Fluorescence lifetime studies of NO2. IV. Temperature dependence of fluorescence spectra and of collisional quenching of fluorescence

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Abstract
In the laser‐excited, low pressure, low resolution fluorescence spectrum of NO2, resolved banded features are seen to decrease relative to unresolved ’’continuum’’ emission as the temperature is raised from 175 ° to 356 °K. This behavior is explained in terms of a breakdown of the ΔK=0 selection rule which becomes more important in higher rotational levels of the excited NO2 molecule. The effect of interelectronic mixing in this mechanism is discussed. Quenching rate constants, which differ for banded features and the underlying continuum were measured in the range of 235–360 °K. The faster rate constant for quenching of banded features, kB, is found to be temperature independent while the other rate constant, kC, exhibits a slight negative temperature dependence. This observation is shown to be consistent with a model of rapid, collision‐induced, internal V–R relaxation followed by a slower vibrational cascade process in the perturbed excited state.