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 investigate d by ab initio quantum chemistry, using coupled cluster methods and ba sis sets of triple zeta quality including f functions, Three states ar e considered: the 1(2)A '' (1(2) Pi) and 1(2)A' (1(2) Pi) states are t he two components of the Renner-Teller pair originating in the lowest electronic state, while the 2(2) Pi state is the first electronically excited state, showing no Renner-Teller distortion. Equilibrium geomet ries, vibrational frequencies and excitation energies were calculated. The calculated data are compared with the limited spectroscopic infor mation available. While the calculated values are in agreement with th e microwave and infrared results, practically no common points, with t he UV spectrum reported by Krishnamachari and Venkatasubramanian were found. This indicates that a reinterpretation of the spectrum is neces sary.