FLUORESCENCE EXCITATION-SPECTRA OF HCO (B)OVER-TILDE-(2)A'-(X)OVER-TILDE(2)A' IN A SUPERSONIC JET

The HCO radical was produced by photolysis of acetaldehyde in a supers onic molecular jet. HCO B2 A'-X2 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 transitio ns are from the B state, not the C state. The quantum yield of fluores cence abruptly decreased at lines approximately 2770 cm-1 above the ze ro vibrational state of B, indicating the onset of a channel leading t o predissociation. Rotational spectra of the lowest six vibrational le vels of the B state are analyzed. (C) 1994 Academic Press, Inc.