Theoretical study of the electron affinities of Cu, Cu2, and Cu3

Modified coupled pair functional (MCPF) calculations are shown to yield the electron affinities of Cu, Cu₂, and Cu₃ to nearly equal accuracy. The structural results for Cu^-₃, together with the experimental negative ion photoelectron results, show conclusively that Cu^-₃ is linear in its (¹Σ⁺_g) ground state. The weak feature in the Cu^-₃ photoelectron spectrum at an electron binding energy of 1.5 eV is due to ionization from the ³A^'₂ (equilateral triangle) excited state of Cu^-₃.