Circularly Polarized Synchrotron Radiation Research Articles

The Use of Circularly Polarized Synchrotron Radiation in Diffraction and Spectral Studies of Noncentrosymmetric Crystals

The Use of Circularly Polarized Synchrotron Radiation in Diffraction and Spectral Studies of Noncentrosymmetric Crystals

Intense Vibronic Modulation of the Chiral Photoelectron Angular Distribution Generated by Photoionization of Limonene Enantiomers with Circularly Polarized Synchrotron Radiation.

Photoionization of the chiral monoterpene limonene has been investigated using polarized synchrotron radiation between the adiabatic ionization threshold, 8.505 and 23.5 eV. A rich vibrational structure is seen in the threshold photoelectron spectrum and is interpreted using a variety of computational methods. The corresponding photoelectron circular dichroism-measured in the photoelectron angular distribution as a forward-backward asymmetry with respect to the photon direction-was found to be strongly dependent on the vibronic structure appearing in the photoelectron spectra, with the observed asymmetry even switching direction in between the major vibrational peaks. This effect can be ultimately attributed to the sensitivity of this dichroism to small phase shifts between adjacent partial waves of the outgoing photoelectron. These observations have implications for potential applications of this chiroptical technique, where the enantioselective analysis of monoterpene components is of particular interest.

Surface spin-polarized currents generated in topological insulators by circularly polarized synchrotron radiation and their photoelectron spectroscopy indication

A new method for generating spin-polarized currents in topological insulators has been proposed and investigated. The method is associated with the spin-dependent asymmetry of the generation of holes at the Fermi level for branches of topological surface states with the opposite spin orientation under the circularly polarized synchrotron radiation. The result of the generation of holes is the formation of compensating spin-polarized currents, the value of which is determined by the concentration of the generated holes and depends on the specific features of the electronic and spin structures of the system. The indicator of the formed spin-polarized current can be a shift of the Fermi edge in the photoelectron spectra upon photoexcitation by synchrotron radiation with the opposite circular polarization. The topological insulators with different stoichiometric compositions (Bi1.5Sb0.5Te1.8Se1.2 and PbBi2Se2Te2) have been investigated. It has been found that there is a correlation in the shifts and generated spin-polarized currents with the specific features of the electronic spin structure. Investigations of the graphene/Pt(111) system have demonstrated the possibility of using this method for other systems with a spin-polarized electronic structure.

Heptanuclear [FeIII6CrIII]3+ Complexes Experimentally Studied by Means of Magnetometry, X-ray Diffraction, XAS, XMCD and Spin-Polarized Electron Spectroscopy in Cross-Comparison with [MnIII6CrIII]3+ Single-Molecule Magnets

Subsequent to the similar [MnIII6CrIII]3+ single-molecule magnets (SMM), the recently studied [FeIII6CrIII]3+ structural type adsorbed thin films prepared on Si and gold-coated glass substrates have been experimentally studied by means of spin-polarized electron spectroscopy (SPES) and X-ray magnetic circular dichroism (XMCD) at the Fe L3,2 edge using circularly-polarized synchrotron radiation. The results are cross-compared to the corresponding data obtained from the recently published measurements with Mn-based SMM [1], also in terms of the local spin and orbital magnetic moments obtained. Furthermore, [FeIII6CrIII]3+ single crystals have been experimentally studied by means of magnetometry and X-ray diffraction.

円偏光光電子顕微鏡による磁性体解析

円偏光光電子顕微鏡による磁性体解析

Photoreaction of rac‐Leucine in Ice by Circularly Polarized Synchrotron Radiation: Temperature‐Induced Mechanism Switching from Norrish Type II to Deamination

The delivery of extraterrestrial organics to primitive Earth is considered to have triggered the origin and subsequent evolution of life. Indeed, enantiomerically enriched amino acids of nonterrestrial origin have been found in carbonaceous meteorites, and enantioselective photodecomposition by circularly polarized light (CPL) in outer space has been proposed to have played some role in the initial enantiomeric bias. To experimentally examine this possibility and elucidate the photoreaction mechanisms, we have studied the photolysis of racemic leucine (rac-Leu) in acidic and neutral ice/water media at 21-298 K with left- and right-CPL in an attempt to detect enantiomerically enriched D- and L-Leu, respectively. Comprehensive product analyses revealed that the CPL-induced deracemization of Leu proceeds in both acidic and neutral ice matrices even at 21 K, and that the main mechanism switches from Norrish-type II γ-hydrogen abstraction to SN i deamination on lowering the temperature. The potential role of the CPL-induced photodecomposition of amino acids as a source of the enantiomer imbalance in meteorites is discussed.

