Shape resonances in low-energy-electron collisions with halopyrimidines

Abstract

We report calculated cross sections for elastic collisions of low-energy electrons with halopyrimidines, namely, 2-chloro, 2-bromo, and 5-bromopyrimidine. We employed the Schwinger multichannel method with pseudopotentials to compute the cross sections in the static-exchange and static-exchange plus polarization levels of approximation for energies up to 10 eV. We found four shape resonances for each molecule: three of π* nature localized on the ring and one of σ* nature localized along the carbon-halogen bond. We compared the calculated positions of the resonances with the electron transmission spectroscopy data measured by Modelli et al. [J. Phys. Chem. A 115, 10775 (2011)]. In general the agreement between theory and experiment is good. In particular, our results show the existence of a π* temporary anion state of A2 symmetry for all three halopyrimidines, in agreement with the dissociative electron attachment spectra also reported by Modelli et al. [J. Phys. Chem. A 115, 10775 (2011)].

Theoretical and experimental study on electron interactions with chlorobenzene: Shape resonances and differential cross sections

“…This is the same effect as observed when comparing halopyrimidines and pyrimidines molecules. 10 There are at least two previous works available in the literature reporting cross sections for low-energy electron scattering by benzene. 50,51 Especially, we highlight the ab initio calculation performed by Bettega et al, 50 also using the SMC method, which placed the π * resonances at 2.23 eV and 8.39 eV, with the first resonance being double degenerate.…”

“…33 and were given elsewhere. 10,25 The d-type orbitals were considered as having five components to avoid linear dependency in the basis set.…”

“…11 Chlorobenzene (ClB) is a prototype for radiosensitizers and also a seemingly simple system with a peculiar spectrum of transient anion states. As in the closely related halopyrimidine molecules, 10 the halogen substituent gives rise to σ * resonances and tends to stabilize the π * anion states. 10,12 Similar trends are expected in ClB, but interesting features also arise from the halogen-induced symmetry breaking, i.e., the lifting of the degeneracy of the π * (E 2u ) anion state of benzene located at 1.14 eV.…”

“…As in the closely related halopyrimidine molecules, 10 the halogen substituent gives rise to σ * resonances and tends to stabilize the π * anion states. 10,12 Similar trends are expected in ClB, but interesting features also arise from the halogen-induced symmetry breaking, i.e., the lifting of the degeneracy of the π * (E 2u ) anion state of benzene located at 1.14 eV. 13 In fact, vibronic effects underlying the dynamics of the π * (B 1 ) and π * (A 2 ) resonances in ClB have been inferred from the available electron transmission spectroscopy (ETS), 14,15 22 reported total cross sections (TCSs) at very low collision energies (<1 eV) for halobenzenes, mainly driven by the dipole-allowed rotational excitations.…”

“…2 Since then, intense theoretical and experimental activity has focused on better understanding the interactions of LEEs with biomolecules and their precursors, [3][4][5] in particular the characterization of transient anion states (resonances) and their role in the dissociation processes. More recently, halogenated DNA and RNA bases, [6][7][8][9] as well their precursors, 10 have also gained attention. In this case, the motivation is the potential radiosensitizing activity of the halogenated species that can be incorporated into the gene sequence and give rise, through the dissociative electron attachment (DEA) mechanism described above, to radicals that subsequently damage the DNA.…”