Effects of multiquantum transitions on molecular populations in grain-forming circumstellar environments

Details Effects of multiquantum transitions on molecular populations in grain-forming circumstellar environments Effects of multiquantum transitions on molecular populations in grain-forming circumstellar environments

Jun 1985

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1985apj...293..463n&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 293, June 15, 1985, p. 463-469.

Astronomy and Astrophysics

Astrophysics

5

Energy Transfer, Molecular Interactions, Stellar Envelopes, Transition Probabilities, Carbon Monoxide, Molecular Collisions, Nonequilibrium Thermodynamics, Vibrational Spectra

Scientific paper

Simplification of astrophysical calculations can be achieved by invoking the condition of local thermodynamic equilibrium; however, recent investigations suggest that this assumption may not be valid for certain astrophysical regions. To examine the effects of multiquantum translation to vibration transitions in expanding circumstellar envelopes, vibrational populations of the lowest 20 levels of CO have been calculated as a function of pressure and radiation density for H atom-CO collisions. Significant departure from local thermodynamic equilibrium is indicated, which implies lower dissociation rates for molecular components and a subsequent enhancement in the rate of grain formation by many orders of magnitude. Stabilization of intermediate species before they can dissociate may facilitate the formation of refractory grain cores in very hot, dilute outflows. As the present calculations indicate, laboratory measurements of state-to-state translation to vibration rates are needed for a more complete understanding of circumstellar chemistry.

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