Infrared multiple photon dissociation spectroscopy of TaO(OH)2+ and Ta(OH)4+ cations

Transition metal oxides are promising candidates for water activation, a key step in hydrogen production, as they have shown their potential as catalysts. In this study, we present tag-free infrared multiple photon dissociation (IRMPD) spectra of formally singly and doubly hydrated TaO 2 + cations in the 350 - 1650 cm -1 range, measured using the free-electron laser for intracavity experiments (FELICE). In combination with vibrational spectra obtained by quantum chemical calculations, the experimental spectra reveal that the hydroxide species TaO(OH) 2 + and Ta(OH) 4 + are the dominant species in the experiment. These two structures are also the lowest lying isomers, about 130 kJ mol -1 lower than the energetically closest isomers. The calculated potential energy surfaces and transition states align with earlier studies, confirming the formation of these hydroxide complexes via sequential proton transfers upon complexation of TaO 2 + with one and two water molecules, respectively. This work presents the first tag free spectra of these complexes, complementing the spectroscopic picture especially in the low wavenumber region. • Water activation by metal oxides is relevant for catalysis. • Tantalum dioxide cation complexes with one and two water molecules are characterized by infrared multiple photon dissociation spectroscopy. • Spectra reveal complete conversion to tantalum hydroxide species. • Calculated potential energy surfaces indicate that kinetic trapping of higher lying isomers is unlikely, because no efficient cooling mechanism is available in the present study.