Portal de Periódicos da CAPES

Microwave spectrum, r0 structure, barriers to internal rotation and ab initio calculations of gauche-1,1-difluoropropane

2005; Elsevier BV; Volume: 742; Issue: 1-3 Linguagem: Inglês

10.1016/j.molstruc.2004.12.057

1872-8014

James R. Durig, Chao Zheng, Gamil A. Guirgis, H. Nanaie,

Spectroscopy and Laser Applications

Abstract The microwave spectra of four isotopomers, CH 3 CH 2 12 CHF 2 , CH 3 CH 2 13 CHF 2 , CD 3 CH 2 12 CHF 2 and CD 3 CD 2 12 CHF 2 , of gauche -1,1-difluoropropane, in the ground vibrational state were recorded and assigned. From the measured frequencies for the R and Q branches of the a-, b- and c-type transitions, accurate values for the rotational constants were obtained along with values for Δ J , Δ JK , δ J and Δ K . The dipole moment components were evaluated from the measurements of the Stark effects of the ground state rotational transitions and the determined values are: | μ a |=2.044(3), | μ b |=0.851(5), | μ c |=0.711(35) and | μ tot |=2.326(3) D. Ab initio molecular orbital calculations have been carried out with valence electron correlation by the perturbation method to second-order with various basis sets up to MP2(full)/6-311+G(d,p) from which structural parameters, barriers to internal rotation, and distortion constants have been obtained. The C–H distance of 1.095±0.002 A for the CHF 2 moiety has been determined from the isolated stretching frequency from the CD 3 CD 2 12 CHF 2 molecule. The r 0 parameters have been obtained by combining the ab initio predicted values with the microwave rotational constants and these parameters for the heavy atoms are: r C 1 –F 5 =1.370(5), r C 1 –F 6 =1.372(5), r C 1 –C 2 =1.505(3), r C 2 –C 3 =1.522(3) A, ∠C 1 C 2 C 3 =112.2(5), ∠C 2 C 1 F 5 =109.8(5), ∠C 2 C 1 F 6 =110.9(5)°. The adjusted r 0 parameters have also been obtained for 2,2-difluoropropane, CH 3 CF 2 CH 3 . The results are compared to those of some similar molecules.