Thermal Rate Coefficients for the Astrochemical Process C + CH$^+$ $\to$ C$_2^+$ + H by Ring Polymer Molecular Dynamics

TL;DR

This study uses ring polymer molecular dynamics to compute more accurate thermal rate coefficients for the astrochemical reaction C + CH$^+$ $ o$ C$_2^+$ + H at low temperatures, revealing significant discrepancies with previous models.

Contribution

It introduces RPMD as a novel approach for calculating astrochemical reaction rates, providing more reliable data where quantum effects are significant.

Findings

RPMD rate coefficients differ significantly from previous models at low temperatures.

Previous models may overestimate reaction rates by several orders of magnitude.

RPMD results serve as state-of-the-art estimates for astrochemical databases.

Abstract

Thermal rate coefficients for the astrochemical reaction C + CH$^+$ $\to$ C$_2^+$ + H were computed in the temperature range 20-300 K by using novel rate theory based on ring polymer molecular dynamics (RPMD) on a recently published bond-order based potential energy surface and compared with previous Langevin capture model (LCM) and quasi-classical trajectory (QCT) calculations. Results show that there is a significant discrepancy between the RPMD rate coefficients and the previous theoretical results which can lead to overestimation of the rate coefficients for the title reaction by several orders of magnitude at very low temperatures. We argue that this can be attributed to a very challenging energy profile along the reaction coordinate for the title reaction, not taken into account in extenso by either the LCM or QCT approximation. In the absence of any rigorous quantum mechanical or experimental results, the computed RPMD rate coefficients represent state-of-the-art estimates to be included in astrochemical databases and kinetic networks.