We adapt the multiple-scattering method to treat unbound electronic states of molecules in the independent electron approximation. An inhomogeneous linear system is derived whose solution yields the K matrix for the electron-molecule interaction. Using the K matrix, we derive continuum electronic wavefunctions by imposing boundary conditions corresponding to electron-molecule scattering and molecular photoionization, i.e., the wavefunctions satisfy the so-called outgoing-wave and incoming-wave normalization, respectively. These wavefunctions are then used to obtain expressions for elastic scattering and photoionization differential cross sections.

Expressions are obtained for the angular distribution of electrons ejected by electric dipole interaction from molecular targets fixed in the laboratory coordinate frame. The analysis is geometrical and independent of any particular dynamical description of the photoionization process. Thus the results will serve as the framework for study of the dynamics of particular processes, such as photoionization of molecules oriented on surfaces or by molecular beam techniques.

Shape resonances in molecular photoionization are shown to induce strong coupling between vibrational and electronic motion over a spectral range several times broader than the resonances half-width. This coupling is manifested by large deviations from Franck-Condon intensity distributions and strong dependence of photoelectron angular distributions on the vibrational state of the residual ion. These effects are illustrated for the 3a g photoionization channel of N 2 .

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molecule system I=q(-1) is invariant of course.It follows then from (AQ) that the parity I= q( 1-)õ f the molecule alone is a collision invariant for homonuclear molecules. This means that in electron scattering by non-Z homonuclear molecules, the rotational transition hJ = odd integer is allottedb ut only with a simultaneous change of the quantum number g. The occurrence of the 40= odd-integer transition has been emphasized by Temkin and Faisal 20