Knowledge Bank

Measurements of the infrared active fundamental of liquid $CS2$ ($1510cm-1$) indicate as is to be expected that there is a breakdown of the gaseous rotational selection rules. The general aspect of the band is Gaussian. However, deviations from the Gaussian shape strongly suggest that there are a number of sub-bands or branches on either side of the central maximum. As many as 8 of these branches are visible. Theoretical considerations using simple potential functions indicate that the selection rules for a parallel band of a linear molecule in a liquid could be $\Delta M=\backslash O$; $AJ=O,\pm 2,\pm 4$,.... and $\Delta M=\pm 1$; $AJ=\pm 1$ with perhaps the addition of $\pm 3,\pm 5$,.... An interpretation of the band shape in terms of these selection rules and potential functions allows an estimate of the force tending to hold the molecule in a given direction in the liquid.