High resolution infrared, microwave, and millimeter wave spectra of SeCF2 structure determination assisted by ab initio calculations

Monoisotopic Se-80=CF2 has been prepared, and high resolution (2.5-3.3x10(-3) cm(-1)) Fourier transform infrared spectra in the nu(3) (nu 0 431.053 cm(-1)) and nu(4) regions (nu(0) 1208.790 cm(-1)) have been recorded. The hitherto unknown rotational constants that were obtained by means of ground state combination differences assisted the search for microwave transitions of (SeCF2)-Se-M species, M=76, 77, 78, 80, and 82, in the 5-26 GHz range and of millimeter wave transitions for M=78 and 80 in the 152-240 GHz region. Ground state constants up to quartic terms of the five isotopic species were determined by merging all available data. Excited state parameters of the nu(3)=1 and nu(4)=1 states were also determined. It is concluded that these states are unperturbed at the present level of accuracy, which is 4.5x10(-4) cm(-1) for the rms deviation of more than 6000 (nu(3)) and 12000 IR transitions (nu(4)). Ab initio calculations at the correlated levels of second order Moller-Plesset pertubation theory using different basis sets were performed. Experimental and theoretical results were combined to deduce effective (r(0)), average (r(z)) and equilibrium (r(e)) structural parameters. The equilibrium parameters are r(C-F) 1.309(2) Angstrom, r(C=Se) 1.739(2)Angstrom and angle (FCF) 107.74(4)degrees.