An improved Monte Carlo method is developed for the simulation of the ion transport in classical drift tube in the case of ion-molecule asymmetric systems such as O Ϫ /O 2 or N ϩ /N 2 . The aim of this new method is to overcome the problem of incident ions which vanish at relative high electric field due to asymmetric charge transfer or electron detachment. These ion removal processes are compensated by a fictitious ion creation which improves the accuracy of the ion distribution function and

more »

... arm coefficient calculations. The classical ion-molecule collision processes occurring in weakly ionized gases at room temperature ͑elastic collisions including energy exchange and thermal motion of background gases and also inelastic collisions͒ are taken into account. This new method is then validated and the transport and reaction coefficients have been given for a large range of E/N ͑a part of them for the first time in the literature͒ in O Ϫ /O 2 and N ϩ /N 2 systems.