Emergence of Solvent-Separated Na+-Cl- Ion Pair in Salt Water: Photoelectron Spectroscopy and Theoretical Calculations

Gao-Lei Hou; Cheng-Wen Liu; Ren-Zhong Li; Hong-Guang Xu; Yi Qin Gao; Wei-Jun Zheng

doi:10.1021/acs.jpclett.6b02670

Emergence of Solvent-Separated Na⁺-Cl^- Ion Pair in Salt Water: Photoelectron Spectroscopy and Theoretical Calculations

J Phys Chem Lett. 2017 Jan 5;8(1):13-20. doi: 10.1021/acs.jpclett.6b02670. Epub 2016 Dec 9.

Authors

Gao-Lei Hou¹, Cheng-Wen Liu², Ren-Zhong Li¹, Hong-Guang Xu^{1

3}, Yi Qin Gao², Wei-Jun Zheng^{1

3}

Affiliations

¹ Beijing National Laboratory for Molecular Sciences, State Key Laboratory of Molecular Reaction Dynamics, Institute of Chemistry, Chinese Academy of Sciences , Beijing 100190, China.
² Beijing National Laboratory for Molecular Sciences, Institute of Theoretical and Computational Chemistry, College of Chemistry and Molecular Engineering, Peking University , Beijing 100871, China.
³ University of Chinese Academy of Sciences , Beijing 100049, China.

PMID: 27935718
DOI: 10.1021/acs.jpclett.6b02670

Abstract

Solvation of salts in water is a fundamental physical chemical process, but the underlying mechanism remains unclear. We investigated the contact ion pair (CIP) to solvent-separated ion pair (SSIP) transition in NaCl(H₂O)_n clusters with anion photoelectron spectroscopy and ab initio calculations. It is found that the SSIP type of structures show up at n = 2 for NaCl^-(H₂O)_n anions. For neutral NaCl(H₂O)_n, the CIP structures are dominant at n < 9. At n = 9-12, the CIP structures and SSIP structures of NaCl(H₂O)_n are nearly degenerate in energy, coincident to the H₂O:NaCl molar ratio of NaCl saturated solution and implying that the CIP and SSIP structures can coexist in concentrated solutions. These results are useful for understanding the solvation of salts at the molecular level.