S-2-S-0 SPECTRA OF JET-COOLED XANTHIONE AND BENZOPYRANTHIONE - MICROSCOPIC SOLVATION BY RARE-GASES

The laser-induced S-2-S-0 fluorescence excitation and dispersed emissi on spectra of two aromatic thiones, xanthione (XT) and benzopyranthion e (BPT), have been measured under jet-cooled condition?;. These emissi on spectra, together with the corresponding FT-IR and FT-Ramnn spectra and ab initio CEP-31G calculations, have been used to achieve a compl ete vibrational analysis of BPT in its ground state, complementing tha t of XT, previously published. The 1:1 anti 1:2 van der Waals complexe s of XT and BPT with We, Ne? Ar, Kr, and Xe have been synthesized and characterized using their microscopic solvation shifts and the frequen cies of their intermolecular (van der Waas) vibrations. In all cases t he adatom preferentially occupies a position over the pyranthione ring in the 1:1 complex. and the 1:2 complex has a symmetrical sandwich (1 \1) structure. No (2\0) isomer is observed. An analysis of the microsc opic solvent shifts of the origin bands of the complexes indicates tha t dipole-induced dipole interactions contribute significantly to the b inding energies. The binding energies and geometrics of the 1:1 and 1: 2 van der Waals complexes of XT, BPT, and pyranthione (PT) have been c alculated using pairwise atom-atom Lennard-Jones 6-12 potentials and a re consistent with the structures derived from experiment. The out-of- plane intermolecular stretching vibrations can be clearly observed in the excitation spectra of most complexes, and their assignments have b een confirmed using model vibrational potentials. Ab initio SCF calcul ations including second order Moller-Plesset correlation are also repo rted for the PT . rare gas systems, and show nice agreement with the L ennard-Jones calculations and experiment. (C) 1997 Academic Press, Inc .