Laser-induced fluorescence spectroscopy of the B 2Π–X 2A″ band system of HCCO and DCCO

Abstract

The electronic spectroscopy of the B̃ 2Π–X̃ 2A″ band system of the ketenyl radical, H(D)CCO, is investigated using laser-induced fluorescence (LIF) in a free-jet environment. Vibronically resolved 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 the rate of predissociation. The parallel transitions from Ka″=1 in the ground state to the spin-orbit levels, 2Π3/2 and 2Π1/2, of the origin of the B̃ state are completely rotationally resolved for both HCCO and DCCO. Four other parallel transitions originating from Ka″=0 in the ground state and terminating on levels of Σ vibronic symmetry are observed and assigned to the two pairs of Σ states derived from one quantum of excitation in each of the Renner–Teller active modes, the CCO and CCH(D) bend. Rotational analysis provides effective rotational constants and spin-rotation (orbit) couplings for each of these levels. In addition to the Renner–Teller and spin-orbit couplings, there is substantial evidence for additional perturbations among the low-lying bending levels in the B̃ 2Π state of ketenyl.