R-matrix-Floquet theory of molecular multiphoton processes

In this paper we describe a unified R -matrix-Floquet theory which can be used to analyse both multiphoton ionization of diatomic molecules and laser-assisted electron-diatomic molecule scattering. Our treatment is non-perturbative and can be applied to arbitrary multi-electron diatomic molecules. We assume that the laser field is monochromatic, monomode, spacially homogeneous and linearly polarized, where the molecular axis can be oriented in an arbitrary direction relative to this polarization direction. The theory takes advantage of the natural division of configuration space into internal and external regions occurring in the R -matrix method, to choose the most appropriate form of the interaction Hamiltonian in each region. This enables standard multi-centre electron-molecule scattering programs to be modified in a straightforward way to solve the problem in the internal region and single-centre atomic multiphoton propagator programs to be extended to solve the problem in the external region. We illustrate our theory by considering the form of the equations for homonuclear diatomic molecules. We also present results for H2using a simple target wavefunction which provides an important test of the theory and the computer programs and illustrates the role of resonances in two-photon ionization.