE*S1 1 C2H2 5 CPBPER 1 H 3.98E13 0.0 10100.0 Fahr and Stein [50]


TABLE 1

continued


Formation of coronene138. BGHIPER 1 H 5 BGHIPE*S2 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]139. BGHIPER 1 OH 5 BGHIPE*S2 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]140. BGHIPE*S2 1 C2H2 5 CORONEN 1 H 3.98E13 0.0 10100.0 Fahr and Stein [50]

Formation of ethinylfluoranthene141. FLTHN2 1 C2H2 5 FLTHNC2H 1 H 3.98E13 0.0 10100.0 Fahr and Stein [50]

Formation of benzo[ghi]fluoranthene142. FLTHN 1 H 5 FLTHN2 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]143. FLTHN 1 OH 5 FLTHN2 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]144. FLTHN2 1 C2H2 5 BGHIF 1 H 3.98E13 0.0 10100.0 Fahr and Stein [50]

Formation of methylbenzo[ghi]fluoranthene145. BGHIF2 1 CH3 5 BGHIFCH2 1 H 5.00E13 0.0 0.0 Rxn. 16.146. BGHIFCH2 1 H 5 BGHIFCH3 1.00E14 0.0 0.0 Rxn. 17.147. BGHIFCH3 1 H 5 BGHIF 1 CH3 1.20E13 0.0 5148.0 Rxn. 18.

Formation of ethinylbenzo[ghi]fluoranthene148. BGHIF2 1 C2H2 5 BGHIFC2H 1 H 3.98E13 0.0 10100.0 Fahr and Stein [50]

Formation of cyclopentafluoranthene149. FLTHN2 1 C2H2 5 FLTHNR 1 H 3.98E13 0.0 10100.0 Fahr and Stein [50]

Formation of cyclopentabenzo[ghi]fluoranthene150. FLTHNR 1 H 5 FLTHNR*S 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]151. FLTHNR 1 OH 5 FLTHNR*S 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]152. FLTHNR*S 1 C2H2 5 BGHIFR 1 H 3.98E13 0.0 10100.0 Fahr and Stein [50]153. BGHIF 1 H 5 BGHIF2 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]154. BGHIF 1 OH 5 BGHIF2 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]155. BGHIF2 1 C2H2 5 BGHIFR 1 H 3.98E13 0.0 10100.0 Fahr and Stein [50]

Formation of corannulene156. BGHIF2 1 C2H2 5 COR 1 H 3.98E13 0.0 10100.0 Fahr and Stein [48]157. CPCDPYR*S 1 C2H2 5 COR 1 H 3.98E13 0.0 10100.0 Fahr and Stein [48]

Methylation of corannulene158. COR2 1 CH3 5 CORCH2 1 H 5.00E13 0.0 0.0 Rxn. 16.159. CORCH2 1 H 5 CORCH3 1.00E14 0.0 0.0 Rxn. 17.160. CORCH3 1 H 5 COR 1 CH3 1.20E13 0.0 5148.0 Rxn. 18.

Formation of cyclopentacorannulene161. COR 1 H 5 COR2 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]162. COR 1 OH 5 COR2 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]163. COR2 1 C2H2 5 COR1 1 H 3.98E13 0.0 10100.0 Fahr and Stein [50]164. BGHIFR 1 H 5 BGHIFR*S 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]165. BGHIFR 1 OH 5 BGHIFR*S 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]166. BGHIFR*S 1 C2H2 5 COR1 1 H 3.98E13 0.0 10100.0 Fahr and Stein [50]

Formation of C60 and C70 fullerenes (based on Pope and Howard [40, 41]Formation of FB (C50H10)167. COR1 1 H 5 COR12 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]168. COR1 1 OH 5 COR12 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]169. COR12 1 C2H2 5 COR2 1 H 3.98E13 0.0 10100.0 Fahr and Stein [50]170. COR2 1 H 5 COR22 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]171. COR2 1 OH 5 COR22 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]172. COR22 1 C2H2 5 COR3 1 H 3.98E13 0.0 10100.0 Fahr and Stein [50]173. COR3 1 H 5 COR32 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]174. COR3 1 OH 5 COR32 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]175. COR32 1 C2H2 5 COR4 1 H 3.98E13 0.0 10100.0 Fahr and Stein [50]176. COR4 1 H 5 COR42 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]177. COR4 1 OH 5 COR42 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]178. COR42 1 C2H2 5 HB 1 H 3.98E13 0.0 10100.0 Fahr and Stein [50]179. HB 1 H 5 HB2 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]180. HB 1 OH 5 HB2 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]181. HB2 1 C2H2 5 HB1 1 H 3.98E13 0.0 10100.0 Fahr and Stein [50]

