Deep ultraviolet resonance raman excitation enables explosives detection

We measured the 229 nm absolute ultraviolet (UV) Raman cross-sections of the explosives trinitrotoluene (TNT), pentaerythritol tetranitrate (PETN), cyclotrimethylene-trinitramine (RDX), the chemically related nitroamine explosive HMX, and ammonium nitrate in solution. The 229 nm Raman cross-sections are 1000-fold greater than those excited in the near-infrared and visible spectral regions. Deep UV resonance Raman spectroscopy enables detection of explosives at parts-per-billion (ppb) concentrations and may prove useful for stand-off spectroscopic detection of explosives. © 2010 Society for Applied Spectroscopy

Solid state and solution nitrate photochemistry: Photochemical evolution of the solid state lattice

We examined the deep UV 229 nm photochemistry of NaNO3 in solution and in the solid state. In aqueous solution excitation within the deep UV NO3- strong π → π* transition causes the photochemical reaction NO3- → NO2- + O·. We used UV resonance Raman spectroscopy to examine the photon dose dependence of the NO2- band intensities and measure a photochemical quantum yield of 0.04 at pH 6.5. We also examined the response of solid NaNO3 samples to 229 nm excitation and also observe formation of NO2-. The quantum yield is much smaller at ∼10-8. The solid state NaNO3 photochemistry phenomena appear complex by showing a significant dependence on the UV excitation flux and dose. At low flux/dose conditions NO2- resonance Raman bands appear, accompanied by perturbed NO3- bands, indicating stress in the NaNO3 lattice. Higher flux/dose conditions show less lattice perturbation but SEM shows surface eruptions that alleviate the stress induced by the photochemistry. Higher flux/dose measurements cause cratering and destruction of the NaNO3 surface as the surface layers are converted to NO2-. Modest laser excitation UV beams excavate surface layers in the solid NaNO3 samples. At the lowest incident fluxes a pressure buildup competes with effusion to reach a steady state giving rise to perturbed NO3- bands. Increased fluxes result in pressures that cause the sample to erupt, relieving the pressure. © 2011 American Chemical Society