Understanding the dissociation dynamics of small molecules on metal surfaces under wellcontrolled conditions is an important stepping stone toward comprehending the complexities of chemical transformations on catalytic surfaces. Specific questions of interest include determining the absolute dissociative sticking probability measured at the zero coverage limit (S 0 ), understanding its dependence on the energy of the incident reactant molecules (translational, rotational, and vibrational), and determining the magnitude of the activation barrier.