Atomic selectivity in dissociative electron attachment to dihalobenzenes.

Area of Science:

• Physical Chemistry
• Chemical Physics
• Molecular Spectroscopy

Background:

• Dihalobenzene molecules are important in various chemical applications.
• Understanding electron attachment mechanisms is crucial for predicting chemical reactivity.
• Previous studies on electron attachment have not fully elucidated the role of halogen electronegativity in complex molecules.

Purpose of the Study:

• To investigate the mechanism of electron attachment to bromochlorobenzene (BCB), bromoiodobenzene (BIB), and chloroiodobenzene (CIB).
• To determine the preferred site of electron attack in these dihalobenzene molecules.
• To correlate experimental findings with theoretical calculations and molecular orbital theory.

Main Methods:

• Molecular beam photoelectron spectroscopy was employed to study electron attachment.
• Anion mass spectrometry was used to identify the products of electron attachment.
• Ab initio calculations were performed to analyze molecular orbital structures and energies.

Main Results:

• The primary product of electron attachment was the atomic anion of the less electronegative halogen (Br(-) for BCB, I(-) for BIB and CIB).
• Photoelectron spectra for iodine-containing species showed contributions from both molecular anions and atomic I(-) anions.
• Molecular orbital analysis indicated significant orbital energy reordering upon electron attachment.

Conclusions:

• Electron attachment to dihalobenzenes preferentially occurs at the less electronegative halogen atom.
• The observed fragmentation patterns and spectral features are well-explained by molecular orbital theory.
• Halogen electronegativity plays a key role in directing electron attachment and subsequent dissociation pathways.