Temporary π* and σ* Anions and Dissociative Electron Attachment in Chlorobenzene and Related Molecules

Abstract

Coupled-cluster, Hartree-Fock, and B3LYP calculations are employed to study the gas-phase empty-level structures of chlorobenzene, benzyl chloride, and (2-chloroethyl)benzene. All three theoretical approaches reproduce accurately the energy trends of vertical electron attachment observed in the electron transmission spectra and predict the occurrence of the lowest σ* resonance about 2 eV higher in energy than the lowest π* resonance, in contrast with a recent suggestion by others. The relative cross sections for dissociative electron attachment are measured in the benzene derivatives and in saturated chlorohydrocarbons. The Clcurrents and a comparison of the energies of maximum production in the dissociative attachment spectra with the resonance energies located in the electron transmission spectra clearly indicate, that in the benzene derivatives, dissociation follows electron trapping into a ring π* empty orbital and subsequent intramolecular transfer to the chlorine atom, in line with the conclusions of an earlier work.

Dissociative electron attachment in nonplanar chlorocarbons with π∗/σ∗-coupled molecular orbitals

“…The VAEs of the C 6 H 5 -͑CH 2 ͒ n -Cl compounds have been determined using ETS for n = 1 ͑benzyl chloride͒ by Stricklett et al 16 and Distefano et al, 23 and for n=2-4 by Modelli and co-workers, 6,7 and in the present work. As in the chloroethenes, the ‫ء‬ resonances are very prominent, and there is some concern that the VAEs associated with the C-Cl ‫ء‬ resonances could be distorted by their proximity.…”

Temporary anion states and dissociative electron attachment to nitrobenzene derivatives

“…No signals around 1.8 eV, where the ET spectra show a distinct * C-Cl resonance, are detected in the DEA spectra of the chloro nitrobenzenes, as well as in that of chlorobenzene [26]. In the ET spectrum of the latter, the * C-Cl anion state is located at 2.44 eV, whereas the DEA spectrum displays a maximum in the Cl − current at 0.75 eV, i.e., very close in energy to the nearly degenerate 2 A 2 and 2 B 1 ( * 2 and * 3 ) anion states [26].…”

“…In the ET spectrum of the latter, the * C-Cl anion state is located at 2.44 eV, whereas the DEA spectrum displays a maximum in the Cl − current at 0.75 eV, i.e., very close in energy to the nearly degenerate 2 A 2 and 2 B 1 ( * 2 and * 3 ) anion states [26]. The Cl − maximum observed around 0.2 eV in the DEA spectra of the chloro nitrobenzenes is thus reasonably associated with the corresponding 2 A 2 ( * 2 ) anion states, too close to zero energy to be detected in the ET spectra.…”

Intersections of potential energy surfaces of short-lived states: The complex analogue of conical intersections

“…Similar processes have been found to occur in many other unsaturated organic compounds which have in common that a halogen atom is connected to one of the carbon atoms involved in the double bond. Examples are chlorobenzene, 24,47,48 mono-to tetrachloroethene, 48 -50 and chlorouracil. 25,26 DEA to the latter is discussed as an important contribution to radiation damage to DNA.…”

“…A description of the intersections of the resonance states in the chloroethene anion together with molecular dynamics calculations on the complex PES would be extendible to describe many other DEA processes in unsaturated halogenated compounds such as chloro-and bromobenzene 23,24 or the biologically relevant molecule chlorouracil. 25,26 In the next section we start with a short discussion of the general theory of vibronic coupling and of resonance states.…”