Measurement of the autoionization lifetime of the energetically lowest doubly excited $Q_1\,^1\Sigma ^+_\mathrm{u}$ state in H2using electron ejection asymmetry

The autoionization lifetime of doubly excited H2 created by single photon absorption has been measured by means of a kinematically complete study. For dissociative ionization the experimentally observed asymmetry in the electron ejection direction with respect to the emitted proton is used to disentangle the two interfering pathways, direct ionization and autoionization. This allows us to determine the autoionization lifetime of the energetically lowest doubly excited state for a large range of internuclear distances, including the previously inaccessible small values. Excellent agreement with available ab initio calculations is obtained.