Theoretical study of the structure and stability of the Na₂Cl⁺, NaCl ⁻₂ , Na₃Cl ⁺₂ , and Na₂Cl ⁻₃ ions

Abstract

The geometrical parameters, normal vibration frequencies, and thermochemical characteristics of the Na₂Cl⁺, NaCl ⁻₂ , Na₃Cl ⁺₂ , and Na₂Cl ⁻₃ ions in saturated vapors over sodium chloride were calculated by the ab initio methods including electron correlation. According to calculations, the Na₂Cl⁺ and NaCl ⁻₂ triatomic ions have a linear equilibrium D _∞h configuration. The pentaatomic ions can exist in the form of the D _∞h linear isomer, C _2v planar cyclic isomer, or D _3h bipyramidal isomer. At ∼1000 K the Na₃Cl ⁺₂ and Na₂Cl ⁻₃ ions exist predominantly in the form of the linear isomers. The energies and enthalpies of the ion-molecule reactions involving the above ions were calculated. The formation enthalpy of the ions Δ_f H ⁰(0 K) was determined: 230 ± 2 kJ/mol (Na₂Cl⁺), −96 ± 4 kJ/mol (Na₂Cl ⁻₃ ), −616 ± 2 kJ/mol (NaCl ⁻₂ ), and −935 ± 4 kJ/mol (Na₂Cl ⁻₃ ).