Benchmarking an improved statistical adiabatic channel model for competing inelastic and reactive processes

TL;DR

This paper evaluates a statistical quantum model for predicting temperature-dependent rate coefficients of complex inelastic and reactive processes, showing it achieves acceptable accuracy compared to detailed quantum methods.

Contribution

The study introduces and benchmarks an improved statistical adiabatic channel model for complex collision processes, demonstrating its accuracy for astrochemical applications.

Findings

Error less than a factor of 2 for dominant transitions at low temperatures

Model performs well across multiple systems relevant to astrochemistry

Provides a computationally efficient alternative to quantum mechanical methods

Abstract

Inelastic collisions and elementary chemical reactions proceeding through the formation and subsequent decay of an intermediate collision complex, with an associated deep well on the potential energy surface, pose a challenge for accurate fully quantum mechanical approaches, such as the close-coupling method. In this study, we report on the theoretical prediction of temperature-dependent state-to-state rate coefficients for these complex-mode processes, using a statistical quantum method. This statistical adiabatic channel model is benchmarked by a direct comparison using accurate rate coefficients from the literature for a number of systems (H2 + H+, HD + H+, SH+ + H, and CH+ + H) of interest in astrochemistry and astrophysics. For all of the systems considered, an error of less than factor 2 was found, at least for the dominant transitions and at low temperatures, which is sufficiently accurate for applications in the above mentioned disciplines.