R-matrix-Floquet theory of molecular multiphoton processes

In this paper we describe a unified R-matrix-Floquet theory which can be us ed to analyse both multiphoton ionization of diatomic molecules and laser-a ssisted electron-diatomic molecule scattering. Our treatment is non-perturb ative and can be applied to arbitrary multi-electron diatomic molecules. We assume that the laser field is monochromatic, monomode, spacially homogene ous and linearly polarized, where the molecular axis can be oriented in an arbitrary direction relative to this polarization direction. The theory tak es advantage of the natural division of configuration space into internal a nd external regions occurring in the R-matrix method, to choose the most ap propriate 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 si ngle-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 pres ent results for H-2 using a simple target wavefunction which provides an im portant test of the theory and the computer programs and illustrates the ro le of resonances in two-photon ionization.