Knowledge Bank

Hexafluoro-2-butyne, $CF3-C2C-CF3$, has been examined in the infrared from 4000 to $280cm-1$ using a Perkin-Elmer 12B instrument equipped with $CaF2$, NaCl, KBr, and KRS-5 prisms. The Raman spectrum has been obtained on both the liquid and the gas. Qualitative depolarizations were determined for the stronger lines. Fundamental frequencies have been assigned, and all other observed frequencies of reasonable intensity have been explained as overtones or combination tones of these fundamentals. In most cases the observed frequencies agree with the calculated sums within $5cm-1$. Three unobserved fundamentals have been assigned from sum and difference tones, including a torsional frequency of $90cm-1$. It is demonstrated that the selection rules followed are $D3d$, rather than $D3h$.