THEORETICAL-STUDY ON THE GROUND AND EXCITED-STATES OF THE CHROMATE ANION CRO42-

The symmetry adapted cluster (SAC) and SAC-configuration interaction ( SAC-CI) theories are applied to the calculations of the ground and exc ited states of the chromate ion CrO42-. Electron correlations are very large for this molecule and work to relax the charge polarization of the Cr-O bonds in the ground state. The experimental spectrum of CrO42 - is well reproduced by the present calculations, which is the first a b initio study of the excited states including electron correlations. All of the observed peaks are assigned to the dipole allowed transitio ns to the T-1(2) excited states. Furthermore, many kinds of forbidden transitions are calculated in the lower energy region. Both allowed an d forbidden transitions are characterized as the electron-transfer exc itations from oxygen to metal. In comparison with the previous theoret ical studies, the present SAC-CI results are in good agreement with ex periment and give reliable assignments of the spectrum. We also compar e the electronic structures and spectra of CrO42-, MoO42-, MnO4-, RuO4 , and OSO4, which have been studied by the SAC and SAC-CI methods.