STUDY OF POTENTIAL BARRIERS IN SIGMA-STATE OF LI-ASTERISK (3P, 3D)-RARE GAS COLLISION MOLECULES BY MEANS OF LASER EXCITATION SPECTROSCOPY

Excitation spectra of the transitions 2P Lambda --> 3D Lambda and 2P L ambda --> 3P Lambda in LiHe and LiNe collision molecules have been mea sured in the spectral range 15800-17600 cm(-1) about the atomic Li2P - -> 3D line by means of two-step laser excitation. Rainbow satellite ba nds are observed and have been identified as due to maxima in the diff erence potentials 2P Sigma-3D Sigma, 2P Pi-3D Sigma and 2P Lambda-3P S igma, that are in turn related to potential barriers in the upper 3P S igma and 3D Sigma states. For identification of the satellites as well as understanding origin and shape of the potential barriers, approxim ate calculations were performed of interaction energies and dipole tra nsition moments, that are based on the Fermi-Omont treatment of higher excited alkali-rare gas interaction. The satellite bands were analyse d by means of semiclassical Uniform-Franck-Condon calculations of the spectra to yield values for characteristic parameters of the potential barriers. The results for position and height of the 3D Sigma barrier are found to disagree more or less with values from different theoret ical calculations.