15min:

PIERRE CARCABAL, ROMAN SCHMIED, KEVIN K. LEHMANN AND GIACINTO SCOLES, Department of Chemistry, Princeton University, Princeton, NJ 08544.

We have recorded high-resolution ultraviolet spectra of four benzene isotopomers (C₆H₆, C₆H₅D, 1,3,5-C₆H₃D₃, and C₆D₆) in helium nanodroplets in the region of the first Herzberg-Teller allowed vibronic transition ¹\!\mathrmB_2u ¹\!\!\!\!\mathrmA_1g 6₀¹. The spectra could not be observed by laser-induced fluorescence, but were recorded by beam depletion using bolometric detection. Like tetracene and pentacene, these benzene isotopomers show multiple absorption lines spread over 10 cm^-1. The structures of these lines are found to be qualitatively different for the various isotopomers. The zero-phonon lines are blue shifted with respect to the gas phase transitions by 3 to 4 cm^-1, as predicted by Even et al.