Spectroscopic identification and structural characterization of Ag2H2− by mass-selected photoelectron velocity-map imaging

Ag2H2− is identified and characterized by photoelectron velocity-map imaging and quantum chemical calculations. High-resolution mass selection unambiguously confirms the formation of Ag2H2−, yielding a vibrationally resolved spectrum with a distinct progression assigned to the Ag–H stretching mode. Comparison between experiment and theory shows that Ag2H2− adopts a distorted Y-shaped geometry with one bridging H and one terminal H, while for neutral Ag2H2, this geometry is a local minimum. Further bonding analysis of the corresponding neutral counterpart reveals that the unusually low Ag–H stretching frequency originates from synergistic donation and back-donation between the two AgH subunits.