Semiclassical treatment of rotational excitation of NH3 colliding with 4He

Abstract
The semiclassical (classical path) theory is formulated for an atom colliding with a symmetric top molecule. Cross sections for rotational excitation of NH3 colliding with 4He are calculated and compared with numbers obtained from exact quantum, coupled states, and other semiclassical calculations. The validity of the semiclassical coupled states approximation is investigated.