Motional States of Molecules Sorbed in Mordenite

Abstract

Motional states of argon, oxygen, nitrogen and carbon dioxide sorbed in mordenite, were studied from statistical mechanical points of view and by EPR techniques. Above the dry ice temperature, these molecules were freely translating, as a one-dimensional gas, along the pore channel in the mordenite. The rotational freedom was seriously affected by the magnitude of the electric quadrupole moment of the molecule, which interacts with the crystal field in the pore. Oxygen molecule, having a small electric quadrupole moment, was freely rotating in the pore. Nitrogen molecule has a considerably large quadrupole moment, and rotated freely only above 18°C. In the case of carbon dioxide, the rotational hinderance was more serious, on account of its much larger quadrupole moment. Below 50°C, its molecular axis was orientated parallel to the pore axis. Above 160°C, it behaved as a plane rotator in the cross-sectional plane of the pore.