We report the first laser-induced fluorescence (LIF) excitation spectr
um of the ketenyl radical, HCCO, which is produced by the 193 nm photo
lysis of ketene in a free jet expansion. A series of vibronic bands in
the (B) over tilde (2) Pi-(X) over tilde (2)A '' system are observed.
The LIF band positions and rotational structures are in excellent agr
eement with those of a recent photofragment yield (PFY) spectrum [D. L
. Osborn et al., J. Chem. Phys. (to be published)] from the origin at
33 424 cm(-1) to 35 100 cm(-1). At higher energies the LIF spectrum br
eaks off sharply due to a rapid increase in the rate of predissociatio
n. The lifetime of the vibrationless level of the (B) over tilde state
is less than 1 ns; the estimated quantum yield of fluorescence is sim
ilar to 10(-3). (C) 1997 American Institute of Physics.