Knowledge Bank

The lowest frequency nondegenerate fundamental band $\nu 3$ of ethane is Raman active and centered near $992cm-1$. A stimulated Raman spectrum of the Q branch for this band (at a resolution of $0.0055cm-1$) has been recorded by Bermejo $etal.a$ The torsion-rotation branch with $\sigma =3$ is perturbed by over $1cm-1$. The lowest frequency degenerate fundamental band $\nu 9$ is infrared active and occurs in the $12-\mu m$ region. A high resolution $(0.0014cm-1)$ Fourier transform spectrum of this band has been measured by Moazzen-Ahmadi $etal.b$. The observed torsional splittings for this band are substantially larger than expected simply from the observed increase in the barrier height. Because of the proximity of the upper level $(l=-1;K=17,\sigma =0)$ in $\nu 9=1$ with its interacting partner $(\nu 9=0,\nu 4=3)$ a perturbation allowed band $3\nu 4$ has also been observed. We have carried out a combined frequency analysis of $\nu 3,\nu 9$, and $3\nu 4$ bands together with the far infrared torsional spectra in the ground vibrational state (gs). A vibration-torsion-rotation Hamiltonian with 32 fitting parameters was used. Three interacting torsional stacks, one for each of the vibrational state, were considered. The large torsional splitting in the $\nu 9$ band is attributed to Coriolis-like interations between the torsional stacks of gs and $\nu 9=1$ whereas the large shift for the torsion-rotation branch with $\sigma =3$ in the $\nu 3$ band is attributed to a Fermi-like interaction between the torsional stacks of gs and $\nu 3=1$. The details of this analysis will be presented.