Realistic modeling of ion-neutral collisions in quadrupole ion traps

In this study, three ion-neutral collisionmodels have been discussed and compared, including the Langevin, the hard-sphere and the mixed collision models. With the pseudo-potential approximation, analytical expressions of ion secular motions with the hardsphere and mixed collision models have been obtained for the first time. Through numerical simulations and theoretical calculations, it is found that the mixed collision model could be used as a general description of ion-neutral collisions under different conditions. Langevin collision model is a good description of low energy collisions between small ions and neutrals, while hard-sphere collision model could be used to describe high energy collisions and/or ions with higher masses (larger physical sizes). These analytical expressions of ion motion decay profiles enable the creation of direct relationships between time-domain image currents with ion collision cross sections.