Electronic spectra of jet-cooled 5-phenyltropolone. The effect of excitation of the torsional vibrational levels on proton tunneling

The S1-S0 fluorescence excitation and dispersed fluorescence spectra of jet-cooled 5-phenyltropolone were measured to investigate the effect of the excitation of the torsional motion around the bond joining the phenyl group and the seven-membered ring in the S1 state. The tunneling splitting of the origin band of 5-phenyltropolone (18 cm−1) is only slightl smaller than that tr tropolone (18.9 cm−1), while the torsional excitation remarkably decreases the tunneling splitting.