Experimental evidence for metastable states of D3O and its monohydrate by neutralized ion beam spectroscopy

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Abstract
The oxonium radical (H3O) has been generated in its ground state by neutralizing a fast beam of ions in the near resonant electron transfer reaction H3O++K(g)→H3O*+K+. Analysis of neutral beam scattering profiles and collisionally reionized mass spectra indicate that the fully deuterated species (D3O) can be formed in a distribution of dissociative and metastable states (τ>0.6 μs). Thermalization of the precursor D3O+, prior to electron transfer, is required for production of metastable D3O. Neither H3O nor D2HO is observed in metastable states. These isotope effects support earlier theoretical predictions of a shallow local minimum on the oxonium potential surface. The ionization potential of D3O is calculated to be 4.3±0.1 eV. Some spectroscopic implications for this radical are discussed. The oxonium monohydrates (H3O⋅H2O) are also observed to exist in metastable states for several H/D isotopic variants. The ionization potential of D3O⋅D2O is estimated to be ≥3.4 eV.