Photoelectron spectroscopy of the protoporphyrin IX dianion

Photodissociation of permanganate (MnO4-) produces the manganese dioxide anion (MnO2-) in an excited triplet state

Photoelectron imaging, electron action spectroscopy and electronic structure calculations are used to probe the structure and dynamics of MnO4-. Following excitation to the first bright absorption band of MnO4- (11T2), photodetachment, via ground state electron loss, and photodissociation, to produce MnO2-, are both observed to occur simultaneously. MnO2- is produced in an excited electronic state, identified as a triplet state, which indicates that the dissociation proceeds on singlet potential energy surfaces via spin conservation. Furthermore, electronic structure calculations indicate that both photodetachment and photodissociation are multiple photon processes that are mediated by the same 11T2 excited state. Taken together this data indicates that photodissociation of MnO4- occurs via a statistical dissociation on the MnO4- ground state at visible wavelengths.

Kasha's Rule and Koopmans' Correlations for Electron Tunnelling through Repulsive Coulomb Barriers in a Polyanion

The long-range electronic structure of polyanions is defined by the repulsive Coulomb barrier (RCB). Excited states can decay by resonant electron tunnelling through RCBs, but such decay has not been observed for electronically excited states other than the first excited state, suggesting a Kasha-type rule for resonant electron tunnelling. Using action spectroscopy, photoelectron imaging, and computational chemistry, we show that the fluorescein dianion, Fl2-, partially decays through electron tunnelling from the S2 excited state, thus demonstrating anti-Kasha behavior, and that resonant electron tunnelling adheres to Koopmans' correlations, thus disentangling different channels.

Photoelectron Imaging Study of the Diplatinum Iodide Dianions [Pt2I6]2- and [Pt2I8]2

Photoelectron spectroscopy has been used to study the electronic structure, photodetachment, and photodissociation of the stable diplatinum iodide dianions [Pt₂I₆]^2– and [Pt₂I₈]^2–. Photoelectron spectra over a range of photon energies show the characteristic absence of low kinetic energy photoelectrons expected for dianions as a result of the repulsive Coulomb barrier (RCB). Vertical detachment energies of ∼1.6 and ∼1.9 eV and minimum RCBs of ∼1.2 and ∼1.3 eV are reported for [Pt₂I₆]^2– and [Pt₂I₈]^2–, respectively. Both of the diplatinum halides exhibit three direct detachment channels with distinct anisotropies, analogous to the previously reported spectra for PtI₂^– and PtI^–, suggesting a platinum-centered molecular core that dominates the photodetachment. Additionally, evidence for two-photon photodissociation and subsequent photodetachment channels producing I^– are observed for both dianions. Finally, an unexplained feature is observed at photon energies around 3 eV, whose origin is considered. Our work highlights the complex electronic structure of the heavy platinum-halide dianions that are characterized by a dense manifold of electronic states.