Efficient penetration of the basal plane (0001) face of ice Ih by HF at Ts=150 K: dependence on incidence energy, incidence angle, and rotational energy.

Classical trajectory simulations are carried out to investigate the influence of incidence energy, incidence angle, and rotational energy on the penetration of the basal plane (0001) face of ice I(h) by HF at a surface temperature (T(s)) of 150 K. The interaction of HF with ice is modelled by pair interactions, with the pair potential fitted to ab initio (Hartree-Fock+MP2) calculations. The penetration of ice by HF occurs already at very low incidence energies, viz., E(i)>/=20 kJ mol(-1). This is much lower than the threshold incidence energy obtained for penetration of ice by HCl (E(i) approximately 96.5 kJ mol(-1)); the calculated average barrier to penetration of ice by HF is 16.0 kJ mol(-1) and is much lower than that previously reported for HCl. As was the case for HCl, penetration of ice by HF decreases with decreasing incidence energy and increasing incidence angle. Though in general, the penetration probability is independent of the molecule's initial rotational energy, penetration beyond the second bilayer (deep penetration) is suppressed by initial rotation. This suggests that, like was found for HCl, the steering operative in deep penetration is inhibited by initial rotation. Finally, because HF is a weak acid experimental observation of HF penetrated into ice may well be possible using infrared spectroscopy, and we suggest experiments along this line.