IMPROVED MONTE-CARLO METHOD FOR ION-TRANSPORT IN ION-MOLECULE ASYMMETRIC SYSTEMS AT HIGH ELECTRIC-FIELDS

An improved Monte Carlo method is developed for the simulation of the ion transport in classical drift tube in the case of ion-molecule asym metric systems such as O-/O-2 or N+/N-2. The aim of this new method is to overcome the problem of incident ions which vanish at relative hig h electric field due to asymmetric charge transfer or electron detachm ent. These ion removal processes are compensated by a fictitious ion c reation which improves the accuracy of the ion distribution function a nd swarm coefficient calculations. The classical ion-molecule collisio n processes occurring in weakly ionized gases at room temperature (ela stic collisions including energy exchange and thermal motion of backgr ound gases and also inelastic collisions) are taken into account. This new method is then validated and the transport and reaction coefficie nts have been given for a large range of E/N (a part of them for the f irst time in the Literature) in O-/O-2 and N+/N-2 systems. (C) 1998 Am erican Institute of Physics.