The travel time of light across a molecule

In a recent experimental work, we addressed the question whether a spatially extended molecular orbital reacts simultaneously as a single unit on being hit by a photon. We used the P04 beamline at PETRA III (DESY) and applied a reaction microscope to investigate one-photon double ionization of the hydrogen molecule at 800 eV photon energy. We obtained the double-slit-like photoelectron interference pattern in the molecular frame of reference by measuring the three-dimensional momentum vectors of all reaction fragments. Depending on the angle between the photon propagation direction and the molecular axis, we found asymmetries in the interference pattern that can be interpreted as a result of the travel time of light across the molecular orbital, which is 247 zeptoseconds for the average bond length of molecular hydrogen.