Transforming Anion Instability into Stability: Contrasting Photoionization of Three Protonation Forms of the Phosphate Ion upon Moving into Water

0385746 - ÚOCHB 2013 RIV US eng J - Journal Article
Pluhařová, Eva - Ončák, M. - Seidel, R. - Schroeder, C. - Schroeder, W. - Winter, B. - Bradforth, S. E. - Jungwirth, Pavel - Slavíček, P.
Transforming Anion Instability into Stability: Contrasting Photoionization of Three Protonation Forms of the Phosphate Ion upon Moving into Water.
Journal of Physical Chemistry B. Roč. 116, č. 44 (2012), s. 13254-13264. ISSN 1520-6106. E-ISSN 1520-5207
R&D Projects: GA ČR(CZ) GAP208/10/1724; GA ČR GA203/08/0114
Institutional research plan: CEZ:AV0Z40550506
Keywords : multiply-charged anions * ab-initio calculations * aqueous-solution * photoelectron-spectroscopy * ionization energies * emission-spectroscopy
Subject RIV: CF - Physical ; Theoretical Chemistry
Impact factor: 3.607, year: 2012

We use photoelectron emission spectroscopy with vacuum microjet technique and quantum chemistry calculations to investigate electronic structure and stability of aqueous phosphate anions. On the basis of the measured photoelectron spectra of sodium phosphates at different pH, we report the lowest vertical ionization energies of monobasic (9.5 eV), dibasic (8.9 eV), and tribasic (8.4 eV) anions. Electron binding energies were in tandem modeled with ab initio methods, using a mixed dielectric solvation model together with up to 64 explicitly solvating water molecules. We demonstrate that two solvation layers of explicit water molecules are needed to obtain converged values of vertical ionization energies (VIEs) within this mixed solvation model, leading to very good agreement with experiment. We also show that the highly charged PO43- anion, which is electronically unstable in the gas phase, gains the electronic stability with about 16 water molecules, while only 2-3 water molecules are sufficient to stabilize the doubly charged phosphate anion. We also investigate the effect of ion pairing on the vertical ionization energy. In contrast to protonation (leading to a formation of covalent O-H bond), sodiation (leading to an anion center dot center dot center dot Na+ ion pair) has only a weak effect on the electron binding energy.
Permanent Link: http://hdl.handle.net/11104/0007506