On the Energetics of the HCO$^+$ + C $\to$ CH$^+$ + CO Reaction and Some Astrochemical Implications

TL;DR

This study investigates the energetics of a key astrochemical reaction, revealing it is endoergic and suppressed in dark clouds, significantly impacting predicted molecular abundances and emphasizing the need to consider intersystem crossings.

Contribution

It provides a detailed energetic analysis of the HCO$^+$ + C reaction, challenging previous assumptions and updating astrochemical models accordingly.

Findings

Reaction is endoergic and suppressed at dark cloud temperatures.

Updated models alter abundances of 224 species by over a factor of 2.

Highlights importance of intersystem crossings in astrochemical reactions.

Abstract

We explore the energetics of the titular reaction, which current astrochemical databases consider open at typical dense molecular (i.e., dark) cloud conditions. As is common for reactions involving the transfer of light particles, we assume that there are no intersystem crossings of the potential energy surfaces involved. In the absence of any such crossings, we find that this reaction is endoergic and will be suppressed at dark cloud temperatures. Updating accordingly a generic astrochemical model for dark clouds changes the predicted gas-phase abundances of 224 species by greater than a factor of 2. Of these species, 43 have been observed in the interstellar medium. Our findings demonstrate the astrochemical importance of determining the role of intersystem crossings, if any, in the titular reaction.