Resonance excitation of ions stored in a quadrupole ion trap Part II. Further simulation studies

Abstract

Further simulation studies have been carried out on the behaviour of ions stored in a quadrupole ion trap and subjected to small auxiliary potentials oscillating at frequencies related to the secular frequencies of ion motion. Quadrupolar excitation at frequencies of β r Ω and β z Ω, that is, twice the fundamental radial and axial secular frequencies, respectively, results in parametric resonance which induces rapid excitation of ion motion. Frequency analysis of ion axial and radial motions has been carried out to determine the effects of collisions on ion motion, and of auxiliary potential amplitude and frequency for several working points in the stability diagram. A systematic survey was carried out of the variation, as a function of working point, of ion kinetic energy averaged over the final three r.f. cycles prior to ejection. The chosen working points lay on the locus of β r Ω = β z Ω, the two main areas of the stability diagram for which β z Ω < β r Ω and β r Ω < β z Ω, the q z axis, and working points for which a z was varied at constant q z . Ion kinetic energies averaged over the final three r.f. cycles are interpreted in terms of potential well-depths, while the irradiation times required for ion ejection indicate relative efficiencies for energy absorption by the subject ion from the resonance radiation.