quantum chemical study on reaction of o(3p) with clono2
TRANSCRIPT
Quantum chemical study on reaction of O(3P) with ClONO2
Wei Shena,b, Ming Lia,*, Dianyong Tanga
aDepartment of Chemistry, Southwest-China Normal University, Chongqing 400715, ChinabDepartment of Chemistry, Fuling Normal University, Chongqing 408003, China
Received 5 May 2003; accepted 6 October 2003
Abstract
The reaction of O(3P) with ClONO2 was studied by means of the density functional method at the B3PW91/6-31G(d) level and the
correlation energy correction method at the MP2/6-311G(2df) level. Geometries, energies, and vibrational frequencies of reactants, transition
states, intermediates and products for the investigated reaction were examined. The energies were also computed by employing the quadratic
CI calculation at the QCISD/6-311G(2df) level. The reaction mechanism was investigated.
q 2004 Published by Elsevier B.V.
Keywords: Chlorine nitrate; O(3P); Mechanism; MP2; QCISD
1. Introduction
There is considerable interest in the mechanisms of
chemical reactions that take place in the chemically
perturbed region of the Antarctic ozone hole. The
importance of the chemical reactions taking place on the
surface of polar stratospheric clouds (PSCs) is firmly
established [1–13]. It is determined that chlorine nitrate
(ClONO2) and HCl, two major stratospheric reservoirs of Cl
[14], are involved in the chemical reactions on the PSCs,
and that these reactions lead to the release of Cl in the more
reactive forms of Cl2 and HOCl. Therefore, the property and
reaction of Chlorine nitrate, ClONO2, are always attached
importance to Refs. [10–12]. Chlorine nitrate is formed
from the reaction of ClO with NO2 in the presence of a third
body [15] and is removed via photolytic, heterogeneous, or
free radical reactions. In general, the reactions of ClONO2
with free radicals are less important than its photolytic and
heterogeneous reactions in the lower stratosphere. There are
many investigations on the reaction of ClONO2 with O(3P)
[16–20], but a few for its reaction mechanism. ClONO2
reacts with O(3P) as follows
Oð3PÞ þ ClONO2 !ClONOþ O2 ðaÞ
!ClOþ NO3 ðbÞ
!OClOþ NO2 ðcÞ
!ClOOþ NO2 ðdÞ
!ClOþ NOþ O2 ðeÞ
!ClNO2 þ O2 ðfÞ
!ClNOþ O3 ðgÞ
!Clþ NO2 þ O2 ðhÞ
The four latter reaction channels in the above list are the
subsequent steps for the four former reaction channels. Cai
et al. studied the mechanism for the reaction of O(3P) with
ClONO2 by employing the density functional method at the
B3LYP/6-31G(d) level [21], but only are the first two
reaction channels involved in their investigation. In order to
analyze the reaction mechanism in detail, therefore, the four
former reaction channels in the above list are studied by
means of the quantum chemical methods in the present
work.
2. Computation methods
The geometries of the reactants, products, intermediates,
and transition states for the examined reaction are optimized
bymeans of the density functional method at the B3PW91/6-
31G(d) level and the correlation energy correction method at
0166-1280/$ - see front matter q 2004 Published by Elsevier B.V.
doi:10.1016/j.theochem.2003.10.013
Journal of Molecular Structure (Theochem) 671 (2004) 45–51
www.elsevier.com/locate/theochem
* Corresponding author.
E-mail address: [email protected] (M. Li).
the MP2/6-311G(2df) level. Computations of the vibrational
frequencies for all the species are also performed at the same
computational levels. All the species are positively identified
for local minima with zero of the number of imaginary
frequencies and for transition states with the sole imaginary
frequency. To obtain more reliable energies of various
species on the potential energy surface (PES), the QCISD
single point energies are calculated at the QCISD/6-
311g(2df) level, with the optimized geometries obtained
from the MP2/6-311g(2df) optimization. In addition, the
wave functions obtained from the MP2/6-311g(2df) optim-
ization are used to compute the electron densities of the bond
critical points (BCP) for the intermediates and the transition
states by means of the AIM2000 programmer [22].
