Ab initio study of HCl and HF interaction with crystalline ice.: I.: Physical adsorption

A quantum-mechanical ab initio study is presented concerning the physisorption of HCl and HF on ice surfaces, modeled with periodic, proton-ordered thin films. Three methods are adopted: (1) Periodic two-dimensional calculations concerning ice surfaces, both clean and covered with ordered overlayers; (2) embedded cluster calculations, concerning two-dimensional ordered structures interacting with a single molecule; (3) molecular:cluster calculations, simulating a portion of the surface. The combined and interactive use of these techniques has permitted us to recognize some deficiencies of molecular cluster models of ice and to correct for them. The energy of physisorption of HCl on a perfect basal surface of ice is estimated to be about 8 kcal/mol, on prismatic faces about 11 kcal/mol. Adsorption energies of HF are larger by 4 to 5 kcal/mol. (C) 1998 American Institute of Physics.