Spectroscopic studies of 1,4-dibromobutyne-2

Abstract

Infrared spectra of 1,4-dibromobutyne-2 have been recorded over the 4000-200 cm −1 region in the vapour, liquid, amorphous and crystalline states Raman spectra were extended to ca. 20 cm −1 in the same states of aggregation, except for the non-recorded vapour phase spectrum. The temperature was varied between −190 and 160 °C, and the pressure up to 10 kbar. A high proportion of the molecules exhibited free, internal rotation in the vapour and liquid phases, but to a smaller extent in the amorphous state at −190 °C. For those molecules not being excited beyond the potential barrier, an unsymmetric conformation was preferred, whereas in the crystalline state the molecules possessed the anti conformation ( C 2 h ) both at low temperature and at high pressure at ambient temperature. A vibrational analysis based upon force field calculations was carried out and the mean amplitudes of vibration computed. The data have been related to preliminary results from dipole moment and electron diffraction investigations.