8 H. RICHTER ET AL.

TABLE 1

continued


182. HB1 1 H 5 HB12 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]183. HB1 1 OH 5 HB12 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]184. HB12 1 C2H2 5 HB2 1 H 3.98E13 0.0 10100.0 Fahr and Stein [50]185. HB2 1 H 5 HB22 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]186. HB2 1 OH 5 HB22 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]187. HB22 1 C2H2 5 HB3 1 H 3.98E13 0.0 10100.0 Fahr and Stein [50]188. HB3 1 H 5 HB32 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]189. HB3 1 OH 5 HB32 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]190. HB32 1 C2H2 5 HB4 1 H 3.98E13 0.0 10100.0 Fahr and Stein [50]191. HB4 1 H 5 HB42 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]192. HB4 1 OH 5 HB42 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]193. HB42 1 C2H2 5 TB 1 H 3.98E13 0.0 10100.0 Fahr and Stein [50]194. TB 1 H 5 TB2 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]195. TB 1 OH 5 TB2 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]196. TB2 1 C2H2 5 TB1 1 H 3.98E13 0.0 10100.0 Fahr and Stein [50]197. TB1 1 H 5 TB12 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]198. TB1 1 OH 5 TB12 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]199. TB12 1 C2H2 5 TB2 1 H 3.98E13 0.0 10100.0 Fahr and Stein [50]200. TB2 1 H 5 TB22 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]201. TB2 1 OH 5 TB22 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]202. TB22 1 C2H2 5 TB3 1 H 3.98E13 0.0 10100.0 Fahr and Stein [50]203. TB3 1 H 5 TB32 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]204. TB3 1 OH 5 TB32 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]205. TB32 1 C2H2 5 TB4 1 H 3.98E13 0.0 10100.0 Fahr and Stein [50]206. TB4 1 H 5 TB42 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]207. TB4 1 OH 5 TB42 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]208. TB42 1 C2H2 5 FB 1 H 3.98E13 0.0 10100.0 Fahr and Stein [50]Formation of C60

209. FB 1 H 5 FB2 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]210. FB 1 OH 5 FB2 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]211. FB2 1 C2H2 5 FB1 1 H 3.98E13 0.0 10100.0 Fahr and Stein [50]212. FB1 1 H 5 FB12 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]213. FB1 1 OH 5 FB12 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]214. FB12 1 C2H2 5 FB2Q 1 H 3.98E13 0.0 10100.0 Fahr and Stein [50]215. FB2Q 5 FB2QR 8.51E12 0.0 62860.0 Brouwer and Troe [61]216. FB2QR 1 H 5 FB2QR2 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]217. FB2QR 1 OH 5 FB2QR2 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]218. FB2QR2 5 FB2QRD 1 H 1.00E13 0.0 0.0 Frenklach et al. [22]219. FB2QRD 1 H 5 FB2QRD2 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]220. FB2QRD 1 OH 5 FB2QRD2 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]221. FB2QRD2 1 C2H2 5 FB3Q 1 H 3.98E13 0.0 10100.0 Fahr and Stein [50]222. FB3Q 1 H 5 FB3Q2 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]223. FB3Q 1 OH 5 FB3Q2 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]224. FB3Q2 5 FB3QD 1 H 1.00E13 0.0 0.0 Frenklach et al. [22]225. FB3QD 1 H 5 FB3QD2 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]226. FB3QD 1 OH 5 FB3QD2 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]227. FB3QD2 1 C2H2 5 FB4Q 1 H 3.98E13 0.0 10100.0 Fahr and Stein [50]228. FB4Q 1 H 5 FB4Q2 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]229. FB4Q 1 OH 5 FB4Q2 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]230. FB4Q2 5 FB4QD 1 H 1.00E13 0.0 0.0 Frenklach et al. [22]231. FB4QD 1 H 5 FB4QD2 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]232. FB4QD 1 OH 5 FB4QD2 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]233. FB4QD2 1 C2H2 5 FB5Q 1 H 3.98E13 0.0 10100.0 Fahr and Stein [50]234. FB5Q 1 H 5 FB5Q2 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]235. FB5Q 1 OH 5 FB5Q2 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]236. FB5Q2 5 FB5QD 1 H 1.00E13 0.0 0.0 Frenklach et al. [22]


TABLE 1

continued


237. FB5QD 1 H 5 FB5QD2 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]238. FB5QD 1 OH 5 FB5QD2 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]239. FB5QD2 5 C60A 1 H 1.00E13 0.0 0.0 Frenklach et al. [22]Formation of C70

240. FB12 1 C2H2 5 FB2 1 H 3.98E13 0.0 10100.0 Fahr and Stein [50]241. FB2 1 H 5 FB22 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]242. FB2 1 OH 5 FB22 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]243. FB22 1 C2H2 5 FB3 1 H 3.98E13 0.0 10100.0 Fahr and Stein [50]244. FB3 1 H 5 FB32 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]245. FB3 1 OH 5 FB32 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]246. FB32 1 C2H2 5 FB4 1 H 3.98E13 0.0 10100.0 Fahr and Stein [50]247. FB4 1 H 5 FB42 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]248. FB4 1 OH 5 FB42 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]249. FB42 1 C2H2 5 XB 1 H 3.98E13 0.0 10100.0 Fahr and Stein [50]250. XB 1 H 5 XB2 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]251. XB 1 OH 5 XB2 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]252. XB2 1 C2H2 5 XB1 1 H 3.98E13 0.0 10100.0 Fahr and Stein [50]253. XB1 1 H 5 XB12 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]254. XB1 1 OH 5 XB12 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]255. XB12 1 C2H2 5 XB2Q 1 H 3.98E13 0.0 10100.0 Fahr and Stein [50]256. XB2Q 5 XB2QR 8.51E12 0.0 62860.0 Brouwer and Troe [61]257. XB2QR 1 H 5 XB2QR2 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]258. XB2QR 1 OH 5 XB2QR2 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]259. XB2QR2 5 XB2QRD 1 H 1.00E13 0.0 0.0 Frenklach et al. [22]260. XB2QRD 1 H 5 XB2QRD2 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]261. XB2QRD 1 OH 5 XB2QRD2 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]262. XB2QRD2 1 C2H2 5 XB3Q 1 H 3.98E13 0.0 10100.0 Fahr and Stein [50]263. XB3Q 1 H 5 XB3Q2 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]264. XB3Q 1 OH 5 XB3Q2 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]265. XB3Q2 5 XB3QD 1 H 1.00E13 0.0 0.0 Frenklach et al. [22]266. XB3QD 1 H 5 XB3QD2 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]267. XB3QD 1 OH 5 XB3QD2 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]268. XB3QD2 1 C2H2 5 XB4Q 1 H 3.98E13 0.0 10100.0 Fahr and Stein [50]269. XB4Q 1 H 5 XB4Q2 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]270. XB4Q 1 OH 5 XB4Q2 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]271. XB4Q2 5 XB4QD 1 H 1.00E13 0.0 0.0 Frenklach et al. [22]272. XB4QD 1 H 5 XB4QD2 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]273. XB4QD 1 OH 5 XB4QD2 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]274. XB4QD2 1 C2H2 5 XB5Q 1 H 3.98E13 0.0 10100.0 Fahr and Stein [50]275. XB5Q 1 H 5 XB5Q2 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]276. XB5Q 1 OH 5 XB5Q2 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]277. XB5Q2 5 XB5QD 1 H 1.00E13 0.0 0.0 Frenklach et al. [22]278. XB5QD 1 H 5 XB5QD2 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]279. XB5QD2 1 OH 5 XB5QD2 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]280. XB5QD2 5 C70A 1 H 1.00E13 0.0 0.0 Frenklach et al. [22]

