Infrared and Raman spectra, conformations and ab initio calculations of 1,1,1-trifluoropropyl trifluorosilane

The infrared spectra of 1,1,1-trifluoropropyl trifluorosilane were recorded in the vapour, amorphous and crystalline solid phases in the range 4000-50 cm(-1). Additional MIR spectra of the compound isolated in argon and nitro gen matrices at 5 K before and after annealing to temperatures in the range 15-35 It were obtained. Raman spectra of the liquid were recorded at vario us temperatures between 298 and 163 K. Spectra of the amorphous solid on a copper finger were recorded and spectra of crystalline solids cooled by dif ferent techniques were obtained. The spectra showed the existence of two co nformers - anti and gauche - present in the vapour and in the liquid. Appro ximately five Raman bands present in the fluid phases vanished upon crystal lization, but only small changes occurred in the corresponding infrared spe ctra. From intensity variations with temperature in the Raman spectra of th e liquid, the enthalpy difference was determined to be Delta H(gauche-anti) = 3.2 kJ mol(-1) Ab initio calculations were performed using the Gaussian 94 program with th e HF/6-311G* basis set and gave optimized geometries, infrared and Raman in tensities and scaled vibrational frequencies for the anti and gauche confor mers. The conformational energy was calculated to be 5.3 kJ mol(-1) with an ti being the low energy conformer. (C) 1999 Elsevier Science B.V, All right s reserved.