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

Abstract

Building on the past studies of the O2n− and O2−(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 [O2n(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 O4− core anion, indicated in the past work on the pure-oxygen clusters. All clusters studied can be therefore described in terms of O4−(H2O)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 O2−(H2O)l (l<m) anionic products. The low-electron kinetic energy O2− autodetachment features, prominent in the photoelectron images, signal that the fragments are vibrationally excited. The relative intensity of photoelectrons arising from 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.