Realistic modeling of ion-neutral collisions in quadrupole ion traps

Abstract

In this study, three ion-neutral collision models 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 hard-sphere 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.

GPU Assisted Simulation Study of Ion–Ion Reactions within Quadrupole Ion Traps

“…Although many collision models exist for ion-molecule collisions, such as the Langevin collision model, the hard-sphere collision model, and the mixed collision model [35], no ion-ion reaction model has been proposed and implemented in ion trajectory simulations. Estimated reaction rates could be found in literature [13], however, without detailed derivations.…”

“…Helium was used as the buffer gas and the hard-sphere collision model was applied to model the ionneutral collisions. Since the cations studied in this work have high masses, the hard-sphere collision model is more realistic than the Langevin collision model [35]. The calculation of energy transfer of ion and neutral molecules is based on the assumption of elastic collision.…”

Ion collision crosssection measurements in quadrupole ion traps using a time–frequency analysis method

“…In a practical system, ions trapped within a quadrupole ion trap could be affected by high-order electric elds, which will result in nonlinear resonances [43][44][45][46] and "mass shi". 47 When considering both the effects, ion-neutral collisions will induce ion motion amplitude decay, and reduced ion motion amplitude will lead to ion motion frequency shis with the presence of high-order elds. 37 Besides high-order elds, ion motion could also be affected by ion-neutral collisions.…”

Collision cross section (CCS) measurement by ion cyclotron resonance mass spectrometry with short‐time Fourier transform

“…The hard‐sphere collision model treats both the ion and the neutral as small hard spheres. The hard‐sphere model is generally preferred for higher energy collisions and ions of large sizes . The energetic hard‐sphere model aims to describe ion‐neutral collisions with higher energy than the range of the hard‐sphere model .…”

“…The hard-sphere model is generally preferred for higher energy collisions and ions of large sizes. 27 The energetic hard-sphere model aims to describe ion-neutral collisions with higher energy than the range of the hard-sphere model. 26,28 In an FTICR mass spectrometer with a higher magnetic field and large ICR cell radius, the hard-sphere model or the energetic hard-sphere model should both be appropriate.…”