The reaction of isotope-substituted hydrated iodide I(H 182O)− with ozone: the reactive influence of the solvent water molecule

Abstract

We report an investigation of the reaction of isotope-substituted hydrated iodide I(H¹⁸₂O)⁻ with ozone ¹⁶O₃ to examine the involvement of the water molecules in the oxidation reactions that terminate with the formation of IO₃⁻. Experimentally, we studied the reaction in the gas phase as elementary reactions using a radio-frequency (RF) ion-trap combined with a quadrupole mass spectrometer (QMS). In approximately 1.2% of the reactions of I(H¹⁸₂O)⁻ and ¹⁶O₃, the ¹⁸O atom is found to appear in iodine oxide anions, thus giving evidence for a close involvement of the water molecule in a non-negligible number of the reactions towards IO₃⁻. As a part of the experimental investigation, the reaction rate constant for the exchange reaction I(H¹⁸₂O)⁻ + H¹⁶₂O → I(H¹⁶₂O)⁻ + H¹⁸₂O at 300 K was found to be (1.3 ± 0.1) × 10⁻⁸ cm³ s⁻¹. Quantum chemical calculations are exploited to establish the energetic difference between I(H¹⁸₂O)⁻ and I(H¹⁶₂O)⁻.