  The multiconfiguration time-dependent Hartree-Fock (MCTDHF) method is
formulated for treating the coupled electronic and nuclear dynamics of diatomic
molecules without the Born- Oppenheimer approximation. The method treats the
full dimensionality of the electronic motion, uses no model interactions, and
is in principle capable of an exact nonrelativistic description of diatomics in
electromagnetic fields. An expansion of the wave function in terms of
configurations of orbitals whose dependence on internuclear distance is only
that provided by the underlying prolate spheroidal coordinate system is
demonstrated to provide the key simplifications of the working equations that
allow their practical solution. Photoionization cross sections are also
computed from the MCTDHF wave function in calculations using short pulses.
