Large Molecules Reveal a Linear Length Scaling for Double Photoionization

Abstract

We have measured the ratio of doubly to singly charged parent ions of benzene, naphthalene, anthracene, and pentacene using monochromatized synchrotron radiation up to 30 eV above the corresponding threshold. Our measurements show a striking similarity between the ratio of doubly charged to all parent ions and the ratio for helium. Moreover, the magnitudes of the ratios for these molecules scale linearly with their lengths with an amazing accuracy. A high ratio, i.e., a high relative double-photoionization probability, makes a molecule an important source of low-energy electrons that can promote radiation damage of biomolecules [B. Boudaïffa et al., Science 287, 1658 (2000)].

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

“…1 ), as it can be seen in Fig.2a (whose vertical axis is logarithmic not linear). In organic molecules, the ratio of single to double ionization has been reported to be around 2%, 19 which is of the same magnitude as our findings in the case of photodetachment. Similarly, for BSA protein polyanions (33-charge state), thresholds at 12.2 eV and 15 eV were obtained for double and triple photodetachments (see Table I).…”

Hydrogen rearrangements in the fragmentation of anthracene by low-energy electron impact

“…Murakami et al [24] have performed measurements with fs circularly polarized laser light. Using synchrotron radiation, Hartman et al [25,26] have measured the ratios of doubly to singly-charged molecular parent ions for anthracene and other aromatic hydrocarbons. Wehlitz [27] has reviewed double photoionization of hydrocarbons and aromatic molecules.…”

Valence shell direct double photodetachment in polyanions

“…Also, to our knowledge, it is the first observation of direct multiple photodetachment occurring in the valence region in a protein polyanion. At 15 eV, and for short irradiation durations, double photodetachment amounts to ≈2% of the detachment cross section, a figure that is quite similar, for the same excess energy above the DPD onset, to the one measure for double ionization of large organic molecules [14], and that should increase with the photon energy. Several processes might account for DPD as reported for the Cl − anion, which is the most strongly bound atomic anion with a comparable electron affinity to those of peptides [11].…”

“…First, direct double valence ionization following single-photon absorption might happen, an effect due to electron correlations, which therefore cannot be described within independent electron models. The 'knock-out' inelastic model [12,13] appears to account very well for this direct non-local process even in quite large organic molecules [14]. Doubly charged species may also be produced following inner-shell excitation/ionization, in which case the primary excited monocation relaxes through the Auger effect by emission of a second electron, leading to a doubly charged cation.…”