Measurement and theoretical simulation of the HCCOÀ anion photoelectron spectrum

The HCCO radical is of great interest in combustion chemistry because it is a key intermediate in the oxidation of small hydrocarbons such as acetylene. Spectroscopic information has been limited to a handful of experiments, none of which has adequately characterized the Renner–Teller interaction of the two lowest-lying electronic states. In this paper, theory recently developed to describe the Renner–Teller effect in tetra-atomics in combination with the Franck–Condon principle is used to compute the photoelectron spectrum of HCCO. The theoretical results are compared with a new photoelectron spectrum of HCCO obtained at 355 nm ~4.493 eV!. Rotational and vibrational spectroscopies have determined several properties of the ground state. From the submillimeter spectrum of HCCO, Endo et al. were able to determine the geometry of the X A9 ground state. The anomalous K dependence of the spin–rotational splittings confirmed the presence of the close-lying Renner–Teller component. Ohshima et al. further characterized the HCCO ground state by determining the hyperfine constants of the hydrogen nucleus using Fourier transform microwave spectroscopy. While performing experiments to elucidate the absorption spectroscopy of the C2H radical, Jacox and Olson observed a transition at 2020 cm and attributed it to the HCCO radical. Several other transitions in their spectrum were not identified and may be attributed to the HCCO radical as well. Motivated by this finding, Curl and co-workers confirmed this result in the gas phase via infrared flash kinetic spectroscopy and assigned it to the n2 stretching mode. The B P excited state has been studied using photo-