Fluorescence polarization of helium negative-ion resonances excited by polarized electron impact

We have investigated helium (1s3d) 3D → (1s2p) 3P (588 nm) fluorescence produced by electron impact excitation in the vicinity of the (2s22p) 2P and (2s2p2) 2D negative-ion resonances at 57.2 and 58.3 eV, respectively. In contrast to previous work, we use spin-polarized incident electrons and report the relative Stokes parameters P1, P2, and P3 in the 55–60 eV region. Our failure to see discernable resonance effects in P2 indicates that even though the lifetime of these resonances is significant (~10 fs), magnetic forces acting on the temporarily captured electron are small. Resonant structures in the values of P1 and P3 are observed because the polarization contributions of resonant states are generally different than those from direct excitation of the 3 3D state

Chirally Sensitive Electron-Induced Molecular Breakup and the Vester-Ulbricht Hypothesis

We have studied dissociative electron attachment in sub-eV collisions between longitudinally polarized electrons and chiral bromocamphor molecules. For a given target enantiomer, the dissociative Br anion production depends on the helicity of the incident electrons, with an asymmetry that depends on the electron energy and is of order 3 × 10−4. The existence of chiral sensitivity in a well-defined molecular breakup reaction demonstrates the viability of the Vester-Ulbrict hypothesis, namely, that the longitudinal polarization of cosmic beta radiation was responsible for the origins of biological homochirality

Chirally-sensitive electron-molecule interactions

All molecular forms of life have chemically-specific handedness. However, the origin of these asymmetries is not understood. A possible explanation was suggested by Vester and Ulbricht immediately following the discovery of parity violation in 1957: chiral beta radiation in cosmic rays may have preferentially destroyed one enantiomeric form of various biological precursors. In the experiments reported here, we observed chiral specificity in two electronmolecule interactions: quasi-elastic scattering and dissociative electron attachment. Using lowenergy longitudinally spin-polarized (chiral) electrons as substitutes for beta rays, we found that chiral bromocamphor molecules exhibited both a transmission and dissociative electron attachment rate that depended on their handedness for a given direction of incident electron spin. Consequently, these results, especially those with dissociative electron attachment, connect the universal chiral asymmetry of the weak force with a molecular breakup process, thereby demonstrating the viability of the Vester-Ulbricht hypothesis

Measurement of the Integrated Stokes Parameters of Zn 468 nm Fluorescence Excited by Polarized-Electron Impact

The integrated Stokes parameters P1, P2, and P3 of Zn (43P0,1 – 53S1) fluorescence resulting from transversely-spin-polarized electron impact excitation of the Zn (4s5s)53S1 state have been measured. This work was motivated by similar studies reported several years ago, in which non-zero values of the integrated Stokes parameter P2 between the threshold for the (4s5s)53S1 excitation and the first cascading (4s5p)53PJ threshold were measured. We observe optical excitation functions in agreement with previous experimental and theoretical results, but find integrated P2 Stokes parameter values which are consistent with zero and inconsistent with those measured previously

TWO-CENTER EFFECTS IN ION-ATOM COLLISIONS: A Symposium in Honor of M. Eugene Rudd, Lincoln, NE May 1994 — Contents and Preface

Following a distinguished career in atomic physics, sketched in the accompanying biography, M. Eugene Rudd retired From the faculty of the University of Nebraska in the spring of 1993. In order to celebrate his many research accomplishments, a two day scientific conference, held on 13-14 May 1994, was organized in Lincoln. It was felt that the special spirit that Rudd brought to the lab would be highlighted by a conference designed to analyze in detail a subject of current research in which he was a pioneer: two center-effects in ion-atom ionizing collisions. Prior to 1980, primarily as a result of the experiments of Rudd and his co-workers, a standard view of ionizing collisions had developed. This view held that almost all the ionized electrons could be associated with either the ionized target or the receding projectile. The former, having mostly small momenta, were produced in soft collisions with the projectile, and emerged almost isotropically from the collision region. The remaining electrons had velocities similar to that of the projectile, and formed a cusp distribution about its velocity vector in the forward direction. Beginning in the mid-1980\u27s however, it became increasingly clear that electronic trajectories that were manifestly determined by a combination of the action of the two Coulomb centers, both target and projectile acting together, might be observed. The topic of this meeting was to consider such effects in detail. The speakers were chosen because of their expertise in this area, and included a number of Professor Rudd\u27s students and immediate colleagues. Eugen Merzbacher delivered the banquet address on The Crisis at the Physical Review. In addition to the four scientific sessions for invited speakers, a poster session was held with 17 contributions. We intend that this Festschrift will serve as a useful summary of the current status of this field, and as a goad starting point for researchers interested in studying this topic. We hope that it will also give the scientific community at large an indication of the influence of M. E. Rudd\u27s career, and of the high esteem in which his colleagues hold both it and him

Dynamics of Antimatter-Atom Collisions

Classical-trajectory Monte Carlo calculations have been used to study ionizing collisions between charged particles (p, p̅ , ℯ+, ℯ-) and He atoms at an incident velocity of 2.83 a.u. While differences in the total single-ionization cross sections for these projectiles are small, our calculations reveal large effects at all angles in the ionized electron spectra, and provide qualitative evidence for a Barkas effect in p and p̅ collisions. Experimental data agree well with our fully classical calculations, including cross sections involving ejected electrons of long wavelength

Dynamics of Antimatter-Atom Collisions

Classical-trajectory Monte Carlo calculations have been used to study ionizing collisions between charged particles (p, p̅ , ℯ+, ℯ-) and He atoms at an incident velocity of 2.83 a.u. While differences in the total single-ionization cross sections for these projectiles are small, our calculations reveal large effects at all angles in the ionized electron spectra, and provide qualitative evidence for a Barkas effect in p and p̅ collisions. Experimental data agree well with our fully classical calculations, including cross sections involving ejected electrons of long wavelength

An inline optical electron polarimeter

The design and operation of a simple inline optical electron polarimeter is presented. It is based on exchange excitation of ground state neon atoms. The electron polarization is determined from the degree of circular polarization of the subsequent 2p53p 3D3→2p53s 3P2 (6402 Å) fluorescence. This device can characterize both longitudinally and transversely polarized electron beams in a nondestructive fashion, and is inexpensive and easily constructed

Production of a high-density state-selected metastable neon beam

We have developed a high-density source of metastable neon and have selectively quenched both metastable species using a standing-wave dye laser. The source is compact, stable, and produces an average intensity of 3.6 x 1014 sr -1 s -1 and a density on target of 7.7 x 106 cm-3

Transverse measurements of polarization in optically pumped Rb vapor cells

We have developed a simple heuristic method for determining the polarization of an optically pumped alkalimetal vapor. A linearly polarized probe beam traverses a vapor cell perpendicular to the pump-beam propagation direction, and the transmitted beam intensity is monitored for orthogonal linear polarizations. As the probe beam is scanned in frequency across the D1 transition, its linear-polarization-dependent transmission can be used as a measure of the atomic orientation of the vapor. We analyze these transmission differences and their dependence on the alkali-metal number density in the vapor