Photolysis of rac‐Leucine with Circularly Polarized Synchrotron Radiation

Amino acids that pass the RNA machinery in living organisms occur in L-configuration. The question on the evolutionary origin of this biomolecular asymmetry remains unanswered to this day. Amino acids were detected in artificially produced interstellar ices, and L-enantiomer-enriched amino acids were identified in CM-type meteorites. This hints at a possible interstellar/circumstellar origin of the amino acids themselves as well as their stereochemical asymmetry. Based upon the current knowledge about the occurrence of circularly-polarized electromagnetic radiation in interstellar environments, we subjected rac-leucine to far-UV circularly-polarized synchrotron radiation. Asymmetric photolysis was followed by an analysis in an enantioselective GC/MS system. Here, we report on an advanced photolysis rate of more than 99% for leucine. The results indicate that high photolysis rates can occur under the chosen conditions, favoring enantioselective photolysis. In 2014, the obtained results will be reexamined by cometary mission Rosetta.

Asymmetric Vacuum UV photolysis of the Amino Acid Leucine in the Solid State

One hand clapping: Based on solid-state circular dichroism data, the leucine (π*, π1)-electronic transition is excited with right circularly polarized synchrotron radiation (r-CPSR) at 182 nm (see scheme). This treatment induced an enantiomeric excess of 2.6 % of D-leucine. The results support the assumption that interstellar asymmetric photoreactions are capable of inducing significant enantiomeric enrichments in solid-state amino acids.

Evolution of the Angular Distribution of Circularly Polarized Synchrotron Radiation with Charge Energy

A complete investigation of the evolution of the angular distribution of circularly polarized synchrotron radiation with particle energy has been performed within the framework of the classical theory. To describe the familiar qualitative features of synchrotron radiation, exact quantitative characteristics have been introduced.

Absolute asymmetric photoreactions of aliphatic amino acids by circularly polarized synchrotron radiation: critically pH-dependent photobehavior.

The absolute asymmetric photoreaction (AAP) of racemic aliphatic amino acids, such as alanine (Ala) and leucine (Leu), by left- and right-handed circularly polarized light (l- and r-CPL) irradiation was investigated in aqueous solutions at various pHs, by using the Onuki-type polarizing undulator installed in an electron storage ring. The magnitude of the optical purity (op) generated and the enantiomer-enriching mechanism operative in the AAP were found to be entirely dependent on the ionic state (and thus pH) of the amino/carboxylic acid moieties. At pH 1, the op of Ala and Leu determined by circular dichroism (CD) spectral measurement gradually developed with CPL irradiation, according to Kagan's equation. In contrast, irradiation at pH 7 gave op's much smaller than the theoretical values predicted by Kagan's equation. However, it turned out that the photodecomposition at pH 7 produces the corresponding alpha-hydroxycarboxylic acids stereoselectively, the CD sign of which is just opposite to that of the remaining amino acid, thus affording the apparently small op. It is concluded that, irrespective of solution pH, the AAP of amino acid proceeds upon CPL irradiation. At pH 1, the photodecomposition of valine, Leu, and isoleucine occurs via a Norrish type II mechanism, which is also applicable to other amino acids possessing a gamma-hydrogen. In the case of amino acids lacking a gamma-hydrogen, such as glycine and Ala, the photodecomposition mechanism is a photodeamination/hydroxylation and a Norrish type I reaction. At pH 7, the main photoproducts were ammonia and alpha-hydroxycarboxylic acids that were produced via photodeamination.