Changes in this work relative to R. A. Shandross [47]Formation of cyclopentadienyl281. C6H5 1 O 5 C5H5 1 CO 9.00E13 0.0 0.0 Tan and Frank [62]Formation of naphthalene282. C6H5 1 C2H2 5 C8H6 1 H 3.98E13 0.0 10100.0 Fahr and Stein [50]283. C8H6 1 H 5 A1YNE* 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]284. C8H6 1 OH 5 A1YNE* 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]285. C8H6 1 CH3 5 A1YNE* 1 CH4 1.67E12 0.0 15057.0 Marinov et al. [23]286. A1YNE* 1 C2H2 5 C10H7S 3.98E13 0.0 10100.0 Fahr and Stein [50]287. C10H7S 1 H 5 C10H8 1.00E14 0.0 0.0 Marinov et al. [23]288. C10H7P 1 H 5 C10H8 1.00E14 0.0 0.0 "

10 H. RICHTER ET AL.

tained after H abstraction from the center ringof anthracene. The model consists of 246 spe-cies and 834 reactions, and a listing of thecomplete interpreter-output file as well as thethermodynamic and transport properties areprovided elsewhere [57]. The PAH included inthe present mechanism are shown in Fig. 3.

FORMATION OF NAPHTHALENE,PHENANTHRENE, AND RELATEDSPECIES

Naphthalene

Naphthalene (C10H8) formation is the first stepin the growth process to larger and largermolecules. There are two contributing path-ways, two consecutive H-abstraction/C2H2-addi-tions via phenylacetylene and the reaction be-tween two cyclopentadienyl radicals 2C5H5 Nnaphthalene 1 2H initially suggested by Dean[64] but with H2 as product and by Marinov etal. [23] using a rate coefficient about 100-foldlarger than that of Dean [64]. In the presentwork, the Marinov et al. rate coefficient wasreduced arbitrarily by a factor 10 in order toensure a reasonably good agreement betweenpredicted and experimental naphthalene pro-files in Flame II (Fig. 4), despite an overpredic-tion of cyclopentadienyl radicals by the modelas shown in Fig. 1a reflecting the remaininguncertainties on benzene oxidation chemistry.The cyclopentadienyl pathway is found to bepredominant for naphthalene formation, its re-moval leading to a 50-fold reduction of the peak

mole fraction predicted in Flame II despite thesatisfactory agreement for phenylacetylene (Fig.1b). Cyclopentadienyl is mainly formed by theoxidation of C6H5 followed by the degradationof C6H5O:

C6H6 1 ON C6H5O 1 H

C6H5 1 O2N C6H5O 1 O

C6H5ON C5H5 1 CO

C6H5 1 ON C5H5 1 CO

The formation of benzoquinone by the reac-tion C6H5 1 O2N C6H4O2 1 H [62, 65] whichleads to a significant reduction of phenoxy andconsequently of cylcopentadienyl radical con-centrations was tested in the nearly sootingbenzene flame [11] and ruled out due to apredicted peak mole fraction of about 100-foldhigher than the experimental value at 108 amucommonly attributed to the different cresolisomers, species with the same molecular massas benzoquinone.

Methylnaphthalene and Acenaphthalene

Naphthalene reacts to 1- and 2-naphthyl radi-cals. The peak values predicted for both naph-thyl radicals in Flame II are about 3–4 timessmaller than the experimental data obtained viascavenging reaction by Hausmann et al. [12], astill acceptable agreement considering potentialuncertainties on rate coefficients and experi-ments. The reaction of 1-naphthyl with acety-lene leads to acenaphthalene (A2R5, C12H8).

