Photodissociation spectroscopy and dynamics of the HCCO free radical

The photodissociation spectroscopy and dynamics of the HCCO radical have been investigated using fast radical beam photofragment translational spectroscopy. An electronic band with origin at 33 424 cm has been identified. This band exhibits rotational resolution near the band origin, but the well-defined rovibronic structure is homogeneously broadened at higher photon energies. Based on the rotational structure this band is assigned to the B̃ P←X̃ A9 transition. Photofragment translational energy and angular distributions were obtained at several excitation energies. At excitation energies close to the origin, the excited, spin-forbidden CH(a S)1CO channel dominates, while the ground state CH(X P)1CO channel is the major channel at higher photon energies. The translational energy distributions provide evidence of competition between intersystem crossing and internal conversion dissociation mechanisms, with some evidence for nonstatistical dynamics in the CH(X P)1CO channel. This work yields an improved heat of formation for HCCO, DHf ,298 0 51.8360.03 eV. © 1997 American Institute of Physics. @S0021-9606~97!00324-3#