Investigation of ion association kinetics in Na2SO4-H2O by excess Raman spectroscopy and 2D correlation Raman spectroscopy.

[Display omitted] • Analysis of ion dynamics in Na 2 SO 4 -H 2 O using excess and 2D correlation Raman. • Evidence is provided for the formation of ion pairs and small ion clusters in Na 2 SO 4 -H 2 O. • MD calculations reveal that small ion clusters primarily consist of 2 and 3 ion pairs.. The ion association of salts aqueous solutions have long captivated the attention of researchers within the field of physical chemistry. In this paper, we have performed a comprehensive analysis of ion interactions in sodium sulfate (Na 2 SO 4) aqueous solutions using a combination of high-resolution techniques, including excess (ERS) and two-dimensional correlation (2DCRS) Raman spectroscopy in conjunction with molecular dynamics (MD) calculations. The Raman spectrum shows that two inflection points in the Raman shift of the O–H vibration are observed with the increase in Na 2 SO 4 concentration. Simultaneously, a new peak of the SO 4 2- vibration appears at first inflection point, representing the formation of ion association. Further analysis based on ERS and 2CRS reveals that these two inflection points correspond respectively to the formation of ion pairs (CIPs) and small ion clusters. Importantly, MD simulations confirm the above experimental results. Our study provides evidence for ion association and clustering in aqueous in salt ion aqueous solutions. [ABSTRACT FROM AUTHOR]