Isotope Effect in D₂O Negative Ion Formation in Electron Transfer Experiments: DO–D Bond Dissociation Energy

Abstract

H2O/D2O negative ion time-of-flight mass spectra from electron transfer processes at different collision energies with neutral potassium yield OH–/OD–, O–, and H–/D–. The branching ratios show a relevant energy dependence with an important isotope effect in D2O. Electronic state spectroscopy of water has been further investigated by recording potassium cation energy loss spectra in the forward scattering direction at an impact energy of 205 eV (lab frame), with quantum chemical calculations for the lowest-lying unoccupied molecular orbitals in the presence of a potassium atom supporting most of the experimental findings. The DO–D bond dissociation energy has been determined for the first time to be 5.41 ± 0.10 eV. The collision dynamics revealed the character of the singly excited (1b2–1) molecular orbital and doubly excited states in such K–H2O and K–D2O collisions.