Optical transitions in excited alkali plus rare-gas collision molecules and related interatomic potentials: Li*+He

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 Sigma 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 Sigma 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 Sigma potential extremum around 12 a(0). The vibrational energies in the 2P Pi and 3D Delta states calculated with the nb initio, potentials reproduce to within a few cm(-1) those obtained from rotationally resolved band spectra reported in the literature.