Imaging the photodissociation dynamics of neutral metal clusters: copper dimer, Cu2, and copper oxide, CuO

Abstract

The spectroscopy and UV photodissociation dynamics of Cu₂ and CuO have been studied using a combination of one- and two-colour excitation and velocity map imaging. Resonant excitation of Cu₂via the J ← X ¹Σ_g⁺ transition leads to significant fragmentation which is interpreted in terms of a combination of direct dissociation of Cu₂^{+ 2}Π produced in the resonant two-photon ionization process and dissociation of excited Cu₂ states above the ionization threshold. By fitting of the kinetic energy release spectra obtained from the velocity map images, we determine a value for the dissociation energy of the cation of D₀ (Cu₂⁺, X ²Σ_g⁺) of 1.713 ± 0.025 eV, which, when combined with known ionization energies, yields D₀ (Cu₂, X ¹Σ_g⁺) = 1.886 ± 0.026 eV. In other experiments, resonant two colour (1 + 1′) excitation of CuO via a range of excited states (C, D, F, H), yields unusually simple VMI images indicating fragmentation into a single dissociation channel which has been identified as Cu* ²D_3/2 + O* ¹D. Taken together, this data gives a CuO bond dissociation energy of 3.041 ± 0.030 eV. Finally, the production of Cu₂⁺ with kinetic energy = 705 ± 75 cm⁻¹ is tentatively interpreted as photolysis of Cu₃ yielding Cu* + Cu₂ X ¹Σ_g⁺ from which a dissociation energy of Cu₃ of 0.605 ± 0.030 eV is deduced.