Modification of dielectric properties of porous glass by adsorption of hydrogen

We have investigated the dielectric properties of a porous glass ~Vycor 7930, typical pore radius: ’ 3n m ! with submonolayer coverages of H2, HD, or D 2 on the pore surface by means of a capacitive technique between 5 and 20 K. The adsorption of hydrogen influences, depending on the hydrogen species as well as on the coverage, the dielectric glass properties. We discuss our observations in terms of the thermally activated dynamics of atoms in the combined glass/hydrogen system, where atoms denote atoms which build the porous glass as well as adsorbed hydrogen molecules. @S0163-1829~97!51822-4# Confined molecular systems have been attracting a lot of attention since such molecules show very different characteristics compared to their bulk counterparts. One prominent example is the nature of phase transitions of such materials confined into restricting geometries, which is different from the bulk behavior, as can be seen from freezing temperature depression ~see our previous publication 1 and references therein!, different critical exponents at the phase transitions, 2 and the phase separation behavior of binary liquids. 3 The dynamics of confined molecular systems are also of great interest. 4,5 However, the confining geometries are often as