Laser-induced fluorescence of the B-X system of the HCO radical

The spectroscopy of the B̃ 2A′–X̃ 2A′ system of the formyl radical has been studied by laser-induced fluorescence. HCO was generated by photolysis of acetaldehyde, and a tunable laser operated near 245 nm excited eight bands of B̃–X̃. The (0,0,2)–(0,0,0) band has been rotationally analyzed, yielding A′=14.46 cm−1 and (B′+C′)/2=1.13 cm−1 for this slightly asymmetric top; asymmetry splitting and spin doubling are observed. The intense branches have ΔK=0 but there also are weaker perpendicular components with the transition moment near the b axis. Vibronic transition energies agree with those from matrix absorption but with a 130 cm−1 blueshift. Resolved fluorescence spectra to X̃ levels as high as 15 000 cm−1 furnish vibrational constants for the ground state.