Core-hole excited states of H2O : symmetries and relative oscillator strengths

Tunable and polarized soft x-ray radiation was used to excite core electrons of H2O. Angle-resolved proton yields were measured by retarding potential analyzers at 0° and 90° with respect to the polarization vector of the radiation. The ability of angle-resolved detection to reveal hidden resonances in rich molecular spectra is demonstrated, and the anisotropy parameter obtained from the two ion yields identifies the symmetries and the relative oscillator strengths of the core-hole excited states in the near-edge region of the spectrum. The analysis of the data substantiates the validity of the axial recoil approximation and provides evidence for ultrafast dissociation. Comparisons with the results of theoretical calculations are made.