High Resolution Sub-Doppler Experiments on Benzene

It is shown that sub-Doppler spectroscopy enables one to resolve
individual rotational states in the S^ manifold of polyatomic
molecules. This i s an essential to the understanding of the
primary photophysics within the molecule. Spectra of benzene are
found to undergo substantial changes as the vibrational energy i s
raised within S^. Due to the increased density of vibrational
states, Coriolis coupling, which is already seen at low energies,
can lead to effective IVR above 3000 cm""1 excess energy. This
onset of IVR may be responsible for the onset of "Channel Three" in
benzene and probably produces gross changes in the photophysical
behavior of any polyatomic molecule.