Laser-induced fluorescence from the predissociating formyl radical. Part 2.—Analysis of dispersed emission from the ÖX transition

Abstract

Using laser-induced fluorescence spectroscopy dispersed emission spectra of HCO and DCO have been recorded. The formyl radical was produced by the UV photolysis of acetaldehyde (d₀ and d₄) and detected via the òA″–X ²A′ transition, with excitation into single vibronic levels of the first excited state. We report, for the first time, emission into the overtone of the C—H stretching frequency, demonstrating the large anharmonic motion of this, the weakest of known CH bonds. Also, the fully resolved emission bands of DCO are shown. The three fundamental modes of DCO are observable, as a result of an accidental degeneracy of the three vibrational frequencies ω₁≈ 2ω₂≈ω₃. The spectra are interpreted and the associated vibrational frequencies are calculated and compared with ab initio calculations. Additional bands recorded in the absence of a photolysis laser have been attributed to Raman scattering from the parent acetaldehyde.