Structure and dynamics of ice Ih films upon HCl adsorption between 190 and 270 K. II. Molecular dynamics simulations

Classical molecular dynamics simulations are carried out between 190 and 250 K on an ultrathin ice film doped by HCl deposition with a coverage varying from 0.3 to 1.0 monolayer. These conditions are similar to those defined in the experiments described in the companion paper. Within the assumption that the hydracid molecule remains in its molecular form, the order parameters and the diffusion coefficients for the H2O molecules are determined in the HCl doped ice film, and compared to the experimental data. The residence times of HCl at the ice surface are also calculated. Below 200 K, the HCl molecules are found to remain localized at the ice surface, while above 200 K, the HCl diffusion inside the film is easy and leads to a strong disorder of the ice structure. Although the formation of hydrates cannot be interpreted by the present calculations, the lowering of the ice melting temperature by 15 K measured in neutron experiments for an HCl doped ice film is qualitatively explained by simulation results. (C) 2002 American Institute of Physics.