Properties of the π* and σ* states of the chlorobenzene anion determined by electron impact spectroscopy

Abstract

The selectivity of vibrational excitation by electron impact has been used to unambiguously assign the negative ion states (resonances) of chlorobenzene and to settle a recent controversy on this subject. The excitation functions of the ring deformation vibrations exhibit bands in the 0.8-1.4 eV range, identifying them as temporary electron captures in the b 1 and a 2 p* orbitals. A broad band peaking at 2.6 eV appears in the excitation functions of the C-Cl stretch vibration but is missing in the excitation functions of the ring deformation vibrations, proving that it corresponds to a temporary electron capture in the s à C Cl orbital. A more detailed insight into the properties of the potential surfaces of the anion is gained from the excitation functions of many vibrations, and from their comparison with anion potential curves based on the Koopmans theorem. Slopes of the potential curves in the Franck-Condon region reproduce well the observed intensities of totally symmetric vibrations. Strong excitation of out-of-plane vibrations, corroborated by the calculations, reveal vibronic coupling of the b 1 p* and the s* anion states. The a 2 p* state and the s* state are coupled by vibrations with a 2 symmetry. Excitation of in-plane non-totally symmetric vibrations (b 2 ) reveals vibronic coupling between the two p* states b 1 and a 2 , which is also reproduced by the calculated potential curves. The results indicate that symmetry lowering induced by vibronic coupling provides the path for dissociation of the p* states of the chlorobenzene anion.

Bond Breaking and Temporary Anion States in Uracil and Halouracils: Implications for the DNA Bases

“…2 for uracil, fall close to the VAEs of the resonances [9]. As observed previously in many studies of DEA in planar halocarbons [15], this process takes place through vibronic mixing of the states with repulsive valence anion states and will not be discussed here further.…”

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

“…However, our fixed-nuclei calculations cannot account for the vibrational structure present in both the electron transmission 15 and energy loss spectra. 20 In fact the lack of vibronic couplings in the ICS computations prevents the description of the feature around 1.15 eV in the ETS data. The resonance around 2.8 eV in the A 1 symmetry arises from electron attachment into the σ * CCl LUMO+2 orbital (see Figure 3) and is found in good agreement with the experimental data, as discussed above.…”

Dissociative electron attachment and electron energy-loss spectra of phenyl azide

“…This is because, although dissociation of the chlorobenzene anion is allowed through vibronic coupling and ensuing symmetry lowering, and proceeds without any activation barrier [38], the anion has to distort from the planar geometry in the initial stages of the dissociation and the slope of the potential hypersurface along the reaction coordinate is consequently initially smaller in the phenyl compound than in the benzyl compound.…”

“…Interesting parallels and differences can consequently be recognized by comparing the DEA of phenyl and benzyl azide with the corresponding halides, for example the chlorobenzene and benzyl chloride shown in figure 1. The following observations were made in the chloro compounds ( [9,26,36,38] and references therein).…”