Influence of molecular orientation on the multiple differential cross sections for the (e,2e) process on a water molecule

Eightfold and fivefold differential cross sections (8DCS and 5DCS, respectively) for the (e,2e) process on a water molecule are calculated within the framework of the first Born approximation, and the role of the molecular orientation on the collision process is studied and analyzed. The molecular wave functions are described by the linear combination of atomic orbitals (LCAO) (self-consistent-field LCAO molecular orbitals method). We present results for electron impinging at an intermediate energy of 250 eV and in an asymmetric coplanar geometry and kinematics. When particular molecule orientations are chosen, the 8DCS exhibit large differencies, in shape as well as in magnitude. A comparison of these results with an averaged-space calculation (integration of the 8DCS over Euler angles) confirms the necessity to take properly into account the molecular orientation in the calculations of the ionization cross sections of polyatomic molecules.