Diffuse-reflectance IR spectra of ortho-hydrogen and para-hydrogen adsorbed on zeolite BaX at 77 K and their interpretation in terms of the Stark effect

The vibrational and vibrational-rotational spectra of hydrogen adsorbed on zeolite BaX at 77 K were examined by diffuse-reflectance IR spectroscopy ov er a wide range of wavenumbers. The use of hydrogen enriched in the para is omer and of molecular deuterium allowed us to reliably assign the absorptio n bands to orthohydrogen and para-hydrogen and compare the experimentally o bserved band splitting with the theoretically calculated shifts of the corr esponding levels resulted from the Stark effect. In the calculations, an ad sorption site was simulated as a positive point charge. Although this appro ximation is rough, the IR spectra of adsorbed hydrogen and deuterium are ad equately described in terms of the Stark effect. A decrease in the frequenc y of stretching vibrations of H-H (D-D) bonds in the molecules coordinated to Ba2+ cations, a decrease in the intensity of vibrational-rotational abso rption bands, and the band splitting in the spectra of adsorbed para-hydrog en and orthohydrogen were explained.