Vibrational relaxation of CO (v=1) by inelastic collisions with 3He and 4He

Calculations of the vibrational relaxation rate constants of the CO–3He and CO–4He systems are extended to lower temperatures than in any previous calculation and a comparison made with new experimental results in the temperature range 35–295 K for CO–3He and previously published results in the range 35–2300 K for CO–4He. Both the coupled states (CS) and infinite‐order sudden (IOS) approximations are used, with the self‐consistent‐field configuration interaction CO–He interaction potential of Diercksen and co‐workers. The CS approximation is found to give a similar level of agreement with experiment for the two isotopic species, while the performance of the IOS approximation is system dependent. The discrepancy between experimental and theoretical IOS rate constants is quite different for collisions involving 3He and 4He, so that it is not profitable to compare IOS results directly with experiment for these two systems at temperatures below 300 K. The differences between the measured and the CS calculated...