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Spectroscopic measurements of the reaction H3+ + H2 H2 + H3+
Kyle N. Crabtree, Carrie A. Kauffman, Brian A. Tom, Eftalda Becka, Brett A. McGuire, Benjamin J. McCall University of Illinois
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66th OSU International Symposium on Molecular Spectroscopy
H3+ + H2 H2 + H3+ H3+ + H2 reaction important for thermalization of H3+ in interstellar clouds (see TF09, 160 MA, 3:52 pm) 1 “identity” H5+ 3 “hop” para-H3+ ortho-H3+ 1/2 3/2 a = kH/kE 6 “exchange” 20 June 2011 66th OSU International Symposium on Molecular Spectroscopy
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Previous experimental work
M. Cordonnier et al., J. Chem. Phys. (2000), 113, a = K 20 June 2011 66th OSU International Symposium on Molecular Spectroscopy
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Other experimental work
hop exch hop:exchange Experimental data a increases with increasing T temperature 20 June 2011 66th OSU International Symposium on Molecular Spectroscopy
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66th OSU International Symposium on Molecular Spectroscopy
Experimental setup 20 June 2011 66th OSU International Symposium on Molecular Spectroscopy
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66th OSU International Symposium on Molecular Spectroscopy
Hollow cathode cell 20 June 2011 66th OSU International Symposium on Molecular Spectroscopy
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66th OSU International Symposium on Molecular Spectroscopy
Target transitions R(3,0) cm-1 R(3,1)u cm-1 R(3,2)u cm-1 R(3,3)l cm-1 R(2,1)u cm-1 Kinetic and rotational temperature p-H3+ fraction (p3) R(2,2)l cm-1 R(1,0) cm-1 R(1,1)u cm-1 20 June 2011 66th OSU International Symposium on Molecular Spectroscopy
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H3+ pressure dependence
Uncooled cell (350 K) Liquid N2 cooled cell (135 K) Decrease in H3+ number density with increasing pressure 3-body collisions (H3+ + 2H2 H5+ + H2) To measure hop:exchange ratio of the bimolecular H3+ + H2 reaction, measure p3 as a function of p2 at two pressures for each temperature 20 June 2011 66th OSU International Symposium on Molecular Spectroscopy
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H3+/H2 para fraction relationships
Uncooled cell (350 K) Liquid N2 cooled cell (135 K) 2-body HT 3-body HT Low temperature 20 June 2011 66th OSU International Symposium on Molecular Spectroscopy
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Uncooled plasma (350 K) fit
No evidence for influence of nuclear-spin-dependent 3-body collisions in data 20 June 2011 66th OSU International Symposium on Molecular Spectroscopy
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Liquid N2 cooled plasma (135 K) modeling
Tkin = 135 K 20 June 2011 66th OSU International Symposium on Molecular Spectroscopy
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Summary of experimental data
T = 450 K a decreases with temperature: 1.6 at 350 K down to 0.5 at 135 K 20 June 2011 66th OSU International Symposium on Molecular Spectroscopy
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66th OSU International Symposium on Molecular Spectroscopy
H3+ + H2 H2 + H3+ 1 “identity” H5+ 3 “hop” 6 “exchange” 20 June 2011 66th OSU International Symposium on Molecular Spectroscopy
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Dynamics of Reaction D2d C2v C2v hop exchange
PES: Z. Xie, B. J. Braams, & J. M. Bowman, J. Chem. Phys. (2005) 122, D2d 3000 cm-1 C2v 1500 cm-1 50 cm-1 C2v hop exchange Hop is dynamically faster than exchange; short complex lifetime favors hop At low temperatures, “statistical” hop/exchange = 0.5 seems valid 20 June 2011 66th OSU International Symposium on Molecular Spectroscopy
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66th OSU International Symposium on Molecular Spectroscopy
Acknowledgements Kisam Park More information: Tomorrow, TF09, 160 MA K. N. Crabtree, B. A. Tom, B. J. McCall, J. Chem. Phys. (2011) 134, K. N. Crabtree et al., J. Chem. Phys. (2011) 134, 20 June 2011 66th OSU International Symposium on Molecular Spectroscopy
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