Quantum Calculation of Inelastic CO Collisions with H. III. Rate Coefficients for Ro-vibrational Transitions

TL;DR

This paper provides comprehensive and accurate rate coefficients for ro-vibrational transitions of CO colliding with H atoms across a wide temperature range, improving astrophysical models significantly.

Contribution

It introduces a new extrapolation scheme for rate coefficients and offers the most detailed data set for H-CO ro-vibrational de-excitation, surpassing previous models.

Findings

Rate coefficients differ significantly from previous assumptions.

Extrapolation scheme validated by close-coupling calculations.

Line fluxes in models change by 20-70% at high temperatures.

Abstract

We present calculated rate coefficients for ro-vibrational transitions of CO in collisions with H atoms for a gas temperature range of 10 K $\leq T \leq$ 3000 K, based on the recent three-dimensional ab initio H-CO interaction potential of Song et al(2013). Rate coefficients for ro-vibrational $v=1,j=0-30 \rightarrow v'=0, j'$ transitions were obtained from scattering cross sections previously computed with the close-coupling method by Song et al(2015). Combining these with the rate coefficients for vibrational $v=1-5 \rightarrow v' < v$ quenching obtained with the infinite-order sudden approximation, we propose a new extrapolation scheme that yields the rate coefficients for ro-vibrational $v=2-5,j=0-30 \rightarrow v',j'$ de-excitation. Cross sections and rate coefficients for ro-vibrational $v=2, j=0-30 \rightarrow v'=1,j'$ transitions calculated with the close-coupling method confirm the effectiveness of this extrapolation scheme. Our calculated and extrapolated rates are very different from those that have been adopted in the modeling of many astrophysical environments. The current work provides the most comprehensive and accurate set of ro-vibrational de-excitation rate coefficients for the astrophysical modeling of the H-CO collision system. Application of the previously available and new data sets in astrophysical slab models shows that the line fluxes typically change by 20-70% in high temperature environments (800 K) with an H/H$_2$ ratio of 1; larger changes occur for lower temperatures.