Absolute Band Intensity of the Iodine Monochloride Fundamental Mode for Infrared Sensing and Quantitative Analysis

Iodine monochloride (ICl) is a potential off-gas product of molten salt reactors; monitoring this heteronuclear diatomic molecule is of great interest for both environmental and safety purposes. In this paper, we investigate the possibility of infrared monitoring of ICl by measuring the far-infrared absorption cross section of its fundamental band near 381 cm–1. We have performed quantitative studies of the neat gas in a 20 cm cell at 25, 35, 50, and 70 °C at multiple pressures up to ∼9 Torr and investigated the temperature and pressure dependencies of the band’s infrared cross section. Quantitative measurements were problematic due to sample adhesion to the cell walls and windows as well as reactions/possible hydrolysis of ICl to form HCl gas. Effects were mitigated by measuring only the neat gas, using short measurement times, and subtracting out the partial pressure of the HCl­(g). The integrated band strength is shown to be temperature independent and was found to be equal to 9.1 × 10–19 (cm2/molecule) cm–1. As expected, the temperature dependence of the band profile showed only a small effect over this limited temperature range. We have also investigated using the absorption data along with inverse least squares multivariate methods for the quantitative monitoring of ICl effluent concentrations under different scenarios using infrared (standoff) sensing and compare these results with traditional Beer’s law (univariate) techniques.