Electron interaction with laser-desorbed thymidine and guanine in the gas phase.

Abstract: In the present study we investigated electron attachment to the nucleoside thymidine (Td) and the nucleobase guanine (G) using a laser desorption source to transfer the compounds into the gas phase. Previous studies with Td indicated that the compound is thermally labile and may degrade upon thermal heating in standard molecular beam source. The present negative ion mass spectra for laser-desorbed Td and resistively heated Td share the same most three abundant fragment anions. Among those is the dehydrogenated parent anion (Td-H)^- which is strongly enhanced for laser-desorbed Td. We also find a considerable change of the fragmentation pattern for less abundant peaks in the mass spectra as well as changed characteristic in the total and mass selected anion efficiency curves of fragment anions. Electron attachment to G proceeds predominantly at electron energies below 3 eV. We ascribe this property to formation of a dipole-bound anion acting as a precursor state for efficient formation of the dehydrogenated anion (G-H)^-. The present results complement previous electron attachment studies with other nucleobases showing that the dehydrogenated parent anion is the most abundant fragment anion for G as well.

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Supplementary information: The online version contains supplementary material available at 10.1140/epjd/s10053-025-01023-9.