3. Results and discussion
The energies for all the species are summarized in
Table 1. Their optimized geometries are described,
respectively, in Figs. 1 and 4. The electron density contours
and the bond-critical points (BCP) for some species are
illustrated in Figs. 2 and 5. Figs. 3 and 6 show, respectively,
the profiles of the PESs for the reaction of O(3P) with Cl of
ClONO2 and the reaction of O(3P) with O of ClONO2.
3.1. On the reaction of O(3P) with Cl
For the reaction of O(3P) with Cl of ClONO2 in the gas
phase, there are several reaction channels through which the
different reaction products are generated. These reaction
channels are shown as follows
Oþ ClONO2 ! 1IM !1TS
1IM2! ClOþ NO3 ð1Þ
Oþ ClONO2 ! 1IM !2TS
2IM2! OClOþ NO2 ð2Þ
Oþ ClONO2 ! 1IM !3TS
3IM !4TS
4IM2! ClOþ NO3 ð3Þ
OþClONO2!1IM!3TS
3IM!5TS
5IM2!ClOOþNO2 ð4Þ
As presented, the reaction of O(3P) with Cl of ClONO2,
as the first step, leads to the intermediate 1IM. 1IM
generates the intermediates 1IM2, 2IM2, and 3IM,
respectively, with passing through the transition states
1TS, 2TS, and 3TS. 3IM passes through the transition states
4TS and 5TS and leads to the intermediates 4IM2 and
5IM2. Further, the intermediates 1IM2, 2IM2, 4IM2, and
5IM2 generate the reaction products. The optimized
geometries of the reactants, products, transition states, and
intermediates for the reaction of O(3P) with Cl of ClONO2
are shown in Fig. 1 and their electron density contours are
shown in Fig. 2.
Geometries. In the first reaction pathway, the OCl–ONO2
distances in 1IM, 1TS, and 1IM2 are 0.1708, 0.1902, and
0.1920 nm, respectively. The O–Cl–O bond angles are
113.98, 107.98, and 115.28. The electron densities of the BCP
for theOCl–ONO2 bonds in 1IM, 1TS, and 1IM2 are 0.2126,
0.1408 and 0.0602, respectively. It is clear that the Cl–ONO2
bond in ClONO2 is greatly weakened with the reaction going
on. Finally, the fracture of the OCl–ONO2 bond in 1IM2
results in the reaction products, ClO þ NO3 (P1).The second reaction channel leads to the fracture of the
OClO–NO2 bond in 1IM. The OClO–NO2 distances in
2TS and 2IM2 are, respectively, 0.1750 and 0.1963 nm.
Compared with 0.1570 nm in 1IM, they are increased
considerably. The electron densities of the BCP for the
OClO–NO2 bonds in 2TS and 2IM2 are, respectively,
0.0404 and 0.0942, which are much smaller than 0.2317 in
1IM. This result implies that the OClO–NO2 bonds in 2TSand 2IM2 are quite weak. The fracture of the OClO–NO2
bond in 2IM2 leads to the products, OClO þ NO2 (P2).
