The H3+ + H2 Reaction; A Possible Mechanism for para- H3+ Enrichment in the Diffuse Interstellar Medium Lieutenant Colonel Brian A. Tom, USAF University.

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Presentation transcript:

The H3+ + H2 Reaction; A Possible Mechanism for para- H3+ Enrichment in the Diffuse Interstellar Medium Lieutenant Colonel Brian A. Tom, USAF University of Illinois at Urbana-Champaign Inaugural MWAM, 2008

H3+ - Abundant and Reactive (Science, 279, 1910, 1998) (Nature, 384, 334, 1996) (ApJ, 183, L17-20, 1973) (ApJ, 185, 505, 1973) (Phys. Rev., 26, 44, 1925)

H3+ - An Astrophysical Probe Ortho Para (3:1) H3+ Ortho Para (2:1) T. Oka, PNAS, 103, 12235, (2006)

Para-H3+ is Enriched in Diffuse Clouds Texcitation measured from H3+ is consistently ~ 40 K lower than H2 – derived Trot ~ 70 K This indicates para-H3+ is enriched to ~ 65% ortho-H3+ para-H3+ Indriolo et al., Ap. J., 671, 1736, (2007) The cause? Reaction-induced spin modification H3+ + H2 H2 + H3+

Theory of spin modification in H3+ + H2 →H2 + H3+

H3+ + H2 H2 + H3+ + + + Identity Hop Exchange M. Cordonnier et al., J. Chem. Phys., 113, 3181, (2000)

H3+ + H2 H2 + H3+ ortho-H3+ + ortho-H2 ortho-H2 + ortho-H3+ para-H3+ + ortho-H2 → ortho-H3+ para-H3+ Hop 2/3 1/3 Exchange 1/3 2/3 para-H3+ + para-H2 → ortho-H3+ para-H3+ Hop 0 1 Exchange 1/3 2/3 ortho-H3+ + ortho-H2 ortho-H3+ + para-H2 para-H3+ + ortho-H2 para-H3+ + para-H2 ortho-H2 + ortho-H3+ ortho-H2 + para-H3+ para-H2 + ortho-H3+ para-H2 + para-H3+ T. Oka, J. Mol. Spec., 228, 635, (2004)

H3+ + H2 H2 + H3+ Problem Previous model does not account for energy ortho-H2 para-H2 120 cm-1 Previous model does not account for energy differences between ortho and para ground states Problem Park and Light have addressed this K. Park and J. Light, J. Chem. Phys., 126, 044305, (2007)

Experiment

Spectroscopy Temperature Para-H3+ fraction J 1 2 3 K (ortho) (para) (para) (ortho) J 500 1 2 3 E(cm-1) K R(1,0) R(1,1)u 64 cm-1 169 cm-1 315 cm-1 237 cm-1 87 cm-1 Temperature Para-H3+ fraction

Spectroscopy Pulsed Source Para-H2 generator Telescope InSb LiNbO3 Achromat Glan Prism Nd:YAG λ/4 λ/2 AOM Wavemeter Ti:Sapphire λ/2

Results

Temperature and Para Fraction

An Explanation for Enrichment? 0.79 ± 0.11 Using  = 0.51 ± 0.11, and  = 0.79 ± 0.11; The average para-H3+ fraction measured from 9 diffuse cloud sightlines is 0.65 ± 0.15 Y. Sheffer et al., accepted for Astrophys. J. (2008)

Conclusions H3+ plays an important role in the interstellar medium We have inferred  = kH/kE = 0.79 ± 0.11 for 60-100 K Could explain para-H3+ enrichment in diffuse ISM More experiments are necessary to understand the underlying process Texcitation by itself is not a reliable measure of rotational temperature in the ISM

Acknowledgments Andrew Mills, Kyle Crabtree, Michael Wiczer McCall Group

Backup slides

H Motivation H2+ + H2 → H3+ + H H+ and H2+ He Cosmic Rays H2+ H3+ H+ O, C, N, Ne, Mg, Si, Fe… T. R. Hogness and E. G. Lunn, Phys. Rev., 26, 44, (1925) T. Oka, PNAS, 103, 12235, (2006)

DR - Spectroscopy