Metal-acetylene binding in gaseous WC₂H₂⁺

The binding energy between W⁺ and C₂H₂ in gaseous WC₂H₂⁺ has been investigated by photodissociation in the cell of a Fourier transform ion cyclotron resonance spectrometer, and by quantum-chemical calculations. It is found that the only low-energy structure of WC₂H₂⁺ is a metallacyclopropene, which dissociates only to bare W⁺ and C₂H₂ under visible irradiation. The binding energy determined both experimentally and theoretically is 3.3±0.4 eV, significantly larger than any of the previously determined metal-acetylene bond energies in the gas phase. The experimental value is determined from both single- and two-photon dissociation thresholds. No absorption is detected below 1.5 eV of photon energy, in reasonable agreement with the first allowed transitions being calculated at 1.1 and 1.5 eV.