Mixing of the vibrational angular momentum components of multiply degenerate vibronic states of benzene by vibrational l-type resonance

The rotationally resolved spectra of the 6011002 and 6011602
vibronic transitions of benzene at low rotational temperat reported
and analyzed in detail. Deperturbed spectroscopic constants for the
61102 and 61162 states are reported which reproduce the observed
line positions to within experimental accuracy. The splitting of
17.9 cm−1 between the two subbands of the 6011002 transition and of
6.2 cm−1 for the 6011602 transition is found to be due to
vibrational l-type resonances with matrix element 8.91 and 2.65
cm−1, respectively. These large resonances cause strong distortions
of the rotational structure and mix the vibrational angular
momentum substates ν6minus-or-plus sign + 2ν100 and ν6± + 2ν10±2
nearly completely and the substates ν6minus-or-plus sign + 2ν160
and ν6± + 2ν16minus-or-plus sign2 substantially. The importance of
the mixing for the intramolecular vibrational redistribution (IVR)
and the decay behaviour of S1 benzene is discussed.