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Issue 20, 2017
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Electron stimulated desorption from condensed pyrimidine and pyridazine

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Low energy electron (LEE) interactions and the formation of transient negative ions play a dominant role in radiation-induced dissociation of condensed-phase biomolecules (e.g. in radiotherapy). Here we present data on the LEE-induced dissociation and desorption of the DNA/RNA-base and radiosensitizing agent analogues pyrimidine and pyridazine. Vapors of each molecule were condensed on either a Pt or Ar substrate to form a multilayer film or a submonolayer molecular target, respectively. These were irradiated with electrons of 0–80 eV and the desorbing anionic and cationic fragments analysed via time of flight mass spectrometry. The detected cations are the same species seen in gas-phase mass spectra, albeit of differing relative intensity. Anion yield functions exhibit strong maxima, indicating that transient negative ions contribute significantly, via dissociative electron attachment (DEA), to molecular dissociation below 20 eV. For both molecules, the <5 eV shape resonances, seen experimentally and predicted by theory, do not result in fragment desorption. The main anionic fragments are H and CN for both molecules, additionally the fragments C, CH C2H and CHN desorb from pyrimidine and C and C2H from pyridazine, with some resonances lying above the ionization limit. Pyrimidine shows higher anion desorption yields than pyridazine for all species except H. The anion signal also comprises dipolar dissociation (DD), investigated in both anionic and cationic yield functions. From analysis of anion and cation yields, fragmentation pathways are suggested. The direct ionization pathway provides information on the appearance energies for cations and their production processes in condensed phase.

Graphical abstract: Electron stimulated desorption from condensed pyrimidine and pyridazine

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Publication details

The article was received on 01 Feb 2017, accepted on 28 Apr 2017 and first published on 28 Apr 2017

Article type: Paper
DOI: 10.1039/C7CP00715A
Citation: Phys. Chem. Chem. Phys., 2017,19, 13038-13048
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    Electron stimulated desorption from condensed pyrimidine and pyridazine

    L. Ellis-Gibbings, A. D. Bass, P. Cloutier, G. García and L. Sanche, Phys. Chem. Chem. Phys., 2017, 19, 13038
    DOI: 10.1039/C7CP00715A

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