Laser-induced fluorescence spectroscopy of the (B)over-tilde(2)Pi-(X)over-tilde(2)A '' band system of HCCO and DCCO

The electronic spectroscopy of the (B) over tilde( 2)II-(X) over tilde (2)A " band system of the ketenyl radical, H(D)CCO, is investigated using laser -induced fluorescence (LIF) in a free-jet environment. Vibronically resolve d excitation spectra for HCCO are obtained from 33 400 cm(-1) to 35 100 cm( -1); at higher energies the LIF spectra cutoff due to a rapid increase in t he rate of predissociation. The parallel transitions from K-a" = 1 in the g round state to the spin-orbit levels, (II3/2)-I-2 and (II1/2)-I-2, of the o rigin of the (B) over tilde state are completely rotationally resolved for both HCCO and DCCO. Four other parallel transitions originating from K-a" = 0 in the ground state and terminating on levels of Sigma vibronic symmetry are observed and assigned to the two pairs of S states derived from one qu antum of excitation in each of the Renner-Teller active modes, the CCO and CCH(D) bend. Rotational analysis provides effective rotational constants an d spin-rotation (orbit) couplings for each of these levels. In addition to the Renner-Teller and spin-orbit couplings, there is substantial evidence f or additional perturbations among the low-lying bending levels in the (B) o ver tilde (II)-I-2 state of ketenyl. (C) 1999 American Institute of Physics .