The laser induced fluorescence spectrum and radiative lifetime of PO2

Abstract

The ultraviolet spectrum of PO2 first observed in absorption by Verma and McCarthy has been studied by laser induced fluorescence for the first time. The spectra are similar in many respects to those observed in the visible system of NO2 and no predissociation is observed. The loss of rotational structure is attributed instead to mixing with one or more near continuous ‘‘background’’ states, with the amount of mixing apparently related to excitation of the bending vibration. The radiative decays are observed to be nonexponential but are accurately described by a double exponential form. This gives collision free radiative lifetimes of about 0.5 and 4.5 μs for the structured and continuous states, respectively, with the effective lifetime of the structured state varying strongly with the amount of mixing. Collisional quenching rate constants are roughly constant at (6±1)×10−10 and (4±1)×10−11 cm3 molecule−1 s−1 for the two states, with the very rapid quenching rate of the structured state probably being for nonradiative transfer to the background continuum. From observations of the wavelength dependence of the fluorescence the ground state ν2 and ν1 frequencies are found to be about 387 and 1117 cm−1, respectively. The emission is very extensive and strongly red shifted and lends further evidence that these states of PO2 are responsible for the chemiluminescence observed in phosphorus/oxygen reactions.