Vibration-rotation relaxation in He-H₂

Vibration-rotation relaxation calculations for He⁴-(para-H ₂) are presented over the range 200≤T≤700°K. The relaxation equations are solved for up to 12 vibration-rotation states. The rate constants were obtained from previously calculated quantum mechanical collision cross sections. It is shown that the eigenvalues and eigenvectors of the relaxation matrix may be physically interpreted in terms of different relaxation modes. Details of the relaxation are followed as a function of time. A rich variety of rotational relaxation behavior is shown to be possible at short times followed by a quiescent induction period and finally vibrational relaxation. Breathing sphere calculations were also performed, and they were found to be inadequate for describing the vibrational relaxation. The rotational states significantly participate in the vibrational relaxation of He-H₂.