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Near-threshold electron transfer in anion-nucleobase clusters: does the identity of the anion matter?

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Version 2 2019-09-28, 07:41
Version 1 2019-07-02, 09:54
journal contribution
posted on 2019-09-28, 07:41 authored by Rosaria Cercola, Edward Matthews, Caroline E. H. Dessent

Laser dissociation spectroscopy of I·adenine (I·A) and H2PO3·adenine (H2PO3·A) has been utilised for the first time to explore how the anion identity impacts on the excited states. Despite strong photodepletion, ionic photofragmentation is weak for both clusters, revealing that they decay predominantly by electron detachment. The spectra of I·A display a prominent dipole-bound excited state in the region of the detachment energy which relaxes to produce deprotonated adenine. In contrast, near-threshold photoexcitation of H2PO3·A does not access a dipole-bound state, but instead displays photofragmentation properties associated with ultrafast decay of an adenine-localised π→π* transition. Notably, the experimental electron detachment onset of H2PO3·A is around 4.7 eV, which is substantially lower than the expected detachment energy of an ion-dipole complex. The low value for H2PO3·A can be traced to initial ionisation of the adenine followed by significant geometric rearrangement on the neutral surface. We conclude that these dynamics quench access to a dipole-bound excited state for H2PO3·A and subsequent electron transfer. H2PO3·A represents an important new example of an ionic cluster where ionisation occurs from the neutral cluster component and where photodetachment initiates intra-molecular hydrogen atom transfer.

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