Physical Interpretation of the ''Kinetic Energy Release'' Effect in the Double Photoionization of H2

A physical interpretation is given for the variation with internuclear separation of the fully differential cross section for double photoionization of H2. This effect is analyzed in a geometry where the fourbody interaction is completely probed. Excellent agreement is found between experiment and time-dependent close-coupling theory after convoluting the latter over the relevant solid angles. We show the observed variations are purely due to the eΣ component of the polarization vector e along the molecular axis, a conclusion which is supported through calculations of the photoionization of H2+.