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Temporary negative ion states and dissociative attachment in dichloroalkanes
Abstract
Absolute total Dissociative Attachment (DA) cross sections and Vertical Attachment Energies (VAE) for electron-dichloroalkane molecule scattering have been measured. The family of dichloroalkanes included in this study are the normal dichloroalkanes with the chlorine atoms at the two ends of the chain, CnH2nCl2 for n = 1–6, 8 and 9, three geminal dichloro compounds, 1,1-dichloroethane, 1,1-dichloropropane and 2,2-dichloropropane, three vicinal dichloro compounds, 1,2-dichloropropane, 1,2-dichloro-2-methylpropane and 2,3-dichlorobutane, and one cyclic compound, trans.1,2-dichlorocyclohexane and the compound 1,3-dichlorobutane. In the apparatus for DA cross section measurement, a long interaction region (10 cm) facilitates total collection of negative ions. Because of the small energy separation of the two anion states associated with the temporary occupation of the C-Cl σ* orbital, a single peak in the DA cross sections at electron energies between 0.30 to 1.25 eV for all of these compounds is observed. In several compounds with large C-Cl σ* orbitals interaction, however, it was possible to detect the upper anion state from a semilog plot of the negative ion yield versus electron energy. In general, the relative magnitude of the DA cross sections follows the ordering geminal > vicinal > normal dichloroalkanes, excluding dichloromethane. VAEs were measured using Electron Transmission Spectroscopy (ETS) in a separate apparatus. In each apparatus, the low energy electron beam is produced using a trochoidal electron monochromator. Our ETS studies show a single resonance for normal dichloroalkanes owing to near degeneracy of the anion states. The geminals show two distinct resonances while the anion states of the vicinals are again heavily overlapped. Including similar data for monochloroalkanes, the peak DA cross sections decline exponentially with increasing VAE with the exception of dichloromethane. This correlation spans five orders of magnitude in the peak cross section . We also examined the effect of methyl substitution on temporary anion energies. We find by plotting VAE stabilization upon methyl substitution versus VAE, that a “balance” point VAE of 1.4 eV exists. A resonance originally above or below this energy, is stabilized or destabilized, respectively, upon methyl substitution.
Subject Area
Molecular physics|Atomic physics
Recommended Citation
Aflatooni, Kayvan, "Temporary negative ion states and dissociative attachment in dichloroalkanes" (1998). ETD collection for University of Nebraska-Lincoln. AAI9917816.
https://digitalcommons.unl.edu/dissertations/AAI9917816