Knowledge Bank

The infrared spectra of gascous methyl acetylene, chloride and bromide, isolated in dilute argon matrices, (1:1000) have been observed in the region of $3000cm-1$ at 4 and $20\circ K$ under high dispersion. The $20\circ K$ spectra, for all the molecules consist of three bands which correspond closely to $\nu 1$, $\nu 4$ and $2\nu 5$. At $4\circ K$. the intensity of these bands increase and the perpendicular band $\nu 4$ splits into 3 distinct components in the ease of methyl acetylene and bromide, showing only incipient splitting in the chloride. The central component of $\nu 4$ is the most intense and the two weaker components are spaced equally on either side of the central component. The strong feature in this triad is assigned to and the weaker component to and . The results can be interpreted using the same model as in the ease of the hydrogen halides.