Energetic degeneracy and electronic structures of germanium trimers doped with titanium

Geometries and electronic structures of germanium trimer clusters doped with titanium TiGe₃^−/0 were studied making use of the complete active space self-consistent field followed by second-order perturbation theory, explicitly correlated coupled cluster singles and doubles method with perturbative triples corrections CCSD(T)-F12, and Tao-Perdew-Staroverov-Scuseria methods. Two electronic states (²A′ and ²A″) of the anion (pyramid shape) were determined to be nearly degenerate and energetically competing for the anionic ground state of TiGe₃⁻. These two anionic states are believed to be concurrently populated in the experiment and induce six observed anion photoelectron bands. Total 14 electronic transitions starting from the ²A′ and ²A″ states were assigned to five out of six visible bands in the experimental anion photoelectron spectrum of TiGe₃⁻. Each band was proven to be caused by multiple one-electron detachments from two populated anionic states. The last experimental band with the highest detachment energy is believed to be the result of various inner one-electron removals.