Y. Pak et al., COUPLED-CLUSTER ANHARMONIC-FORCE FIELDS, SPECTROSCOPIC CONSTANTS, ANDVIBRATIONAL ENERGIES OF ALF3 AND SIF3+, The Journal of chemical physics, 107(6), 1997, pp. 1717-1724
Anharmonic force fields and re-vibrational spectroscopic properties of
AlF3 and SiF3+ have been investigated in detail, using the coupled cl
uster method with single and double substitutions augmented by a pertu
rbative treatment of triple excitations [CCSD(T)] with a triple zeta b
asis set of 124 contracted Gaussian-type orbitals (cGTOs). A complete
set of re-vibrational spectroscopic constants for each species has bee
n calculated using second order perturbation theory. The geometry only
was calculated with a quadruple zeta basis set (224 cGTOs). Our best
estimates of the equilibrium bond distances r(e) (Al-F) and r(e) (Si-F
) are 1.624 Angstrom and 1.508 Angstrom, respectively, based on the qu
adruple zeta CCSD(T) bond distances and corrections derived from spect
roscopically related known molecules. The CCSD(T) fundamental frequenc
ies are 689 cm(-1)(nu(1)), 301 cm(-1)(nu(2)), 951 cm(-1)(nu 3), and 24
1 cm(-1)(nu(4)) for AlF3 and 853 cm(-1)(nu(1)), 357 cm(-1)(nu(2)), 118
7 cm(-1)(nu(3)), and 307 cm(-1)(nu(4)) for SiF3+. Energies of a number
of low lying vibrational states (less than or equal to 2400 cm(-1)) h
ave been calculated by three methods: (1) standard second order pertur
bation theory formulas; (2) Van Vleck perturbation theory based on rai
sing and lowering operators to second order and to fourth order; and (
3) a variational method. (C) 1997 American Institute of Physics.