Ring-breaking electron attachment to uracil: Following bond dissociations via evolving resonances

Abstract

Calculations are carried out at various distinct energies to obtain both elastic cross sections and S-matrix resonance indicators (poles) from a quantum treatment of the electron scattering from gas-phase uracil. The low-energy region confirms the presence of pi(*) resonances as revealed by earlier calculations and experiments which are compared with the present findings. They turn out to be little affected by bond deformation, while the transient negative ions (TNIs) associated with sigma(*) resonances in the higher energy region ( approximately 8 eV) indeed show that ring deformations which allow vibrational redistribution of the excess electron energy into the molecular target strongly affect these shape resonances: They therefore evolve along different dissociative pathways and stabilize different fragment anions. The calculations further show that the occurrence of conical intersections between sigma(*) and pi(*)-type potential energy surfaces (real parts) is a very likely mechanism responsible for energy transfers between different TNIs. The excess electron wavefunctions for such scattering states, once mapped over the molecular space, provide nanoscopic reasons for the selective breaking of different bonds in the ring region.

Elastic and inelastic low-energy electron collisions with pyrazine

“…In addition to the poor characterization of the possible higher-lying resonances in pyrimidine DNA bases, previous studies [18][19][20][22][23][24][25] have struggled to produce parameters of, especially, the third (highest-lying) π * resonance in satisfactory agreement with experimental values. For this reason, Winstead and McKoy investigated elastic electron collisions with a model molecule, pyrazine.…”

“…These are significantly narrower than the σ * resonance characterized by Gianturco et al in their uracil work 19 and our analysis indicated that they probably have some core-excited character; nonetheless one of these might be the pyrazine equivalent of the σ * uracil resonance. An extremely wide resonance (as postulated by Burrow et al), would probably be undetectable by simple examination and fitting of the eigenphase sums.…”

“…Theoretical calculations of electron collisions with uracil by Gianturco et al 18,19 and Winstead and McKoy 20 suggest the presence of at least one higher-lying broad σ * shape resonance located at energies above 8 eV, much higher-than the σ * resonance postulated by others. 11 Consequently it has been proposed 19 that the oba) Electronic mail: z.masin@open.ac.uk. b) Electronic mail: j.gorfinkiel@open.ac.uk.…”

Selective Bond Cleavage in Potassium Collisions with Pyrimidine Bases of DNA

“…13,15 Such discrepancies between DEA and electron transfer experiments have already been detected in other molecules, most notably regarding the NCO − yield in uracil and thymine. 23 Briefly, it was shown that, owing to the presence of the potassium cation in the vicinity of the molecular anion, a delay in the autodetachment process of the extra electron occurs, allowing π * orbitals to be populated long enough for the electron to be transferred to a highly dissociative σ * orbital, 23,35 which will subsequently lead to fragmentation. Indeed, a recent DEA study to D-ribose shows a resonance profile for OH − formation consisting of one dominant peak at near-zero energy and a weak wider structure at around 7 eV, the latter assigned to a shape resonance.…”

Comment on “Ring-breaking electron attachment to uracil: Following bond dissociations via evolving resonances” [J. Chem. Phys. 128, 174302 (2008)]

“…2 In a subsequent Comment, 3 Burrow pointed out that the claimed agreement depended on misidentifying the first and second calculated * resonances with, respectively, the second and third experimental resonances. A recent paper by Gianturco et al 4 reports new calculations for uracil employing substantially the same scattering model and again claims close agreement with experimental * resonance positions, and also with those of other calculations. 5,6 Although the resonance positions that Gianturco et al obtain ͑1.7, 3.5, and 6.5 eV͒ ͑Ref.…”