Infrared and Raman spectra and Urey—Bradley force fields for dithiocarbamate and dithiocarbamate- d2 anions. Use of a correlation matrix to determine force field uniqueness

Abstract

The infrared and Raman spectra of ammonium and potassium salts of dithiocarbamate and dithiocarbamate- d 2 anions have been obtained and the nine in plane and three out of plane fundamental vibrational frequencies have been assigned for the anions in the C 2ν point group. A single least squares converged Urey—Bradley force field was developed for both isotopic species and was compared to force fields for metal complexed dithiocarbamates. Although 23 vibrational fundamentals were assigned a single unique set of 14 Urey—Bradley type force constants could not be found. This observation was attributed to a high degree of correlation in certain combinations of force constants. A matrix was generated from the least squares Jacobian matrix and the former matrix showed that the five force constants K CS, H SCS, H SCN, F SS and F SN were so highly correlated that any number of combinations of numerical values could be used for these force constants without raising the standard deviation of the entire observed—calculated frequency fit above 2.0%. The correlation matrix as a test for a unique force field is discussed and an alternate force field with repulsive force constants fixed at Lennard Jones potential values is presented.