Abstract
Various types of force constant refinement procedures have been reviewed. A program has been written for the damping least squares method in which a small factor is added to the diagonal elements of the normal matrix. This program was developed as part of a study of the force field of the hyponitrite ion N[2]O[2][--]. A previous study by McGraw et al was unsatisfactory because only the information from the normal isotope was used and this gave a very large discrepancy (67cm[-1]) for one of the calculated frequencies. In the present work it is found that a reversal of the McGraw assignment for the assymetric stretching and out-of-plane deformation vibrations gives a better measure of fit when the isotopic frequencies are used to calculate an almost complete general valence force field. For the normal molecule frequencies the reversed assignment gave almost the same measure of fit as the McGraw assignment for their proposed 5 constant force field. For an alternative choice of 5 constant force field the new assignment gave an even lower measure of fit whilst the McGraw assignment could not be fitted at all well.