Inelastic Scattering from a Diatomic Molecule: Rotational Excitation upon Collision between He andH2andH2andH2

Abstract

The formalism developed by Arthurs and Dalgarno has been used in the distorted wave approximation to calculate the inelastic scattering cross section for rotational excitation from the $j=0$ to the $j=2$ rotational state in collisions between a helium atom and a hydrogen molecule or two hydrogen molecules. All necessary computations were done with a digital computer, thus, allowing the Arthurs-Dalgarno formalism to be applied with no added approximations. The interaction energy between He and ${\mathrm{H}}_{2}$ obtained in the preceding paper was used for the He-${\mathrm{H}}_{2}$ calculation while the interaction energy given by Takayanagi was used for the ${\mathrm{H}}_{2}$-${\mathrm{H}}_{2}$ problem. Values for the total inelastic cross sections are given as well as graphs for the He-${\mathrm{H}}_{2}$ differential scattering cross section. Incident kinetic energies up to only 0.25 eV in the center-of-mass system were considered; for these low energies, vibrational or electronic excitation is impossible so that change in rotational quantum number is the only inelastic process possible. The results obtained for the ${\mathrm{H}}_{2}$-${\mathrm{H}}_{2}$ cross section do not agree with the rate of de-excitation from the $j=2$ rotational level in ${\mathrm{H}}_{2}$ gas as measured by dispersion experiments with ultrasonic waves. The disagreement may be due to an incorrect ${\mathrm{H}}_{2}$-${\mathrm{H}}_{2}$ interaction potential or failure to consider all important de-excitation mechanisms.