Polarizability series of aqueous polyatomic anions revealed by femtosecond Kerr effect spectroscopy

Abstract

The polarizability or hyperpolarizability of aqueous anions is closely related to important processes such as the surface tension change of water and the empirical Hofmeister effect. Herein, we measured the hyperpolarizabilities of six polyatomic anions (HPO₄²⁻, HSO₄⁻, CO₃²⁻, CH₃COO⁻, NO₃⁻ and SCN⁻) in their aqueous potassium salt solutions using femtosecond optical Kerr effect spectroscopy. We found that the hyperpolarizability of these six aqueous anions increased in the following order: HPO₄²⁻ ∼ HSO₄⁻ < CO₃²⁻ < CH₃COO⁻ < NO₃⁻ < SCN⁻, which correlated well with the Hofmeister series of aqueous anions in their decreasing ability to precipitate proteins. However, the CO₃²⁻ anion is the exceptional anion. The current study is useful for disclosing these fundamental physicochemical properties in aqueous salt solutions.