Trapping-desorption and surface penetration of argon on ice

Molecular dynamics simulations of trapping-desorption and surface penetrati on of argon atoms on the surface of ice Ih are presented. At a surface temp erature of 180 K, 64% of the trapped atoms follow an ordinary first-order d esorption process with a rate constant k = 2.1 x 10(10) s(-1), while 36% pe netrate the ice surface and diffuse into subsurface interstitial sites as a result of thermally produced disorder in the topmost bilayer of the ice cr ystal. The surface penetration process provides a mechanism for rapid incor poration of reactants into the ice lattice, and implications for reactions on stratospheric ice particles are discussed. (C) 1999 Elsevier Science B.V . All rights reserved.