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 6(0)1 10(0)2 and 6(0)1 16(0)2 vibronic transitions of benzene at low rotational temperature are reported and analyzed in detail. Deperturbed spectroscopic constants for the 6(1) 10(2) and 6(1) 16(2) 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 6(0)1 10(0)2 transition and of 6.2 cm-1 for the 6(0)1 16(0)2 transition is found to be due to vibrational l-type resonances with matrix elements of 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 nu-6 +/- + 2-nu-10(0) and nu-6 +/- + 2-nu-10 +/-2 nearly completely and the substates nu-6 +/- + 2-nu-16(0) and nu-6 +/- + 2-nu-16 +/-2 substantially. The importance of the mixing for the intramolecular vibrational redistribution (IVR) and the decay behaviour of S1 benzene is discussed.