PHASE-SHIFTING ACCELERATION OF IONS IN AN ION-CYCLOTRON RESONANCE SPECTROMETER - KINETIC-ENERGY DISTRIBUTION AND REACTION DYNAMICS

The kinetic energy distribution of trapped ions in an ion cyclotron re sonance spectrometer (ICR) under a periodically phase-reversed rf pote ntial is determined. At the operating pressures typical for the ICR (1 0(-7)-10(-5) Torr), the ions eventually achieve a kinetic energy distr ibution that varies across short time intervals (0.1 ms) but is consta nt on the time scale of bimolecular collisions. This provides the oppo rtunity to study quantitatively the translational energy dependence of bimolecular reactions and sequential collisional activation processes . The kinetic energy distribution, although not Maxwell-Boltzmann, is readily calculable. Results obtained for the kinetic energy dependence of the reaction of Cl- + CH3Br are qualitatively and quantitatively c onsistent with reported nonstatistical behavior in that system. Experi mental considerations are discussed.