Sticking of hyperthermal CO to the (0001) face of crystalline ice

We present the results of classical trajectory calculations on the sticking of hyperthermal CO to the basalplane (0001) face of ice Ih, for normal and off-normal incidence at surface temperature (Ts) ) 150 K. Thesticking probability decreases with the incidence energy (Ei) and with the incidence angle (ýi) for ýi > 20°.At normal incidence, the sticking probability can be fitted to a simple decay function: Ps ) 0.9 e-0.012Ei(kJ/mol).The energy transfer from the impinging molecule to the surface is found to be efficient and fast: most of Eiis transferred to the surface within 0.5-1.0 ps. For off-normal incidence, the energy transfer becomes lessefficient for ýi > 20°. In the case of backscattering at off-normal incidence, the hotter molecules scatter atlarger angles. At high Ei, no surface penetration occurs, but the impinging molecule may damage the surfacesignificantly when it hits the surface in the center of a hexagonal ring. The energy minimization calculationssuggest that CO is adsorbed either on top of an OH dangling group, or on top of the center of a waterhexagonal ring, interacting mostly with an electron lone-pair oxygen atom in the first monolayer or with afour-coordinated oxygen in the second monolayer. The molecular dynamics calculations predict that the averagebinding energy of the adsorbed CO is 4.33 kJ/mol, with a maximum value of 10.4 kJ/mol. The results of ourcalculations are compared with the experimental and the previous theoretical data on the CO-ice and N2-ice systems.