CALCULATIONS OF INELASTIC CROSS SECTIONS FOR ROTATIONAL EXCITATION .I. ORBITING RESONANCES FOR J=0 TO J=2 TRANSITION OF N2 IN LOW ENERGY COLLISIONS WITH HE

Cross sections for scattering of N2 (j=0) molecules on He atoms have been calculated for relative energies below 5 · 10-3 eV (58 °K). The time independent scattering formalism of Arthurs and Dalgarno was used together with an assumed Lennard-Jones type potential with anisotropic P2(cos θ{symbol}) terms in the attractive and repulsive parts. The resulting system of coupled differential equations was solved in the distorted wave and close coupling approximations for the differential and integral cross sections for elastic and inelastic (j=0→j=2) scattering. In the integral inelastic cross section several sharp resonances were found to contribute 40% to the cross section at energies below 40 °K. The resonance peaks are attributed to orbiting or short-lived compound states since they are also observed in the elastic cross section at energies which are lower by the excitation energy of 1.5 · 10-3 eV. Finally, the effect of varying the potential parameters on the integral inelastic cross section was studied at 50 °K and a rough formula for the cross section as a function of the parameters is obtained. The formula shows that a certain ratio of repulsive and attractive anisotropies leads to a small inelastic cross section indicating a mutual cancellation. © 1968 Springer-Verlag.