Vibrationally resolved photoelectron spectra of CuCN⁻ and AgCN⁻ and ab initio studies of the structure and bonding in CuCN

Vibrationally resolved photoelectron spectroscopy is combined with ab initio calculations to investigate the structure and chemical bonding in CuCN, $CuCN−,$ AgCN, and $AgCN−.$ The photoelectron spectra were measured at two photon energies, 532 and 355 nm and only detachment to the ground state of the neutral was observed at both detachment energies. The adiabatic electron affinity and metal-C vibrational frequency were obtained to be 1.466 (0.010) eV and 480(30) cm⁻¹, 1.588 (0.010) eV and 390(30) cm⁻¹ for CuCN and AgCN, respectively. In the ab initio calculations, both CuCN and $CuCN−$ were found to have linear $C∞V$ structures. Isocyanide CuNC and $CuNC−$ were found to be 10.7 and 6.5 kcal/mol [at the $CCSD(T)/6-311+G(3d)//CCSD(T)/6-311+G*$ level of theory] higher in energy. Cyclic structures were found to be transition states for the cyanide–isocyanide isomerization. The calculated electron binding energies and vibrational frequency are in good agreement with the experimental measurements. The combined experimental and theoretical efforts allow us to elucidate the structures of CuCN and $CuCN−,$ and the nature of their chemical bonding.