Recommended Thermal Rate Coefficients for the C + H${}_3^{+}$ Reaction and Some Astrochemical Implications

Abstract

We have incorporated our experimentally derived thermal rate coefficients for C + H${}_3^{+}$ forming CH${}^{+}$ and CH${}_2^{+}$ into a commonly used astrochemical model. We find that the Arrhenius-Kooij equation typically used in chemical models does not accurately fit our data and use instead a more versatile fitting formula. At a temperature of 10 K and a density of 10${}^4$ cm${}^{-3}$, we find no significant differences in the predicted chemical abundances, but at higher temperatures of 50, 100, and 300 K we find up to factor of 2 changes. Additionally, we find that the relatively small error on our thermal rate coefficients, $\sim 15\%$, significantly reduces the uncertainties on the predicted abundances compared to those obtained using the currently implemented Langevin rate coefficient with its estimated factor of 2 uncertainty.

19 pages, 5 figures. Accepted for publication in ApJ