ChemInform Abstract: First Absolute Asymmetric Synthesis with Circularly Polarized Synchrotron Radiation in the Vacuum Ultraviolet Region: Direct Photoderacemization of (E)‐Cyclooctene.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Magnetic Circular Dichroism in X-Ray Fluorescence

ABSTRACTX-ray fluorescence spectra from magnetized iron excited by circularly polarized synchrotron radiation are reported. The Fe L2.3 emission band gives rise to a distinct dichroic signal in confirmation of a recent theoretical prediction. These preliminary experiments carried out with “white” and only partially circularly-polarized synchrotron radiation nevertheless reveal an asymmetry which reflects the spin polarization of the Fe 3d valence electrons. The usefulness of developing specialized high flux circularly-polarized sources is clearly established.

Design and construction of beamline-NE1 for circularly polarized synchrotron radiation from the 6-GeV TRISTAN Accumulation Ring

The beamline for the circularly polarized synchrotron radiation at the 6-GeV Accumulation Ring for the TRISTAN project is now under construction. The insertion device of this beamline was designed to produce circularly polarized x rays at the photon energy range of 200 eV∼100 keV. The beamline is divided into the following three branches: (1) High resolution Compton scattering and magnetic Compton scattering experiments; (2) multipurpose experiments such as magnetic x-ray scattering and magnetic x-ray absorption; and (3) completely circularly polarized soft x rays.

Angle-, Energy- and Spin-Resolved Photoelectron Emission Using Circularly Polarized Synchrotron Radiation

With the development of BESSY a light source of circularly polarized vuv radiation with sufficiently high intensity has become available to make angle- and energy-resolved photoelectron spin-polarization studies with circularly polarized radiation feasible. This paper reviews the recent experimental activities performed with free atoms, physisorbed adsorbates and solid surfaces (metals as well insulator) in the past three years. The spin-polarization of photoelectrons measured under certain conditions to be almost complete studies atomic effects as auto-ionization resonances in the gas phase as well as even in the photo-emission of adsorbates. The cross comparison of photoemission data from Xe in its different structural phases (free atom, adsorbate in different structures and on different substrates, three dimensional crystal) yields symmetry characterizations of the electronic states (assignment of quantum numbers, determination of dipole matrix elements and phase shifts; spin resolved band mapping) and shows the ability of spin-polarization spectroscopy to build a bridge between atomic and surface physics.

Characterization of Symmetry Properties of Pt(111) Electron Bands by Means of Angle-, Energy-, and Spin-Resolved Photoemission with Circularly Polarized Synchrotron Radiation

An angle-, energy-, and spin-resolved photoemission experiment has been performed for Pt(111) with the circularly polarized synchrotron radiation of the new German dedicated storage ring BESSY. The photoelectron polarization measured as function of the kinetic energy at different photon energies between 6.5 and 24 eV for normal incidence and normal emission shows a pronounced spectral variation up to \ifmmode\pm\else\textpm\fi{}55%. The electron intensities and polarizations observed allow a symmetry-resolved band characterization of Pt in the $\ensuremath{\Gamma}\ensuremath{-}L$ direction.

Angular Dependence of the Spin-Polarization Transfer from Circularly Polarized Synchrotron Radiation onto Photoelectrons from Atomic Xe5p6

The photoelectron emission from atomic xenon has been simultaneously resolved with respect to photon energy, photon (circular) polarization, photoelectron emission angle, electron kinetic energy, and spin-polarization components by use of synchrotron radiation of wavelengths between 48 and 90 nm from the new dedicated electron storage ring BESSY. The angular dependence of the spin polarization and the energy dependence of the dynamical spin parameters experimentally obtained show good agreement with theoretical predictions.

Circularly Polarized Synchrotron Radiation in Dipolar Magnetic Fields with Application to the Planet Jupiter

This paper is a preliminary account of the calculation of the circularly polarized synchrotron radiation received from a distribution of electricallycharged particles confined to a thin shell in the magnetic field of a dipole. Calculations of the total radiation and the degree of linear polarization have previously been carried out, and these calculations are duplicated in part.