Knowledge Bank

The low-frequency Raman and far infrared spectra of gaseous cis- and trans-2-butene have been recorded from 70 to $450cm-1$. Considerable torsional data have been obtained for the trans-2-butene, molecule with the $Au$ torsional fundamental being observed at $163.6cm-1$ in the infrared spectrum. The overtone of the B fundamental was observed in the Raman spectrum at $432cm-1$. The potential function based on a semi-rigid model and the effective barrier was found to be $703cm-1$ (2.04 kcal/mole). The cosine-cosine coupling term, $V33$, was found to be zoro whereas the sine-sine coupling term, $V33$ has a value of -$48cm-1$ (-0.14 kcal/mole) and $V60=V06=-4cm-1$ (-0.01 kcal/mole). For the cis-2- butane molecule only the $B2$ torsional mode was observed at $101.0cm-1$ which gives an effective barrier of $250cm-1$ (0.87 kcal/mole). These data are compared to the corresponding quantities obtained earlier by other methods.