A study of electronically excited nitrogen dioxide in its first predissociation region: Fluorescence emission, lifetimes, and electronic quenching

摘要

Fluorescence behavior of NO2in the first predissociation region (3979 to 4200 Aring;) was studied in great detail with fluorescence excitation spectroscopy (FEX) and the phasehyphen;shift technique. The fluorescence quantum yield decreases with increasing pressure due to selfhyphen;quenching but the shape of the excitation spectrum is insensitive to pressure variation. The observed fluorescence decay time is independent of exciting wavelength from 3979 to 4200 Aring;, although it becomes shorter at higher pressures. These observations imply the presence of afluorescingspecieswith a constant intrinsic lifetime of sim;7times;10minus;5sec and apredissociatingspecieswith a very short lifetime (10minus;7sec) which does not show collisional fluorescence stabilization at ordinary pressures. Bimolecular electronic selfhyphen;quenching constants have been determined in the predissociation region to be sim;4times;10minus;11cm3moleculeminus;1sdot;secminus;1. Rotationally hot molecules can predissociate, although their photon energy contents are less than the dissociation threshold energy of 25thinsp;105 cmminus;1, by releasing the original rotational energy to the rsquo;rsquo;bondhyphen;breakingrsquo;rsquo; vibration. The predissociation limit determined by fluorescence excitation spectroscopy is sim;3980 Aring;, very close to the previously determined value of 3979 Aring; by absorption line diffuseness lsqb;A. E. Douglas and K. P. Huber, Can. J. Phys. 43, 74 (1965)rsqb;.