Rotation dynamics of 2-methyl butane and n-pentane in MCM-22 zeolite: a molecular dynamics simulation study.

Molecular dynamics (MD) simulations have been performed to investigate the rotational diffusive motion for 2-methyl butane (2-MeC4) and n-pentane (n-C5) in the cages of MCM-22 zeolite from 200-340 K. The rotation intermediate scattering function I(R) (Q,t) for 2-MeC4 and n-C5 confined in the supercages of MCM-22 was calculated. The dynamic scattering functions S(inc)(Q,omega) obtained via Fourier transformation of this intermediate scattering function are in good agreement with those of quasi-elastic neutron scattering experiments. The rotational intermediate scattering functions of 2-MeC4 decay more rapidly than those of n-C5 before 1.0 ps. In the longer time region, the rotational intermediate scattering functions of both molecules intersect. It is shown that n-C5 molecules move more easily from supercage to supercage compared to 2-MeC4, rotating for a longer time in the confinement of the MCM-22 supercage.