SCF Wavefunctions for the NH3 Molecule. Potential-Energy Surface and Vibrational Force Constants

SCF wavefunctions have been calculated for the NH₃ molecule in a number of geometrical configurations, using a basis set of Gaussian s‐ and p‐type functions. The equilibrium geometry was $R_{\mathrm{NH}}\text{°\hspace{0.17em}=\hspace{0.17em}0.996 Å}$ and ${\alpha }_{\mathrm{HNH}}\text{°\hspace{0.17em}=\hspace{0.17em}114.6}\mathrm{deg}$ , the total energy was − 56.18517 hartree and the inversion barrier was 0.00127 hartree. Energies for configurations without $C_{\text{3υ}}$ 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 $R_{\mathrm{NH}}\text{°\hspace{0.17em}=\hspace{0.17em}1.102 Å}$ and ${\alpha }_{\mathrm{HNH}}\text{°\hspace{0.17em}=\hspace{0.17em}106.2}\mathrm{deg}$ , the total energy was − 56.19821 and the inversion barrier was 0.0118 hartree.