Infrared spectroscopy of O˙ − and OH − in water clusters: evidence for fast interconversion between O˙ − and OH˙OH −

We present infrared multiple photon dissociation (IRMPD) spectra of (H2O)nO˙− and (H2O)nOH− cluster ensembles for ≈ 8 and 47 in the range of 2400–4000 cm−1. Both hydrated ions exhibit the same spectral features, in good agreement with theoretical calculations. Decomposition of the calculated spectra shows that bands originating from H2O⋯O˙− and H2O⋯OH− interactions span almost the whole spectral region of interest. Experimentally, evaporation of OH˙ is observed to a small extent, which requires interconversion of (H2O)nO˙− into (H2O)n–1OH˙OH−, with subsequent H2O evaporation preferred over OH˙ evaporation. The modeling shows that (H2O)nO˙− and (H2O)n–1OH˙OH− cannot be distinguished by IRMPD spectroscopy.