Anomalous isotope effect for hindered rotations:H2O adsorbed on metal surfaces

The frequency shift of the hindered rotation of a deuterated ${\mathrm{H}}_2$O molecule adsorbed on a metal surface departs substantially from that given by the classical Teller-Redlich rule. Because of the large zero-point motion of the molecule a quantum-mechanical treatment is necessary to relate the isotope frequency shift with the change in the mass. The ratio of the corresponding electron-energy-loss line intensities provides an important additional check of the mode assignment.