Rotational effect in the ionization of a highly excited atom by collision with a polar molecule

If the collisional ionization is chiefly due to energy transfer from the polar-molecule rotation to an electron in a high Rydberg state of the atom, then theory predicts that the cross section averaged over a thermal distribution of rotational states should show step-like structure as a function of the energy of the Rydberg state. This structure has been experimentally detected, and it can be considered as direct evidence of the rotational effect in the collisional ionization. (U.S.)