Ab initio study of scandium fluoride molecules: ScF, ScF2, AND ScF3

Equilibrium geometric parameters, normal mode frequencies and intensities in IR spectra, atomization enthalpy, and relative energies of low-lying electronic states of scandium fluoride molecules (ScF, ScF2, and ScF3) are calculated by the coupled-cluster method (CCSD(T)) in triple-, quadruple, and quintuple-zeta basis sets with the subsequent extrapolation of the calculation results to the complete basis set limit. The ScF molecule is also studied by the CCSDT technique. The error in the approximate calculation of triple excitations in the CCSD(T) method does not exceed 0.002 angstrom for the equilibrium internuclear distance R-e, 4 cm(-1) for the vibrational frequency, and 0.2 kcal/mol for the dissociation energy of the molecule. In the ground electronic state ($X) over tilde (2)A(1) (C-2v) of ScF 2 molecules, Re (Sc-F) = 1.827 angstrom and alpha(e) (F-Sc-F) = 124.2 degrees; the energy barrier to bending (linearization) h = E-min (D-infinity h) - E-min (C-2v) = 1652 cm(-1). The relative energies of (A) over tilde (2)Delta(g) and (B) over tilde (2)Pi(g) electronic states are 3522 cm(-1) and 14633 cm(-1) respectively. The bond distance in the ScF 3 molecule ((X) over tilde (1)A'(1,) D-3h) is refined: Re (Sc-F) = 1.842 angstrom. The atomization enthalpies Delta H-at(298)0 of ScFk molecules are 139.9 kcal/mol, 289.0 kcal/mol, and 444.8 kcal/mol for k = 1, 2, 3 respectively. Keywords: scandium fluorides, molecular structure and spectra, atomization enthalpy, quantum chemistry, coupled-cluster method, extrapolation to the limit of the complete basis set.