Trapping-desorption and surface penetration of argon on ice

Molecular dynamics simulations of trapping-desorption and surface penetration of argon atoms on the surface of ice Ih are presented. At a surface temperature of 180 K, 64% of the trapped atoms follow an ordinary first-order desorption process with a rate constant k = 2.1 x 10(10) s(-1), while 36% penetrate the ice surface and diffuse into subsurface interstitial sites as a result of thermally produced disorder in the topmost bilayer of the ice crystal. The surface penetration process provides a mechanism for rapid incorporation 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.