Thermal accommodation of inert He gas atoms colliding on a nanometer-sized Ar or N-2 particle was analyzed using molecular dynamics simulations. The instantaneous values of apparent thermal accommodation coefficient (alpha(th)) showed a distribution close to the normal distribution but with a longer tail toward lower values. The mean and standard deviation of alpha(th) for Ar particle were about 0.39 and 0.54, respectively, and 0.44 and 0.56 for a N-2 particle. Those values were almost independent of gas temperature or pressure. with less than 10% variation over a three- or four-fold variation of the gas conditions. The thermal accommodation coefficient per collision (alpha(0)), which was calculated from the apparent alpha(th) and the average number of collisions on the particle surface, was about 0.18 on the Ar particle and 0.20 on the N-2 particle, both of which are in good agreement with theoretical predictions based on single interactions between free molecules. (C) 2011 Elsevier Ltd. All rights reserved.