Session IW4: Electron and Photon Collisions

Chiral Sensitivity in Electron-Molecule Interactions

All molecular forms of life possess a chiral asymmetry, with amino acids and sugars found respectively in L- and D-enantiomers only. The primordial origin of this enantiomeric excess is unknown. One possible explanation is given by the Vester- Ulbricht hypothesis [1], which suggests that left-handed electrons present in beta-radiation, produced by parity-violating weak decays, interacted with biological precursors and preferentially destroyed one of the two enantiomers. Experimental tests of this idea have thus far yielded inconclusive results [2]. We show direct evidence for chirally-dependent bond breaking through a dissociative electron attachment (DEA) reaction when spin-polarized electrons are incident on gas-phase chiral molecules [3]. This provides unambiguous evidence for a well-defined, chirally-sensitive destructive molecular process and, as such, circumstantial evidence for the Vester-Ulbricht hypothesis. I will also present the results of our systematic study of the DEA asymmetry for different chiral halocamphor molecules. Three halocamphor molecules were investigated: 3-bromocamphor (C$_{10}$H$_{15}$BrO), 3-iodocamphor (C$_{10}$H$_{15}$IO), and 10-iodocamphor. The DEA asymmetries collected for bromocamphor and iodocamphor are qualitatively different, suggesting that the atomic number of the heaviest atom in the molecule plays a crucial role in the asymmetric interactions. The DEA asymmetry data for 3- and 10-iodocamphor have the same qualitative behavior, but the 10-iodocamphor asymmetry is about twice as large at the lowest energies investigated, so the location of the heavy atom in the camphor molecule also affects the asymmetries. This work was performed at the University of Nebraska-Lincoln. \\[4pt] [1] T.L.V. Ulbricht and F. Vester, Tetrahedron \textbf{18}, 629 (1962).\\[0pt] [2] See, e.g., W.A. Bonner, Chirality \textbf{12}, 114 (2000).\\[0pt] [3] J.M. Dreiling and T.J. Gay, Phys. Rev. Lett. \textbf{113}, 1181 (2014).   

Effects of polarization direction on laser-assisted free-free scattering

This work will detail the effects of laser polarization direction (relative to the momentum transfer direction) on laser-assisted free-free scattering. Experimental results will be presented for electron-helium scattering in the presence of an Nd:YAG laser field ($h\nu$ = 1.17 eV) where the polarization direction was varied both in, and out of, the scattering plane. To date, all of our experimental results are well described by the Kroll-Watson\footnote{N. M. Kroll and K. M. Watson, Phys. Rev. A 8, 804 (1973)} approximation (KWA). The good agreement between our experiments and calculations using the KWA includes the case where the polarization is perpendicular to the momentum transfer direction, for which the KWA predicts vanishing cross section; other workers have found that the KWA tends to be inaccurate for cases where it predicts small cross sections.\footnote{e.g., M. O. Musa, A. MacDonald, L. Tidswell, J. Holmes, and B. Wallbank, J. Phys. B, 43 (17):175201, 2010} We also present simulations of the effects that multiple scattering might have on experimental measurements.   

What can the measurement of the transverse velocity of atoms tell us about strong-field interactions with atoms?

In this paper we present a theoretical and experimental investigation of the ionization of atoms though the interaction of light in the strong-field regime. We show that the measurement of the transverse electron momentum distribution of ionised atoms as a function of the ellipticity of the ionizing light in the over-the-barrier and the tunnelling regime evolve in qualitatively different ways and in the case of the use of linearly polarized light demonstrates that the strong-field approximation is not valid.   

Stopping and Coulomb explosion of energetic carbon clusters in a plasma irradiated by an intense laser field

The interaction of a charged particle beam with a plasma is a very important subject of relevance for many fields of physics, such as inertial confinement fusion (ICF) driven by ion or electron beams, high energy density physics, and related astrophysical problems. Recently, a promising ICF scheme has been proposed, in which the plasma target is irradiated simultaneously by intense laser and ion beams. For molecular ion or cluster, slowing down process will company the Coulomb explosion phenomenon. In this paper, we present a study of the effects of intense radiation field (RF) on the interaction of energetic carbon clusters in a plasma. The emphasis is laid on the dynamic polarization and correlation effects of the constituent ions within the cluster in order to disclose the role of the vicinage effects on the Coulomb explosion and energy deposition of the clusters in plasma. On the other hand, affecting of a strong laser field on the cluster propagating in plasma is considered, the influence of a large range of laser parameters and plasma parameters on the Coulomb explosion and stopping power are discussed.