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

摘要

In the laserhyphen;excited, low pressure, low resolution fluorescence spectrum of NO2, resolved banded features are seen to decrease relative to unresolved rsquo;rsquo;continuumrsquo;rsquo; emission as the temperature is raised from 175thinsp;deg; to 356thinsp;deg;K. This behavior is explained in terms of a breakdown of the Dgr;K=0 selection rule which becomes more important in higher rotational levels of the excited NO2molecule. 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 235ndash;360thinsp;deg;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, collisionhyphen;induced, internalVndash;Rrelaxation followed by a slower vibrational cascade process in the perturbed excited state.