Trapping ions from a fast beam in a radio-frequency ion trap: Exploring the energy exchange with the longitudinal radio-frequency field

摘要

Single-photon ionization leading to two vacancies in the 2p subshell of argon is investigated experimentallynusing the photoelectron time-of-flight magnetic bottle coincidence technique. Three peaks correspondingnto the 3P, 1D, and 1S states of the dication are found in the ionization energy range 535 to 562 eV.nMulticonfigurational Dirac-Fock calculations were performed to estimate the single-photon double-ionizationncross sections. Reasonable agreement between the measured and simulated spectra is found if single and doublenexcitations are taken into account in the wave-function expansion.nThe possibility of injecting ions from an initially fast moving beam into a multipole radio-frequency (RF) ionntrap without the use of buffer gas is described. The chosen trap geometry gives rise to an oscillating electricnfield along the direction of the incoming ions, and through an analytical model as well as numerical simulationsnit is demonstrated that the energy exchange between the injected ions and this oscillating field governs thentrapping dynamics. Most notably, if ions arrive at the trap during specific phases of the RF field, they can beneffectively decelerated and stored with low kinetic energy even if their kinetic energy initially exceeds the depthnof the trapping potential well. An experimental apparatus for trapping ions from a fast beam is described, andnexperimental investigations demonstrating the described trapping dynamics are presented.