Electron diffraction from oriented molecules: e-CH3Cl

The additional molecular interference contributions to the differential elastic electron scattering cross sections for spatially oriented and partially state-selected CH3Cl molecules have been measured at an incident energy of 1 keV. Using the electrostatic hexapole technique, the molecules were oriented with their axes preferentially parallel or antiparallel to the electron beam. Deviations from the diffraction pattern of unoriented molecules of up to 4% were observed as a function of momentum transfer. A change of the orientational distribution in the state ensemble gave rise to a significantly altered interference pattern with alignment contributions dominating in both cases. For comparison with the data the fractional population of the various states present in the molecular beam was calculated and the independent atom model was applied to obtain the scattering pattern using the formalism of Kohl and Shipsey. (orig.)