Effect of Vibrational Anharmonicity on Hydrogen-Deuterium Exchange Equilibria Involving Ammonia Molecules

Abstract

The anharmonicity correction to the zero‐point energy of isotopic ammonias is theoretically evaluated. The G₀ term, which is usually ignored, is found to make a significant contribution to this correction. The comparison of the corrections leads to the conclusion that the anharmonicity corrections to the isotopic self‐exchange equilibria among the ammonias are negligible. Other correction factors to the self‐exchange equilibrium constants calculated in the usual harmonic approximation are also considered and found to be quite negligible. The calculated self‐exchange equilibrium constants are compared with experiment and good agreement is found. Agreement is also found between theory and experiment for the isotopic exchange equilibrium constant between ammonia and hydrogen.