Mutual vibrational quenching in CO + H2 collisions

•Computational studies of simultaneous vibrational quenching of CO and H2 are presented.•The coupled-states approximation is tested against the close-coupling formulation.•Five-dimensional dynamics are tested against full six-dimensional dynamics.•Vibrational quenching of CO dominates over H2 at high energies with the reverse at low energies.•Simultaneous vibrational quenching is less probable than single molecule vibrational quenching.

Vibrational quenching of CO and H2 is studied quantum mechanically for collisions where both molecules are vibrationally excited. A five-dimensional (5D) coupled states (CS) approximation is used to formulate the dynamics. The approximation is tested against six-dimensional (6D) results for CO + H2 with single vibrational excitation using both the CS approximation and the full close-coupling (CC) method. The 5D approximation is shown to provide a practical and reliable numerical approach for obtaining state-to-state cross sections in the computationally challenging case of mutual rovibrational de-excitation. State-resolved and partially-summed cross sections are presented for this astrophysically important collision system over a wide range of energies, and prospects for developing a database of rovibrational quenching rate coefficients are discussed.

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