Core-excited and shape-type resonances in the micro-solvated Uracil: A CASSCF study

Electronic resonances play an important role in electron attachment-induced processes in biomolecules, and their properties can be significantly influenced by the local molecular environment. Here, we investigate the effect of amino acid micro-solvation on the uracil resonances by employing uracil-glycine as a model system. The resonance spectrum of the uracil-glycine complex consists of four {\pi}-type shape resonances and three core-excited resonances, including an additional glycine-centered resonance, as characterized using the CASSCF/Resonance via Pad\'e (RVP) methodology. Comparison with isolated uracil and the uracil(ghostGly) model shows that explicit interaction with glycine stabilizes both the shape and core-excited resonances by lowering their energies and increasing their lifetimes, while the ghost calculations demonstrate that basis-set extension alone cannot account for the observed stabilization. The core-excited resonances exhibit states that retain non-negligible lifetimes despite their much higher energy, suggesting that they may play an important role in electron-induced dissociation pathways. Overall, the present results demonstrate that amino acid micro-solvation significantly modifies the resonance landscape of uracil, highlighting the importance of explicitly accounting for local biomolecular interactions in theoretical studies of electron attachment.