We have studied excess electron distributions of binary cluster negative ions consisting of sodium atoms and carbon disulfied molecules, Na n(CS2)2 - (n= 1 and 2) by using photoelectron spectroscopy and quantum chemical calculations based on the density functional theory (DFT). The photoelectron spectra indicate the existence of at least two isomers for both n=1 and 2 anions. From the DFT calculations, mainly two types of isomers are found to coexist in the Na(CS 2)2 -; one has a van der Waals (vdW) type CS2 dimer core and another has a covalently bonded C 2S4 core, both of which were known for CS2 molecular cluster anions. In the latter isomers, the C2S4 portion possesses almost two electrons, which is caused by the valence electron transfer from the Na atom. Also for n=2, we found the isomers of vdW and covalently bonded types. In the isomers with covalently bonded core, the C 2S4 portion has more than two electrons, an excess electron and double valence-electron transfer from both of the sodium atoms.
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