Optical interaction potentials from high-resolution differential cross section measurements at thermal energies. II. He(21S)+Ar

Abstract

For pt.I see ibid., p.2693 (1976). Differential cross sections for He(2¹S)+Ar have been measured for six relative kinetic energies between 21 and 180 MeV. At low kinetic energies the small-angle oscillations are clearly resolved. Except for the lowest energy (21 MeV) a well resolved rainbow peak is observed in the differential cross sections. The real and imaginary parts of the interaction potential are obtained from the data. The real part has an intermediate maximum in the potential ( Delta E=25 MeV, r_max=7 au) which causes the rainbow peaks. The imaginary part can be expressed by an exponential plus a Gaussian. The velocity dependence of the total and ionization cross sections is calculated and the possibility of an energy-dependent width of the potential is indicated.