# Inelastic cross sections and rate coefficients for collisions between CO and H2

## TL;DR

This paper develops a computational approach to calculate collision cross sections and rate coefficients for CO and H2, providing new data for astrophysical models, validated against more exact methods for low-energy states.

## Contribution

It introduces a 5D-CS approximation for CO+H2 collisions, enabling calculations for highly excited states beyond previous methods, with validation against 6D-CC results.

## Key findings

- Good agreement with 6D-CC for energies >10 cm-1
- Two comprehensive databases for different rovibrational states
- Provides previously unavailable astrophysical collision data

## Abstract

A five-dimensional coupled states (5D-CS) approximation is used to compute cross sections and rate coefficients for CO+H2 collisions. The 5D-CS calculations are benchmarked against accurate six-dimensional close-coupling (6D-CC) calculations for transitions between low-lying rovibrational states. Good agreement between the two formulations is found for collision energies greater than 10 cm-1. The 5D-CS approximation is then used to compute two separate databases which include highly excited states of CO that are beyond the practical limitations of the 6D-CC method. The first database assumes an internally frozen H2 molecule and allows rovibrational transitions for v < 5 and j < 30, where v and j are the vibrational and rotational quantum numbers of the initial state of the CO molecule. The second database allows H2 rotational transitions for initial CO states with v < 5 and j < 10. The two databases are in good agreement with each other for transitions that are common to both basis sets. Together they provide data for astrophysical models which were previously unavailable.