Ion and radical chemistry in (H₂O₂)_N clusters

We investigate the ionization induced chemistry of hydrogen peroxide in (H₂O₂)_N clusters generated after the pickup of individual H₂O₂ molecules on large free Ar_M, M[combining macron]≈ 160, nanoparticles in molecular beams. Positive and negative ion mass spectra are recorded after an electron ionization of the clusters at energies 5-70 eV and after a slow electron attachment (below 4 eV), respectively. The spectra demonstrate that (H₂O₂)_N clusters with N≥ 20 are formed on argon nanoparticles. This is the first experimental report on hydrogen peroxide clusters in molecular beams. The major negative cluster ion series (H₂O₂)_nO₂^- indicates O₂^- ion formation. The dissociative electron attachment to H₂O₂ molecules in the gas phase yielded only OH^- and O^- (Nandi et al., Chem. Phys. Lett., 2003, 373, 454). These ions and the series containing them are much less abundant in the clusters. We propose a sequence of ion-molecule and radical reactions to explain the formation of O₂^-, HO₂^- and other ions observed in the negatively charged cluster ion series. Since hydrogen peroxide plays an important role in many areas of chemistry from the Earth's atmosphere to biological tissues, our study opens new horizons for experimental investigations of hydrogen peroxide chemistry in complex environments.