Binding of multiple SO₂ molecules to small gold cluster anions (Au_N ⁻, Au_NOH⁻, N = 1-8)

The binding of SO₂ on gas-phase gold cluster anions, Au_N ⁻, and their hydroxide counterparts, Au_NOH⁻, have been studied using density functional theory combined with flow reactor/time-of-flight mass spectrometry techniques. SO₂ is adsorbed on all of the Au_N ⁻ and Au_NOH⁻ clusters (N = 1-8) and the hydroxide clusters are more active than the bare anionic clusters. Successive additions of SO₂ molecules (up to four) have been analyzed. In all cases, anionic clusters are shown to bind multiple SO₂ molecules. Theoretical analyses are in agreement with the experimental results, showing that the addition of more than one molecule is thermodynamically favorable. Larger clusters do not necessarily absorb more molecules, as different SO₂ binding motifs on these clusters are present. These results provide important insight for the potential use of these anionic clusters as SO₂ hunters.