Knowledge Bank

The structure of $H3O+$ is determined by ab initio SCF MO calculation (IBMOL IV - Clementi-Veillard) including polarization orbitals on both 0 and H and variation of bond angles and bond distances. A planar structure is obtained. Force constants derived from the preceding minimization are compared with a complete set of force constants obtained by an analytical method using monocentric wave function. Semi-empirical methods are applied (including the CNDO/2 method of Pople and Segal) and lead to a non-planar structure for $H3O+$. By comparison with the ab initio calculations, a calibration of the CNDO/2 method is performed, and the calibrated method is used to determine the structure and force constants of the other ions.