Optical transitions in excited alkali + 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 3DΣ barrier predicted agrees with experiment to within ±15 cm-1, whereas its position is too large by 0.3 a0; (ii) potentials obtained with various semi-empirical methods reproduce the satellite structure qualitatively, but are generally too repulsive in the 3DΣ 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 3PΣ potential extremum around 12 a0. The vibrational energies in the 2PΠ and 3DΔ 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. (Author)