Knowledge Bank

From infrared and Raman spectra a complete assignment was proposed for the 24 vibrational fundamentals of the ZZ (cis-cis) isomer of 1,4-difluorobutadiene, which is a centrosymmetric molecule of $C2h$ symmetry. A few adjustments in this initial assignment were made on the basis of ab initio predictions of all the frequencies and the intensities in the infrared spectrum. The experimental assignments in $cm-1$ are: $(ag:R,pol;IR,-)3088,3047,1676,1410,1247,1133,946,750,232;(ag:R,-;IR,C-typebands)914,762,330,78;(bg:R,dpol;IR,-)897,789,559;(bu:R,-;IR$, A/B-type bands) $3109,3042,1624,1340,1215,1044,649,165$. These experimental values will be compared with the ab initio predictions, which were based on the hybrid density-functional theory/Hartree-Fock Adiabatic Connection Method (ACM) with use of a TZ2P basis set.