Flexible H₂O₂ in Water: Electronic Structure from Photoelectron Spectroscopy and Ab Initio Calculations

Abstract

The effect of hydration on the electronic structure of H(2)O(2) is investigated by liquid-jet photoelectron spectroscopy measurements and ab initio calculations. Experimental valence electron binding energies of the H(2)O(2) orbitals in water are, on average, 1.9 eV red-shifted with respect to the gas-phase molecule. A smaller width of the first peak was observed in the photoelectron spectrum from the solution. Our experiment is complemented by simulated photoelectron spectra, calculated at the ab initio level of theory (with EOM-IP-CCSD and DFT methods), and using path-integral sampling of the ground-state density. The observed shift in ionization energy upon solvation is attributed to a combination of nonspecific electrostatic effects (long-range polarization) and of the specific interactions between H(2)O(2) and H(2)O molecules in the first solvation shell. Changes in peak widths are found to result from merging of the two lowest ionized states of H(2)O(2) in water due to conformational changes upon solvation. Hydration effects on H(2)O(2) are stronger than on the H(2)O molecule. In addition to valence spectra, we report oxygen 1s core-level photoelectron spectra from H(2)O(2)(aq), and observed energies and spectral intensities are discussed qualitatively.

Simulations of light induced processes in water based on ab initio path integrals molecular dynamics. II. Photoionization

“…This approach can, however, not be used for extended clusters due to a rapidly increasing computational expense with the system size combined with a relatively slow basis set saturation. 51 As an alternative, we have used the following composite approach. We first calculate the first ionization energy (IE) as a difference between the ground state energy of the ion and the neutral molecule.…”

“…The quantitative disagreement can be interpreted as a consequence of the insufficient basis set; the EOM-IP-CCSD typically exhibits pronounced basis set dependence. 51 The augmentation of the basis set leads to ionization energies (calculated in the global minimum) which approximate better the energies of maxima in the FIG. 1.…”

Reaction selectivity in an ionized water dimer: nonadiabatic ab initio dynamics simulations

“…19 These ionization peaks correspond to the ejection of electrons from 1b 1 , 3a 1 , 1b 2 and 2a 1 molecular orbitals (MO). Later, ionization of water clusters and liquid water drew much attention of both experimentalists 12,[20][21][22][23][24][25][26][27][28] and theoreticians. 20,[29][30][31] The structure of the photoelectron spectrum remains the same in liquid water but the whole spectrum shifts by more than 1 eV (ref.…”

H2O2‐induced hydrogen bond water networks enhanced on stimulated Raman scattering

“…Especially, when the distance between the oxygen of H 2 O and the closest oxygen of H 2 O 2 molecules in aqueous solutions (O‐O distance is 2 Å), the ionization energy drop is almost 0.5 eV for H 2 O and 1.3 eV for H 2 O 2. And when the molecules are at interaction distances, the ionized states of individual molecules start to resonantly interact. This result leads to H 2 O 2 being a stronger H‐bond donor .…”