Electron attachment by haloalkenes and halobenzenes

Abstract

Electron transmission spectra and mass spectra of negative ions from dissociative electron attachment have been obtained for four series of halogenated alkenes: vinyl halides, chloroethylenes, halobenzenes, para-dihalobenzenes. The stabilizing effect of halogen substituents upon anion state energies is obvious. Systematic observations permit assignment ofã nd n anion states. Dissociative attachment usually proceeds through the n anion state. An enormous enhancement of the cross section for dissociative attachment of threshold electrons is observed in some cases.

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

“…22, since (i) we account for short-range (other than dipole) interactions in the lower partial waves, which would be important for scattering at higher angles; (ii) our Born corrections employ an overestimated dipole moment magnitude (consistent with the HF description of the target molecule); (iii) our model amounts to an approximate rotationally summed cross section from the rotational ground state of the target, without accounting for thermal averages over the initial rotational states (see Oliveira et al 47 for details); and (iv) we do not correct the cross sections to account for undetected electrons at low scattering angles as described by Lunt et al, 22 although we integrate the Regarding the resonances, the lowest-lying structure in the SMCPP ICS, about 0.7 eV, is related to the nearly degenerate π * (B 1 ) and π * (A 2 ) resonances (see below). The peak position agrees with the experimental TCS 22,23 (0.75 and 0.8 eV, respectively), as well as with the ETS data 14,15 (0.73 eV-0.75 eV) and the DEA data 14,[16][17][18] (∼0.7 eV). There is also agreement for the second structure, arising from the σ * CCl anion state, since the peak at 2.8 eV in the SMCPP ICS is consistent with the experimental data (∼2.5 eV).…”

“…From our calculated ICSs, we could identify the shape resonances of ClB and compare the results with the available ETS data. 14,15 We also report experimental DCSs for impact energies ranging from 8 eV to 50 eV and angular range from 7.0 • to 110 • and compare the measurements with the present DCSs computed with the SMCPP and IAM-SCAR methods. Since, to our knowledge, DCSs have not been reported for electron-ClB collisions, it is desirable to compare the present data with DCSs for the parent molecule benzene.…”

“…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. Finally, Makochekanwa et al 23 also obtained TCSs for electron and positron collisions with ClB, for impact energies from 0.2 up to 1000 eV.…”

Dinâmica de íons temporários de biomoléculas halogenadas

“…Por outro lado, a formação doânion induz forte excitação vibracional, em especial do modo dominado pelo estira- mento C−Cl. A molécula de cloroeteno apresenta duas ressonâncias, uma π * e uma σ * [88,89]. Medidas do espectro de fragmentos gerados por colisão com elétrons aponta um pico na formação do fragmento Cl − exatamente na posição da ressonância π * , sugerindo a existência de um mecanismo indireto de dissociação [88,89].…”

“…As energias dos estados doânion são comparados com os valores experimentais existentes [83][84][85][86][88][89][90]. Também comparamos a seção de choque integral elástica do clorometano com dois trabalhos experimentais [91,92].…”