ELECTRONIC SPECTRA OF BENZENE ISOTOPOMERS IN HELIUM NANODROPLETS

$^{a}$M. Hartmann, A. Lindinger, J. P. Toennies, and A. F. Vilesov, Phys. Chem. Chem. Phys. 4, 4839 (2002) $^{b}$U. Even, I. Al-Hroub, and J. Jortner, J. Chem. Phys. 115, 2069 (2001)Author Institution: Department of Chemistry, Princeton UniversityWe have recorded high-resolution ultraviolet spectra of four benzene isotopomers $(C_{6}H_{6}$, $C_{6}H_{5}D$, $1,3,5-C_{6}H_{3}D_{3}$, and $C_{6}D_{6})$ in helium nanodroplets in the region of the first Herzberg-Teller allowed vibronic transition $^{1}B_{2u} \leftarrow^{1}A_{1g} 6^{1}_{0}$. The spectra could not be observed by laser-induced fluorescence, but were recorded by beam depletion using bolometric detection. Like tetracene and pentacene,$^{a}$ these benzene isotopomers show multiple absorption lines spread over ${\sim} 10 cm^{-1}$. 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.^{b}