The transition state 3TS involves anO–O–Cl–O–N five-
membered ring. As shown in Fig. 1, the O–ON–O and Cl–
ON–O distances are 0.2340 and 0.2264 nm, respectively. The
fracture of the Cl–ON–O bond in 3TS leads to the
intermediate 3IM. The O2N–OOCl and O2NO–ClO bonds
in 3IM are, respectively, 0.1606 and 0.1360 nm. It is shown in
Fig. 2 that there is a ring-critical point (RCP) in the transition
state 3TS and the electron density for this RCP is 0.0159. It
may imply that the O–O–Cl–O–N five-membered ring in
3TS is of stability. Furthermore, the electron density of
Table 1
Energy differences, DE (kcal/mol), for various species in the O(3P) þ
ClONO2 reaction
B3PW91
6-31G(d)
MP2 6-311G(2df) MP2 þ ZPE QCISD
6-311G(2df)
Rea 0 0 0 0
1IM 222.8 233.5 231.9 216.9
1TS 219.7 229.0 227.2 212.8
1IM2 225.8 231.5 230.2 215.5
P1 224.7 217.2 214.2 29.3
2TS 24.9 231.6 230.8 9.0
2IM2 213.1 232.6 231.2 210.3
P2 45.1 24.9 2.5 58.6
3TS 214.2 221.5 220.4 0.6
3IM 248.5 248.1 246.2 237.2
4TS 228.0 228.2 227.3 217.2
4IM2 235.9 231.1 230.8 223.5
5TS 241.0 245.0 243.7 220.3
5IM2 246.7 251.8 247.7 242.6
P3 239.6 230.7 227.8 232.8
1IM0 20.5 7.0 9.8 24.4
1TS0 17.2 12.1 11.9 29.5
P4(cis) 214.0 218.6 220.6 215.1
2TS0 23.9 7.1 9.5 54.2
2IM20 2.1 4.8 3.8 17.7
P5(trans) 31.6 86.0 82.3 31.9
3IM0 7.9 17.00 17.7 16.8
3TS0 8.1 11.1 11.1 26.3
P4(trans) 28.1 214.7 216.9 212.0
4TS0 15.4 2.4 5.2 33.0
4IM20 1.4 228.7 227.5 17.1
P5(cis) 12.5 60.8 57.7 14.1
a Total energies of O(3P) þ ClONO2: B3PW91/6-31G(d), 2511597.63;
MP2/6-311G(2df), 2511067.82; MP2 þ ZPE, 2511057.93; QCISD/6-
311G(2df), 2511075.14 kcal/mol.
W. Shen et al. / Journal of Molecular Structure (Theochem) 671 (2004) 45–5146
the bond critical point for the O2NO–ClO bond in 3IM is
0.3646,which ismuchgreater than 0.0628 in 3TS. Obviously,
the O2NO–ClO bond in 3IM is quite stable.
The fracture of the O2NO–ClO bond or the O2N–OOCl
bond in 3IM, with passing through the transition state 4TS
or 5TS, leads to the intermediate 4IM2 or 5IM2. In the
3IM–4TS–4IM2 reaction, the O2NO–ClO distances in
3IM, 4TS, and 4IM2 are 0.1360, 0.1780, and 0.2216 nm,
respectively. The electron densities of the O2NO–ClO
BCP are 0.3646, 0.1318 and 0.0470, respectively. These
results show that the O2NO–ClO bond in 3IM is
weakened considerably with the reaction going on. For
the 3IM–5TS–5IM2 reaction, the O2N–OOCl distances
in 3IM, 5TS, and 5IM2 are 0.1606, 0.1790, and
Fig. 1. The optimized structures of all the species for the reaction of O(3P) with Cl of ClONO2 (bond lengths in nm, bond angles in degree).
W. Shen et al. / Journal of Molecular Structure (Theochem) 671 (2004) 45–51 47
0.2010 nm. The electron densities of the O2N–OOCl BCP
are 0.2193, 0.1111 and 0.0885, respectively. It is obvious
that the O2N–OOCl bond in 3IM is also weakened greatly
with the reaction going on. Further, the fracture of the
O2NO–ClO bond in 4IM2 or the O2N–OOCl bond in
5IM2 generates the reaction products ClO þ NO3 (P1) orClOO þ NO2 (P3).
Reaction mechanism. The QCISD PES for the reaction of
O(3P) with Cl of ClONO2 is shown in Fig. 3. The reaction of
O(3P) with ClONO2 leads to the intermediate 1IM. As
demonstrated in Fig. 3 and Table 1, this reaction step is
exothermic and barrierless. The energy of 1IM is lower than
that of the reactants O(3P) þ ClONO2 (Re) by 216.9 kcal/
mol. There are three reaction channels for 1IM found. These
three channels pass, respectively, through the transition
Fig. 2. Two-dimensional electron density contours in the reaction of O(3P) with Cl of ClONO2 and electron densities of some selected BCPs at the MP2/6-
311g(2df) level.
