The 'KER' effect in the double photoionization of H(2)

Recent experimental and theoretical work examining the double photoionization of H(2) has uncovered surprising changes in the fully differential cross sections as a function of the kinetic energy released to the protons (which is equivalent to different internuclear separations of the molecule). We describe the recent joint theoretical and experimental investigations which have uncovered the physical reasons for this phenomenon. We show that the observed variations are solely due to the epsilon(Sigma) component of the polarization vector along the molecular axis. Our conclusions are supported by further investigations of the photoionization of H(2)(+), in which similar dramatic variations in the photoelectron angular distributions for the sigma(g) -> sigma(u) transition are found as the internuclear separation is varied. The angular distributions for the sigma(g) -> pi(u) transition show little dependence on the internuclear separation.