Ultraviolet Raman scattering from persistent chemical warfare agents

Abstract

Laser induced Raman scattering at excitation wavelengths in the middle ultraviolet was examined using a pulsed tunable laser based spectrometer system. Droplets of chemical warfare agents, with a volume of 2 µl, were placed on a silicon surface and irradiated with sequences of laser pulses. The Raman scattering from V-series nerve agents, Tabun (GA) and Mustard gas (HD) was studied with the aim of finding the optimum parameters and the requirements for a detection system. A particular emphasis was put on V-agents that have been previously shown to yield relatively weak Raman scattering in this excitation band.

Raman Scattering Techniques for Defense and Security Applications

“…In particular, Kullander et al found that excitation at 270 nm causes a large peak to appear at 1650 cm –1 and becomes the strongest spectral peak. This feature is absent in the spectrum taken at 330 nm; no such changes were found for sulfur mustard (HD) or Tabun (GA) . These data highlight that the precise choice of laser wavelength can impact the detection of these materials.…”

“…Owing to their extreme toxicity, much of the work on CWAs has been conducted on simulant chemicals with similar molecular features, such as organophosphates or on the hydrolysis products of these materials. ,,,− It is worth noting that many of simulants used are the same as the hydrolysis products. As such, they remain valuable detection targets in their own right, with the potential to act as markers of the release of CWAs.…”

“…As such, they remain valuable detection targets in their own right, with the potential to act as markers of the release of CWAs. In addition, work using CWAs continues to be conducted to assess the performance of sensors and protective measures. − ,− One of the primary issues with the detection of CWAs is the need to reach extremely low limits of detection, often in the low parts per billion (ppb) range. While some agents, such as cyanide, are easily detectable due to the intense, distinct CN band, many have extremely poor Raman scattering cross sections associated with their vibrational modes.…”

“…As an example, the G series agents, GA, GB, GD, and GF have been experimentally determined to have cross sections ranging between 1 × 10 –30 and 1.0251 × 10 –27 cm 2 /sr/molecule associated with their various vibrational modes . In a bid to help mitigate this poor scattering efficiency, several studies have attempted to exploit the relationship between shorter wavelengths and increased Raman scattering by working with excitation sources in the UV range. ,,, …”

Measurements of Raman scattering in the middle ultraviolet band from persistent chemical warfare agents

“…Our previous experiments 6 0.1 to 1 µl in volume 7 in simplified laboratory conditions. In this work we have only used 1 µl droplets, although detection of much smaller droplets will be possible.…”