The induced infrared spectrum of H₂ Adsorbed on NaCl film at 8 K. Rotation of ortho‐H₂ in the state J = 1 on the surface

The induced fundamental infrared spectrum of H 2 adsorbed on NaCl film at 8 K has been observed under ultrahigh vacuum conditions. There are two adsorption sites. For each site a splitting of the vibrational fundamental into a doublet is resolved. The doublet is assigned to para‐H 2 and ortho‐H 2 by its close resemblance to the doublet Q 1 (0) and Q 1 (1) calculated and observed in gaseous and matrix‐isolated H 2 . According to Ben Ephraim and Folman the lowest adsorption potential corresponds to a H 2 orientation parallel to the surface and slightly perturbed free rotation about an axis normal to the surface. However, because of space quantization, the ortho‐H 2 molecules are tilted up in the rotational state J = 1 and perform a hindered rotation about an axis tilted to the surface.