Angular distribution of different vibrational components of the X and B states reached after resonant Auger decay of core-excited H ₂O: Experiment and theory

Vibrationally resolved spectra have been obtained for the lowest-lying cationic states X ²B ₁, A ²A ₁, and B ²B ₂ of the water molecule reached after participator resonant Auger decay of core-excited states. The angular distribution has been measured of the first four vibrational components of the X state in the photon energy regions including the O 1s→4a ₁ and the O 1s→2b ₂ core excitations, and for different portions of the vibrational envelope of the B state in the photon energy region including the O 1s→2b ₂ core excitation. For the X state, a large relative spread in β 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 β 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 β values primarily in terms of coupling between direct and resonant photoemission by interaction terms of different sign for different final vibrational states.