Elastic and state changing collisions of a high Rydberg atom with a neutral atom or molecule

For several years, collision processes between a high Rydberg atom and a neutral particle have been theoretically investigated. This is based on the model in which an excited electron behaves as if it were ''free'' and slow. (Hereafter this model is called ''free'' electron model). These theoretical results are in fairly good accord with experimental findings. Recently, high resolution spectroscopy using laser technique has allowed the acquisition of more detailed information on collision processes. Conversely, the possibility of learning about scattering of a very slow electron by a neutral atom or molecule is given by the ''free'' electron model. By using the modified effective range theory for electron-rare gas scattering and correspondence principle, expression for the cross section of the titled process has been derived. The typical results are shown for elastic collision and l-changing collision between a high Rydberg Na atom and an argon atom at 428 deg. K. Also the l-changing or n-changing collision between a high Rydberg atom and an asymmetric-top polar molecule accompanied by rotational de-excitation of the molecule has been studied. n, l and m are the quantum numbers of a high Rydberg atom. In a table, two typical results at 300 deg. K are also shown. The collision cross sections with polar molecule are large as compared with those with rare gas as is expected. (Wakatsuki, Y.)