Fig. 3. Energy profile for the reaction of O(3P) with Cl of ClONO2.
W. Shen et al. / Journal of Molecular Structure (Theochem) 671 (2004) 45–5148
states 1TS, 2TS, and 3TS and lead to the intermediates
1IM2, 2IM2, and 3IM. The QCISD activating energies for
1TS, 2TS, and 3TS are, respectively, 4.1, 25.9, and
17.5 kcal/mol. The intermediate 1IM2, via a barrierless
and endothermic process, leads directly to the free radicals
ClO þ NO3 (P1) and the QCISD energy difference for this
endothermic process is 6.2 kcal/mol. The intermediate
2IM2 leads to the free radicals OClO þ NO2 (P2) and the
QCISD energy difference for the barrierless process is
68.9 kcal/mol. Two reaction channels for 3IM are found.
They pass, respectively, through the transition states 4TS
and 5TS and generate the intermediates 4IM2 and 5IM2.
The activating energies for 4TS and 5TS are 20.0 and
16.9 kcal/mol, respectively. The formation of the free
radicals ClO þ NO3 (P1) or ClOO þ NO2 (P3) generated,
respectively, from 4IM2 or 5IM2 is barrierless and
endothermic. The corresponding energy differences are
14.2 kcal/mol for P1 and 9.8 kcal/mol for P3. Furthermore,
it is found that the activating energy for 1TS is much lower
than the activating energies for other transition states are.
Therefore, the reaction of O(3P) with Cl of ClONO2 leads
mainly to the free radicals ClO and NO3, which is in
agreement with the experiment [15].
3.2. On the reaction of O(3P) with O
For the reaction of O(3P) with O of ClONO2, The cis- and
trans-products are generated. The channels for this reaction
Fig. 4. The optimized structures of all the species for the reaction of O(3P) with O of ClONO2 (bond lengths in nm, bond angles in degree).
W. Shen et al. / Journal of Molecular Structure (Theochem) 671 (2004) 45–51 49
are shown as follows
Oþ ClONO2 ! 1IM0 !1TS0
OOþ ClONOðcisÞ ð1Þ
Oþ ClONO2 !2TS0
2IM20 ! OClþ OONOðtransÞ ð2Þ
Oþ ClONO2 ! 3IM0 !3TS0
OOþ ClONOðtransÞ ð3Þ
Oþ ClONO2 !4TS0
4IM20 ! OClþ OONOðcisÞ ð4Þ
As shown, the reaction of O(3P) with O of ClONO2 results in
the intermediates 1IM0 and 3IM0. 1IM0 leads to the products
OO þ ClONO(cis), passing through the transition state 1TS0,
and to the intermediate 2IM20 that leads to the products
OCl þ OONO(trans), passing through the transition state
2TS0. Like 1IM0, 3IM0 also has two reaction channels. One
leads to the products OO þ ClONO(trans) and the other to
the intermediate 4IM20 that gives the products OCl þ
OONO(cis) passing through the transition state 4TS0. The
optimized geometries for all the species are shown in Fig. 4
and their electron density contours are shown in Fig. 5.
Geometries. The OO–NO2Cl distances in 1IM0 and 1TS0
are 0.1390 and 0.1570 nm, respectively. The O–O–N bond
angle are 116.38 for 1IM0 and 113.88 for 1TS0. The electron
densities of the OO–NO2Cl BCP are 0.3460 for 1IM0 and
0.1817 for 1TS0. It is clear that the OO–NO2Cl bond in 1TS0
is weakened greatly, compared with that in 1IM0. The
fracture of the OO–NO2Cl bond in 1TS0 results in the
products P4(cis), O2 þ ClONO(cis).
