SPECTROSCOPY AND CONFORMATION OF 2-PHENYLIDOLE

Abstract

Employing techniques of fluorescence excitation and dispersed fluorescence, we have recorded the $S_{1} \leftarrow S_{0}$ electronic spectra of 2PI in a supersonic jet. All spectra exhibit extended low frequency progressions which we assign to torsional motion around the bond joining the benzene and indole moieties. The $S_{0}$ and $S_{1}$ torsional potentials have been determined from a vibrational analysis of the spectra by fitting the torsional vibrational spacings to a one-dimensional potential of the form $V(\phi) = {^{1}}/_{2} \Sigma V_{n} (1-\cos {\rm n} \phi)$. The potentials provide a detailed picture of the conformations of 2PI in $S_{0}$ and $S_{1}$, yielding accurate torsional barriers. Additional features displayed in the spectra provide interesting information about vibronic coupling effects involving the $S_{1}$ and $S_{2}$ states of 2PI.