The depletion of stratospheric ozone at high latitudes is caused by gas-phase catalytic cycles involving active chlorine compounds produced through heterogeneous chemical reactions involving HCl. In this Letter, results aimed at understanding the activation of chlorine on ice cloud particle surfaces are presented. We focus specifically on HCl interacting with the ice surface prior to reaction. We conclude that, in regions with a low surface density of dangling OH groups, HCl may be either ionically or molecularly adsorbed, but in regions with a high surface density of dangling OH groups, HCl is ionically adsorbed.