PHOTOFRAGMENTATION OF HYDRATED IRON IONS FE(H2O)(N)(-9) AT 532, 355 AND 266 NM() (N = 1)

Photofragmentation of Fe(H2O)(n)(+) clusters (n = 1-9) is investigated at three different wavelengths, 532, 355 and 266 nm. Two fragmentatio n pathways are observed depending essentially on the photon energy, bu t also on the parent size n. The fragmentation products belong to two ion families, Fe(H2O)(m)(+) and FeOH(H2O)(m)(+), which correspond to d ehydration and intracluster dehydrogenation reactions respectively. Th e ion yields are studied as a function of the laser fluence in order t o determine the number of photons implied in the photofragmentation pr ocess. This allows us to estimate that the D[(H2O)(n-1)Fe+-(H2O)] blon d energy is ranging between 0.44 eV and 0.55 eV for 5 less than or equ al to n less than or equal to 9. Photon absorption cross sections are also derived from the fluence experiments, and two different behaviors are observed: i) At 355 nm, far away from any Fe+ transition; progres sive solvation of the metal ion results in an increasing absorption cr oss section from n = 2 to n = 9. This can be attributed to a forbidden transition of bare Fe+, which becomes progressively allowed because o f the interaction with more and more water ligands. ii) At 266 nm, clo se to several allowed transitions of bare Fe+, a distinct maximum is o bserved for the absorption of Fe(H2O)(2)(+) ion. It may be attributed to a change in the spin multiplicity when switching from Fe+ and Fe(H2 O)(+) on one hand to Fe(H2O)(n greater than or equal to 2)(+) on the o ther.