Photoelectron spectroscopy of cold hydrated sulfate clusters, SO4(2-)(H2O)n (n = 4-7): temperature-dependent isomer populations.
Sulfate is an important inorganic anion and its interactions with water are essential to understand its chemistry in aqueous solution. Studies of sulfate with well-controlled solvent numbers provide molecular-level information about the solute-solvent interactions and critical data to test theoretical methods for weakly bounded species. Here we report a low-temperature photoelectron spectroscopy study of hydrated sulfate clusters SO(4)(2-)(H(2)O)(n) (n = 4-7) at 12 K and ab initio studies to understand the structures and dynamics of these unique solvated systems. A significant increase of electron binding energies was observed for the 12 K spectra relative to those at room temperature, suggesting different structural isomers were populated as a function of temperature. Theoretical calculations revealed a competition between isomers with optimal water-solute and water-water interactions. The global minimum isomers all possess higher electron binding energies due to their optimal water-solute interactions, giving rise to the binding energy shift in the 12 K spectra, whereas many additional low-lying isomers with less optimal solvent-solute interactions were populated at room temperature, resulting in a shift to lower electron binding energies in the observed spectra. The current work demonstrates and confirms the complexity of the water-sulfate potential energy landscape and the importance of temperature control in studying the solvent-solute systems and in comparing calculations with experiment.
Wang
Xue-Bin
XB
Department of Physics, Washington State University, 2710 University Drive, Richland, Washington 99354, USA. xuebin.wang@pnl.gov
Sergeeva
Alina P
AP
Yang
Jie
J
Xing
Xiao-Peng
XP
Boldyrev
Alexander I
AI
Wang
Lai-Sheng
LS