Study of potential barriers in Σ states of Li* (3P, 3D)-rare gas collision molecules by means of laser excitation spectroscopy

Excitation spectra of the transitions 2P ΛA → 3D Λ and 2P Λ → 3PΛ in LiHe and LiNe collision molecules have been measured in the spectral range 15800–17600 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 due to maxima in the difference potentials 2PΣ-3DΣ, 2PΠ-3DΣ and 2PΛ-3PΣ, that are turn related to potential barriers in the upper 3PΣ and 3DΣ 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 3DΣ barrier are found to disagree more or less with values from different theoretical calculations.