PNNL

Abstract

The stability, energetics, and structures of three common inorganic phosphate species, H2PO4?, H2P2O7²?, H3P3O10²?, and their corresponding neutral radical and monoanions, were investigated in the gas phase using photodetachment photoelectron spectroscopy and theoretical calculations. We found that H2P2O7²? and H3P3O10²? are stable in the gas phase with adiabatic electron binding energies of 1.16 and 2.45 eV, respectively. A very high adiabatic electron binding energy of 4.57 eV was measured for H2PO4?. The intramolecular Coulomb repulsion energies in H2P2O7²? (~2.7 eV) and H3P3O10²? (~2.3 eV) were estimated from photon-energy-dependent photoelectron spectra. Density-functional theory calculations were used to search the optimal geometries for both the doubly and singly charged species. We found only one minimum energy conformation for H2P2O7²? with two intramolecular H-bonds and C2 symmetry and three minimum energy structures for H3P3O10²?. The lowest energy structure of H3P3O10²? has three intramolecular H-bonds that do not share a common oxygen atom. The calculated electron detachment energy of H2PO4? agrees with the experimental value well, but the calculated detachment energies for H2P2O7²? and H3P3O10²? are ~0.3 and ~0.7 eV smaller than the experimental values, respectively. The observed spectral features, due to removal of electrons from lone-pair oxygen orbitals in the phosphate groups, were assigned qualitatively on the basis of the theoretical calculations.