Comparative SCF and CI studies of NH3 and PH3

Abstract

A comparative study of geometry, bonding, and physical properties of NH₃ and PH₃ utilizing both SCF and CI techniques is presented. One‐electron physical properties of both molecules are examined for several basis sets; properties calculated for NH₃ are in good agreement with experimental values, while for PH₃ only fair agreement is obtained. In PH₃ phosphorus d orbitals are found to contribute directly to sigma bonding. In NH₃, however, nitrogen d orbitals produce an angular effect which tends to reduce the calculated HNH internuclear angle to a value significantly closer to the experimental angle than is predicted in computations where d orbitals are not employed. Configuration interaction does little to improve the agreement of calculated properties with experimental values, but does lower the total energy significantly. Factors influencing the difference in geometry of the two molecules are discussed.