Abstract
The HCO radical was produced by photolysis of acetaldehyde in a supersonic molecular jet. HCO B̃ ̃ 2 A′-X̃ 2 A′ transitions were detected by laser-induced fluorescence. Eight vibronic bands were observed that showed both a- and b-type transitions, indicating that the observed transitions are from the B̃ ̃ state, not the C̃ state. The quantum yield of fluorescence abruptly decreased at lines 2770 cm -1 above the zero vibrational state of B̃, indicating the onset of a channel leading to predissociation. Rotational spectra of the lowest six vibrational levels of the B̃ state are analyzed. © 1994 Academic Press. All rights reserved.