On the N1-H and N3-H Bond Dissociation in Uracil by Low Energy Electrons: A CASSCF/CASPT2 Study

Israel González-Ramírez; Javier Segarra-Martí; Luis Serrano-Andrés; Manuela Merchán; Mercedes Rubio; Daniel Roca-Sanjuán

doi:10.1021/ct300153f

On the N1-H and N3-H Bond Dissociation in Uracil by Low Energy Electrons: A CASSCF/CASPT2 Study

J Chem Theory Comput. 2012 Aug 14;8(8):2769-76. doi: 10.1021/ct300153f. Epub 2012 Jul 26.

Authors

Israel González-Ramírez¹, Javier Segarra-Martí¹, Luis Serrano-Andrés¹, Manuela Merchán¹, Mercedes Rubio¹, Daniel Roca-Sanjuán²

Affiliations

¹ Instituto de Ciencia Molecular, Universitat de València , P.O. Box 22085, 46071 València, Spain.
² Department of Chemistry-Ångström, Theoretical Chemistry Program, Uppsala Univeristy , P.O. Box 518, 75120 Uppsala, Sweden.

PMID: 26592118
DOI: 10.1021/ct300153f

Abstract

The dissociative electron-attachment (DEA) phenomena at the N1-H and N3-H bonds observed experimentally at low energies (<3 eV) in uracil are studied with the CASSCF/CASPT2 methodology. Two valence-bound π(-) and two dissociative σ(-) states of the uracil anionic species, together with the ground state of the neutral molecule, are proven to contribute to the shapes appearing in the experimental DEA cross sections. Conical intersections (CI) between the π(-) and σ(-) are established as the structures which activate the DEA processes. The N1-H and N3-H DEA mechanisms in uracil are described, and experimental observations are interpreted on the basis of two factors: (1) the relative energy of the (U-H)(-) + H fragments obtained after DEA with respect to the ground-state equilibrium structure (S0) of the neutral molecule (threshold for DEA) and (2) the relative energy of the CIs also with respect to S0 (band maxima). The π1(-) state is found to be mainly responsible for the N1-H bond breaking, whereas the π2(-) state is proved to be involved in the cleavage of the N3-H bond.