Measurement of the Frequency of Torsional Vibration in the Ethane Molecule

The direct excitation of the torsional vibration of the two methyl groups in ethane was observed in a slow-neutron inelastic-scattering experiment. Theoretical curves fit to the data indicate that the energy of transition from the zero to first excited state of this oscillation is 0.0332 eV (268 cm−1) if the potential is assumed to be harmonic or 0.0344 eV (277 cm−1) if the potential is assumed to be represented by ½V0(1+cos3θ). To observe the transition, the scattering at small angles was observed through an evacuated scattering chamber and with careful consideration of multiple neutron scattering.