TABLE 1

continued


289. C10H8 1 H 5 C10H7P 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]290. C10H8 1 OH 5 C10H7P 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]291. C10H8 1 C2H3 5 C10H7P 1 C2H4 5.00E13 0.0 16000.0 Harris et al. [63]292. C10H8 1 C2H 5 C10H7P 1 C2H2 5.00E13 0.0 16000.0293. C10H8 1 H 5 C10H7S 1 H2 2.50E14 0.0 16000.0 Kiefer et al. [48]294. C10H8 1 OH 5 C10H7S 1 H2O 2.10E13 0.0 4600.0 Madronich and Felder [49]295. C10H8 1 C2H3 5 C10H7S 1 C2H4 5.00E13 0.0 16000.0 Harris et al. [63]296. C10H8 1 C2H 5 C10H7S 1 C2H2 5.00E13 0.0 16000.0 "297. 2C5H5 5 C10H8 1 H 1 H 2.00E12 0.0 4000.0 this workToluene formation298. C6H5 1 CH3 5 C7H7 1 H 5.00E13 0.0 0.0 estim. based on [23]


Methylnaphthalene is formed via reaction ofboth naphthyl radicals with CH3 while a similarreaction sequence also gives methylacenaphtha-lene. As shown in Fig. 4, the model predicts theright location for the peak value of acenaphtha-

lene in Flame II but underpredicts the magni-tude by nearly 20-fold, possibly indicating theexistence of another yet unknown formationpathway already suggested by Hausmann et al.[12]. A pathway via methylnaphthalene [23] was

Fig. 3. PAH contributing to the growth process.


tested and found to be negligible. Similar tophenyl, both naphthyl radicals are also oxidized,the resulting naphthoxy radicals are stabilizedvia the formation of naphthol (C10H7OH) ordecay to indenyl via CO loss. The comparison ofthe present model predictions to the experimen-tal data of Hausmann et al. for Flame II [12]reveals good agreement for indene formationbut the lack of total depletion in the postflamezone indicates supplementary pathways that arenot considered in the present model. A signifi-cant overprediction was observed for indenyl(60-fold) and naphthol (20-fold) which reflectspoor knowledge of naphthalene oxidation, in-dene formation, and the corresponding ratecoefficients. The lack of complete indenyl de-pletion in the postflame-zone shows again evi-dence of further consumption pathways. Thecontribution of indene and indenyl to PAH andparticle growth cannot be excluded.

Phenanthrene

Phenanthrene (A3, C14H10), a key species forfurther PAH growth, is mainly formed by thereaction of C2H2 with biphenyl radicals [24]. Aslight overprediction is observed for C14H10species in Flame II and can be attributed to anoverprediction of phenyl radicals, shown in Fig.1b, and related to uncertainties in the benzenedestruction chemistry. The MBMS techniqueused in the measurements [11] could not distin-

guish between phenanthrene and anthracene(also C14H10), so only an overall profile includ-ing both species is available and is compared tothe model predictions in Fig. 5. The predictedhigher abundance of phenanthrene than of an-thracene is consistent with the measurements inFlame I [42], although partial sublimation ofC14H10 species prevented a comparison of ab-solute quantities to the prediction. Phenan-threne formation by two consecutive H-abstrac-tion/acetylene-additions is included in themechanism but is found to be negligible underthe present conditions. Use of this pathwayalone underpredicts by 650-fold the peak con-centration in Flame II.

Anthracene and Benzo[a]anthracene

Anthracene (A3L, C14H10) is formed corre-sponding the hydrogen-abstraction/acetylene-addition pathway [22]. Two consecutive H-ab-straction/C2H2-additions begin with 2-naphthyland lead to an anthracene peak concentrationabout 100-fold smaller than that of phenan-threne in Flame I. This result is consistent withthe experimental observation [42] of only tracesof anthracene in Flame I, but a partial sublima-tion of anthracene during sample preparationcannot be ruled out.

Using only consecutive H-abstraction/C2H2-addition for anthracene formation and a similarpathway for benzo[a]anthracene (A4L, C18H12)

Fig. 4. Comparison between experimental mole fractionprofiles [11] and model predictions in a nearly sootingbenzene/oxygen flame (f 5 1.8, 30% argon, v258C 5 50 cms21, 2.67 kPa); Flame II. Naphthalene: F (experiment),

(prediction). Acenaphthalene: } (experiment), ----(prediction).

Fig. 5. Comparison between the experimental mole fractionprofile of C14H10 [11] and model prediction for the corre-sponding species in a nearly sooting benzene/oxygen flame(f 5 1.8, 30% argon, v258C 5 50 cm s21, 2.67 kPa); FlameII. C14H10: F (experiment). Phenanthrene: (predic-tion). Anthracene: ---- (prediction).


underpredicts the measured peak concentrationof the latter [42] by more than 100-fold. Thebenzo[a]anthracene underprediction is reducedto less than 10-fold (Fig. 6) by using the isomer-ization of phenanthrene to anthracene sug-gested by Colket and Seery [16] and used byMarinov et al. [23]. Nevertheless, the impor-tance of this reaction remains questionable con-sidering the pyrolysis results of Scott and Ro-elofs [66] showing the reverse reaction tophenanthrene to be of little or no significance.

Chrysene

The formation of chrysene (CHRYSEN,C18H12) is described by means of a H-abstrac-tion/C2H2-addition sequence beginning withprimary phenanthryl radicals (2- and 7-phenan-thryl, A3*P) and forming the correspondingphenanthryl-acetylene as intermediate. In thenext steps the hydrogen atom adjacent to theacetylene group is abstracted and then the ringclosure achieved by means of another acetylene-addition. The resulting secondary chrysene rad-ical is stabilized by reaction with atomic hydro-gen.

