Skip to main content

Advertisement

MD simulation for H2 formation on amorphous ice

Article metrics

  • 241 Accesses

  • 10 Citations

Abstract

Recent advances in a series of studies based on the molecular dynamics (MD) computer simulation that was performed to investigate the whole of H2 formation process on the surface of dust grains throughout within a single model are reviewed. Amorphous water ice slabs were generated at 10 K and 70 K as a model surface of dust grains, and then the first and second incident H atoms were thrown onto the surface. The following fundamental processes of H2 formation via two H atoms’ recombination, H+H → H2, were studied in detail; 1) the sticking of H atom onto the surface, 2) the diffusion of H atom on the surface, 3) the reaction of two H atoms on the surface, 4) the ejection of H2 from the ice surface. The sticking probability, the mobility, the reaction probability, and the ejection lifetime were selfconsistantly obtained for the above processes. The product energy distribution of H2 molecules formed on icy mantles of dust grains was also studied, and it was found that H2 molecules can be highly vibrationally excited by formation pumping mechanism.

References

  1. Buch, V, Identification of two distinct structual and dynamical domains in an amorphous water cluster, J. Chem. Phys., 93, 2631–2639, 1990.

  2. Buch, V. and J. P. Devlin, Preferential adsorption of ortho-H2 with respect topara-H2 on the amorphous ice surface, J. Chem. Phys., 98, 4195–4206, 1993.

  3. Buch, V. and J. P. Devlin, Interpretation of the 4141 inverse centimeters (2.415 microns) interstellar infrared absorption feature, Astrophys. J., 431, L135–L138, 1994.

  4. Buch, V. and Q. Zhang, Sticking probability of H and D atoms on amorphous ice: computational study, Astrophys. J., 379, 647–652, 1991.

  5. Duley, W. W. and D. A. Williams, The formation of interstellar H2 on amorphous silicate grains, Mon. Not. R.Astron. Soc., 223, 177–182, 1986.

  6. Duley, W. W. and D. A. Williams, The formation of H2 on interstellar dust, Mon. Not. R. Astron. Soc., 260, 37–42, 1993.

  7. Fletcher, N. H., The Chemical Physics of Ice, 264 pp., Cambridge University Press, London, 1970.

  8. Flubacher, P., A. J. Leadbetter, and J. A. Morrison, Heat capacity of ice at low temperatures, J. Chem. Phys., 33, 1751–1755, 1960.

  9. Hansen, J. P. and I. R. McDonald, Theory of Simple Liquids (2nd edition), 547 pp., Academic Press, New York, 1986.

  10. Herbst, E., Chemistry in the interstellar medium, Annu. Rev. Phys. Chem., 46, 27–53, 1995.

  11. Herzberg, G., Molecular Spectra and Molecular Structure I. Spectra of Diatomic Molecules (2nd edition), 620 pp., Van Nostrand, New York, 1950.

  12. Hollenbach, D. and E. E. Salpeter, Surface adsorption of light gas atoms, J. Chem. Phys., 53, 79–86, 1970.

  13. Hunter, D. A. and W. D. Watson, The translational and rotational energy of hydrogen molecules after recombination on interstellar grains, Astrophys. J., 226, 477–482, 1978.

  14. Jenniskens, P. and D. F. Blake, Structual transitions in amorphous water ice and astrophysical implications, Science, 265, 753–756, 1994.

  15. Jenniskens, P., D. F. Blake, M. A. Wilson, and A. Pohorille, High-density amorphous ice, the frost on interstellar grains, Astrophys. J., 455, 389–401, 1995.

  16. Jorgensen, W. L., The revised TIPS for simulations of liquid water and aqueous solutions, J. Chem. Phys., 77, 4156–4163, 1982.

  17. Leitch-Devlin, M. A. and D. A. Williams, Sticking coefficients for atoms and molecules at the surfaces of interstellar dust grains, Mon. Not. R. Astron Soc., 213, 295–306, 1985.

  18. Masuda, K. and J. Takahashi, The sticking probability of a hydrogen atom onicy mantle, Adv. Space Res., 19, 1019–1022, 1997.

  19. Masuda, K., J. Takahashi, and T. Mukai, Sticking probability and mobility of a hydrogen atom on icy mantle of dust grains, Astron. Astrophys., 330, 773–781, 1998.

  20. Takahashi, J., M. Nagaoka, and K. Masuda, Quantum mechanical treatment for the diffusion process of a hydrogen atom on the amorphous water ice surface, Int. J. Quantum Chem., 70, 379–385, 1998.

  21. Takahashi, J., K. Masuda, and M. Nagaoka, The formation mechanism of molecular hydrogen on icy mantles of interstellar dust, Mon. Not. R. Astron. Soc., 306, 22–30, 1999a.

  22. Takahashi, J., K. Masuda, and M. Nagaoka, Product energy distribution of molecular hydrogen formed on icy mantles of interstellar dust, Astrophys. J., 520, 724–731, 1999b.

  23. Usuda, T., Ph.D. Thesis, Univ. Tokyo, Japan, 1996.

  24. Williams, D. A., Physical andchemical processes on dust, in Dust and Chemistry in Astronomy, edited by T. J. Millar and D. A. Williams, Institute of Physics Publishing, Philadelphia, pp. 143–170, 1993.

  25. Zhang, Q. and V. Buch, Computational study of formation dynamics and structure of amorphous ice condensates, J. Chem. Phys., 92, 5004–5016, 1990.

  26. Zhang, Q., N. Sabelli, and V. Buch, Potential energy surface of H—H2O, J. Chem. Phys., 95, 1080–1085, 1991.

Download references

Author information

Correspondence to Junko Takahashi.

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Takahashi, J. MD simulation for H2 formation on amorphous ice. Earth Planet Sp 51, 1215–1222 (1999) doi:10.1186/BF03351595

Download citation

Keywords

  • Dust
  • Vibrational Energy
  • Translational Energy
  • Interstellar Dust
  • Sticking Probability