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

TL;DR

This study provides experimentally derived thermal rate coefficients for the C + H$_3^+$ reaction, demonstrating their impact on astrochemical models and highlighting the importance of accurate rate data for predicting molecular abundances.

Contribution

The paper introduces experimentally obtained thermal rate coefficients for C + H$_3^+$, replacing the commonly used Arrhenius-Kooij fit with a more versatile formula, improving astrochemical modeling accuracy.

Findings

At higher temperatures, predicted abundances vary by up to a factor of 2.

Using precise rate coefficients reduces abundance prediction uncertainties.

No significant abundance differences at 10 K despite new rate data.

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, $\sim15\%$, 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.