Geometries and spectroscopic properties of germanium and tin hexamers (Ge-6, Ge-6(+), Ge-6(-), Sn-6, Sn-6(+), and Sn-6(-))

Ground and excited electronic states of neutral, cationic and anionic germa nium and tin hexamers (Ge-6 and Sn-6) are investigated. Different geometrie s such as tetragonal bipyramid (D-4h,D-2h) and edge-caped trigonal bipyrami d (C-2v) (ECTBP) were studied. We have employed a number of high level elec tron correlation techniques such as large scale multireference singles+doub les configuration interaction (MRSDCI) computations that included up to 16 million configurations, complete active-space multiconfiguration self-consi stent filed (CAS-MCSCF), and Moller-Plesset (MP2) techniques to investigate the low-lying electronic states, their geometries and energy separations. A (1)A(1g) tetragonal bipyramid structure (D-4h symmetry) is found as the g round state for both Ge-6 and Sn-6, in accord with the previously suggested experimental assignments. The excitation energies, atomization energies, i onization potentials and vertical and adiabatic electron affinities are com puted and compared with the experimental results. Our computations of the e xcited states of these species have facilitated assignment of the anion pho todetachment spectra of the anions of these clusters and comparison with th e photoionization spectra of the neutral species. (C) 2001 American Institu te of Physics.