Laser-induced fluorescence spectrum of the FCO radical

Abstract

Laser-induced fluorescence spectra of FCO are reported between 29 000 cm−1 and 32 800 cm−1. FCO was prepared by three separate procedures: photolysis of CF2O and C2F2O2, and photolysis of F2 in the presence of CO. The observation of the same spectral features from all three production schemes confirms the assignment of FCO as the spectral carrier. Although the LIF spectrum lies in the same wavelength region as the UV absorption spectrum, the two spectra do not have the same appearance and so represent different upper states. The LIF spectrum is assigned as a transition to the A″ Renner–Teller component of a linear 2Π state predicted by ab initio calculations. The spectrum shows a progression of bands at approximately 430 cm−1 intervals, in good agreement with the predicted spacing of bending levels in the 2Π state. The lower frequency stretching mode ν1 occurs at approximately 960 cm−1. The vibronic bands are strongly degraded to the red, consistent with the calculated geometry of the linear state but not the bent A state to which the absorption spectrum in this region is assigned. Resolved emission from the longest wavelength prominent bandhead at 29 872 cm−1 shows progressions in the C–O stretch and bend modes of the ground state. The fluorescence lifetime of this band extrapolated to zero pressure is 95±4 ns, while that of the band at 31 136 cm−1 is 63±5 ns.