Articles you may be interested inA new ab initio potential energy surface for the collisional excitation of HCN by para-and ortho-H2 Analytic Morse/long-range potential energy surfaces and predicted infrared spectra for CO-H2 dimer and frequency shifts of CO in (para-H2) N N = 1-20 clustersWe simulate H 2 adsorbed within zeolite Na-A. We use a block Lanczos procedure to generate the first several ͑9͒ rotational eigenstates of the molecule, which is modeled as a rigid, quantum rotor with an anisotropic polarizability and quadrupole moment. The rotor interacts with Na cations and O anions; interaction parameters are chosen semiempirically and the truncation of electrostatic fields is handled with a switching function. A Monte Carlo proceedure is used to sample a set of states based on the canonical distribution. Potential energy surfaces, favorable adsorbtion sites, and distributions of barriers to rotation are analyzed. Separation factors for ortho-parahydrogen are calculated; at low temperatures, these are controlled by the ease of rotational tunneling through barriers.