implications of the h 3 + + h 2 h 2 + h 3 + reaction for the ortho- to para-h 3 + ratio in...
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Implications of the HImplications of the H33++ + H + H22 H H22 + +
HH33+ + reaction for the reaction for the ortho-ortho- to to para-para-HH33
++ ratio in interstellar clouds ratio in interstellar clouds
Kyle N. Crabtree, Lt. Col. Brian A. Tom, USAF, Carrie A. Kauffman, Brett A. McGuire, and
Benjamin J. McCall
University of Illinois22 March 2010
http://bjm.scs.uiuc.edu
OverviewOverview
H3+ in interstellar clouds
Symmetry, Nuclear Spin, and H3+
H3+ + H2 H2 + H3
+
Experimental Details Results
Periodic TablePeriodic Table
Astronomer’s Periodic TableAstronomer’s Periodic Table
AstronomicalAstronomicalSpectroscopy of HSpectroscopy of H33
++
R(1,0)36685 Å
R(1,1)u
36681 Å
B. J. McCall Ph.D. Thesis, University of Chicago (2001).
B. J. McCall, T. R. Geballe, K. H. Hinkle, and T. Oka ApJ (1999), 522, 338-348.
HH33++ Spectroscopy Spectroscopy
N. IndrioloPrivate Communication
HH33++ Temperature Temperature
Observed R(1,0) and R(1,1)u lines Tex
Tex = 30 K in both diffuse and dense clouds
T01 (H2 J=0,1 states) = 60 K in diffuse clouds
Dense cloud temperatures: 10-30 K
OverviewOverview
H3+ in interstellar clouds
Symmetry, Nuclear Spin, and H3+
H3+ + H2 H2 + H3
+
Experimental Details Results
Nuclear Spin Constraints on Nuclear Spin Constraints on Rotational StatesRotational States
Nuclear Spin Constraints on Nuclear Spin Constraints on Rotational StatesRotational States
Ortho and para-H3+
are distinct species Tex ≠ temperature
n(1,0)/n(1,1) related to ortho/para ratio
“Low” Tex overabundance of para-H3
+
H3+ + H2 H2 + H3
+ reaction allows H3+
population to transfer between ortho and para spin configurations
OverviewOverview
H3+ in interstellar clouds
Symmetry, Nuclear Spin, and H3+
H3+ + H2 H2 + H3
+
› Reaction Outcomes› High Temperature› Low Temperature
Experimental Details Results
HH33++ + H + H22 H H22 + H + H33
++
“identity”
“hop”
“exchange”
H5+
1
3
6
not well understood:branching ratio
α = hop/exchange quantum effects at low T
simplest bimolecular reaction involving a polyatomic
most common bimolecular reaction in the universe: ~1052 s-1
Nuclear Spin StatisticalNuclear Spin StatisticalWeightsWeights
1/2 0 = 1/2 3/2 0 = 3/2
+ → +++
para para paraortho
H3+ H2 Type o-H3
+ p-H3+
para ortho hop 2/3 1/3
para ortho exch. 1/3 2/3
para para hop 0 1
para para exch. 1/3 2/3
p3 ≡ [p-H3+]/[total
H3+]
p2 ≡ [p-H2]/[total H2] ≡ khop/kexchange
M. Cordonnier et al., J. Chem Phys (2000), 113, 3181.T. Oka, J. Mol. Spec. (2004), 228, 635.
High Temperature ModelHigh Temperature Model
High Temperature ModelHigh Temperature Model
Key Features
•Linear
•p3 = 0.5 w/n-H2
M. Cordonnier et al., J. Chem Phys (2000), 113, 3181.
Need for Another Model?Need for Another Model?
p-H2; J = 0
o-H2; J = 1
ΔE = 170 K
K. Park and J. Light, J. Chem. Phys. (2007), 126, 044305.
Dynamics of Floppy Molecules Session123N Moscone CenterThursday 1:30 pm Pub #705
Experimental measurements of the H3+ + H2 →
(H5+)* → H2 + H3
+ reaction
Kyle N Crabtree, Brian A Tom, Carrie A Kauffman, Brett A McGuire, Benjamin J McCall
Low Temperature ModelLow Temperature Model
Low Temperature ModelLow Temperature Model
Key Features
•Curvature
•p3 not necessarily 0.5 with n-H2
Model LimitationsModel Limitations
HT model only considers conservation of angular momentum; LT model adds energetic considerations
Neither model takes into account the H5
+ potential energy surface LT model only uses rate coefficients
from (1,0) and (1,1) states, not all ortho and para states
OverviewOverview
H3+ in interstellar clouds
Symmetry, Nuclear Spin, and H3+
H3+ + H2 H2 + H3
+
Experimental Details› Difference Frequency Generation Laser› Para-H2 Production› Supersonic Ion Source/cw-CRDS› Hollow Cathode/Direct Absorption
Results
Difference Frequency Difference Frequency Generation Laser (DFG)Generation Laser (DFG)
Spectral Range: 2.2-4.8 μmOutput Power: 500-700 μW
Para-HPara-H22 Production Production
15 K>99.9% purity
B. A. Tom, S. Bhasker, Y. Miyamoto, T. Momose, and B. J. McCall Rev. Sci. Inst (2009), 80, 016108
Ferric Oxide catalyst
Hollow Cathode CellHollow Cathode Cell
T = 130 – 300 K
Piezo Pulsed Supersonic Piezo Pulsed Supersonic Expansion Ion SourceExpansion Ion Source
Piezo disc
Plunger
T < 130 K
OverviewOverview
H3+ in interstellar clouds
Symmetry, Nuclear Spin, and H3+
H3+ + H2 H2 + H3
+
Experimental Details Results
Hollow Cathode: T=310 KHollow Cathode: T=310 K
Hollow Cathode: T=180 KHollow Cathode: T=180 K
Hollow Cathode: T=130 KHollow Cathode: T=130 K
Supersonic Expansion:Supersonic Expansion:T=110 KT=110 K
Low Temperature ModelLow Temperature Model
Diffuse Cloud ObservationsDiffuse Cloud Observations
Survey of diffuse cloud sightlines with known H2 (1)/(0) measurements
H3+ measured in:
› ζ-Per UKIRT (CGS4)› X-Per UKIRT (CGS4)› HD 154368 Gemini
South (Phoenix) More data from VLT
(CRIRES) and Keck (NIRSPEC)
UKIRT
Gemini South
Diffuse Cloud ObservationsDiffuse Cloud Observations
ConclusionsConclusions
Observed (1,1):(1,0) ratio ortho:para- H3
+ ratio, not temperature
Likely represents steady state of H3+ +
H2 reaction, not thermalization Decrease of with temperature H3
+ ortho:para ratio possibly allows determination of H2 ortho:para ratio in dense clouds where H2 not observable
AcknowledgementsAcknowledgements
McCall Research Group
Kisam Park
Funding: