MONTE-CARLO AND MOLECULAR-DYNAMICS SIMULATION OF ARGON CLUSTERS AND N-ALKANES IN THE CONFINED REGIONS OF ZEOLITES

Geometry and energy of argon clusters confined in zeolite NaCaA are co mpared with those of free clusters. Results indicate the possible exis tence of magic numbers among the confined clusters. Spectra obtained f rom instantaneous normal mode analysis of free and confined clusters g ive a larger percentage of imaginary frequencies for the latter indica ting that the confined cluster atoms populate the saddle points of the potential energy surface significantly. The variation of the percenta ge of imaginary frequencies with temperature during melting is akin to the variation of other properties. It is shown that confined clusters might exhibit inverse surface melting, unlike medium-to-large-sized f ree clusters that exhibit surface melting. Configurational-bias Monte Carte (CBMC) simulations of n-alkanes in zeolites Y and A are reported . CBMC method gives reliable estimates of the properties relating to t he conformation of molecules. Changes in the conformational properties of n-butane and other longer n-alkanes such as n-hexane and n-heptane when they are confined in different zeolites are presented. The chang es in the conformational properties of n-butane and n-hexane with temp erature and concentration is discussed. In general, in zeolite Y as we ll as A, there is significant enhancement of the gauche population as compared to the pure unconfined fluid.