A3 1 H, OHN A3*P 1 H2, H2O

A3*P 1 C2H2N A3YNE 1 H

A3YNE 1 H, OHN A3YNE*S 1 H2, H2O

A3YNE*S 1 C2H2N CHRYSEN*S

CHRYSEN*S 1 HN CHRYSEN

The chrysene concentration profile for Flame Icompared against experimental data [42] re-veals encouraging agreement concerning shapeand peak location but a 3- to 5-fold underpre-diction of the peak value (Fig. 6). This discrep-ancy could be explained by uncertainties in therate coefficients for H-abstraction/C2H2-ab-straction but also by a contribution of thereaction between two indenyl radicals, similar tothe main pathway of naphthalene formation.

FORMATION OF FLUORENE ANDBENZO[A]FLUORENE

The formation of fluorene (FLUOREN,C13H10) starts with the reaction of benzene orphenyl with benzyl radical (C7H7, C6H5CH2)and, after H-abstraction, is achieved by theclosure of a new five-membered ring:

C6H6 1 C7H7N Benzylbenzene 1 H

C6H5 1 C7H7N Benzylbenzene

Benzylbenzene 1 H,OHN Benzylbenzene-

radical 1 H2, H2O

Benzylbenzene-radicalN Fluorene 1 H

Comparison against experimental data (Fig. 7)shows the predicted consumption in the burnt

Fig. 6. Comparison between experimental mole fractionprofiles [42] and model predictions in a sooting premixedbenzene/oxygen flame (f 5 2.4, 10% argon, v258C 5 25 cms21, 5.33 kPa); Flame I. Benzo[a]anthracene: F (experi-ment), (prediction). Chrysene: } (experiment), ----(prediction).

Fig. 7. Comparison between experimental mole fractionprofiles [42] and model predictions in a sooting premixedbenzene/oxygen flame (f 5 2.4, 10% argon, v258C 5 25 cms21, 5.33 kPa); Flame I. Fluorene: F (experiment, left scale),

(prediction, left scale). Fluoranthene: } (experiment,right scale), ---- (prediction, right scale).


gas to be too slow, possibly attributable tomissing reactions.

Benzo[a]fluorene (C17H12) is formed by asimilar mechanism but with naphthalene and2-naphthyl as reactants. Its predicted peak con-centration in Flame I is about 60 times smallerthan that of fluorene, consistent with beingbarely detectable by HPLC in flame samples[42].

FORMATION OF FLUORANTHENE ANDBENZO[K]FLUORANTHENE

Similar to acenaphthalene, the formation offluoranthene (FLTHN, C16H10), a key speciesfor fullerene formation as discussed later, startswith 1-naphthyl reacting with benzene or phenyl[23]:

1-naphthyl 1 C6H5N fluoranthene 1 2H

1-naphthyl 1 C6H6N fluoranthene 1 H2 1 H

A supplementary significant pathway isisomerization of acephenanthrylene (see be-low). Fluoranthene is consumed by reactionsforming the isomers benzo[ghi]fluoranthene(BGHIF, C18H10) and cyclopenta[cd]fluoran-thene (FLTHNR, C18H10), described below,and by methylation and ethynylation. Figure 7shows the comparison of the prediction withthe experiment for Flame I while for Flame IIonly an experimental profile including allC16H10 isomers is available (Fig. 8). Thestriking underprediction of consumption inthe burnt gas is observed for nearly all PAH asdiscussed below.

Benzo[k]fluoranthene (BKFLUOR, C20H12)is formed in a similar way but with naphthaleneand 1- or 2-naphthyl as reactants. The predic-tion of a peak mole fraction of 5 3 1028 inFlame I is consistent with the measured concen-tration being close to the detection limit [42]. Incontrast to the experimental data, the predictedmole fraction is constant through the burnt gasdue to the lack of consumption reactions.

FURTHER GROWTH OF PHENANTHRENE

Besides primary phenanthryl radicals leading tothe above described formation of chrysene, two

different secondary phenanthryl radicals areinvolved in the present model. The first one(A3S*1), assigned to 1-, 8-, 9- and 10-phenan-thryl gives, after acetylene addition, acephenan-thrylene (ACEPHA, C16H10) while its reactionwith phenyl or benzene leads to benzo[b]flu-oranthene (BBFLUOR, C20H12). The othersecondary phenanthryl radical represents 4- and5-phenanthryl which via acetylene additiongives pyrene, another C16H10 isomer, or viamethylation and with methylphenanthrene(A3CH3, C15H12) as intermediate, cyclopenta-[def]phenanthrene (A3CH2R, C15H10).

Evidence for the thermal interconversion be-tween acephenanthrylene and fluoranthene hasbeen shown by Scott and Roelofs [66]. Based ontheir results, the isomerization acephenan-thrylene N fluoranthene was included in themechanism and leads to about 50% increase ofthe fluoranthene concentration and to a 4-folddecrease of the acephenanthrylene peak con-centration in Flame I. This behavior is consis-tent with experimental results [42] showing onlysmall quantities of acephenanthrylene close tothe detection limit. A similar situation is pre-dicted in Flame II where the acephenanthrylenepeak mole fraction represents less than 10% ofthe fluoranthene one (Fig. 8). The prediction ofbenzo[b]fluoranthene formation (Fig. 9) in theflame front of Flame I is 2.5 to 5 times lowerthan the experimental data [42] and its con-

Fig. 8. Comparison between the experimental mole fractionprofile of C16H10 [11] and model prediction for the corre-sponding species in a nearly sooting benzene/oxygen flame(f 5 1.8, 30% argon, v258C 5 50 cm s21, 2.67 kPa); FlameII. C16H10: F (experiment). Fluoranthene: (predic-tion). Pyrene: ---- (prediction). Acephenanthrylene: zzzz

(prediction).


sumption in the postflame zone cannot be re-produced because no further reactions are in-cluded in the mechanism.

