Total and partial cross sections for breakup of ground rovibronic state of H$_2^+$by photon impact are calculated using the exact nonadiabatic nonrelativistic Hamiltonian without approximation. The converged results span six orders of magnitude. The breakup cross section is divided into dissociative excitation and dissociative ionization. The dissociative excitation channels are divided into contributions from principal quantum numbers 1 through 4. For dissociative ionization the kinetic energy sharing is calculated using a formally exact expression. These results are compared with approximate expressions, and it is shown that the Born-Oppenheimer result is surprisingly accurate, whereas using Born-Oppenheimer final states to extract the cross sections from the full nonadiabatic wave function produces pathologies near threshold.
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