Infrared chemiluminescence and vibraluminescence in the NO — O — NO2 reaction system

Abstract

Infrared emission from the low-pressure gas-phase NO — О reaction system has been studied from 1 to 7,0 microns. An infrared integrating sphere has been used for the reaction cell to provide increased lightgathering efficiency, and because of the relatively weak source, the emission spectra were obtained with an interferometer spectrometer. The « continuum « associated with the NO + O recombination decreases monotonically and extends to at least 3,7 microns. Vibrational-rotational spectra from NO and NO2 have been observed and their relative intensities studied versus concentrations of the reactants. An unidentified band is observed at 3,7 microns whose intensity varies directly with the intensity of both the continuum and the NO2 ν3 fundamental at 6,3 microns. The intensity of the vibrational-rotational emission relative to the continuum radiation has been found to be pressure-dependent due to the considerably different radiative lifetimes and collisional deactivation processes involved. The ν3 fundamental band of NO2 at 6,3 microns excited by chemiluminescence in the NO + О → NO2 * reaction is broader and, therefore, excited to higher vibrational levels than it is when excited by vibrational exchange with O2 [math] (vibraluminescence). The vibrational excitation of O2 occurs in the fast reaction NO2 + О → NO[math] + O2 [math]. Chemiluminescence from NO[math] is also observed in this reaction which demonstrates excitation of both the newly formed bound and the unbroken bond simultaneously.