Van der Waals complexes of xanthione and benzopyranthione with rare gases. S 2S 0 fluorescence excitation spectroscopy and microscopic solvation effects

Abstract

The 1:1 and 2:1 van der Waals complexes of xanthione and benzopyranthione with He, Ne, Ar, Kr and Xe have been observed by S 2S 0 laser-induced fluorescence excitation spectroscopy in a supersonic jet. The adatom is located over the pyranthione ring in the 1:1 complex, and the 2:1 complex has a symmetrical sandwich structure. An analysis of the microscopic solvent shifts indicates that the thiones have substantially smaller electric dipole moments in the S 2 state than in the ground state, in qualitative agreement with previous semi-empirical calculations. The dipole moment of xanthione S 2 is estimated to be only 2.0 D, so that thione—adatom interactions are almost exclusively dispersive in the upper state.