Methylphenanthrene and cyclopenta[def-]phenanthrene were detected in Flame I byGrieco [42] but very low concentrations did notallow quantifications. The validation for pyrenein Flame I (Fig. 9) shows a good agreement ofits formation but it must be concluded that itsconsumption by further growth reactions, meth-ylation, and oxidation [24] as considered in thepresent model is not sufficient to explain itsdepletion in the burnt gases as observed exper-imentally [42]. Oxidation was tested and foundto account for about 35% reduction of the molefraction in the burnt gas while barely affectingthe peak value.

In the following pyrene growth reactions,distinction is drawn between primary 2-pyrenylradicals and two types of secondary pyrenylradicals, all of them formed by H-abstractionfrom pyrene with H and OH.

FORMATION OF BENZO[A]PYRENE ANDANTHANTHRACENE

Two subsequent H-abstraction/acetylene-ad-dition sequences beginning with 2-pyrenyllead to benzo[a]pyrene (BAPYR, C20H12).Benzo[a]pyrene is oxidized and reacts viaH-abstraction/acetylene-addition to anthanthra-cene (ANTHAN, C22H12). Anthanthracene

decays by further oxidation partially to ben-zo[a]pyrene. Benzo[a]pyrene mole fractionspredicted for Flame I (Fig. 10) show a peakconcentration close to the scatter of the ex-perimental data considering a relative error of613% for PAH concentrations obtained byGC/MS analysis as quoted by Grieco et al.[42] and an additional error due to samplecollection and flame reproducibility. A furtherincrease of concentration in the burnt gasafter the consumption following the peakreflects missing sinks for PAH in the post-flame zone. The impact of oxidation of an-thanthracene on its mole fraction profile wastested for Flame I (Fig. 10). Removal of alloxidation reactions leads to slight shift of theprofile towards the burnt gases and to thedisappearance of the local maximum at about0.4 cm. Both predictions, with and withoutoxidation show a similar increase in the post-flame zone so that additional sinks responsi-ble for PAH depletion must exist. An-thanthracene was found to be present inFlame I [42] but could not be quantified dueto difficulties associated with high molecularspecies [67] leading to an increase of thedetection limits. A predicted local maximumof 2 3 1028 for the anthanthracene molefraction profile (with oxidation) is in agree-ment with the experimental findings.

Fig. 9. Comparison between experimental mole fractionprofiles [42] and model predictions in a sooting premixedbenzene/oxygen flame (f 5 2.4, 10% argon, v258C 5 25 cms21, 5.33 kPa); Flame I. Benzo[b]fluoranthene: F (experi-ment), (prediction). Pyrene: } (experiment), ----(prediction).

Fig. 10. Comparison between experimental mole fractionprofiles [42] and model predictions in a sooting premixedbenzene/oxygen flame (f 5 2.4, 10% argon, v25°C 5 25 cms21, 5.33 kPa); Flame I. Benzo[a]pyrene: F (experiment),

(prediction). Anthanthracene (with oxidation): ----(prediction). Anthanthracene (without oxidation): zzzz

(prediction).


FORMATION OF CYCLOPENTA[CD]PYRENE, BENZO[E]PYRENE ANDINDENO[1,2,3-CD]PYRENE

Two pyrene radicals, 4- and 9-pyrenyl, are rep-resented in the model by one secondary radical(PYRENE*S1), which reacts with acetylene toform cyclopenta[cd]pyrene (CPCDPYR, C18H10)and with benzene and phenyl to form in-deno[1,2,3-cd]pyrene (INPYR, C22H12). Simi-larly, 5- and 10-pyrenyl is represented by the othersecondary radical (PYRENE*S2) which under-goes two H-abstraction/acetylene-addition stepsto form benzo[e]pyrene (BEPYREN, C20H12).

The formation of cylcopenta[cd]pyrene ispredicted well (Fig. 11) but not the consump-tion, as it can be seen by the concentration inthe burnt gas to be greatly overpredicted. Anefficient sink for PAH in the burnt gas is missingfrom the model. Similarly, the prediction ofindeno[1,2,3-cd]pyrene formation in Flame Iagrees with experiment [42] but the depletion inthe burnt gas is underpredicted reflecting againthe lack of adequate consumption reactions(Fig. 11).

A striking phenomenon is the absence of dicy-lopentapyrenes (DCPP, C20H10) in fullerene-forming flames as described by Lafleur et al. [68]and confirmed by Flame I data [42]. In the presentwork a direct pathway by acetylene addition fromcylcopenta[cd]pyrene-radicals to corannulene, incompetition with the formation of the different

dicylcopentapyrenes is assumed. This reaction re-quires an isomerization leading to a five-mem-bered ring which could occur at an energized stateon the potential surface which would allow asubstantial reduction of the activation barrier. Amore detailed investigation will be necessary inorder to assess the importance of this reaction.The prediction of a dicyclopentapyrene mole frac-tion of about 1 3 1026 is inconsistent with its notbeing detectable in Flame I [42] and could beexplained by the preponderance of the coran-nulene pathway in fullerene forming flames. Thepredicted and experimental values of corannuleneconcentration are discussed below.

