Knowledge Bank

The infrared spectrum of $CD4$ has been examined from $900cm-1$ to $7000cm-1$ with the University of Tennessee prism-grating spectrograph, utilizing gratings of 15,000, 7200, and 3600 lines per inch. In order to detect overtone and combination bands, the lead sulfide region was mapped using a multiple reflection cell 50 cm in length with up to forty traversals. About twenty bands were resolved, including those originally measured by Nielsen and $Nielsen.1$ These bands, $\nu 3,\nu 4$, and $\nu 1+\nu 4$, were observed at considerably higher resolving power, and a more complex structure seemed to be indicated than was shown in the original measurements. In particular, the rotational lines in the high-frequency branch of the fundamental vibration, $\nu 4$, were resolved into multiplets. Because of the Coriolis interaction between the modes, $\nu 2$ and $\nu 4$, it is possible for the normally infrared inactive mode, $\nu 2$, to appear in the infrared if the two modes of vibration are of approximately the same frequency. A band identified as $\nu 2$ was observed at $1092cm-1$ whereas $\nu 4$ appeared at $996cm-1$. This value for the band center differs considerably from the value obtained from the Raman spectrum of the first overtone, $2\mu 2$. An analysis of the rotational structure has been made for the vibrational states, $\nu 2,\nu 3,\nu 4,2\nu 3$, and $\nu 1+\nu 4$, taking into account the Coriolis interaction between vibration and rotation, but not the K-splitting of the rotational lines. Rotational analysis is progressing on other bands, but because of the overlapping of bands, it has been possible to identify only a few lines near the band centers up to the present time.