SCF wavefunctions for the NH₃ molecule. Potential-energy surface and vibrational force constants

Abstract

SCF wavefunctions have been calculated for the NHS molecule in a number of geometrical configurations, using a basis set of Gaussian s- and p-type functions. The equilibrium geometry was RNH°=0.996 Å and αHNH° = 114.6 deg, the total energy was -56.18517 hartree and the inversion barrier was 0.00127 hartree. Energies for configurations without C3v symmetry were fitted to an assumed potential function which included all second- and third-degree terms, and the vibrational force constants were determined. The addition of d-type functions to the basis set gave much better results for the equilibrium geometry and inversion barrier. With this basis set, the equilibrium geometry was RNH° = 1.102 Å and αHNH° = 106.2 deg, the total energy was -56.19821 and the inversion barrier was 0.0118 hartree.