Angular Distribution of Different Vibrational Components of the X- and B-States Reached after Resonant Auger Decay of Core-Excited H2O: Experiment and Theory

Vibrationally resolved spectra have been obtained for the lowest-lying cationic states X(2B1), A(2A1) and B(2B2) of the water molecule reached after participator resonant Auger decay of core-excited states. The angular distribution has been measured for the first four vibrational components of the X-state in the photon energy regions including the O1s->4a1 and the O1s->2b2 core excitations, and for different portions of the vibrational envelope of the B-state in the photon energy region including the O1s->2b2 core excitation. For the X-state, a large relative spread in beta values of the different vibrational components is observed across both resonances. For the B-state, a very different trend is observed for the high binding energy side and the low binding energy side of the related spectral feature as a function of photon energy. A theoretical method based on the scattering K-matrix has been used to calculate both the photoabsorption spectrum and the beta values, by taking both interference between direct and resonant photoemission and vibrational/lifetime interference into account. The numerical results show qualitative agreement with the trends detected in the experimental values and explain the conspicuous variations of the beta values primarily in terms of coupling between direct and resonant photoemission by interaction terms of different sign for different final vibrational states.