Structures of cobalt oxide cluster cations studied by ion mobility mass spectrometry

Structures of cobalt oxide cluster cations have been investigated by ion mobility mass spectrometry. When the ions were injected into a drift cell with 250 eV kinetic energy, ( CoO ) n + and Co n O n - 1 + were observed. Collision cross sections were experimentally determined for ( CoO ) 2 - 7 + and Co n O n - 1 + (n = 5–7). Orientation-averaged collision cross sections were calculated for optimized structures of these ions obtained in quantum chemical calculations. By comparison between experimental and theoretical cross sections, ( CoO ) 3 - 5 + ions are found to have monocyclic-ring structures. By contrast, ( CoO ) 6 , 7 + have compact tower structures. Therefore, structural transition from the ring to compact structures occurs at ( CoO ) 6 + .