A fluorescence characterization of the p-difluorobenzene-argon van der Waals complex. Energy levels, geometries and dissociation energies

Abstract

Fluorescence excitation spectra of p-difluorobenzene (pDFB) seeded in a supersonic argon expansion have been used to identifyS1-S0 abso pumping the 0° level of each complex and the van der Waals stretching fundamental in pDFB-Ar are presented. Assignments of the spectra and of other dispersed fluorescence spectra not presented establish values of seven ring fundamentals in both the S1 and S0 states of pDFB-Ar: ν3, ν5, ν6, ν8, ν27, ν29, and ν30. Within a 3 cm-1 uncertainty, in th from the free pDFB value. Only one, the out-of-plane ring distortion ν8, is perturbed more than 2 cm-1 in the S1 state. Vibrational observations in pDFB-Ar2 involve ν″3, ν″5, ν″6, and ν″8 in the S0 state and ν′5 and ν′6 in ωeχe= 1.5 cm-1 is seen in fluorescence progressions members of σ in the S0 state. The observed pDFB-Ar rotational band cont are consistent with Ar centered on the ring at a distance 3.5±0.5 Å in the S0 state and with a contraction of 0.1±0.04 Å in the S1 state. The pDFB-Ar dissociation energy D′0 is estimated from spectroscopic information to be 190 cm-1≲ D′0 $ ̌242 cm-1 wi D′0-D″0 = 30cm-1. © 1991.