A mathematical model of sublimation (evaporation) of thin films of explosives based on the molecular-kinetic theory of evaporation is presented. An expression is obtained for the film evaporation time until equilibrium between the evaporation and condensation of explosives is reached. An estimate of the unevaporated mass is given. A parametric study of the model was carried out. The calculation of evaporation dynamics for a film of trinitrotoluene on glass with a surface density of 100 ng/cm2 is giv. The heat of sublimation of trinitrotoluene and the coefficient of evaporation from glass based on a comparison with the experiment of evaporation of such a film of TNT were determined.

The results of the measurements of 2,4,6-trinitrotoluene (TNT) vapor concentration over its trace amounts, called thin films, on the glass surface with a concentration of 100 ng/cm2 in a square area with a side of 1 cm over time are presented. The trace amounts of TNT on the glass were formed by applying a solution of TNT in the acetonitrile diluted with the chemically pure acetone, followed by the evaporation of the solvents. In order to measure the TNT vapor concentration, an EKHO-V-IDTS portable multibacillary gas-chromatograph with preliminary TNT vapor concentration was used. A sampling of the TNT vapor above the object was carried out with a remote vortex sampler. The vapor sample was taken from a distance of 2 cm from the glass surface. The concentration in the mode of the complete capture of TNT vapors was carried out to the stainless-steel wire mesh. The vapor concentration was determined from the chromatographic peak amplitude. It was found that the concentration of vapor over the examined surface with an area of 1 cm2 decreases from 10-13 to 10-14 g/cm3 within 2.6 ± 0.3 hours. TNT vapor concentration value of 10-14 g/cm3 corresponds to the threshold concentration of TNT vapor for the modern detectors. Based on the assumption that the vapor concentration is proportional to the amount of the TNT mass on the surface for the considered trace amounts of TNT, it was estimated that the initial surface concentration of trinitrotoluene of 100 ng/cm2 on the glass surface decreases to 12 ng/cm2 within 2.6 ± 0.3 hours due to sublimation into an open half-space. It was shown that the use of vortex sampling of vapor intensifies the sublimation of TNT from the glass surface.

Представлены результаты одновременного определения следов взрывчатых веществ (ВВ) на поверхности объектов, содержащих ВВ в пропускных порталах безопасности.Лазерным дистанционным методом для идентификации твёрдых следов, и газохроматографическим методом для определения следов пара над твёрдыми следами.Цель: экспериментальное сравнение методов по возможности определения следов ВВ с разной летучестью на поверхности объектов в антитеррористическом контроле.Использовали портативный поликапиллярный газовый хроматограф (ГХ) и лидарный обнаружитель (ЛО) ВВ на основе эффекта лазерной фрагментации/лазерно-индуцированной флуоресценции NOфрагментов [1].В качестве модельных объектов использовали картонную коробку с имитатором ВВ, укрываемую тканью и открытые эластичные имитаторы ВВ.Лидарное определение твёрдых ВВ осуществляли с 5 метров, отбор паров ВВ вихревым пробоотбором для анализа на ГХс расстояния 2-3 см от объекта.Характеристики приборов и условий определения: ГХпорог определения ТНТ 10 -12 г в пробе, время отбора пробы на концентратор 5-10 секунд, время анализа и принятия решения 20-40 секунд, ЛО -порог обнаружения с дистанции 5 м: паров ТНТ -(1-10)×10 -13 г/см 3 , твёрдых следов на поверхности -1 нг/см 2 , время определения 10 секунд.Критерием обнаружения объектов было превышение сигнала над шумом.Результаты экспериментального сравнения методов.1. Имитатор ТНТ.Укрытый тканью (чёрным сатином) обнаруживается ГХ.Лидаром не обнаруживается объект, укрытый тканью, но обнаруживается открытый имитатор ТНТ.2. Открытый имитатор гексогена.ГХ -не обнаруживается при комнатной температуре, но обнаруживается при облучении имитатора лазером.Объект обнаруживается ЛО.3. Открытый имитатор ТЭН.При комнатной температуре не обнаруживается ГХ.Но обнаруживается ГХ при облучении имитатора лазером.Объект обнаруживается ОЛ.4. ЛО эффективен в обнаружении ВВ по твёрдым следам, чем по парам.Эффективность дистанционного ЛО по сравнению с пробоотборным газоаналитическим ярко проявляется при обнаружении труднолетучих ВВ типа ТНТ, гексогена, ТЭН.

The gas-phase reactions of molybdenum oxide cluster ions MoxOy+ (x = 1-3, y =;1-9) with small alcohols have been investigated using Fourier transform ion cyclotron resonance mass spectrometry. The product branch ratios are reported. The reactions of MoxOy+ with alcohols can be envisioned as proceeding via metal insertion into C-H and C-O bonds. C-H bond insertion leads to alcohol dehydrogenation and aldehyde elimination, whereas insertion into the C-O bonds results in alcohol dehydration and formation of metal-alkyl groups. Moreover, an increase of the chain length and branching lead to C-C bond cleavage. The most intriguing process is the reaction of the Mo3O9+ ion with more than one CH3OH molecule yielding Mo3O9(C2H5)(+) and Mo3O9(C3H7)(+) ions. The Mo3O9CH3+ ion was found to be the key intermediate of the polymerization process. Molybdenum oxides are protonated in the presence of alcohols. The upper and lower limits for the MoxOy, proton-affinities were estimated as PA(MoO) < 180 kcal/mol, PA(Mo2O4, Mo2O5, Mo3O8) = 188 +/- 8 kcal/mol, PA(MoO2)= 202 +/- 5 kcal/mol, PA(MoO3, Mo2O6, Mo3O9) > 207 kcal/mol.

