NO2fluorescence, excited by fixed visible frequencies of a Ndhyphen;YAG laser, was measured as a function of time, pressure, and fluorescence wavelength. The low resolution fluorescence spectrum at all excitation wavelengths consists of strong banded features, assignable to ground state vibrational progressions, superimposed on an apparent continuum. The ratio of bandedhyphen;tohyphen;continuum intensity decreases with increasing pressure, indicating that the continuum is partially of collisional origin at high pressures. There is also a red shift of fluorescence at high pressures, indicative of vibrational relaxation within the emitting state. A residual continuum is found under collisionhyphen;free conditions (0.1ndash;0.01 mtorr) and ascribed to violation of the Dgr;K=0 selection rules in the initially excited levels of the highly perturbed2B2state. The time dependent decay of fluorescence excited at the banded features contains a fast componentkBand a weaker, longhyphen;lived componentkC, identified with the underlying continuum. Rate constants ofkB=5.9times;10minus;10andkC=1.1times;10minus;10cm3thinsp;secminus;1were measured for quenching by NO2. The slow process has been identified with stepwise vibrational quenching while the fast process is best interpreted as a collision induced change in the rotational quantum state of the initially excited state. Computer modelling was used to fit the pressure dependence of the bandedhyphen;tohyphen;continuum intensity ratio and of the fluorescence red shift, using the measured lowhyphen;pressure spectrum, the two measured quenching rate constants, and a single adjustable parameter Dgr;egr;vib=1000plusmn;500 cmminus;1, the amount of vibrational energy transferred per vibrationalndash;quenching collision. Quenching rate constantskBandkCwere also measured for He, Ar, O2, N2, D2, H2, SF6, CO2, ND3, NH3, H2O and D2O. They range from 0.38 to 2.0 times gas kinetic forkBand from 0.041 to 0.52 times gas kinetic forkC.
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