Probing trapped ion energies via ion-molecule reaction kinetics: Fourier transform ion cyclotron resonance mass spectrometry.

The kinetic energy-dependent Ar(+)+ N2 ion-molecule reaction has been used as a chemical "thermometer" to determine the kinetic energy of ions produced by electron ionization and trapped by using a Fourier transform ion cyclotron resonance (FTICR) mass spectrometer. The rate constant for this reaction obtained on the FTICR mass spectrometer was compared to previous work, which allowed a kinetic energy estimate to be made. In addition, the effects of varying parameters such as trapping voltage and pressure on ion kinetic energy were investigated. No evidence of the differing reactivity of higher energy electronic states of Ar(+), such as (2)P1/2, was observed and the results of a model of this system are presented that support this observation. Pressure studies revealed that with an average of as few as 13 ion-molecule collisions, Ar(+) ions are collisionally relaxed to an extent unaffected by additional collisions. Based on recent variable temperature selected ion flow drift tube measurements, FTICR ion energies are estimated to be slightly above thermal.