Femtosecond dissociation dynamics of core-excited molecular water

The fragmentation of the water molecule upon resonant core excitation and s ubsequent Auger decay has been studied by electron-ion coincidence spectros copy. A qualitative comparison between the fragmentation patterns for H2O a nd D2O reveals that the anti-bonding nature of the core-excited (*) interme diate state causes appreciable dissociation of the H2O* (D2O*) into HO* + H (DO* + D) during the lifetime (3.3 fs) of the Ols core hole. A 'core-hole clock' model is used to derive approximate quantitative values for the char acteristic dissociation time of the core-excited water molecule. The result s demonstrate how such a procedure is useful for quantitative experiments w ith a very high degree of spatial and temporal localization. (C) 1999 Elsev ier Science B.V. All rights reserved.