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Gianturco and Lucchese have recently presented calculations reporting resonances in the electron scattering cross section of the RNA base uracil and discussed the role of these temporary negative ion states in various fragmentation processes. Such efforts in complex systems are highly commendable. However, the authors have not made a proper comparison of their calculated anion states with those measured and assigned earlier, although this latter work is cited in their paper. In particular, they omit any reference to the lowest-lying resonance observed previously.
The amplitudes and nodal characteristics of the resonance orbitals sat the geometry of the neutral moleculed certainly give clues to the impulses delivered to the nuclei during the lifetimes of the resonances. In the absence of bond strengths, electron affinities of the fragments and the potential surface gradients, however, these properties alone are not sufficient to predict the products.