Raman spectra and cross sections of ammonia, chlorine, hydrogen sulfide, phosgene, and sulfur dioxide toxic gases in the fingerprint region 400-1400 cm−1

Abstract

Raman spectra of ammonia (NH3), chlorine (Cl2), hydrogen sulfide (H2S), phosgene (COCl2), and sulfur dioxide (SO2) toxic gases have been measured in the fingerprint region 400-1400 cm−1. A relatively compact (<2′x2′x2′), sensitive, 532 nm 10 W CW Raman system with double-pass laser and double-sided collection was used for these measurements. Two Raman modes are observed at 934 and 967 cm−1 in NH3. Three Raman modes are observed in Cl2 at 554, 547, and 539 cm−1, which are due to the 35/35 35/37, and 37/37 Cl isotopes, respectively. Raman modes are observed at 870, 570, and 1151 cm−1 in H2S, COCl2, and SO2, respectively. Values of 3.68 ± 0.26x10−32 cm2/sr (3.68 ± 0.26x10−36 m2/sr), 1.37 ± 0.10x10−30 cm2/sr (1.37 ± 0.10x10−34 m2/sr), 3.25 ± 0.23x10−31 cm2/sr (3.25 ± 0.23x10−35 m2/sr), 1.63 ± 0.14x10−30 cm2/sr (1.63 ± 0.14x10−34 m2/sr), and 3.08 ± 0.22x10−30 cm2/sr (and 3.08 ± 0.22x10−34 m2/sr) were determined for the differential Raman cross section of the 967 cm−1 mode of NH3, sum of the 554, 547, and 539 cm−1 modes of Cl2, 870 cm−1 mode of H2S, 570 cm−1 mode of COCl2, and 1151 cm-1 mode of SO2, respectively, using the differential Raman cross section of 3.56 ± 0.14x10−31 cm2/sr (3.56 ± 0.14x10−35 m2/sr) for the 1285 cm−1 mode of CO2 as the reference.

Facile All-Optical Method for In Situ Detection of Low Amounts of Ammonia

“…To understand the signatures of this spectrum, we performed a normal mode frequency analysis for ammonia and its aqueous formations via density functional theory (DFT) calculations, visualized in Figure 1 B. These formations are addressed thoroughly in previous works and are most widely accepted contributors to vibrational spectrum of ammonia aqueous solution ( Buckley and Ryder, 2017 ; Gardiner et al., 1973 ; Simonelli and Shultz, 2001 ; Sosa et al., 1996 ; Ujike and Tominaga, 2002 ; Yeo and Ford, 1991 ; Aggarwal et al., 2016 ; Langseth, 1932 ; Li and Keppler, 2014 ; Mysen and Fogel, 2010 )—ammonia (NH 3 ), ammonium ion (NH 4 + ), ammonia dimer (NH 3 -NH 3 ), ammonia-water complex (NH 3 -H 2 O), and solvated ammonia complex (not shown in Figure 1 ).

Figure 1 Raman Spectrum of Ammonia in Water and Calculated Spectral Positions Based on Various Stretching Modes (A) Spontaneous Raman spectrum of bulk ammonia solution (0.3 wt%, 30,000 ppm).

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“…To understand the signatures of this spectrum, we performed a normal mode frequency analysis for ammonia and its aqueous formations via density functional theory (DFT) calculations, visualized in Figure 1b. These formations are addressed thoroughly in previous works and are most widely accepted contributors to vibrational spectrum of ammonia aqueous solution 37,38,[44][45][46][47][48][49][50][51] -ammonia (NH3), ammonium ion (NH4 + ), ammonia dimer (NH3-NH3), ammonia-water complex (NH3-H2O) and solvated ammonia complex (not shown in Figure 1). Positions and relative intensities of the observed lines and their corresponding theoretical predictions are in excellent agreement.…”

Remote Raman spectroscopy of explosive precursors

“…We notice a characteristic ν 1 band (symmetric stretch) at 1041 cm −1 for all the samples. 6 Above 0.5 mg, some secondary vibrational modes appear respectively from left to right at 1285 cm −1 (ν 3 ), a double peak at 1408 and 1452 cm −1 . In the region between 1400 and 1500 cm −1 those vibrational modes are related to the NH 4 deformation and the NO 3 stretching.…”

“…1 Among many available laser-based techniques, Raman spectroscopy is a powerful tool to detect and uniquely identify unknown substances. It is non-destructive and highly selective [2][3][4][5][6] while other techniques such as infrared spectroscopy suffers more on the background surface (surface reflectivity and roughness) and sample size (thickness), which affects peak positions and intensities, 7 or laser-induced fluorescence, which is highly sensitive but poorly selective. 7 Spectroscopic detection of explosive traces and their precursors is a very important topic for homeland security applications to reduce the threat of improvised explosive devices (IED).…”

Deep-UV Remote Raman Detection of Chlorine

“…1b was acquired changing the cell material to a Crystran Raman grade calcium fluoride (CaF2) [8] to avoid spectral overlapping regions around chlorine. Chlorine signal can be clearly distinguished as a sharp peak at 554 cm -1 [9] while residual air peaks are located at 1556 cm -1 for atmospheric oxygen and 2331 cm -1 for atmospheric nitrogen [6]. Within this study, it was possible to enhance the quality of the chlorine Raman signal resulting in improved detection times of 5 seconds of acquisition time overcoming the spectral overlapping from a gas cell material initially founded.…”