A peak mole fraction of about 6 3 1028 forbenzo[e]pyrene in Flame I agrees with the ex-perimental value close to the detection limit[42]. A significant increase of the predictedconcentration in the postflame gas reveals aconsiderable lack of consumption reactions inthis zone of the flame. Benzo[ghi]perylene(BGHIPER, C22H12) is formed in the nextH-abstraction/acetylene-addition sequenceyielding about a 10-fold underprediction of thepeak concentration but a significant overpredic-tion in the burnt gas (Fig. 12), again reflecting amissing sink in this flame region. In the follow-ing step two different benzo[ghi]perylene-radi-cals (BGHIPE*S1 and BGHIPE*S2), formed byH-abstraction, react via acetylene-addition to cy-clopentabenzo[ghi]perylene (CPBPER, C24H12)and coronene (CORONEN, C24H12). As in thecase of dicyclopentapyrene, the different cyclo-

Fig. 11. Comparison between experimental mole fractionprofiles [42] and model predictions in a sooting premixedbenzene/oxygen flame (f 5 2.4, 10% argon, v25°C 5 25 cms21, 5.33 kPa); Flame I. Cyclopenta[cd]pyrene: F (experi-ment), (prediction). Indeno[1,2,3-cd]pyrene: } (exper-iment), ---- (prediction).

Fig. 12. Comparison between experimental mole fractionprofiles [42] and model predictions in a sooting premixedbenzene/oxygen flame (f 5 2.4, 10% argon, v25°C 5 25 cms21, 5.33 kPa); Flame I. Benzo[ghi]perylene: F (experiment,left scale), (prediction, left scale). Benzo[ghi]fluoran-thene: } (experiment, right scale), ---- (prediction, rightscale).


pentabenzo[ghi]perylene isomers are representedas only one species in the model since theirthermodynamic properties are indistinguishableusing group additivity. Use of sufficiently highlevel calculation of thermodynamic properties todifferentiate between those isomers as well as toassess the energies of different radical sites be-yond the primary, secondary, and tertiary distinc-tions of group additivity would be interesting forfuture work. Two cyclopentabenzo[ghi]peryleneisomers and coronene were found in Flame I [42]but could not be quantified. The predicted cyclo-pentabenzo[ghi]perylene peak mole fraction isabout 6 3 1029 in Flame I which is reasonable,whereas the concentration in the burnt gas isoverpredicted, again indicating missing consump-tion reactions. The predicted peak mole fractionof coronene in the reaction zone of Flame I isabout 3 3 1028 consistent with coronene detectedbut not being quantifiable [42].

FORMATION OF C60 AND C70

FULLERENES

Homann et al. [27, 38, 39] suggest thatfullerenes could form by a so-called zippermechanism, the reaction of two large PAHfollowed by hydrogen loss and bond formation;Frenklach and Ebert [69] suggest the formationcould occur by a sequence of alternating hydro-gen abstractions and acetylene additions. Directgrowth to C60 and C70 by sequential C2H2addition combined with internal rearrangementand hydrogen loss was formulated by Pope et al.[40, 41]. Also fullerene formation via reactivecoagulation of C30H10 units with subsequenthydrogen loss and bond formation was takeninto account but less than 3 3 1027 of the C60 1C70 came from the coagulation pathway [40]. Apreliminary kinetics test [40, 41] of the Pope etal. mechanism using a plug flow simulator andexperimental flame species concentrations asinput gave peak C60 and C70 mole fractionsclose to experimental flame measurements [29–31]. Thermodynamic constraints in the directgrowth mechanism have been considered andno insuperable thermodynamic barriers wererevealed [70].

In the present work the above described PAHgrowth mechanism was combined with the di-

rect fullerene growth mechanism [40, 41], withH abstraction by OH as well as H taken intoaccount. OH is even more important than H upto a temperature of 1400 K which is reached atabout 3 mm above the burner. Preliminary teststo include reactive coagulation showed a negli-gible contribution, 105- to 108-fold smaller thanthat by the direct pathway.

The fullerene growth begins with fluoran-thene which forms benzo[ghi]fluoranthene(BGHIF, C18H10) via H-abstraction/C2H2-addi-tion. The predicted concentration of benzo[ghi-]fluoranthene compared with experimental data[42] shows good agreement close to the burnerbut the peak value is 3-fold overpredicted anddisplaced downstream, and there is insufficientdepletion in the postflame zone (Fig. 12). Theoverprediction of the peak value could be ex-plained by an inaccurate assessment of thebranching between benzo[ghi]fluoranthene(BGHIF, C18H10) and cyclopenta[cd]fluoran-thene (FLTHNR, C18H10), another product ofacetylene addition to fluoranthene radicals.Benzo[ghi]fluoranthene is methylated and ethy-nylated and forms in the next H-abstraction/acetylene-addition sequence corannulene(COR, C20H10), the smallest bowl-shaped PAH,which has a curvature and a carbon frameworksimilar to those of fullerenes [71]. Corannuleneformation from cyclopenta[cd]pyrene (seeabove) leads to an approximately 2-fold in-crease of its peak mole fraction, and in thepostflame zone an increase that is even largerbut not significant due to the missing PAH sinkin that region. The methylation of corannuleneis included in the mechanism. The presence ofcorannulene in Flame I was confirmed experi-mentally but quantification was not possiblebecause of low concentration [42], consistentwith a predicted mole fraction of 5.6 3 1027.

Cylcopenta[cd]corannulene (COR1, C22H10)is the product of the next H-abstraction/acetylene-addition growth step but is alsoformed in an additional pathway. Beginningwith fluoranthene three H-abstraction/C2H2-addition sequences via cyclopenta[cd]fluoran-thene (FLTHNR, C18H10) and cylcopenta[cd]-benzo[ghi]fluoranthene (BGHIFR, C20H10),which is also formed from benzo[ghi]fluoran-thene, lead to cylcopenta[cd]corannulene. Cy-clopenta[cd]fluoranthene was synthesized [72]


and found in ethylene flames [73], and will besearched for in the present flames.

