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 (2.5-3.3 x10(-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 re corded. The hitherto unknown rotational constants that were obtained b y means of ground state combination differences assisted the search fo r 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 quarti c terms of the five isotopic species were determined by merging all av ailable data. Excited state parameters of the nu(3)=1 and nu(4)=1 stat es were also determined. It is concluded that these states are unpertu rbed 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 orde r Moller-Plesset pertubation theory using different basis sets were pe rformed. Experimental and theoretical results were combined to deduce effective (r(0)), average (r(z)) and equilibrium (r(e)) structural par ameters. 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.