Absolute differential cross sections for very-small-angle elastic scattering in He+He collisions at keV energies

Absolute differential cross sections for He+He elastic scattering at laboratory angles in the range 0.0180--0.50 have been measured for projectile energies of 0.5, 1.5, and 5.0 keV. The experiment employs a position-sensitive detector for determining the angular distribution of scattered particles. The differential cross sections exhibit a transition from classical to quantum behavior within the range of angles studied, and excellent agreement is observed with partial-wave-theory calculations using phase shifts derived from the He-He interaction potentials of Ceperley and Partridge [J. Chem. Phys. 84, 820 (1986)] and Foreman, Rol, and Coffin [J. Chem. Phys. 61, 1658 (1974)]