Spectroscopic studies of the B 2A′′-X 2A′′ system of the jet-cooled vinoxy radical

Abstract

We apply several techniques to the study of the B̃ 2A′′-X̃ 2A′′ band system of the jet-cooled vinoxy 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 (⩽3 K) provide rotational constants for 9 B̃-state levels. We also measure the fluorescence lifetimes of 19 B̃-state levels and obtain high-quality dispersed fluorescence (DF) spectra from seven of the most strongly fluorescing levels in the B̃ 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 B̃ state and for 57 levels in the first 3100 cm−1 of the X̃ state. These assignments include the identification of the a′ fundamentals for ν4 through ν9 and all three a′′ overtones, 2ν10 through 2ν12, 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 B̃ 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 à 2A′ or C̃ 2A′ 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.