Femtosecond dissociation dynamics of core-excited molecular water

The fragmentation of the water molecule upon resonant core excitation and subsequent Auger decay has been studied by electron–ion coincidence spectroscopy. A qualitative comparison between the fragmentation patterns for H2O and D2O reveals that the anti-bonding nature of the core-excited (*) intermediate state causes appreciable dissociation of the H2O* (D2O*) into HO*+H (DO*+D) during the lifetime (3.3 fs) of the O1s core hole. A `core–hole clockʹ model is used to derive approximate quantitative values for the characteristic dissociation time of the core-excited water molecule. The results demonstrate how such a procedure is useful for quantitative experiments with a very high degree of spatial and temporal localization.