| Résumé | The biradical radiationless decay mechanism of the excited electronic state structure of the cytidine, 5-fluorocytidine, and deoxycytidine nucleosides are studied at CIS and coupled cluster CC2 levels with the cc-pVDZ basis set. Nucleoside radiationless decay pathways are compared with those of the isolated bases. For the ground state geometry, cytidine and deoxycytidine as well as isolated cytosine have S1 [pi]H[pi]L* states. In moving towards lower energy configurations, this doorway [pi][pi]* state crosses over to a biradical excited state, which in turn intersects the ground electronic state and is responsible for the S1?-->?S0 internal conversion. Qualitatively, the radiationless decay mechanisms of cytidine nucleosides are similar to the isolated cytosine base. |
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