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The H 3 + + H 2 Reaction; A Possible Mechanism for para - H 3 + Enrichment in the Diffuse Interstellar Medium

The H 3 + + H 2 Reaction; A Possible Mechanism for para - H 3 + Enrichment in the Diffuse Interstellar Medium. Lieutenant Colonel Brian A. Tom, USAF University of Illinois at Urbana-Champaign Inaugural MWAM, 2008. H 3 + - Abundant and Reactive. (Science, 279 , 1910, 1998) .

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The H 3 + + H 2 Reaction; A Possible Mechanism for para - H 3 + Enrichment in the Diffuse Interstellar Medium

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  1. 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

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

  3. H3+ - An Astrophysical Probe H2 H3+ Para Para Ortho Ortho (3:1) (2:1) T. Oka, PNAS, 103, 12235, (2006)

  4. 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% para-H3+ ortho-H3+ Indrioloet al., Ap. J., 671, 1736, (2007) The cause? Reaction-induced spin modification H3+ + H2H2 + H3+

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

  6. H3+ + H2H2 + H3+ Identity + + + + + + Hop Exchange M. Cordonnier et al., J. Chem. Phys., 113, 3181, (2000)

  7. 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 H3+ + H2H2 + H3+ ortho-H3+ + ortho-H2 ortho-H2 + ortho-H3+ ortho-H3+ + para-H2 ortho-H2 + para-H3+ para-H3+ + ortho-H2 para-H2 + ortho-H3+ para-H3+ + para-H2 para-H2 + para-H3+ T. Oka, J. Mol. Spec., 228, 635, (2004)

  8. H3+ + H2H2 + H3+ Problem ortho-H2 • Previous model does • not account for energy • differences between • ortho and para ground • states 120 cm-1 para-H2 • Park and Light have • addressed this K. Park and J. Light, J. Chem. Phys., 126, 044305, (2007)

  9. Experiment

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

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

  12. Results

  13. Temperature and Para Fraction

  14. 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. Shefferet al., accepted for Astrophys. J. (2008)

  15. 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

  16. Acknowledgments • Andrew Mills, Kyle Crabtree, Michael Wiczer • McCall Group

  17. Backup slides

  18. Motivation H2+ + H2 → H3+ + H He Cosmic Rays H2+ H+ and H2+ H 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)

  19. DR - Spectroscopy

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