Single Photon Simultaneous K-shell Ionization and K-shell Excitation. I. Theoretical Model Applied to the Interpretation of Experimental Results on H2O.

We present in detail a theoretical model that provides absolute cross sections for simultaneous core-ionization core-excitation (K−2V ) and compare its predictions with experimental results obtained on the water molecule after photoionization by synchrotron radiation. Two resonances of different symmetries are assigned in the main K−2V peak and comparable contributions from monopolar (direct shake-up) and dipolar (conjugate shake-up) core-valence excitations are identified. The main peak is observed with a much greater width than the total experimental resolution. This broadening is the signature of nuclear dynamics.