Abstract

Photodissociation of gas-phase compounds using a laser at suitably short UV wavelengths can produce electronically excited photofragments. Detection of fluorescence from these excited fragments, particularly atomic fragments, allows sensitive and quantitative density measurements, while signal strength as a function of dissociation laser wavelength allows differentiation among compounds that yield the same photofragment. Sensitive techniques are needed for the detection of highly corrosive gas-phase alkali compounds in the combustion of coal gas to drive gas turbines. We present here an evaluation of photofragment fluorescence based on the results of experiments to study the photodissociation of the chlorides and hydroxides of sodium and potassium. Alkali compound vapors were irradiated at 193 nm from an ArF laser and other wavelengths generated by stimulated Raman scattering. Fluorescence from electronically excited alkali atoms in the lowest ²P⁰ level was observed, and the dependence of the fluorescence intensity on temperature, was investigated. The atomic emission intensities quantita-tigated. The atomic emission intensities quantitatively track the density of the alkali compounds over a wide dynamic range, and detection at sub-part-per-billion concentration levels is readily achievable. Discrimination among different compounds of the same alkali metal based on the dissociation laser wavelength dependence is also discussed.

© 1985 Optical Society of America