The electronic structure of CuCl2 and CuBr2 from anion photoelectron spectroscopy and ab initio calculations

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Abstract
The electronic structures of CuX 2 ( X=Cl and Br) have been investigated in the gas phase by means of anion photodetachmentphotoelectron spectroscopy and ab initio theory. The photoelectron spectra of CuX 2 − were recorded at two photon energies, 193 and 157 nm. Well-resolved and rich photodetachment features in the spectra provide unprecedented details for the low-lying electronic states of CuCl 2 and CuBr 2 . The excitation energies for five low-lying electronic states of CuX 2 were determined, and they explain well the two previously observed optical absorption bands. The electron affinities for CuCl 2 and CuBr 2 were determined to be identical, 4.35±0.05 eV within the experimental uncertainty. Both the anions and neutral CuX 2 species were calculated to be linear with only a slight bond length variation between the charged and neutral species. The calculated electron affinities and vertical excitation energies for the excited states agree well with the experimental values, yielding a definite assignment for the electronic states of CuCl 2 and CuBr 2 .