Laser-induced fluorescence spectroscopy of the ketenyl radical

We report the first laser-induced fluorescence ~LIF! excitation spectrum of the ketenyl radical, HCCO, which is produced by the 193 nm photolysis of ketene in a free jet expansion. A series of vibronic bands in the B̃ P– X̃ A9 system are observed. The LIF band positions and rotational structures are in excellent agreement 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 to 35 100 cm . At higher energies the LIF spectrum breaks off sharply due to a rapid increase in the rate of predissociation. The lifetime of the vibrationless level of the B̃ state is less than 1 ns; the estimated quantum yield of fluorescence is ;10. © 1997 American Institute of Physics. @S0021-9606~97!02526-9#