Ab initio investigation of the vibronic spectrum involving the two lowest-lying electronic states of HCCO

The results of ab initio calculations of the vibronic spectra involving bot h lowest-lying states X (2)A " and A (2)A' of the ketenyl radical HCCO are presented. Potential energy surfaces are computed by means of the coupled c luster method with perturbative triple corrections [CCSD(T)]. A recently de veloped ab initio approach for the treatment of the Renner-Teller effect in tetra-atomic asymmetric molecules is applied to calculate the vibronic ene rgy levels. (C) 1999 American Institute of Physics. [S0021-9606(99)30416-5] .