Gas-phase N3 was generated by the F + NH3 reaction and detected by using laser-induced fluorescence in a flow reactor.The ( 2 "+,000 *-X2ng,000) and the ( 2 "+,010 •*-£2IIg,010) excitations were investigated. Evidence was obtained for an upper-state lifetime of <20 ns. The Renner-Teller splitting of the £(2 ,010) level or the smaller spin-orbit splitting in the (2 ,000) level can be utilized for monitoring of N3 by the LIF technique using a monochromator to disperse the fluorescence. Very weak A(000) -» £(020 and 100) transitions were identified, and these could be useful for monitoring the laser-induced fluorescence of N3 with an interference filter.

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The concentration-modulation approach to the study of absorption spectra of atoms and molecules developed with mode-locked dye lasers is extended in this paper to continuous-wave lasers. A 'gain' theory is developed for use with C.W. lasers and a comparison is made between the 'gain' measurements of our C.W. experiments and those of earlier studies using pulsed lasers. The experimental agreement between the measured C.W. 'gain' and the pulsed 'gain', after correcting for differences between the experimental arrangements employed, provides strong support for the 'gain' theory developed here. It is clearly seen that by means of this theory and the derived equations it will be possible to evaluate species concentrations where the state lifetimes are known, or the lifetimes where the concentrations are known. These studies provide a firm foundation for expansion of the applicability of this highly sensitive absorption technique for kinetic and spectroscopic investigation of chemical systems.

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