Theoretical investigation of rotational rainbow structures in X–Na2 collisions using CI potential surfaces. III. Rigid-rotor X = Ne scattering

Abstract

A thorough investigation of rotational rainbow structures in differential cross sections for the prototypical Ne–Na2 system is presented. The scattering calculations are performed using an accurate CI potential energy surface, which includes electron correlation effects for the bond orbital of Na2 and the L-shell orbitals of Ne together with the dispersion attraction between the two subsystems using the method of self-consistent electron pairs (SCEP). The surface is dominantly repulsive and highly anisotropic. A very shallow van der Waals minimum of about 0.3 meV is obtained at large internuclear distances. Coupled states and infinite-order-sudden differential cross sections are compared for a wide range of collision energies which allows for a critical test of the energy-sudden condition. The applicability of the centrifugal sudden approximation for Ne–Na2 is also discussed. In particular, we investigate the dependence of the rotational rainbow structures on collision energy and initial rotational state. The positions of the primary rotational rainbows obtained with the CI and the corresponding Hartree–Fock surface are compared to experimental results. We find satisfactory agreement for the CI surface but considerable deviations if the Hartree–Fock surface is used. Finally, we compare the scattering results for Ne–Na2 with those for He–Na2 and conclude that at low energies (E≲100 meV) the drastic differences are mainly due to the different masses rather than the potential energy surfaces.