A new method for the size-selective EXAFS of neutral free clusters

Recently we have measured Photoelectron Photoion Coincidence (PEPICO) spectra for selenium dimer Se2 and larger species such as Se5 at the beamline BL-12C in Photon Factory. The PEPICO spectra reveal that the multiply charged ions, Se(z+), are produced as a result of de-excitation processes following the inner-shell excitation and fragmented to atomic ions owing to the Coulomb explosion. The branching ratios from the parent clusters to the daughter ions exhibit clear dependence on the size of the parent clusters. In particular, the branching ratios in the non-resonant absorption region are well reproduced by assuming that the charges are randomly distributed within the clusters before the Coulomb explosion. Based upon these findings, we propose a new method for the size-selective EXAFS of neutral free clusters by utilizing the PEPICO measurements.