Rotationally resolved dicopper (Cu₂) laser-induced fluorescence spectra

We have used an RF sputter source to produce gas-phase copper dimer molecules for study with laser-induced fluorescence spectroscopy. Rotationally resolved spectra of transitions from the electronic ground (X) state to the A, B, C, G, and J states have been obtained. Previous rotational analyses of the X, A, and B states are confirmed. Analysis of the X-C spectrum shows the C state to have Π(Ω = 1) symmetry, and a bond length of 2.26 Å. Its vibrational constants are refined slightly. The J state has a bond length of 2.15 Å, and shows evidence of extensive perturbation. Emission lifetimes at the bandheads of its lowest two vibrational states are 80 ns. Franck-Condon factors for the X-C and X-J transitions have also been obtained. The new J state bond length supports conclusions drawn from a recently obtained photoelectron spectrum of Cu2: the cation ground state indeed corresponds to loss of a 4sσ electron, and the excited state is due to removal of a 3d electron. Bond strengths and distances in the various states of the neutral are rationalized in terms of 4sσ bonding orbitals and nonbonding (slightly repelling) 3d cores; creation of a 3d vacancy allows 3d shell bonding to occur, increasing bond strengths and vibrational frequencies slightly. © 1991 American Institute of Physics.