We used a split-mirror setup attached to a reaction microscope at the free-electron laser in Hamburg (FLASH) to perform an XUV-pump–XUV-probe experiment by tracing the ultrafast nuclear wave-packet motion in the D2+(1sσg) with <10 fs time resolution. Comparison with time-dependent calculations shows excellent agreement with the measured vibrational period of 22±4 fs in D2+, points to the importance of accurately knowing the internuclear distance-dependent ionization probability, and paves the way to control sequential and nonsequential two-photon double-ionization contributions.Received 25 February 2010DOI:https://doi.org/10.1103/PhysRevA.81.051402©2010 American Physical Society