On the determination of intensities for electron photodetachment and photoionization spectra involving states coupled by conical intersections: Total integral cross sections for polyatomic molecules

The formal underpinning is derived for the computational determination of electron photodetachment and photoionization total integral cross sections for molecules in which the residual species, which can be a neutral or an ion, has states that are strongly coupled by conical intersections. The theory takes full account of the requisite antisymmetry of all the electrons and the potential nonorthogonality of the orbital for the scattering electron to the occupied molecular orbitals of the residual. The breakdown of the Born-Oppenheimer approximation requires significant modifications to the standard adiabatic state theory. The developed theory builds on ideas from theories of low-energy electron scattering, in which the scattered electron is described by an orbital taken as channel dependent, but independent of nuclear coordinates. The derived computational approach is based on the accurate description of the vibronic levels of the residual species using the nonadiabatic vibronic coupling theory of Koppel, Domcke, and Cederbaum. The electron scattering problem is solved using the complex rotation L(2) method of Han and Reinhardt. This approach has the advantage that both Coulomb and free electron boundary conditions can be treated in the same approach. (C) 2010 American Institute of Physics. [doi:10.1063/1.3503166]