Photofragment Fluorescence As A Sensitive Probe For Gas-Phase Alkali Compounds And Their Photochemistry

Richard C. Oldenborg; Steven L. Baughcum; Douglas E. Hof; Kenneth R. Winn

doi:10.1117/12.976135

20 November 1985 Photofragment Fluorescence As A Sensitive Probe For Gas-Phase Alkali Compounds And Their Photochemistry

Richard C. Oldenborg, Steven L. Baughcum, Douglas E. Hof, Kenneth R. Winn

Author Affiliations +

Proceedings Volume 0540, Southwest Conf on Optics '85; (1985) https://doi.org/10.1117/12.976135
Event: 1985 Albuquerque Conferences on Optics, 1985, Albuquerque, United States

Abstract

Sensitive techniques are needed for the detection of highly corrosive gas-phase alkali compounds in coal gasifier gas turbine streams. We report on the use of photofragment fluorescence as a very sensitive, selective probe for alkali compounds. Photodissociation of a gas-phase alkali compound using a laser at suitably short ultraviolet (uv) wavelengths produces an electronically excited alkali atom. Detection of fluorescence from these excited atoms allows sensitive and quantitative density measurements of a compound while signal strength as a function of dissociation laser wavelength allows differentiation of compounds. We present here an evaluation of this approach based on the results of experiments to study the photodissociation of the alkali compound KC1. The KC1 vapor was contained in a heated quartz cell and irradiated at 193 nm with an ArF laser and at other Raman-generated wavelengths. Emission at 766 nm was observed from atomic potassium (4²P°) produced in the photodissociation process. The spectral dependence for the production of excited potassium atoms is distinct enough that discrimination from other compounds, such as KOH, appears likely. The atomic emission intensity quantitatively tracks the KC1 density over at least 5 orders-of-magnitude. As little as 4 x 10⁷ KC1 molecules/cc, or a 0.5 ppb KC1 concentration, can be measured on a single laser shot, making this a very sensitive diagnostic technique. Experiments on other alkali compounds are now in progress.

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Richard C. Oldenborg, Steven L. Baughcum, Douglas E. Hof, and Kenneth R. Winn "Photofragment Fluorescence As A Sensitive Probe For Gas-Phase Alkali Compounds And Their Photochemistry", Proc. SPIE 0540, Southwest Conf on Optics '85, (20 November 1985); https://doi.org/10.1117/12.976135

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