The trapping probability of Ar on Pt(111) has been measured as a function of incident kinetic energy Ei and angle θi for surface temperatures Ts of 80, 190 and 273 K. This probability decreases with increasing Ei in a manner that depends on both θi and Ts. For each surface temperature the measured trapping probability at different angles can be reduced to a common curve if it is plotted as a function of the variable Ei cosnθi. For Ts=80, 190 and 273 K, we find optimal values of n of approximately 1.5, 1.0 and 0.5, respectively. These results indicate that parallel momentum dissipation becomes increasingly more important to the trapping dynamics as Ts increases. © 1989.