A study of the reactions of molecular hydrogen with small gold clusters

Abstract

This work presents a study of reactions between neutral and negatively charged ${\mathrm{Au}}_n$ clusters $\text{(n=2,3)}$ and molecular hydrogen. The binding energies of the first and second hydrogen molecule to the gold clusters were determined using density functional theory (DFT), second order perturbation theory (MP2) and coupled cluster (CCSD(T)) methods. It is found that molecular hydrogen easily binds to neutral ${\mathrm{Au}}_2$ and ${\mathrm{Au}}_3$ clusters with binding energies of 0.55 eV and 0.71 eV, respectively. The barriers to ${\mathrm{H}}_2$ dissociation on these clusters with respect to ${\mathrm{Au}}_n{\mathrm{H}}_2$ complexes are 1.10 eV and 0.59 eV for $\text{n=2}$ and 3. Although negatively charged ${\mathrm{Au}}_n^{-}$ clusters do not bind molecular hydrogen, ${\mathrm{H}}_2$ dissociation can occur with energy barriers of 0.93 eV for ${\mathrm{Au}}_2^{-}$ and 1.39 eV for ${\mathrm{Au}}_3^{-}.$ The energies of the ${\mathrm{Au}}_2{\mathrm{H}}_2^{-}$ and ${\mathrm{Au}}_3{\mathrm{H}}_2^{-}$ complexes with dissociated hydrogen molecules are lower than the energies of ${\mathrm{Au}}_2^{-}+{\mathrm{H}}_2$ and ${\mathrm{Au}}_3^{-}+{\mathrm{H}}_2$ by 0.49 eV and 0.96 eV, respectively. There is satisfactory agreement between the DFT and CCSD(T) results for binding energies, but the agreement is not as good for barrier heights.