MassKinetics: a theoretical model of mass spectra incorporating physical processes, reaction kinetics and mathematical descriptions

A theoretical framework and an accompanying computer program (MassKinetics, www.chemres.hu/ms/masskinetics) is developed for describing reaction kinet ics under statistical, but non-equilibrium, conditions, i.e. those applying to mass spectrometry. In this model all the important physical processes i nfluencing product distributions are considered: reactions, including the e ffects of acceleration, collisions and photon exchange. These processes occ ur simultaneously and are taken into account by the master equation approac h. The system is described by (independent) product, kinetic energy and int ernal energy distributions, and the time development of these distributions is studied using transition probability functions. The product distributio n at the end of the experiment corresponds to the mass spectrum. Individual elements in this scheme are mostly well known: internal energy-dependent r eaction rates are calculated by transition state theory (RRK or RRKM formal isms). In the course of collisions, energy transfer and other processes may occur (the latter usually resulting in the 'loss' of ion signal). Collisio ns are characterized by their probability and by energy transfer in a singl e collision. To describe single collisions, three collision models are used : long-lived collision complexes, partially inelastic collisions and partia lly inelastic collisions with cooling. The latter type has been developed h ere, and is capable of accounting for cooling effects occurring in collisio n cascades. Descriptions of photon absorption and emission are well known i ll principle, and these are also taken into account, in addition to changes in kinetic energy due to external (electric) fields. These changes in the system occur simultaneously, and are described by master equations (a set o f differential equations). The usual form of the master equation (taking in to account reactions and collisional excitation) was extended to consider a lso radiative energy transfer, kinetic energy changes, energy partitioning and ion loss collisions. Initial results show that close to experimental ac curacy can be obtained with MassKinetics, using few or no adjustable parame ters. The model/program can be used to model almost all types of mass spect rometric experiments (e.g. MIKE, CID, SORI and resonant excitation). Note t hat it was designed for mass spectrometric applications, but can also be us ed to study reaction kinetics in other non-equilibrium systems. Copyright ( C) 2001 John Wiley & Sons, Ltd.