ANHARMONIC-FORCE FIELDS AND SPECTROSCOPIC PROPERTIES OF BF3 AND CF3-CLUSTER METHOD( USING THE COUPLED)

Anharmonic force fields and ro-vibrational spectroscopic properties of BF3 and CF3+ have been 3 investigated, using the coupled cluster meth od with single and double substitutions augmented by a perturbative es timate of triple excitations [CCSD(T)] with a basis set of 120 contrac ted Gaussian-type orbitals (cGTOs). A complete set of re-vibrational s pectroscopic constants for each species has been calculated using seco nd-order perturbation theory. For BF3 the CCSD(T) equilibrium bond dis tance is larger than the experimental value by 0.0058 Angstrom, and th e fundamental frequencies are within 5 cm(-1) of experiment, except fo r v(3), which shows a deviation of 16 cm (-1). The CCSD(T) method yiel ds vibration-rotation interaction constants alpha(e) in excellent cm a greement with available experimental values (within 3 MHz). The CCSD(T ) bond distance of CF3+ is 1.2305 Angstrom with a basis set of 220 cGT Os, which is corrected to 1.2272 Angstrom by applying a correction der ived from the identical level of calculation on BF3. The fundamental f requencies v(1), v(2), v(3), v(4) for CF3+ are predicted to be 1044 cm (-1), 813 cm(-1), 1683 cm(-1), and 593 cm(-1), respectively. (C) 1997 American Institute of Physics.