Including anharmonic and Duschinsky effects

CASSCF/MRCI/aug-cc-pVQZ~no g! and RCCSD~T!/aug-cc-pVQZ potential energy functions were reported for the à B1 and X̃ A1 states of CF2 , respectively. Vibrational wave functions of the symmetric stretching and bending modes of the two states of CF2 were obtained in variational calculations, employing Watson’s Hamiltonian for a nonlinear molecule and anharmonic vibrational wave functions expressed as linear combinations of harmonic basis functions. Franck–Condon factors ~FCFs! were computed for à B1→X̃ A1 CF2 single vibronic level ~SVL! emissions and the SVL emission spectra were simulated with the computed FCFs. When compared with the observed spectra, the simulated spectra obtained in the present investigation, which include allowance for anharmonicity and the Duschinsky effect, were found to be significantly superior to those reported previously, based on the harmonic oscillator model. Using the iterative Franck–Condon analysis procedure, with the geometry of the X̃ A1 state fixed at the recently determined experimental equilibrium geometry, the geometry of the à B1 state of CF2 , which gave the best match between simulated and observed spectra, was found to be re(CF!51.317 Å and ue(FCF)5121.25 °. © 2001 American Institute of Physics. @DOI: 10.1063/1.1398103#