Mass fragmentation processes, reactions observed

The first reliable spectroscopic analysis of saturated sulfur vapor was published by Berkowitz and Marquart [28] who used a combination of a Knud-sen effusion cell with a mass spectrometer and generated the sulfur vapor by evaporating either elemental sulfur (low temperature region) or certain metal sulfides such as HgS which decompose at high temperatures to sulfur and metal vapor. These authors observed ions for all molecules from S2 to Ss and even weak signals for Sg and Sio. From the temperature dependence of the ion intensities the reaction enthalpies for the various equilibria (1) were derived (see Table 1). Berkowitz and Marquart careMly analyzed their data to minimize the influence of fragmentation processes in the ion source of the spectrometer. They also calculated the total pressure of sulfur vapor from their data and compared the results with the vapor pressure measurements by Braune et al. [26]. The agreement is quite satisfactory but it probably... 

The chemical ionisation mass spectral data indicate that intramolecular exchange reactions predominate in the primary thermal fragmentation process of polyethylene oxalate resulting in the formation of cyclic oligomers. These products are not stable in the electron ionisation (El) mode and are therefore not directly observed in the El mass spectrum. 

Analytical systems based on Py-MS are intended to perform pyrolytic reactions and to analyse the composition of the resultant pyrolysate by mass analysis of ions formed through the ionization of its components molecules. The structural complexity of the spectra recorded is usually considerable, owing to the formation of fragments with the same nominal mass from originally different components and the absence of reliable separation procedures. In addition, the observed complexity originates from secondary fragmentation processes, hence various techniques have been used that minimize these... 

A second model was developed to describe the pyrolysis kinetics on a more fundamental basis (Westerhout et al., 1997). The model accounts for the fact that both physical and chemical processes play an important role during the pyrolysis of polymers. When an apparatus, such as a TGA, is used for a kinetic study of a pyrolysis process, the rate of evaporation of pyrolysis products is measured, but not the intrinsic chemical reaction (the breaking of bonds) rate. Not every broken bond in the polymer chain leads to the evaporation of product. Only polymer chain fragments small enough to evaporate at the given reaction temperature will actually leave the polymer sample. This implies that both physical and chemical processes influence the measured rate of change of the polymer mass and hence the observed pyrolysis kinetics. 

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