Photofragmentation-laser induced fluorescence: a new method for detecting atmospheric trace gases

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Abstract
A new method for the in situ detection of nonfluorescing molecular species is proposed: photofragmentation-laser induced fluorescence (PF-LIF). In this approach, the species to be detected is first laser photolyzed at a wavelength λ1, producing one or more vibrationally excited photofragments. Before vibrational relaxation occurs, one of these photofragments is pumped into a bonding excited state by a second laser pulse centered at wavelength λ2. Fluorescence is sampled at a wavelength λ3, where λ3 < λ2 and λ1. This pumping configuration thus permits massive discrimination against Rayleigh and Raman scattering as well as white noise fluorescence from the laser wavelengths λ1 and λ2. The technique should be both highly sensitive and selective for numerous atmospheric trace gases. Specific sampling schemes for detecting NO2, NO3, and HNO2 are proposed. Various noise sources and chemical interferences are discussed. Specific calculations that estimate the sensitivity of the PF-LIF system for detecting NO2, NO3, and HNO2 are given.

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