Henric Östmark

Resonance-Enhanced Raman Spectroscopy on Explosives Vapor at Standoff Distances

Resonance-enhanced Raman spectroscopy has been used to perform standoff measurements on nitromethane (NM), 2,4-DNT, and 2,4,6-TNT in vapor phase. The Raman cross sections for NM, DNT, and TNT in vapor phase have been measured in the wavelength range 210–300 nm under laboratory conditions, in order to estimate how large resonance enhancement factors can be achieved for these explosives. The results show that the signal is enhanced up to 250,000 times for 2,4-DNT and up to 60,000 times for 2,4,6-TNT compared to the nonresonant signal at 532 nm. Realistic outdoor measurements on NM in vapor phase at 13 m distance were also performed, which indicate a potential for resonance Raman spectroscopy as a standoff technique for detection of vapor phase explosives. In addition, the Raman spectra of acetone, ethanol, and methanol were measured at the same wavelengths, and their influence on the spectrum from NM was investigated.

Raman spectra of P4 at low temperatures

Raman spectra of solid P4 have been recorded from 12 K up to room temperature using Fourier transform-Raman spectroscopy. The three Raman-active modes corresponding to Td symmetry have been resolved, and line shifts depending on temperature and matrix environment have been measured. Two phase transitions have been observed at T≈80 K (irreversible) and T≈195 K (reversible) corresponding to the γ→β and β↔α transitions, respectively. In the β phase, the ν2 mode is split into two lines, νsplit≈7.7 cm−1. The splitting of the ν2 mode is an indication of a breaking of Td symmetry for the β phase. A matrix shift of ≈3 cm−1 for P4 in a N2 matrix (1:5) was measured. Comparing experimental transitions of pure P4 with literature values on matrix isolated P4 in N2 (1:1000) we can conclude that there is a matrix shift in nitrogen of between 6 and 9 cm−1 depending on vibrational mode. The line positions found for pure P4 in the γ phase at 12 K are ν1=599.8 cm−1, ν2=361.6 cm−1, and ν3=459.0 cm−1. The corresponding values...

Stand-off detection of vapor phase explosives by resonance enhanced Raman spectroscopy

Stand-off measurements on nitromethane (NM), 2,4-DNT and 2,4,6-TNT in vapor phase using resonance Raman spectroscopy have been performed. The Raman cross sections for NM, DNT and TNT in vapor phase have been measured in the wavelength range 210-300 nm under laboratory conditions, in order to estimate how large resonance enhancement factors can be achieved for these explosives. The measurements show that the signal is greatly enhanced, up to 250.000 times for 2,4-DNT and 60.000 times for 2,4,6-TNT compared to the non-resonant signal at 532 nm. For NM the resonance enhancement enabled realistic outdoor measurements in vapor phase at 13 m distance. This all indicate a potential for resonance Raman spectroscopy as a stand-off technique for detection of vapor phase explosives.

Standoff Detection of Vapor and Trace Amounts of Explosives by Raman Technique

The large distances required pose several physical difficulties: The intensity of the return light decreases inversely with the distance squared, absorption losses in air (wavelength dependent) and scattering losses in air (wavelength dependent).

Real-Time Detection of IED Explosives with Laser Ionization Mass Spectrometry

The ESSEX system (Extremely Sensitive and Selective Explo- sives detector) is a system that can be used for standoff or remote detection of suicide bombers at a distance of up to a few meters via the trace amounts of explosives present in vapor phase around explosives with a high vapor pressure. The ESSEX detection method is based on laser ionization mass spectrometry (LI-MS). Direct sampling of air with explosives in vapor phase will allow detection of explosives with relatively high vapor pressure, such as TATP (suspected to have been used in the recent suicide bombings in Lon- don as well as numerous suicide bombings in Israel) and EGDN (normally found in dynamite explosives such as the ones used in the Madrid bomb- ings). The LI-MS method has a potential to detect all or nearly all explosives. For explosives with low vapor pressure (e.g. RDX, HMX, PETN, AN) it is probably necessary to sample particles as well. Other aspects of the future potential for this method are that the number of explosives that the method targets can be increased as needed. The method is very suited for data fusion and processing, making it possible to incorporate artificial intelligence (AI) into the system. The uniqueness of LI-MS methods lies in its low detection limit, possibility of real-time detection, its versatility regarding the number of possible substances to detect and its unique selectivity, leading to very few false alarms. The ESSEX concept is appropriate for indoor and outdoor applications, it is benign to humans and property and can be applied in an unnoticeable way. Laser ionization mass spectrometry and specifically reso- nance enhanced multi photon ionization (REMPI) is an ultra-sensitive, highly selective analytical technique that can identify and quantify vapor-phase con- stituents at parts-per-trillion (ppt) levels. The REMPI technique combines the principles of optical spectroscopy and mass spectrometry to provide a two- dimensional detection scheme that yields a high degree of chemical sensitivity