General quadratic force field of the sulfate ion and the relationships between different force fields in tetrahedral molecules

Abstract

The General Quadratic Force Field (GQFF) for the sulfate ion SO 4 2− is obtained fitting all the vibrational fundamental wavenumbers of the totally symmetric 16O and 18O isotopomers. The approximations employed in previously reported force fields are discussed. The effects are studied of the redundancy condition on the value of the GQFF force constants expressed both in valence and Urey—Bradley coordinates, and on the relationships between both force fields for tetrahedral XY 4 molecules. The a 1 and e mode anharmonicity constants and harmonic wavenumbers are obtained.