Vibrational and resonance Raman study of dithiosquarate

The resonance Raman excitation profiles of the dithiosquarate in the solid state, as its thallium salt, and in aqueous solution as its sodium salts were obtained. The assignment of its vibrational frequencies to the normal modes was carried out on basis of ab initio calculations, using the Lee-Yang-Parr correlation functional and the 6-31 + G* basis, and of the potential energy distribution for the calculated frequencies. A correlation between the frequencies of the dithiosquarate, squarate and tetrathiosquarate anions shows good agreement with that obtained using the enhancement factors calculated from the excitation profiles. In the case of dithiosquarate the intensification of non-totally symmetric modes both for the thallium and for the sodium salt suggests the participation of the B-term mechanism, with more than one excited electronic state contributing to the Raman intensities. (C) 2002 Elsevier Science B.V. All rights reserved.