The spectra and electronic structure of tetrahedral ions: I. Chromate and permanganate ions† Supported by the Italian National Research Council

An S.C.F.-M.O.-L.C.A.O. calculation in the Roothaan-Popie scheme, using the Pariser-Parr approximations, has been carried out for the ions [CrO 4 ] -- and [MnO 4 ] - . The necessary integrals have been evaluated semi-empirically. For a more exact evaluation of the spectral transitions, a configuration interaction calculation, extended to the most important mono-excited configurations, has been performed. The order of levels previously suggested by Ballhausen and Liehr and other authors is confirmed by the results of the calculations. A new spectral assignment is presented, attributing to each observed absorption band two electronic transitions occurring between one of the occupied M.O.'s (t 1 , 2t 2 , 1t 2 ) and the two lowest empty M.O.'s (2e, 3t 2 ).