State-changing collision of a high-Rydberg atom with a polar molecule

Cross sections for n- (and l-) changing collisions of a high-Rydberg atom with a polar molecule are evaluated and found to be of the order of 10-14--10-11 cm2. This is based on the model of the quasifree behavior of an excited Rydberg electron, with its interaction with the polar molecule playing a dominant role, and on the mechanism due to energy transfer from molecular rotation to the excited electron. It is shown that the magnitude of the cross sections drastically increases as the energy defect for the collision process becomes small. The calculated results for a symmetric-top as well as a linear polar molecule are in reasonable agreement with recent experimental findings. The possibility of learning about rotational deexcitation of the polar molecule by an extremely slow electron impact from experimental information on these processes is briefly discussed