The in-plane C-H/C-C, out-of-plane C-H, and the fundamental nu(19) C-C stretch vibrations of benzene molecules were monitored by FTIR spectroscopy, for adsorption in MCM-41 at room temperature and at different loadings. The results were compared with the corresponding data on ZSM-5 zeolites. The frequency and, the relative intensity of IR bands point to the development of a compressed state of benzene in the pores of MCM-41,(1) the density of which depended upon loading and lay in general between that of bulk liquid and a solidlike phase formed in the pores of ZSM-5 zeolite on benzene adsorption. Quasi-elastic neutron scattering results reveal that the pore characteristics play a crucial role in deciding the dynamics of benzene molecules in a confined medium. Thus, in contrast to the molecular motions of benzene in ZSM-5 zeolite where only rotational motion was observed in the instrumental time window of 10(-10)-10(-12) s, the benzene molecules adsorbed in MCM-41 exhibit only translational motion. Further, the value observed for the translational diffusion constant (D = 2.18 x 10(-5) cm(2)/S) of benzene occluded at saturation in MCM-41 confirmed the existence of its condensed state. Because of the unhindered mobility in mesopores, a smaller fraction of benzene gets occluded in MCM-41 compared to ZSM-5 zeolite, under the identical conditions of loading. Also, the parallel studies using MCM-41 with different Si/Al ratios and with different charge balancing cations rule out the possibility of any specific coordination of the occluded benzene with the framework sites of molecular sieves. The results are explained in terms of the current theories of capillary condensation of fluids on confinement in narrow pores.