Knowledge Bank

The polarized electronic absorption of a crystalline diacetylene, 2,4-hexadiyne-l,6-diol, at 4.2$\mathrm{<mrow\; data-mjx-texclass="ORD">\circ </mrow>}K$ has been examined under medium resolution ($3cm-1$). Two weak electronic transitions are observed. The lower energy transition, whose origin is estimated to be at 32 500 $cm-1$, consists of a series of broad bands which are separated by approximately $2100cm-1$. The second transition, whose 0 - 0 band lies at 38 455 $cm-1$, is, in contrast to the first, rich in vibronic structure. In the two polarizations examined, the spectra are quite different not only in intensity distribution but also in vibronic structure. The prominent vibration frequencies observed in these spectra are 97, 380, 615, 1156 and $2160cm-1$.