Molecular cloud chemistry and the importance of dielectronic recombination
Abstract
Dielectronic recombination (DR) of singly charged ions is a reaction pathway that is commonly neglected in chemical models of molecular clouds. In this study we include state-of-the-art DR data for He, C, N, O, Na, and Mg in chemical models used to simulate dense molecular clouds, protostars, and diffuse molecular clouds. We also update the radiative recombination (RR) rate coefficients for H, He, C, N, O, Na, and Mg to the current state-of-the-art values. The new RR data has little effect on the models. However, the inclusion of DR results in significant differences in gas-grain models of dense, cold molecular clouds for the evolution of a number of surface and gas-phase species. We find differences of a factor of 2 in the abundance for 74 of the 655 species at times of -- years in this model when we include DR. Of these 74 species, 16 have at least a factor of 10 difference in abundance. We find the largest differences for species formed on the surface of dust grains. These differences are due primarily to the addition of C DR, which increases the neutral C abundance, thereby enhancing the accretion of C onto dust. These results may be important for the warm-up phase of molecular clouds when surface species are desorbed into the gas phase. We also note that no reliable state-of-the-art RR or DR data exist for Si, P, S, Cl, and Fe. Modern calculations for these ions are needed to better constrain molecular cloud models.
Keywords
Cite
@article{arxiv.0809.4504,
title = {Molecular cloud chemistry and the importance of dielectronic recombination},
author = {P. Bryans and H. Kreckel and E. Roueff and V. Wakelam and D. W. Savin},
journal= {arXiv preprint arXiv:0809.4504},
year = {2011}
}
Comments
24 pages, 2 tables, 9 figures. Submitted to ApJ