Circular dichroism of molecules in the continuous absorption region

Cherepkov, N. A.

doi:10.1016/0009-2614(82)83600-2

Cited by 153 publications

(97 citation statements)

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“…Conventional optical absorption measurements on submonolayer coverages of adsorbed molecules which exploit the circular dichroism (a difference in absorption for left-and rightcircularly polarized radiation) are unlikely to be fruitful. However, spatially oriented chiral molecules, such as those adsorbed on a surface, should show circular dichroism in the angular distribution (CDAD) of photoelectrons emitted from these species [7,8]. Indeed, such an effect has recently been observed [9] even for randomly oriented chiral molecules in the gas phase.…”

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confidence: 99%

Circular Dichroism in Core Level Photoemission from an Adsorbed Chiral Molecule

et al. 2004

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The results of experimental measurements and theoretical simulations of circular dichroism in the angular dependence (CDAD) of photoemission from atomic core levels of each of the enantiomers of a chiral molecule, alanine, adsorbed on Cu(110) are presented. Measurements in, and out of, substrate mirror planes distinguish CDAD due to the chirality of the sample and the experimental geometry. The effect due to sample chirality is relatively weak, so such measurements may not provide a routine spectral fingerprint of adsorbate chirality. DOI: 10.1103/PhysRevLett.92.236103 PACS numbers: 68.43.Fg, 33.55.Ad, 79.60.Dp There has been growing interest in the last few years in the properties of chiral molecules adsorbed on surfaces (e.g., [1][2][3][4][5][6]), motivated in part by the potential importance of producing molecular products of a single ''handedness'' (enantioselective) by heterogeneous catalysis. In such studies a simple spectroscopic measurement, which could establish if the surface species (which may be unknown reaction intermediates) are predominantly of a single chirality, would be of great value. Conventional optical absorption measurements on submonolayer coverages of adsorbed molecules which exploit the circular dichroism (a difference in absorption for left-and rightcircularly polarized radiation) are unlikely to be fruitful. However, spatially oriented chiral molecules, such as those adsorbed on a surface, should show circular dichroism in the angular distribution (CDAD) of photoelectrons emitted from these species [7,8]. Indeed, such an effect has recently been observed [9] even for randomly oriented chiral molecules in the gas phase. Here we present the results of experiments, and model calculations, which evaluate this idea using core level photoemission from one model system, alanine on Cu(110); our results confirm the existence of the effect but show it is weak relative to other sources of CDAD unrelated to the surface chirality, casting doubt on the likely utility of this phenomenon to provide a routine spectral fingerprint.We chose core level photoemission for these CDAD studies because the elemental and chemical-state specificity offered by photoelectron binding energies allows one to localize the information on chirality to specific adsorbed species on a surface; this is not true for photoemission from the valence states in which contributions from substrate and coexistent adsorbed species generally overlap. An important aspect of CDAD, however, is that even nonchiral surfaces give rise to a significant signal if the geometry of the experiment is chiral [10]. If the plane defined by the incident (circularly polarized) light and the photoelectron collection direction does not correspond to a mirror symmetry plane of the sample, the experiments conducted with opposite circular polarizations will not be equivalent and so a circular dichroism signal will be observed. This CDAD effect (up to 50% or more) from core levels of atoms in nonchiral surfaces is well established from substrate atoms [...

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confidence: 99%

Circular Dichroism in Core Level Photoemission from an Adsorbed Chiral Molecule

et al. 2004

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“…This is expected since for magnetic circular dichroism, spin orbit (SO) coupling is necessary, but here such coupling is neglected in va- lence and continuum states. Circular dichroism in the angular distribution (CDAD) [53][54][55][56][57][58][59][60] effects are also absent, as the geometrical set up is not chiral. The RPES signal, however, shows a large dichroism, which is maximum for the strongest enhancement of the signal and of opposite sign for the two spin channels.…”

Section: Resultsmentioning

confidence: 99%

Real-space Green's function approach to angle-resolved resonant photoemission: Spin polarization and circular dichroism in itinerant magnets

