Vibrational assignment of the S-1 fluorescence excitation spectrum of formyl fluoride

The S-1 fluorescence excitation spectrum of jet-cooled formyl fluoride, HFCO and DFCO, was recorded from 37 500 to 40 250 cm(-1) at 0.20 cm(-1) resolution. Vibrational bands were assigned primarily to progressions in the Franck-Condon active modes nu(2), nu(5), and nu(6). Tunneling splittings were observed in the nu(6) progression and fit to a model double-well potential Hamiltonian. Vibrational energies were fit to a Dunham expansion modified to account for the inversion doubling in the nu(6) progression. Best fit spectroscopic constants are reported including harmonic frequencies and anharmonic constants. S-0 --> S-1 Franck-Condon factors were calculated with the Duschinsky rotation included and support the vibrational assignment. The S-1 geometry and vibrational potential inferred from the present analysis are compared to ab initio results. (C) 1997 Academic Press, Inc.