Photodetachment, photofragmentation, and fragment autodetachment of [O _2n(H₂ O) _m] ^- Clusters: Core-anion structures and fragment energy partitioning

Building on the past studies of the O _2n^- and O ₂^- (H₂ O) _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 (H₂ O) _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 O₄^- core anion, indicated in the past work on the pure-oxygen clusters. All clusters studied can be therefore described in terms of O₄^- (H₂ O) _m (O₂) _n-2 structures, although the O₄^- core may be strongly perturbed by hydration in some of these clusters. Fragmentation of these clusters yields predominantly O₂^- and O ₂^- (H₂ O) _l (l<m) anionic products. The low-electron kinetic energy O O₂^- autodetachment features, prominent in the photoelectron images, signal that the fragments are vibrationally excited. The relative intensity of photoelectrons arising from O O₂^- 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.