Theoretical studies of excited states of H 3O and of core-excited NH 3: Comparisons with equivalent core analysis of NH 3 core-excitation spectra and implications for the radiation chemistry of aqueous systems

Abstract

The H 3O radical has been studied within the ab initio LCAO SCF MO model. A flexible basis set including diffuse basis functions at both O and H has been used in order to represent the excited states adequately. Calculated excitation energies are 1.87, 2.87–3.16, and 3.36–3.47 eV; the calculated ionization energy is 4.75 eV. These represent well the experimental values (good to ±0.3 eV) of 1.6, 2.9, and 3.5 eV for excitation, and 5.0 eV for ionization, deduced by equivalent core analysis of high energy electron impact energy loss studies of NH 3. Similar explicit calculations on the N-1s core-excited states of NH 3 have also been made to examine directly the equivalent core concept. “Excited states” (relative to the lowest bound core-excited state) at 1.72, 2.85–3.09, and 3.32 eV, and the “ionization energy” of 4.68 eV, agree well with experiment and support the equivalent core concept. The possible significance of these H 3O results in the radiation chemistry of aqueous media is discussed in view of the fact that the maximum in the absorption spectrum of the hydrated electron lies near that of H 3O.