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, C H2CHO. Vibronically resolved excitation spectra are obtained using bot h 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 te mperatures (less than or equal to 3 K) provide rotational constants fo r 9 (B) over tilde-state levels. We also measure the fluorescence life times of 19 (B) over tilde-state levels and obtain high-quality disper sed fluorescence (DF) spectra from seven of the most strongly fluoresc ing levels in the (B) over tilde state. The excitation and DF spectra reveal far more vibrational levels in the two electronic states than h ave been previously observed. In total, we provide assignments for 54 levels observed in the first 3650 cm(-1) of the (B) over tilde state a nd for 57 levels in the first 3100 cm(-1) of the (X) over tilde state. These assignments include the identification of the alpha' fundamenta ls 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 a nd 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 mod e-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 til de(2)A' electronic states, The congestion and complexity of the DF spe ctra at high energies provides direct evidence of extensive intramolec ular vibrational redistribution on the ground-state potential surface. (C) 1997 American Institute of Physics.