The second reaction channel for 1IM0 leads to the
intermediate 2IM20. From 1IM0 to 2IM20, the ClO–NOO2
distance is increased and theClO–O2NOdistance decreased,
the ClO–O2NOdistance is decreased to 0.2140 nm in 2IM20,
whereas the ClO–NOO2 distances in 1IM0, 2TS0, and 2IM20
are 0.1810, 0.1938, and 0.2000 nm, respectively. As shown
in Fig. 4, the intermediate 2IM20 involves an O–O–N three-
membered ring. It is demonstrated in Fig. 5 that there is a
ring-critical point (RCP) in the O–O–N three-membered
ring for 2IM20 and the electron density for this ring-critical
point is 0.0409. This result implies that 2IM20 with the O–
O–N three-membered ring is stable. The fracture of the
ClO–NOO2 and ClO–OONO bonds in 2IM20 result in the
reaction products P5(trans), ClO þ OONO(trans).
The OO–NO2Cl bonds in 3IM0 and 3TS0 are 0.1330 and
0.1605 nm. The electron densities of the OO–NO2Cl BCP
are 0.3258 for 3IM0 and 0.1956 for 3TS0. The OO–NO2Cl
bond in 3TS0 is weakened greatly, compared with that in
3IM0. The fracture of the OO–NO2Cl bond in 3TS0 leads to
the products P4(trans), O2 þ ClONO(trans).
The ClO–NOO2 distances in 3IM0, 4TS0, and 4IM20 are
0.1400, 0.1640and0.2060 nm, respectively.TheClO–OONO
Fig. 5. Two-dimensional electron density contours in the reaction of O(3P) with O of ClONO2 and electron densities of some selected BCPs at the MP2/6-
311g(2df) level.
W. Shen et al. / Journal of Molecular Structure (Theochem) 671 (2004) 45–5150
distance is decreased to 0.1940 nm. Like 2IM20, the
intermediate 4IM20 also has an O–O–N three-membered
ring. As shown in Fig. 5, there is also a ring-critical point in
theO–O–N three-membered ring for 4IM20 and the electron
density for this ring-critical point is 0.0456. The fracture of
the ClO–NOO2 and ClO–OONO bonds in 4IM20 results in
the reaction products P5(cis), ClO þ OONO(cis).
Reaction mechanism. The QCISD PES for the reaction of
O(3P) with O of ClONO2 is shown in Fig. 6. The reaction of
O(3P) with ClONO2 leads to the intermediates 1IM0 and
3IM0. As demonstrated in Fig. 6 and Table 1, the formation
of 1IM0 is endothermic and barrierless. The energy of 1IM0
is higher than that of the reactants O(3P) þ ClONO2 (Re) by
24.4 kcal/mol. There are two reaction channels for 1IM0
found. One generates the products OO þ ClONO(cis)
(P4(cis)), passing through the transition state 1TS0, and
the other, passing through the transition state 2TS0, leads to
the intermediate 2IM20 that gives the products OCl þ
OONO(trans) (P5(trans)). The QCISD activating energies
for 1TS0 and 2TS0 are 5.1 and 29.8 kcal/mol. The
intermediate 2IM20, via a barrierless and endothermic
process, generates directly the free radicals OCl þ
OONO(trans) (P5(trans)) and the QCISD energy difference
for this endothermic process is 14.2 kcal/mol.
Like 1IM0, the formation of 3IM0 is also endothermic
and barrierless. The energy of 3IM0 is higher than that of the
reactants O(3P) þ ClONO2 (Re) by 16.8 kcal/mol. One of
two reaction channels for 3IM0 generates the products
OO þ ClONO(trans) (P4(trans)), passing through the
transition state 3TS0, and the other, passing through the
transition state 4TS0, leads to the intermediate 4IM20 that
gives the products OCl þ OONO(cis) (P5(cis)). The
QCISD activating energies for 3TS0 and 4TS0 are 9.5 and
16.2 kcal/mol. The intermediate 4IM20, via a barrierless and
exothermic process, generates directly the free radicals
OCl þ OONO(cis) (P5(cis)) and the QCISD energy differ-
ence for this exothermic process is 23.0 kcal/mol.
