The electronic structure of PdC2H and PdC2HN determined by anion photoelectron spectroscopy

Abstract

The photoelectron spectra of PdC2H− and PdC2HN− are presented and analyzed. The electron affinity of the PdC2H complex is 1.98±0.03 eV, and the electron affinity of the PdC2HN complex is 2.17±0.03 eV. Both spectra are broadened by unresolved progressions in low-frequency vibrational modes of the neutral. Both also show activation of a higher-frequency mode (1720±170 cm−1 for PdC2H and 1800±200 cm−1 for PdC2HN) which suggests that back donation from the Pd dπ orbitals into the π* orbitals of the ligands is involved in the bonding in these species. The spectrum of PdC2H− also shows a transition to a dissociative excited neutral state with an excitation energy of 0.35±0.15 eV. The electronic structures of PdC2H and PdC2H− are explored by comparison with the isoelectronic PdCN and PdCN− species along with supporting density functional theory calculations. Σ+1, Σ+2, and Π2 terms are proposed for the ground anion, ground neutral, and dissociative neutral states, respectively. A chainlike (nonlinear) Pd–C–C–NH structure is proposed as being consistent with the spectrum of PdC2HN−.