We are studying steric effects in the ionization and excitation of simple molecules by fast electrons. These are experiments in which the orientation of the molecule is known at the time of the excitation process or in the decay from an excited state. The first set of measurements was concerned with the transition from highly excited states. The angular distribution of Auger electrons of N₂ relative to the internuclear axis was measured. We have recently finished a set of measurements on the excitation of H₂. Those experiments measured the ionization and excitation of H₂ as a function of the orientation of the internuclear axis relative to the momentum transfer vector of the scattered electron. We have been able to calculate the angular distributions for these two sets of experiments and compare the experimental results to theory. Presently, we are starting a new set of measurements on the double ionization of molecules as a function of orientation of the internuclear axis relative to the incident beam direction. CO is the test case. Is the ionization cross section different if the fast electron is incident on the C end of the molecule or the O end?

Recent Publications

Q. Zheng, A.K. Edwards, R.M. Wood and M.A. Mangan, "Angular distributions of selected N2 Auger transitions," Phys. Rev. A 52, 3940 (1995).

Q. Zheng, A.K. Edwards, R.M. Wood and M.A. Mangan, "Spheroidal analysis of the angular distribution of Auger electrons emitted by homonuclear diatomic molecules," Phys. Rev. A 52, 3945 (1995).