Coupled-channel investigation of rotationally and vibrationally inelastic collisions between He and H₂

The coupled-channel formalism has been employed for He + H₂ collisions including rotational (j = 0, 2) and vibrational (n = 0, 1) levels and making use of the Kraus-Mies potential energy surface. Integral and differential cross sections are obtained at the total energies 0.3884, 0.9, and 1.4116 eV for rotational and vibrational transitions separately, and for the combined processes. Considerable use has been made of the microscopic reversibility principle to extract cross sections from the S matrix for de-excitations as well as for excitations. Cross sections for vibrational excitation are found to decrease when accompanied by rotational excitation. For vibrational de-excitation, the effect of rotational excitation is to increase the cross sections. Defining a most probable impact parameter b̄_max from the maximum in the partial integral cross sections, vibration excitation is found to occur at low b̄_max, while rotational excitation is observed at comparatively higher values. For simultaneous rotational and transitions, b̄_max decreases with increasing energy transfer.

A deflection angle ©^(cl is defined in terms of the impact parameters and the turning point radii for the initial and final channels, and a correlation between this angle and the maxima in the computed angular distributions is found. The transition probabilities for the rotational excitation j = 0 → 2 with simultaneous vibrational excitation and their physical interpretation are also discussed within the total angular momentum coupling scheme.