The four-body breakup of spatially aligned D2 by 58.8 eV photons from the Advanced Light Source has been investigated by measuring the three dimensional momentum vectors of both fragment ions and one of the two electrons in coincidence. Energy and angular correlation between ions and electrons is discussed. We find rotational symmetry of the electron angular distribution around the polarization vector of the light and significant differences between helium and D 2 as well as between molecular alignment parallel and perpendicular to the polarization axis. [S0031-9007(98)08045-4] PACS numbers: 33.80.Eh, 32.80.Fb Ejection of both electrons from a bound two-electron system by a single photon is a remarkable consequence of electron-electron correlation. This subtle and fundamental process of double photoionization can be studied in the neutral two-electron systems helium and D2 [1‐ 3]. The complete fragmentation of D2 provides a link between atomic and molecular photoionization studies. Here the initial state is a simple molecular system, and the final state is an unbound four-body Coulomb system with no molecular degrees of freedom. Unlike fragmentation of more complex molecules, where the photoejection of an electron is usually followed by molecular rearrangement which eventually leads to fragmentation, double photoionization of D2 leaves two bare ions in a mutually repulsive Coulomb potential. Thus detection of the momentum vectors of the two outgoing nuclei provides a direct image of the spatial alignment of the two nuclear centers at the instant of double ionization [4,5]. In this work we have measured the direction and energy of the two ionic fragments in coincidence with the momentum vector of one of the two electrons from D2 double ionization by linear polarized photons sS1 › 0.99 6 0.01d at Eg › 58.8 eV. At this energy, the two electrons share about 7 eV. This provides the connection between the ionic and the electronic motion in the continuum. It shows the direction in which one electron emerges from the molecule and how the available excess energy is shared between the nuclear fragments and the electrons. Our spectrometer has a 4p solid angle acceptance for ions and electrons. Thus we image the full momentum space of the nuclei and one of the electrons. These data can be integrated over any desired coordinate to obtain ion energy and angular distributions as well as electron energy and angular distributions with respect to the photon polarization axis e and the internuclear axis. They can be compared with similar measurements we have made for helium, the corresponding atomic two-electron system. So far only a few experimental studies have investigated this fundamental four-body problem. Kossmann et al. [4]