Quantum chemical coupled cluster study of the structure and spectra of the ground and first excited states of the ketenyl radical

The structure and spectra of the ketenyl radical have been investigated by ab initio quantum chemistry, using coupled cluster methods and basis sets of triple zeta quality including f functions. Three states are considered: the 12A″(12Π) and 12A′(12Π) states are the two components of the Renner-Teller pair originating in the lowest electronic state, while the 22Π state is the first electronically excited state, showing no Renner-Teller distortion. Equilibrium geometries, vibrational frequencies and excitation energies were calculated. The calculated data are compared with the limited spectroscopic information available. While the calculated values are in agreement with the microwave and infrared results, practically no common points with the UV spectrum reported by Krishnamachari and Venkatasubramanian were found. This indicates that a reinterpretation of the spectrum is necessary.