Spectroscopic studies of the (B)over-tilde(2)A''-(X)over-tilde(2)A'' system of the jet-cooled vinoxy radical

We apply several techniques to the study of the (B) over tilde(2)A ''-(X) over tilde-(2)A '' band system of the jet-cooled vinery radical, CH2CHO. Vibronically resolved excitation spectra are obtained using both laser-induced fluorescence (LIF) and a two-color resonant four-wave mixing (TC-RFWM) scheme that provides the nonlinear equivalent of hole-burning spectra. Rotationally resolved LIF spectra recorded at low temperatures (less than or equal to 3 K) provide rotational constants for 9 (B) over tilde-state levels. We also measure the fluorescence lifetimes of 19 (B) over tilde-state levels and obtain high-quality dispersed fluorescence (DF) spectra from seven of the most strongly fluorescing levels in the (B) over tilde state. The excitation and DF spectra reveal far more vibrational levels in the two electronic states than have been previously observed. In total, we provide assignments for 54 levels observed in the first 3650 cm(-1) of the (B) over tilde state and for 57 levels in the first 3100 cm(-1) of the (X) over tilde state. These assignments include the identification of the alpha' fundamentals for nu(4) through nu(9) and all three alpha '' overtones, 2 nu(10) through 2 nu(12) in both states. The differences between the TC-RFWM and LIF spectra and the measured lifetimes indicate a dramatic increase in the predissociation rate of the (B) over tilde state beginning at 1190 cm(-1) above the origin. The predissociation rate is markedly mode-specific and is enhanced by out-of-plane excitation, possibly due to vibronic coupling with either the (A) over tilde(2)A' or (C) over tilde(2)A' electronic states, The congestion and complexity of the DF spectra at high energies provides direct evidence of extensive intramolecular vibrational redistribution on the ground-state potential surface. (C) 1997 American Institute of Physics.