ANISOTROPIC REORIENTATION DYNAMICS OF BENZENE MOLECULES ADSORBED ON GRAPHITE, ALUMINA, AND ZEOLITE-Y

Frequency-resolved deuteron spin-lattice relaxation times of benzene adsorbed at monolayer coverage on graphitized carbon black and on eta-alumina as well as at full loading in the voids of zeolite NaY were measured at temperatures in the range 250-77 K. The results obtained can be explained by the hexad axis reorientation of the molecules with the following correlation times tau(c)/ps: 0.1 exp(7.9 kJ mol-1/RT) (graphite); 0.1 exp(7.4 kJ mol-1/RT) (eta-alumina); 1.5 exp(4.9 kJ mol-1/RT) (NaY). These results are compared with the correlation times for bulk crystalline benzene and are discussed in the context of recent molecular dynamics simulations.