THE INDUCED INFRARED-SPECTRUM OF H-2 ADSORBED ON NACL FILM AT 8-K - ROTATION OF ORTHO-H-2 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 fu ndamental into a doublet is resolved. The doublet is assigned to para- H-2 and ortho-H-2 by its close resemblance to the doublet Q1(0) and Q1 (1) calculated and observed in gaseous and matrix-isolated H-2. Accord ing to Ben Ephraim and Folman the lowest adsorption potential correspo nds to a H-2 orientation parallel to the surface and slightly perturbe d free rotation about an axis normal to the surface. However, because of space quantization, the ortho-H-2 molecules are tilted up in the ro tational state J = 1 and perform a hindered rotation about an axis til ted to the surface.