Spectroscopic evidence for the coexistence of tetragonal and trigonal minima within the exited state adiabatic potential energy surfaces of hexachlorotellurate and -selenate complexes

Coexistence of Jahn-Teller minima resulting from the coupling to different accepting modes within the adiabatic potential energy surface (APES) is not possible within the framework of linear vibronic coupling theory. For the lowest exited triplet state T-3(1u) of inorganic complexes with s(2) electronic ground-state configuration, such a coexistence, due to quadratic coupling effects, is discussed. As a direct experimental evidence two vibronic progressions with different accepting modes in the emission spectra resulting from a single electronic state are observed in the emission spectra of the title compounds. The observation of vibronic finestructure in the emission spectra of [TeCl6](2-) is reported for the first time. (C) 1998 American Institute of Physics. [S0021-9606(98)00143-3].