The formation of C60 and C70 fullerene struc-tures is completed by sequential C2H2-additioncombined with internal rearrangement andhydrogen loss as suggested by Pope et al. [40,41] taking into account H-abstraction by OHas described above. The molecular structureand the nomenclature of the intermediatesleading finally to C60 and C70 are given inreference [40].

The comparison of C60 and C70 fullereneformation in Flame I with experimental data[29–31] reveals a 50- to 100-fold underpredic-tion of the peak values (Fig. 13). Also, the firstof two maxima in the C60 and C70 experimentalconcentration profiles, at about 1 cm above theburner, was not reproduced by the model. Thisfirst maximum could be attributed to fullereneoxidation, not included in the present mecha-nism, considering a similar shape of the an-thanthracene profile when oxidation is takeninto account (Fig. 10). C60O and C70O, detectedin flame samples [29–31] could be the oxidationproducts but also adsorption on and reactionwith growing soot particles should be consid-ered [42]. The sensitivity of the predicted C60and C70 mole fractions to uncertainties in therate coefficients of H-abstraction and C2H2-addition reactions with larger PAH was tested.A 2-fold increase of the rate coefficient forH-abstraction by hydrogen radicals beginningwith corannulene led to a 3-fold increase of the

final C60 and C70 concentrations; the sameoperation performed for C2H2-addition showeda 2.3-fold increase for C60 and a 4.2-fold in-crease for C70. Also an assumed 6100 K uncer-tainty in the experimental temperature profile[43] gave a 2-fold uncertainty in the predictedpeak concentrations of C60 and C70 fullerenes(and PAH). This result added to an uncertaintyof 615% [42] in fullerene analysis by HPLC andeven an additional error related to the repro-ductivity of the experimental flame conditionsgives a total error that is less than the observeddiscrepancy between model predictions and ex-perimental results.

Consistent with the increasing underpredic-tion of peak concentrations for larger and largerPAH as seen for benzo[ghi]perylene, the under-prediction of C60 and C70 fullerenes may be dueto uncertainties in the rate coefficients for H-abstraction and C2H2-addition with more andmore steps of this sequence being involved.Nevertheless, the existence of other fullereneformation mechanisms [27, 38, 39] cannot beexcluded. Unambiguous identification of largerintermediates would be helpful, but is difficultbecause of limitations in chemical analysis.GC-MS reaches its limits at about 300 amu dueto the sublimation temperature increasing withmolecular mass; state-of-the-art HPLC can beused up to about 450 amu [67]. The synthesis ofpotential intermediates of the suggestedfullerene formation mechanism by means ofmethods of organic chemistry such as high-temperature gas phase cyclization is of greatinterest [74].

CONCLUSIONS

The model developed here was found to giveencouraging predictive capability for the growthof PAH up to coronene in a sooting premixedbenzene flame. The availability of MBMSdata for smaller species and radicals in anearly sooting benzene flame allowed the modelto be tested for smaller and unstable species,and its reliability was confirmed. C60 and C70fullerenes formed by sequential C2H2-additioncombined with internal rearrangement and hy-drogen loss was included in the model but nodefinitive answer concerning the importance of

Fig. 13. Comparison between experimental mole fractionprofiles [42] and model predictions in a sooting premixedbenzene/oxygen flame (f 5 2.4, 10% argon, v25°C 5 25 cms21, 5.33 kPa); Flame I. C60: F (experiment, left scale),(prediction, right scale). C70: } (experiment, left scale), ----(prediction, right scale).


additional fullerene forming pathways could begiven.

The concentrations of nearly all PAH weresignificantly overpredicted in the postflamezone where a rapid depletion observed experi-mentally was not reproduced by the model. Thisdiscrepancy may reflect the absence of PAHsinks such as reactions with smaller radicals(methyl, ethyl, vinyl, . . .), single-ring aromatics,other PAH, soot, etc. In this context it should bementioned that some experimental evidence ofreactive coagulation, e.g. the dimerization ofC14H10 to C28H14 has been shown in laminardiffusion flames by Siegmann et al. [75]. Thecontribution of PAH to soot formation, studiedrecently by Benish et al. [76] receives additionalsupport by the coincidence of fast soot forma-tion and PAH depletion as shown by Grieco etal. [42] indicating the importance of the reactionof PAH with growing soot particles. Those to beconsidered PAH-soot interactions could lead tothe immediate formation of chemical bondsor—taking into account the increasing molecu-lar mass and van der Waals interaction—tophysical adsorption. Stronger, chemical bondscould be established later, during the soot agingprocess. Definitive explanation of PAH con-sumption and fullerene formation will requirethe identification of larger intermediates of thegrowth process.

The study of PAH formation mechanisms wasfunded by the Chemical Sciences Division, Officeof Basic Energy Sciences, Office of Energy Re-search, U.S. Department of Energy under GrantDE-FGO2-84ER13282. Analytical chemistry sup-port was funded by the National Institute ofEnvironmental Health Sciences Center GrantNIH-5P30-ES02109. The testing of the fullereneformation model was funded by the NationalAeronautics and Space Administration underGrant NAG3-1879.

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Received 26 August 1998; revised 16 February 1999; accepted25 February 1999


formation mechanism of polycyclic aromatic hydrocarbons and fullerenes in premixed benzene flames

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