S2−S0 Spectroscopy of the van der Waals Complexes of Azulene with Rare Gases

Abstract

The S2−S0 fluorescence emission and excitation spectra of jet-cooled azulene and its complexes with the rare gases, Ne, Ar, Kr, and Xe, have been measured. Features due to AZ·RGn (n = 1−4 when RG = Ar, Kr, Xe and n = 1 when RG = Ne) are observed in the S2−S0 fluorescence excitation spectra when azulene is coexpanded with the rare gases. The microscopic solvent shifts, δν, of the origin bands for each complex scale linearly with the polarizability of the adatom(s), indicating that binding is dominated by dispersive interactions. This conclusion has been confirmed in calculations of the separate contributions of dispersion and induction to δν. Mildly anharmonic progressions in very low frequency excited-state intermolecular (van der Waals) modes are attached to the origin bands of each AZ·Krn and AZ·Xen complex. The dominant progression is assigned to single quantum changes in that excited-state bending mode which involves motion of the adatom(s) in the plane perpendicular to the azulene ring containing t...