Interaction between probe molecules and zeolites. Part I: Pair-wise addition scheme applied to the calculation of the interaction energy of CO and N2 adsorbed in Na4Ca4A

Abstract

An important problem when studying the interaction between a CO probe molecule and a Na₄Ca₄A type zeolite is the estimation of the central repulsive coefficients versus the internuclear distance of CO. In particular, this dependence cannot be estimated in the case of the unstable linear “framework oxygen–CO molecule” pair due to the electrostatic repulsive interaction. Hence, we discuss the application of two approximate forms of this dependence either allowing or disregarding the repulsive contribution in the interval wherein the vibrational CO probability distribution cannot be neglected. The consequences of these approximations are compared through calculation of the interaction energy and band shift of CO adsorbed inside Na₄Ca₄A. The CO spatial parameters (semi-axes) are estimated by fitting both the band shift, corresponding to two different positions of CO relative to the zeolite, and the interaction energy values to the experimental data obtained at small coverage.