Knowledge Bank

The infrared absorption of $H2$, HD and $D2$, induced by the strong local electric field of the NaCl(l00) surface of film crystallites, reveals a number of spectroscopic features. Some features are assigned to vibrationl transitions of molecules adsorbed on defects and smooth-face surfaces. At the smooth-face, vibrational frequencies for all hydrogen isotopes are red-shifted by less than 1% from their gas phase values and the measured integrated cross-sections agree with the theory of electric field induced absorption. A broad and weak combination band is associated with molecular tangential vibration along the surface. Adsorption isotherms and the spectroscopy are consistent with the hydrogen isotopes, as hindered rotors, physisorbed to NaCl(100) faces.