AZIMUTHAL DEPENDENCE OF THE DIFFERENTIAL CROSS-SECTION IN ELECTRON-SCATTERING FROM FREE ORIENTED CH3CL MOLECULES

An azimuthal dependence for 1-keV electrons scattered elastically at a fixed polar angle from a beam of free, spatially oriented CH3Cl molec ules prepared by an electrostatic hexapole technique was observed. Pro nounced azimuthal distributions with orientation-dependent contributio ns of several percent were measured, demonstrating that for preferenti ally perpendicular orientation of the molecules with respect to the el ectron beam the diffraction pattern is no longer cylindrically symmetr ical and reflects directly the orientation and alignment of the scatte ring state ensemble. The data are compared with model calculations usi ng the independent-atom model and hexapole transmission calculations o f the focused rotational state mixtures, taking both the linear and th e quadratic Stark effect into account. Inclusion of the second-order S tark effect changes the calculated azimuthal distributions significant ly and improves the agreement between experiment and theory.