AB initio study of the structure, isomerism, and vibrational spectra of LiClO₃, NaClO₃, and KClO₃

Abstract

The geometrical structure, force fields, and vibrational spectra of the ClO ⁻₃ ion and LiClO₃, NaClO₃, and KClO₃ molecules are studied using the Hartree-Fock (HF) method and second-order Möller-Plesset (MP2) perturbation theory in double-zeta basis sets complemented with polarization and diffuse functions. Routes of intramolecular rearrangements corresponding to migration of the M⁺ cations around the ClO ⁻₃ anion are investigated. The calculations showed that the molecular structure of alkaline metal chlorates changes in the series LiClO₃ → NaClO₃ → KClO₃. The LiClO₃ molecule has an essentially bidentate configuration of C_s symmetry; the KClO₃ molecule has tridentate coordination of C_3v symmetry. The NaClO₃ molecule exists as two isomeric forms having similar energies: tridentate (C_3v) and bidentate (C_s) forms separated by a low potential barrier (199 cm⁻¹ − HF, 170 cm⁻¹ − MP2); the energy differences between the isomers are ΔE(C_s − C_3v)=−0.5 (HF), 0.4 kJ/mole (MP2). The theoretical vibrational spectra of molecules agree with the available experimental data.