Model of motion in a viscous media with a statistic diffusion for calculation of ion dynamics in a dense gas and strong electric fields

Ion motion in a buffer gas is typically calculated either based on taking into account individual ion-molecular collisions, or using the concept of ion mobility sometimes accomplished with adding statistic diffusion. The former way is inefficient in a dense gas (for example, at atmospheric pressure), while the latter one is adequate only in weak electric fields. In the paper a new method of modeling ion motion in a dense gas is developed based on a combination of statistic diffusion with a directed motion in a quasi-viscous matter, in which the viscosity coefficient is calculated based on the frequency of ion-molecular collisions at different ion velocities. An optimal way of calculation of this frequency is proposed. Comparison of test simulations based on the proposed method and on taking into account individual ion-molecular collisions demonstrates good accuracy of the method in a wide range of gas pressures and electric field strengths.