ICR studies of the interactions between methanol and the family of MoxOy+ ions (x = 1−3, y = 1−9) in the gas phase are reported. Molybdenum oxide ions participate in four types of reactions with the CH3OH molecule that show rather profound similarities with the reactions of methanol over heterogeneous and homogeneous catalysts containing molybdenum−oxygen sites. Molybdenum oxide ions with three metal atoms represent coupling of two and three hydrocarbon fragments of CH3OH to form longer hydrocarbon chains. The formation of acidic proton of MoxOyH+ (x = 1−3, y = 2−9) was found in interactions with CH3OH2+ and its solvates CH3OH2+·(CH3OH)n with n = 1, 2. Acidic protons are able to provide coupling of hydrocarbon fragments of alcohol molecules to produce finally alkenes and alkanes.

The combination of the Knudsen cell with a standard cubic ICR trapping cell produces a number of cluster ions of molybdenum oxides MoxOy+ (x = 1−5, y = 1−15). Ionization of molybdenum trioxide vapors by electron impact yields MoxOy+ with high oxygen-to-metal ratios. Collisions with vacuum gas lead to reduction of oxygen-saturated molybdenum oxide cluster ions and to fragmentation of MoxOy+ ions with x > 3, whereas dimers and trimers are relatively stable. Time and temperature dependencies of MoxOy+ concentrations suggested that Mo4O12+ and Mo5O15+ are the primary products of MoO3 vaporization and other ions are the products of their fragmentation. A simple pair-potential model was used to calculate energy-optimized geometric structures of the clusters. The model identifies the most abundant clusters as having the lowest calculated energy per atom. The six-ring Mo3O9 cluster was found to be the most stable species, and molybdenum oxides with four and five metal atoms also include the six atom ring where on...

The reactivity of rhenium (Re+) and rhenium monocarbonyl (ReCO+) cations in the gas phase toward CO oxidation by oxygen-containing reagents (NO, O-2, and N2O) was studied by ion cyclotron resonance. The presence of a carbonyl ligand significantly affects the ion reactivity. An effective route of metal monocarbonyl ion oxidation by molecular oxygen was found. This step can explain low-temperature activity of a number of oxide catalysts in the reaction of CO oxidation by molecular oxygen.

The reactivity of the Mo+, W+, Ni+, Co+, and Fe+ ions with respect to the activation of the C-S, S-H, and C-H bonds in the molecules of various organosulfur compounds is investigated by ion cyclotron resonance. Unlike the Ni+ and W+ ions, the Ni+ and Co+ ions are shown to interact primarily with the C-S bonds of these molecules irrespective of their structure. On the contrary, the Mo+ and W+ ions undergo the insertion mainly into the C-H bonds and more rarely, into the S-H bonds, while the Ni+ and Co+ ions are inactive when the molecule contains the C-S bond. The experimental data obtained provides additional arguments in favor of the earlier hypothesis on the roles of metals, of the active component of the catalysts for hydrodesulfurization: both the activation of a sulfur-containing molecule and the hydrogenolysis of the CS bond proceed on the Ni+ and Co+ ions, while H-2 activation occurs on MoS2(WS2).

Gas-phase oxidation of CO in the presence of rhenium cations with carbonyl and oxygen ligands has been studied by Fourier transform ion cyclotron resonance (FT-ICR) spectrometry. Rhenium cations have been generated by the electron impact of Re2(CO)10 vapour. Contrary to the unreactive rhenium ions, rhenium monocarbonyi ions have been found to react with O2 molecules yielding rhenium monoxide ions and CO2 molecules. ReO+ ions are subsequently oxidized with O2 to di- and trioxide ions. The bond energies in rhenium oxide ions were estimated as D°(Re+−O)=104±14, D°(ReO+−O)<118, D°ReO 2 + −O)=122±4 kcal/mol. Simultaneous addition of CO and O2 molecules to the reaction volume leads to the gas-phase catalytic oxidation of CO with pairs of rhenium oxide ions ReO 3 + /ReO 2 + serving as the oxidized and reduced forms of the catalyst. The mechanisms of the above reactions are discussed in connection with that for oxidation of CO over solid oxide catalysts.

FT/ICR spectrometry has been used for gas-phase studies of the interaction between singly-charged positive tungsten ions and hydrocarbons (alkanes C2-C-9, alkenes C2-C6, and cycloalkanes C3-C6). It is shown that this interaction results mainly in dehydrogenation products. The number of H-2 molecules eliminated depends upon the size and type of hydrocarbon and varies from 1 to 6. Significant amounts of C-C cleavage products have been found in the cases of cyclopropane and 2-methylpropene only.

Gas phase reactions of Mo+ and W+ ions with the molecules of various oxidants (NO, O2, N2O, CH2O, C2H4O) were studied using ion cyclotron resonance. In oxidation with N2O the mono-, di- and trioxide metal cations are formed consecutively. The trioxide MO3+ ions of both metals react with CO to form CO2 and MO2+ ions. In this way, catalytic reaction N2O + CO → N2 + CO2 occurs in the gas phase with MoO3+ /MoO2+ and WO3+/WO2+ couples as catalysts. The rate constants have been measured for both stages of the catalytic cycle as well as for the stages of the catalyst preparation. Metal-oxygen bond energies were estimated for MoOx+ and WOx+ species with various x. The mechanism of CO oxidation with MoOx+ and WOx+ cations as catalysts in the gas phase is discussed in comparison with that for the oxidation over classical solid oxide catalysts.