ELECTRON-ATTACHMENT TO THE FLUOROMETHANES, BROMOMETHANES, AND IODOMETHANES STUDIED BY MEANS OF ELECTRON TRANSMISSION SPECTROSCOPY AND X-ALPHA CALCULATIONS

The electron transmission spectra of the fluoro-, bromo-, and iodomethanes (except CH2F2) and of some monohaloalkanes are reported. The resonance energies for electron attachment to the halomethanes have also been evaluated by means of bound and continuum multiple scattering X-alpha calculations, which closely reproduce the low-energy experimental data. A large electron affinity increase is observed on going from the fluorine to the heavier halogen derivatives, while within each series of halides the electron affinity increases with increasing number of halogen atoms. The ground anion state is found to be stable in CHBr3, CBr4, and in all the iodomethanes except CH3I. The fragment anion production, as a function of the electron impact energy, has been measured for some of the compounds under investigation, in order to obtain experimental information on anion states very close to zero energy or slightly stable, which are not accessible in electron transmission.