The dynamics of molecular hydrogen adsorbed in the cavities of partially cobalt exchanged type A zeolite (Co4ilNa3i8-A) has been investigated in the energy range 0-40 meV by incoherent inelastic neutron scattering. Both rotational and vibrational excitations are identified in the spectra. The rotational tunnel splitting of the librational ground state of the adsorbed molecular hydrogen is observed at 3.8 meV. Analysis of the data in terms of a 2-fold cosine potential with two degrees of rotational freedom best accounts for the observed spectral features among several models tested. A barrier height of about 1.4 kcal/mol is calculated. A mode at 15.3 meV is accordingly assigned as a vibration of the bound hydrogen. Evidence for the torsional mode of Al(OH)4 complexes, formed in the /3-cages during ion exchange, is found in the vibrational spectra at 21 meV.

The Scienta ESCA300 is a state-of-the-art x-ray photoelectron spectrometer with high intensity, and high energy and spatial resolution. This unique combination of features is made possible by the use of a high-power rotating anode x-ray source with monochromatization, high transmission and imaging electron optics and a multichannel detector. The first ESCA300 has been installed recently at ICI Wilton. We report on the performance of this instrument for conducting samples and as a microanalytical device. Also described are its performance for insulating samples (polymer films) and studies of charge compensation using the Bremsstrahlung-induced electrons from an unmonochromated dual anode x-ray source.

The hindered rotations and vibrations of molecular hydrogen, deuterium, and deuterium hydride adsorbed into partially and fully Ca ion exchanged Na-A zeolites have been studied at low temperatures with the use of inelastic neutron scattering (INS) techniques. A loading of one molecule per supercage was used in an attempt to avoid multiple site occupancies. Nonetheless, the INS spectra of the rotational transitions of H 2 , HD, and D 2 clearly show that physical adsorption occurs on several different sites. Both the CaNa-A and Ca-A samples have strong rotational bands near 6 meV. On this basis, we conclude that the principal adsorption site in CaNa-A is in the vicinity of the Ca 2+ cation where H 2 experiences a rotational barrier of about 4.3 kJ/mol.

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