Adsorption of Chlorinated Methane Derivatives at the Ice Surface: A Grand Canonical Monte Carlo Simulation Study

The adsorption behavior of three chlorinated methane derivative molecules, CH3Cl, CHCl3, and CCl4, is investigated at the (0001) surface of I-h ice at the tropospheric temperature of 200 K by means of grand canonical Monte Carlo simulations. This study completes our earlier investigations concerning the adsorption of CH4, CH2Cl2, and fluorinated methane derivatives. Our results show that neither CHCl3 nor CCl4 exhibits any adsorption. This complete lack of adsorption is 250 attributed to the interplay of the very strong cohesion acting between the adsorbate molecules, and their relatively weak interaction with the ice phase. By contrast, CH3Cl does exhibit a noticeable adsorption on ice, and the adsorbed molecules prefer to turn toward the ice surface by their H atoms, forming weak, C-H center dot center dot center dot center dot O-type hydrogen bonds with surface waters. The lateral (i.e., adsorbate adsorbate) contribution to the total interaction energy of the adsorbed molecules is always considerably larger (in magnitude) than in the case of the corresponding fluorinated analogues, making also the total adsorption energy lower for the chlorinated molecules than for their fluorinated counterpart. As a consequence of this strong attraction between the chlorinated adsorbate molecules, their condensation occurs at lower chemical potential (and, hence, pressure) values than that of the fluorinated analogues, which prevents the formation or completion of the adsorption layer of the chlorinated molecules.