Free-jet electronic spectroscopy of the PO2 radical

The laser fluorescence excitation spectrum of the jet-cooled PO2 radical has been recorded in the wavelength range 325-284 nm. This work extends previous flash photolysis and laser fluorescence studies of the UV electronic transition in PO2. Resolved emission spectra were recorded for excitation of a number of bands. The previous vibrational analyses of both the absorption and emission spectra were extended. The rotational structure of the bands was investigated and found to be very complicated, defying an analysis. The radiative decays of the excited vibronic levels were found to be nonexponential but could be fitted to a double exponential form. The lifetimes were found to be much shorter than those observed in a discharge-flow system by Hamilton [J. Chem. Phys. 1987, 86, 33]. The inferred dependence of the lifetime upon the degree of rotational excitation and the complicated rotational structure of the bands suggest that there is significant electronic state mixing, as in the isovalent NO2 molecule.