PIC-MCC in OOPD1 and three body collision dynamics C.-H. Lim (UCB-ME) The Monte Carlo collision model implemented in OOPD1 is described, and compared to anaytic solutions of fundamental collisional problems. The model includes atomic collisions such as electron- and ion-neutral reactions. A scheme is proposed for extension of the collision model to 3-body interactions necessary for the simulation of mixed gases. The 3-body collision dynamics are described, and a review of 3-body work from the literature, such as p-H three-body collisions, is presented.