Mass spectrometry time-resolved molecular

TIME-RESOLVED MOLECULAR BEAM MASS SPECTROMETRY OF TRANSIENT COMBUSTION PHENOMENA... 

ABSTRACT. We describe an apparatus by which the detonation products of an explosive can be identified and whose relative concentrations can be determined quantitatively. These measurements can be made on products that have been formed in less than one microsecond after the passage of the detonation wave. The technique is based on the rapid quenching of chemical reactions by virtue of the free expansion of the products into vacuum. Of course, products that have been formed over a longer period of time and under different pressure/temperature conditions can also be studied. Time resolved molecular-beam mass spectrometry is used, so that whether detonation occurred or not in forming the products can be determined. We describe optical techniques, principally Schlieren photographs, that also confirm detonation. We report measurements made on six standard explosives, PETN, RDX, HMX, HNS, TNT and TATB, and one research explosive, nitric oxide. For none of the standard explosives do we measure product distributions that agree with model predictions based on equilibrium assumptions. A computer model of the free expansion is described briefly and its importance to the interpretation of the data is emphasized. 

Temperature-programmed vacuum pyrolysis in combination with time-resolved soft ionization mass spectrometry allows principally to distinguish between two devolatilization steps of coal which are related to the mobile and non-mobile phase, respectively. The mass spectrometric detection of almost exclusively molecular ions of the thermally extracted or degraded coal products enables one to study the change of molecular weight distribution as a function of devolatilization temperature. Moreover, major coal components can be identified which are released at distinct temperature intervals. 

The rapid formation of molecular iodine following the flash photolytic dissociation of CHgl has been observed by time-resolved mass spectrometry.60 This has been attributed to the reaction (20) rather than to slow termolecular recombination. The experimental difficulties associated with sampling by this technique have been discussed by Meyer.61 This reaction is further discussed in Section IX.D on reaction of I(52Py2) with alkyl iodides. 

To attain maximum resolution of the components of a mixture by HPLC, the gradient of eluent must be effectively optimized. This procedure can be tedious and time consuming. The rate of sample generation in combinatorial chemistry makes it impossible to find time to optimize the chromatographic conditions for each sample. Fortunately, detection by mass spectrometry alleviates somewhat the need for all compounds to be resolved, since unresolved samples can usually be differentiated on the basis of their molecular... 

Figure 4.2. Experimental set-up for kinetic studies of SiHj reactions by excimer laser photolysis in a tubular slow-flow reactor with time-resolved detection by molecular beam sampling, near-threshold ionization electron impact mass spectrometry...

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