AB-INITIO STUDY OF THE STRUCTURE, ISOMERISM, AND VIBRATIONAL-SPECTRA OF LICLO3, NACLO3, AND KCLO3

The geometrical structure, force fields, and vibrational spectra of th e ClO3- ion and LiClO3, NaClO3, ai td KClO3 molecules are studied usin g the Hartree-Fock (HF) method and second-order Muller-Plesset (MP2) p erturbation theory in double-zeta basis sets complemented with polariz ation and diffuse functions Routes of intramolecular rearrangements co rresponding to migration of the M+ cations around the CLO3- anion are investigated. The calculations showed that the molecular structure of alkaline metal chlorates changes in the series LiClO3 --> NaClO3 --> K ClO3. The LiClO3 molecule has an essentially bidentate configuration o f C-s symmetry; the KClO3 molecule has tridentate coordination of C-3v symmetry. The NaClO3 molecule exists as two isomeric forms having sim ilar energies: tridentate (C-3v) and bidentate (C-s) forms separated b y a low potential barrier (199 cm(-1) - HF, 170 cm(-1) - MP2); the ene rgy differences between the isomers are Delta E(C-s - C-3v)= -0 5 (HF) , 0.4 kJ/mole (MP2). The theoretical vibrational spectra of Molecules agree with the available experimental data.