Classical trajectory study of argon-ice collision dynamics

Classical trajectory simulations have been used to study Ar-ice Ih collisio nal energy transfer, trapping coefficients and scattering distributions for initial Ar kinetic energies between 0.1 and 2.0 eV, incident angles betwee n 0 and 70 degrees and surface temperatures between 0 and 300 K. Collisiona l energy transfer is extremely efficient due to substantial transfer of ene rgy from the Ar atom to the ice surface over typically 2-4 gas-surface enco unters, and the rapid dissipation of this energy away from the collision ce nter, preventing energy transfer back to the Ar atom. This leads to large t rapping coefficients over this range of Ar collision energies, incident ang les and surface temperatures. Scattered gas atoms lose most of their initia l kinetic energy and have broad angular distributions. The large trapping c oefficients obtained for the Ar-ice collisions are expected to be found for similar reactions under stratospheric conditions (e.g., HCl-ice, HOCl-ice and ClONO2-ice). (C) 1999 American Institute of Physics. [S0021-9606(99)711 10-4].