Experimental and theoretical studies of the vibrational spectra of cis-1-bromo-2-fluoroethene

The gas-phase infrared spectrum of cis-1-bromo-2-fluoroethene has been C studied at low resolution in the range 200-6500 cm(-1), leading to a complete assignment of the fundamentals, except the lowest vibrational mode v(9) predicted at 167 cm(-1). The remaining vibrational structure has been mainly interpreted in terms of first overtone or two quanta combination bands. Isotopic Br-79/81 shift has been observed only in the v(8) fundamental. The equilibrium structure and the quadratic force field have been investigated theoretically at CCSD(T) level of theory employing Dunning's correlation consistent triple-zeta basis set. Cubic and semidiagonal quartic force field have been calculated using second-order Moller-Plesset perturbation theory and Ahlrich' split valence (SV) contracted basis set. After a minor scaled quantum mechanical (SQM) adjustment of the quadratic force constants, the vibrational analysis, based on the second-order perturbation theory, has been carried out with the calculated force constants. (C) 2003 Elsevier B.V. All rights reserved