Photodetachment, photofragmentation, and fragment autodetachment of [O2n(H2O)m]- clusters: Core-anion structures and fragment energy partitioning

Building on the past studies of the O-2n(-) and O-2(-)(H2O)(m) cluster anion series, we assess the effect of the strong hydration interactions on the oxygen-core clusters using photoelectron imaging and photofragment mass spectroscopy of [O-2n(H2O)(m)](-) (n=1-4, m=0-3) at 355 nm. The results show that both pure-oxygen and hydrated clusters with n >= 2 form an O-4(-) core anion, indicated in the past work on the pure-oxygen clusters. All clusters studied can be therefore described in terms of O-4(-)(H2O)(m)(O-2)(n-2) structures, although the O-4(-) core may be strongly perturbed by hydration in some of these clusters. Fragmentation of these clusters yields predominantly O-2(-) and O-2(-)(H2O)(l) (l < m) anionic products. The low-electron kinetic energy O-2(-) autodetachment features, prominent in the photoelectron images, signal that the fragments are vibrationally excited. The relative intensity of photoelectrons arising from O-2(-) fragment autodetachment is used to shed light on the varying degree of fragment excitation resulting from the cluster fragmentation process depending on the solvent conditions. (C) 2009 American Institute of Physics. [doi:10.1063/1.3224135]