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

Abstract

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 (cm 2 /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.

Confirmation of PNNL Quantitative Infrared Cross-Sections for Isobutane

“…As seen in Table 2, the first two columns are the previously reported 25 and 50 °C data for the NWIR database; the values agree well with each other as expected (<1% difference for the integrated areas). 28,29 Similar composite fits were constructed for the higher-resolution (0.01 cm −1 ) measurements on the 125HR for both the neat and pressure-broadened experiments as well as lower-resolution (4 cm −1 ) data recorded on the IFS 66v/S spectrometer using the DTGS detector. The DTGS experiments were intended to verify that the nonlinearities (signal voltage vs light intensity) associated with the MCT detectors were sufficiently redressed by the nonlinearity algorithm in the OPUS software for the 125HR measurements.…”

“…While less sensitive than an MCT, a DTGS does not suffer from light/signal voltage nonlinearities. While a similar 66v/S was used for the original PNNL database spectra, the present system was optimized to make only lower-resolution band integral measurements: so long as the integration limits include all hot bands associated with the main band and Fermi resonating bands, the integrated intensity of a band should remain independent of temperature and resolution. , This is also predicated on the assumption that lower resolution does not lead to Beer–Lambert nonlinearities for the stronger vibrational–rotational lines. Based on the measured 298 K spectra of a series of alkanes, , this appears to be a valid assumption for isobutane.…”

On-Line Monitoring of Gas-Phase Molecular Iodine Using Raman and Fluorescence Spectroscopy Paired with Chemometric Analysis

“…The volatile iodine species of most concern for safety in MSRs are I − , I 2(g) , ICl, HI, and HOI. 11,12 This work focuses on I 2(g) as one initial species studied for developing this method of on-line monitoring due to its distinct and strong Raman and fluorescence signatures that allow for both identification and quantification. Furthermore, there is a significant amount of available literature to benchmark against for known gas-phase optical fingerprints.…”

“…Furthermore, there is a significant amount of available literature to benchmark against for known gas-phase optical fingerprints. 13−16 For example, recent work studied the quantification of ICl in the gas phase using Fourier transform infrared (FTIR) spectroscopy, 12 and future work will expand to explore other species. Note that the proposed probe design could be installed in-line to the gas treatment system before and after treatment.…”

Raman Spectroscopy Coupled with Chemometric Analysis for Speciation and Quantitative Analysis of Aqueous Phosphoric Acid Systems

“…In order to effectively reprocess the hazardous materials in these tanks, methods of accurate characterization are necessary, allowing for a more permanent disposal . Offline lab analyses take hours to days to complete, have limited accuracy in dynamic solution environments, and require extraction and handling of hazardous samples. − Fortunately, there now exists remote, immediate, online, and nondestructive analyses using optical spectroscopy. ,, Raman spectroscopy has been employed for accurate quantification of various analytes in complex systems for waste reprocessing and other areas of the nuclear cycle. ,− Raman probes are particularly desirable due to their ability to function in harsh environments without the need for frequent calibration. − Robust detection methods for uranium, plutonium, neptunium, aqueous nitrate, gaseous iodine, and other relevant species have also been established. ,,− Raman and UV–vis microprobes have been used to extend applications to the microscale, further reducing researcher exposure to hazardous materials. ,− Phosphoric acid and its three deprotonated species are Raman active, allowing for the application of Raman spectroscopy to phosphate systems. In our application, a Raman probe is inserted within the fuel reprocessing and related waste streams in direct contact with the solution, allowing in situ measurement.…”