Dissociation of Trinitrotoluene on the Surface of Porous Silicon Under Laser Irradiation

AbstractDissociation of trinitrotoluene (TNT) sorbed on porous silicon (pSi) surface under UV laser irradiation has been studied. A method based on ion mobility spectrometry (IMS) has been used in this study. Excitation and ionization of TNT molecules has been occurred at atmospheric pressure. A dependence of TNT ion spectrum on standing time of TNT molecules on pSi surface has been demonstrated. The ion type has changed from (TNT-H) – to (TNT-NO2) – which indicates a slow chemical reaction between pSi surface and TNT molecules. The first step of (TNT-NO2) – formation has been found to be a result of laser stimulated surface dissociation and subsequent desorption of a neutral TNT-NO2 fragment. The second step of (TNT-NO2) – formation is a capture of an electron emitted from the pSi surface under laser irradiation. The result of this study could be used in the area of explosive detection

Surface-Assisted Laser Desorption/Ionization of Trinitrotoluene on Porous Silicon under Ambient Conditions

Desorption/ionization on silicon (DIOS) is widely used in modern mass spectrometry for obtaining ions of various organic substances. The high efficiency of DIOS suggests that it may be a promising method in ion-mobility spectrometry (IMS) using gas-phase ion separation. The influence of laser wavelength and intensity on DIOS of trinitrotoluene (TNT) molecules under ambient conditions has been studied. If laser with a wavelength of 266 or 355 nm is used, TNT molecules predominantly form (TNT – H)⁻ negative ions. Their formation has been found to result from laser-induced proton transfer from TNT molecules to the porous silicon (pSi) surface, rather than gas-phase ion–molecule reactions. The dependence of the yield of (TNT – H)⁻ ions on the laser intensity has been analyzed. The ion yield curve has been demonstrated to fit the Arrhenius function at laser intensity lower than ∼2.5×10⁷ W/cm². Experiments have shown that the desorption/ionization of TNT molecules is not a purely thermal process. The results demonstrate that DIOS can be widely used in the IMS technology