The impact of optical excitation on the binding in complexes of the cationic gold dimer: Au₂⁺ N₂ and Au₂⁺ N₂O

The vibrationally resolved A(2)Sigma(+) <- X-2 Sigma(+) transitions of Au2+N2 and Au2+N2O are reported together with a detailed characterization of important geometric and electronic properties, enabling a deep understanding of the bonding mechanism at the molecular level. Comparison with time-dependent density functional theory calculations reveals that the ligand stabilizes the Au-2(+) entity in the X-2 Sigma(+) state by donating electron density into the half-filled bonding orbital leading to the strengthening of the Au-Au, N-N, and N-O bonds. This effect is reversed in the A(2)Sigma(+) state, where the Au-Au bonding orbital is already filled and the ligand destabilizes the Au-Au bond by donating into the antibonding orbitals of Au-2(+). The spectral detail obtained provides a deep understanding of the interplay of multiple electronic states in gas-phase metal-complex cations, opening the door for a systematic approach in the study of excited state reactivity in organometallic chemistry.