Determination of Appearance Energies

The techniques used for the determination of appearance energies are essentially identical to those described above for lEs. However, even when using the most accurately defined electron or photon energies, great care has to be taken when AEs are to be determined because of the risk of overestimation due to kinetic shift. Provided that there is no reverse activation energy for the reaction under study, the AE value also delivers the sum of heats of formation of the dissociation products. If substantial KER is observed, the AE may still be used to determine the activation energy of the process. 

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The Lozier tube, illustrated in Figure 3, has been used by several groups for a variety of different studies, including the determination of appearance energies and kinetic energies of ion fragments produced in electron impact-induced dissociation... 

It is fairly safe to say that Gm (source) > Gm (m ), i.e. the ions from the source are detected at least as efficiently as metastable ions. The effect of the form of P(E) can be to favour either 7m (source) or7m (m ) and cannot be treated in general terms. Gaps in the energy distribution, P(E), can influence the determination of appearance energies in just the same way as they influence metastable ion abundances. 

Closely related to the metastable ion structure is the determination of kinetic energy release, which appears as a rather sensitive probe to reaction dynamics3-5. However, a comprehensive analysis of the kinetic energy release is in general a complicated process and requires detailed information regarding the ion-optic system3-5. 

Kinetic and competitive shifts are instrumental effects which, in principle, can always be avoided given sufficient sensitivity. There are other considerations germane to the determination of critical energies from appearance energies which are essential characteristics of the experimental approach. 

Many determinations of translational energy releases in source reactions have been made with a view to correcting appearance energies and obtaining more accurate energies (heats) of formation [676]. 

Electronic energy 45, 64 Electronic spectra 15-21 of aliphatic thiols 306 of aromatic thiols 307 Electronic wavefunction 47 construction of 48-54 Electron impact method, for determination of appearance potentials 335... 

ABSTRACT. The use of mass spectrometry to collect data on the decomposition chemistry of nitramine compounds and the relevance of the data to the processes occurring in these materials when they are used in actu propellant and explosive applications is discussed. The simultaneous thermogravimetric modulated beam mass spectrometry (STMBMS) and time-of-flight (TOF) velocity-spectra techniques and then-application to the study of energetic materials are discussed. The means by which these techniques enhance the amount of information obtained from more conventional mass spectrometric experiments is illustrated with studies on the evaluation of the use of appearance energy measurements to study the thermal decomposition of HMX and on the identiHcation of the HMX pyrolysis products and the determination of their gas formation rates. 

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