Ab initio study of the structure,force field,and vibrational spectrum of the LiClO3 molecule

The geometrical structure and the vibrational spectrum of the LiClO₃ molecule are studied by the Hartree-Fock-Roothaan (HF) and configurational interaction (CI) methods taking into account single and double excitations and Davidson's correction for quadruple excitations. Double-zeta basis sets of Huzinaga-Dunning and McLean-Chandler complemented with polarization and diffuse functions are used. Potential surface sections corresponding to migration of the Li⁺ cation around the ClO ₃ ⁻ fragment are investigated. It was found that the LiClO₃ molecule has a single stable configuration of C_s symmetry with the bidentate coordination of the Li⁺ cation by the ClO ₃ ⁻ anion. The cyclic fragment is nonplanar (the dihedral angle θ(LiO₂Cl)=173°). The tridentate configuration of C_3v symmetry lies higher than the equilibrium configuration by 24.5 (HF) or 18.3 (CI) kJ/mole and is not an isomer. The ab initio force field of the molecule was refined by the scaling method. Some assignments of the IR bands of the matrix-isolated molecular forms existing in vapor over lithium chlorate are corrected. The vibration frequencies (cm⁻¹) and IR intensities (km/mole; in parentheses) are calculated with the refined force field: A′ type 1099(236), 856(81), 630(73), 557(119), 481(87), 156(66); A″ type 887(229), 459(35), 367(23). Ivanovo State Chemical Technological Academy. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 3, pp. 440–449, May–June, 1996.