A comparison is made of experimental far-wing profiles for the system Li(2P → 3D)He with quantum calculations of thermally averaged free-free continua. Using input adiabatic potentials and transition moment functions from both ab initio and semi-empirical approaches, the comparison shows: (i) new ab initio potentials for Li * (2P, 3P, 3D)He reproduce the spectral positions of the observed rainbow satellites well; the height of the 3D barrier predicted agrees with experiment to within ±15 cm −1 , whereas its position is too large by 0.3 a 0 ; (ii) potentials obtained with various semi-empirical methods reproduce the satellite structure qualitatively, but are generally too repulsive in the 3D state at intermediate and large internuclear separations; (iii) transition moment functions for the asymptotically forbidden 2P → 3P transitions reproduce, with different degrees of accuracy, the intensity of the red-wing satellite related to the 3P potential extremum around 12 a 0 . The vibrational energies in the 2P and 3D states calculated with the ab initio potentials reproduce to within a few cm −1 those obtained from rotationally resolved band spectra reported in the literature.

Abstract.Excitation spectra of the transitions 2PA --, 3DA and 2PA ~ 3PA in Lille and LiNe collision molecules have been measured in the spectral range 1 5800-17600 cm-1 about the atomic Li2P ~ 3D line by means of two-step laser excitation. Rainbow satellite bands are observed and have been identified as d~e to maxima in the difference potentials 2PX-3DZ, 2P/7-3DZ and 2PA-3PS, that are in turn related to potential barriers in the upper 3PS and 3DZ states. For identification of the satellites as well as understanding origin and shape of the potential barriers, approximate calculations were performed of interaction energies and dipole transition moments, that are based on the Fermi-Omont treatment of higher excited alkali-rare gas interaction. The satellite bands were analysed 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 3DZ barrier are found to disagree more or less with values from different theoretical calculations.

We have studied the Li3D + He interaction in the 22 molecular state by measurements of the absorption line wing profiles of the upper Li transition 2P--3D, 2 610 nm. Measurements of absolute cross sections normalized to the integrated line absorption have been performed in a two step laser pump and probe scheme in the detuning range _+ 300 cm-1 to both sides of the line center. The analysis of the blue wing on the basis of the quantummechanical theory of the collisional line broadening shows, that the experimental 3 DX potential energy curve is less repulsive in the asymptotic range R ~ 15 20 a.u. than predicted from semiempirical model calculations of Pascale.

No abstract