VIBRATIONAL SPECTRA OF SYMMETRICAL TERACHLORO-AND TETRABROMOETHANE

Author Institution: Pennsylvania State CollegeThe Raman and infrared spectra of liquid 1,1,2,2-tetrachloro- and 1,1,2,2-tetrabromoethane have been investigated. Using a grating spectrograph of 3.8 \AA/mm dispersion, we have observed the chlorine isotope effect for the $\Delta \nu = 353$ and $366 cm^{-1}$ line pair, and have verified the previous results of Rank, Sheppard, and Szasz concerning the anomolous intensity contour exhibited by the $353 cm^{-1}$ vibration. From temperature intensity measurements in the Raman effect and Raman-infrared correspondences, we conclude that the two forms posses $C_{2h}$ and $C_{2}$ symmetry, with the $C_{2}$ form being the more stable one. On the basis of this conclusion we are able to explain the intensity contours observed in the chlorine isotope effect. The value of $\Delta H$ for the reaction $C_{2}\to C_{2h}$ in s-tetrabromoethane was found to be 910 cal/mole