Electron transfer driven decomposition of adenine and selected analogs as probed by experimental and theoretical methods

Cunha, T.; Mendes, M.; Ferreira da Silva, F.; Eden, S.; García, G.; Bacchus-Montabonel, M.-C. and Limão-Vieira, P. (2018). Electron transfer driven decomposition of adenine and selected analogs as probed by experimental and theoretical methods. The Journal of Chemical Physics, 148(13), article no. 134301.

DOI: https://doi.org/10.1063/1.5021888

Abstract

We report on a combined experimental and theoretical study of electron transfer induced decomposition of adenine and a selection of analogue molecules in collisions with potassium atoms (K). Time-of-flight negative ion mass spectra have been obtained in a wide collision energy range (6–68 eV in the centre-of-mass frame), providing a comprehensive investigation of the fragmentation patterns of purine, adenine, 9-methyl adenine, 6-dimethyl adenine and 2-D adenine. Following our recent communication about selective hydrogen loss from the transient negative ions (TNI) produced in these collisions [T. Dunha et al. J. Chem. Phys. 148, 021101 (2018)], this work focuses on the production of smaller fragment anions. In the low-energy part of the present range, several dissociation channels that are accessible in free electron attachment experiments are absent from the present mass spectra, notably NH₂ loss from adenine and 9-methyl adenine. This can be understood in terms of a relatively long transit time of the K⁺ cation in the vicinity of the TNI tending to enhance the likelihood of intramolecular electron transfer. In this case, the excess energy can be redistributed through the available degrees of freedom inhibiting fragmentation pathways. Ab initio theoretical calculations were performed for 9-methyl adenine (9-mAd) and adenine (Ad) in the presence of a potassium atom and provided a strong basis for the assignment the lowest unoccupied molecular orbitals accessed in the collision process.

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