Furthermore, it is known that the energy differences
between all the transition states for the reaction of O(3P)
with O of ClONO2 and the reactants O(3P) þ ClONO2 (Re)
are large. They are, respectively, 29.5 for 1TS0, 54.2 for
2TS0, 26.3 for 3TS0, and 33.0 kcal/mol for 4TS0. Compared
with the reaction of O(3P) with Cl of ClONO2, therefore, the
reaction of O(3P) with O of ClONO2 is difficult.
4. Conclusions
For the reaction of O(3P) with ClONO2, eight different
reaction channels, including nine transition states and 10
reaction intermediates, are found. O(3P) may react with Cl
andO of ClONO2, respectively. The reaction of O(3P)with O
of ClONO2 is difficult, compared with that of O(3P) with Cl
of ClONO2. The reaction of O(3P) with Cl of ClONO2 leads
mainly to the free radicals ClO and NO3, which is in
agreement with the experiment.
Acknowledgements
This work was supported by Natural Science Foundation
of Chongqing City, People’s Republic of China (Grant No.
2002-7473).
References
[1] M.A. Tolbert, M.J. Rossi, R. Malhotra, D.M. Golden, Science 238
(1987) 1258.
[2] M.J. Molina, T.L. Tso, L.T. Molina, F.C. Wang, Science 238 (1987)
1253.
[3] M.J. Rossi, R. Malhotra, D.M. Golden, Geophys. Res. Lett. 14 (1987)
127.
[4] M.A. Tolbert, M.J. Rossi, D.M. Golden, Geophys. Res. Lett. 15
(1988) 847.
[5] M.T. Leu, Geophys. Res. Lett. 15 (1988) 851.
[6] M.A. Quinlan, C.M. Reihs, D.M. Golden, M.A. Tolbert, J. Phys.
Chem. 94 (1990) 3255.
[7] D.J. Hofmann, S.J. Oltmans, Geophys. Res. Lett. 19 (1992) 2211.
[8] D.R. Hanson, A.R. Ravishankara, J. Geophys. Res. 96 (1991) 5081.
[9] M.T. Leu, S.B. Moore, L.E. Keyser, J. Phys. Chem. 95 (1991) 7763.
[10] M.J. Prather, Nature 355 (1992) 534.
[11] D.R. Hanson, A.R. Ravishankara, J. Phys. Chem. 96 (1992) 7674.
[12] J.P.D. Abbatt, M.J. Molina, J. Phys. Chem. 96 (1992) 7674.
[13] S.C. Wofsy, M.J. Molina, R.J. Salawitch, L.E. Fox, M.B. McElroy,
J. Geophys. Res. 93 (1988) 2442.
[14] F.S. Rowland, Annu. Rev. Phys. Chem. 42 (1991) 731.
[15] L. Goldfarb, M.H. Harwood, J.B. Burkholder, A.R. Ravishankara,
J. Phys. Chem. A 102 (1998) 8556.
[16] M.J. Kurylo, Chem. Phys. Lett. 49 (1977) 467.
[17] W.S. Smith, C.C. Chou, F.S. Rowland, Geophys. Res. Lett. 4 (1977)
517.
[18] G.S. Tyndall, C.S. Kegley-Owen, J.J. Orlando, J. Chem. Soc.,
(Faraday Trans.) 93 (1997) 2675.
[19] A.R. Ravishankara, D.D. Davis, G. Smith, Geophys. Res. Lett. 4
(1977) 7.
[20] L.T. Molina, J.E. Spencer, M.J. Molina, Chem. Phys. Lett. 45 (1977)
158.
[21] X.P. Cai, D.C. Fang, X.Y. Fu, Acta Phys. Chem. Sinica 16 (2000) 689.
[22] F. Biegler-Konig, J. Schonbohm, R. Derdau, D. Bayles, R.F.W.
Bader, AIM 2000, Version 1, 2000.Fig. 6. Energy profile for the reaction of O(3P) with O of ClONO2.
W. Shen et al. / Journal of Molecular Structure (Theochem) 671 (2004) 45–51 51