Raman and infrared spectra, vibrational assignment, internal rotational barrier and ab initio calculations for 3,3-difluoro-1-butyne

The Raman spectra (3500-50 cm(-1)) of gaseous, liquid and solid and the inf rared spectra (3500-300 cm(-1)) of gaseous and solid 3,3-difluoro-1-butyne, CH equivalent to CCF2CH3, were obtained. Quantum chemical calculations of the structure and vibrational wavenumbers were obtained using the Hartree-F ock, MP2 and B3LYP methods to assist in the interpretation of the observed spectral data. The far-infrared spectrum of the gas was recorded from 70 to 350 cm(-1) and the 1 <-- 0 transition of the methyl group was observed at 255.8 cm(-1). Based on this wavenumber, the barrier to internal rotation is calculated to be 1634 cm(-1) (19.6 kJ mol(-1)). A complete vibrational ass ignment is proposed, which is supported by normal coordinate calculations, utilizing the force constants from ab initio MP2/6-31G(d) calculations. Com plete equilibrium geometry was determined by ab initio calculations employi ng the 6-31G(d) and 6-311+G(d) basis sets at the level of restricted Hartre e-Pock (RHF) and/or Moller-Plesset (MP) to the second order. The results ar e discussed and compared with those obtained for similar molecules. Copyrig ht (C) 2000 John Wiley & Sons, Ltd.