Large molecules reveal a linear length scaling for double photoionization

Comparison of the double-photoionization processes in triphenylene and corannulene with coronene

We have studied the production of doubly charged molecular ions by a single photon for the aromatic molecules triphenylene (C₁₈H₁₂) and corannulene (C₂₀H₁₀) using monochromatized synchrotron radiation from 18 eV to 270 eV. We compare our results with previously published data for partially deuterated benzene (C₆H₃D₃), pyrene (C₁₆H₁₀), and coronene (C₂₄H₁₂). The question that we address in this paper is how the different but similar molecular structures of coronene, corannulene, and triphenylene affect the photon-energy dependence of the ratio of doubly to singly charged parent ions. A theoretical analysis of the main features in terms of independent molecular subsystems will be discussed.

Dissociation kinetics of excited ions: PEPICO measurements of Os3(CO)12 - The 7-35 eV single ionization binding energy region

In this article, we study the photoinduced dissociation pathways of a metallocarbonyl, Os₃(CO)₁₂, in particular the consecutive loss of CO groups. To do so, we performed photoelectron-photoion coincidence (PEPICO) measurements in the single ionization binding energy region from 7 to 35 eV using 45-eV photons. Zero-energy ion appearance energies for the dissociation steps were extracted by modeling the PEPICO data using the statistical adiabatic channel model. Upon ionization to the excited ionic states above 13 eV binding energy, non-statistical behavior was observed and assigned to prompt CO loss. Double ionization was found to be dominated by the knockout process with an onset of 20.9 ± 0.4 eV. The oscillator strength is significantly larger for energies above 26.6 ± 0.4 eV, corresponding to one electron being ejected from the Os₃ center and one from the CO ligands. The cross section for double ionization was found to increase linearly up to 35 eV ionization energy, at which 40% of the generated ions are doubly charged.

XUV-induced reactions in benzene on sub-10 fs timescale: nonadiabatic relaxation and proton migration

Short XUV pulses produce excited cationic states of benzene. Their dynamics are probed by few-cycle VIS/NIR pulses. Very fast τ ≈ 20 fs nonadiabatic processes dominate the relaxation. In the CH₃⁺ fragmentation channel a non-trivial transient behaviour is observed.

Single-Photon, Double Photodetachment of Nickel Phthalocyanine Tetrasulfonic Acid 4- Anions

Single-photon, two-electron photodetachment from nickel phthalocyanine tetrasulfonic acid tetra anions, [NiPc](4-), was examined in the gas-phase using a linear ion trap coupled to the DESIRS VUV beamline of the SOLEIL Synchrotron. This system was chosen since it has a low detachment energy, known charge localization, and well-defined geometrical and electronic structures. A threshold for two-electron loss is observed at 10.2 eV, around 1 eV lower than previously observed double detachment thresholds on multiple charged protein anions. The photodetachment energy of [NiPc](4-) has been previously determined to be 3.5 eV and the photodetachment energy of [NiPc](3-•) is determined in this work to be 4.3 eV. The observed single photon double electron detachment threshold is hence 5.9 eV higher than the energy required for sequential single electron loss. Possible mechanisms are for double photodetachment are discussed. These observations pave the way toward new, exciting experiments for probing double photodetachment at relatively low energies, including correlation measurements on emitted photoelectrons.

Double photoionization of halogenated benzene

We have experimentally investigated the double-photoionization process in C6BrF5 using monochromatized synchrotron radiation. We compare our results with previously published data for partially deuterated benzene (C6H3D3) over a wide range of photon energies from threshold to 270 eV. A broad resonance in the ratio of doubly to singly charged parent ions at about 65 eV appears shifted in energy compared to benzene data. This shift is due to the difference in the bond lengths in two molecules. A simple model can explain the shape of this resonance. At higher photon energies, we observe another broad resonance that can be explained as a second harmonic of the first resonance.

Enhanced one-photon double ionization of atoms and molecules in an environment of different species

The correlated nature of electronic states in atoms and molecules is manifested in the simultaneous emission of two electrons after absorption of a single photon close to the respective threshold. Numerous observations in atoms and small molecules demonstrate that the double ionization efficiency close to threshold is rather small. In this Letter we show that this efficiency can be dramatically enhanced in the environment. To be specific, we concentrate on the case where the species in question has one or several He atoms as neighbors. The enhancement is achieved by an indirect process, where a He atom of the environment absorbs a photon and the resulting He(+) cation is neutralized fast by a process known as electron transfer mediated decay, producing thereby doubly ionized species. The enhancement of the double ionization is demonstrated in detail for the example of the Mg · He cluster. We show that the double ionization cross section of Mg becomes 3 orders of magnitude larger than the respective cross section of the isolated Mg atom. The impact of more neighbors is discussed and the extension to other species and environments is addressed.

Multiple Electron Ejection from Proteins Resulting from Single-Photon Excitation in the Valence Shell

One-photon multiple ionization is a signature of dynamical electron correlations in atoms and small molecules, as observed in the Auger process when Auger electron emission follows core-shell ionization. In such a process, the high energy needed to remove several electrons is due to the strong Coulombic attraction between the last departing electron(s) and the ionic core. Multiply negatively charged molecules offer the possibility to overcome the Coulombic attraction, opening the way for multielectron photodetachment following valence shell excitation. Here photodetachment studies have been performed on electrosprayed protein polyanions using vacuum ultraviolet synchrotron radiation coupled to a radiofrequency ion trap. Double, triple, and quadruple electron emissions from protein polyanions resulting from single-photon excitation in the valence shell were observed with ionization thresholds below 20 eV photon energy. This suggests the existence of large electronic correlations in proteins between weakly bound electrons standing on distant sites. Besides, the resulting multiradical polyanions appear to be remarkably stable, an important issue in radiobiology.

Photoemission of cooper pairs from aromatic hydrocarbons

We report the discovery of the formation of an electron Cooper pair approximately 40 eV above the double-ionization threshold in benzene, naphthalene, anthracene, and coronene after absorption of a single photon. We have measured the ratios of doubly to singly charged parent ions of the above mentioned molecules as well as pyrrole and furan by using monochromatized synchrotron radiation up to 100 eV above the corresponding thresholds. We also recorded photoelectron spectra of benzene and naphthalene at selected energies. The electron-pair formation is based on the specific structure of the molecules and does not exist for pyrrole and furan.