Knowledge Bank

The depolarized Rayleigh wing spectra($10-300cm-1)$ of liquid pyridine from $-50\circ$ to $80\circ C$ have been studied using the recently described quantity $R(\nu ~)$[1]. Spectra of pyridine and pyridine-$d5$ are compared with far infrared absorption measurements. The $R(\nu ~)$-curve of pyridine shows a maximum at $88cm-1$, which is shifted to $78cm-1$ in pyridine-$d5$. The far infrared absorption curves are much different from the $R(\nu ~)$-curve and show maxima at $\sim 60$ $cm-1$. The temperature dependence of the maximum frequency and band width as well as the isotopic shift support the idea that the presence of librational modes in liquid pyridine gives rise to a band in its low frequency spectrum.