Photolysis of water-radical ions H2O+ in the xuv: Fragmentation through dicationic states

The photofragmentation of the water cation H2O+ through dicationic states has been studied at 35.0 +/- 0.2 nm (35.4 +/- 0.3 eV) and 21.8 +/- 0.2 nm (56.8 +/- 0.5 eV) with a crossed ion-photon beams experiment at the free electron laser FLASH. The dissociation of the dications is found to be similar at the two wavelengths and to proceed into O-0 + 2H(+), OH+ + H+, and O+ + H-2(+), with determined ratios sigma(OH++H+)/sigma(O++H2+) = 4.2 +/- 0.3 and sigma(OH++H+)/sigma(O0+2H+) > 0.7. The measured kinetic-energy releases for these processes are consistent with three-body breakup (O-0 + 2H(+)) occurring mainly through the 2 (3)A '' and 2 (1)A '' states of H2O2+ and two-body breakup (OH+ + H+) occurring through X (3)A '', 1 (3)A', and 1 (1)A '' states of H2O2+, as predicted in a recent theoretical study [Gervais et al., J. Chem. Phys. 131, 024302 (2009)]. In addition to the kinetic-energy releases, we also report on fragment correlation in the three-body channel where the two protons carry the major part of the released momentum. DOI: 10.1103/PhysRevA.87.013402