Nitrogen dioxide fluorescence from N₂O₅ photolysis

The products of ultraviolet photolysis of N₂O₅ are NO₃ and a wavelength dependent mixture of NO₂, NO^*₂, and NO+O, where NO^*₂ represents one or more excited electronic states of nitrogen dioxide. This NO^*₂ emits the visible fluorescence spectrum of nitrogen dioxide (photolysis induced fluorescence, PIF), and this spectrum was compared with monochromatically excited NO₂ fluorescence spectra (laser induced fluorescence, LIF). In a series of experiments, dispersed PIF and LIF spectra were measured where reactant pressure was 200 mTorr, delay time was 30 ns, and observation time was 600 ns. According to results obtained by Sugimoto and co‐workers, under these conditions the continuous spectrum, which reflects the overall internal energy of NO^*₂, had been little modified by collision, although there was degradation of fine structure. The continuous LIF spectra were fit to an empirical function, and the PIF spectra were shown to be well represented by a linear combination of these mono‐energetic excitation spectra. The coefficients of this linear combination plus other considerations were interpreted to give the almost nascent internal energy distribution of the electronically excited nitrogen dioxide molecules produced by N₂O₅ photolysis. This non‐Boltzmann internal energy distribution indicates that electronically excited nitrogen dioxide is produced in the ²B₁ state when N₂O₅ is photolyzed.