Abstract
We present a semiempirical calculation of the interaction energy of a CH4 molecule and one Na+ cation of the zeolite Na A. This energy depends on the distance, R, between the Na+ nucleus and the carbon nucleus of CH4, and on the orientation of the molecule. Taking in account the anisotropy of the repulsion, the most favourable orientation, at any R, is such that the carbon-Na+ axis is a C 2V axis with three hydrogens pointing to the cation, and the least favourable is such that the axis is still a C 3V axis but with one hydrogen pointing to the cation. The results are in agreement with the ones of Sauer et al. obtained by an ab initio calculation.