Knowledge Bank

A number of previous spectroscopic studies have been reported for the Ar-ethylene $complex1,2$. Although the observed vibrational bands were structured in both cases, a complete rotational assignment was not possible in either. We report here the first rotationally resolved spectra for Ar-and Ne-ethylene. The spectra have been assigned and provide an unambiguous determination of the structures, in which the rare-gas atom lies in the plane of the ethylene molecule, next the double bond. Both the $vg$ and $v11$ monomer vibrational bands have been observed for these two systems. The transitions observed in the spectra appear as doublets, indicative of internal rotation of the ethylene sub-unit about the carbon double bond. Spectra have also been obtained for the $CO2$-$C2$$H4$ complex, giving a structure in which the $CO2$ lies above the ethylene plane and is coplanar with the carbon-carbon double bond.