Pieve

Krüger

2013

Phys. Rev. B

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A first principles approach, based on the real space multiple scattering Green's function method, is presented for spin-and angle-resolved resonant photoemission from magnetic surfaces. It is applied to the Fe(010) valence band photoemission excited with circularly polarized X-rays around the Fe L3 absorption edge. When the photon energy is swept through the Fe 2p − 3d resonance, the valence band spectra are strongly modified in terms of absolute and relative peak intensities, degree of spin-polarization and light polarization dependence. New peaks in the spin-polarized spectra are identified as spin-flip transitions induced by exchange decay of spin-mixed core-holes. By comparison with single atom and band structure data, it is shown that both intra-atomic and multiple scattering effects strongly influence the spectra. We show how the different features linked to states of different orbital symmetry in the d band are differently enhanced by the resonant effect. The appearance and origin of circular dichroism and spin polarization are analyzed for different geometries of light incidence and electron emission direction, providing guidelines for future experiments.PACS numbers: 78.20. Bh, 78.20.Ls, In the last decade, magnetic circular dichroism (MCD) and spin polarization studies in resonant inelastic X-ray scattering (RIXS) and resonant photoemission (RPES) have acquired great importance in the study of magnetic and correlated materials. Such spectroscopies probe respectively the radiative and non radiative autoionization decay of a core hole, and the signal can be strongly enhanced with respect to the non resonant mode. The element and orbital selectivity of core level resonant spectroscopies allows to access higher order multipoles which are left unexplored by MCD in X-ray absorption (XAS) [1][2][3][4][5][6], to distinguish and enhance specific electronic excitations and satellites [7,8], collective magnetic excitations [9], ultrafast and charge transfer dynamics [10][11][12] and to detect quadrupolar transitions towards localized empty states [13,14]. In particular, RPES has recently been applied to several correlated materials [15][16][17][18][19] and full two dimensional angular scans of resonantly emitted electrons in moderately correlated materials have also been carried out [20,21]. These works, together with earlier pioneering studies [22,23] on local magnetic properties in macroscopically non magnetic systems, demonstrate the importance of RPES and the need for an advancement in the theoretical description of this spectroscopy, which is the main aim of this work.RPES is in principle an autoionization channel of the * Electronic address: fabiana.dapieve@gmail.com more general process called resonant Auger decay. Depending on whether the core-excited electron participates or not in the Auger decay, the process is termed either participator or spectator channel. In the participator channel the one hole final state is degenerate with the one in direct valence band photoemission (PES, or ARPES if angle reso...

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“…Accordingly, CDAD is driven by the function F 11 and takes values in the interval [−1,+1]. In most experiments performed so far on homonuclear diatomic molecules [18,[22][23][24], CDAD exhibits an antisymmetric behavior with respect to the polar electron emission angle θ e in the plane perpendicular to the light propagation.…”

Section: Circular Dichroism For Photoemission In the Molecular Framementioning

confidence: 99%

“…1 photoelectrons from nonchiral oriented molecules was first investigated theoretically by Ritchie [10], who pointed out that such particular effects may appear due to interferences between the dipolar and higher-order terms in the multipole expansion of the radiation field. Cherepkov [11] predicted the existence of circular dichroism in the angular distributions of photoelectrons from oriented chiral molecules within the dipole approximation but assuming spin-orbit interaction. In a more detailed analysis [12,13], it was demonstrated that CDAD can also exist in oriented linear molecules even within the electric dipole approximation.…”

Section: Introductionmentioning

confidence: 99%

Circular dichroism in molecular-frame photoelectron angular distributions in the dissociative photoionization ofH2andD2molecules

et al. 2014

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The presence of net circular dichroism in the photoionization of nonchiral homonuclear molecules has been put in evidence recently through the measurement of molecular-frame photoelectron angular distributions in dissociative photoionization of H 2 [Dowek et al., Phys. Rev. Lett. 104, 233003 (2010)]. In this work we present a detailed study of circular dichroism in the photoelectron angular distributions of H 2 and D 2 molecules, oriented perpendicularly to the propagation vector of the circularly polarized light, at different photon energies (20, 27, and 32.5 eV). Circular dichroism in the angular distributions at 20 and to a large extent 27 eV exhibits the usual pattern in which inversion symmetry is preserved. In contrast, at 32.5 eV, the inversion symmetry breaks down, which eventually leads to total circular dichroism after integration over the polar emission angle. Time-dependent ab initio calculations support and explain the observed results for H 2 in terms of quantum interferences between direct photoionization and delayed autoionization from the Q 1 and Q 2 doubly excited states into ionic states (1sσ g and 2pσ u ) of different inversion symmetry. Nevertheless, for D 2 at 32.5 eV, there is a particular case where theory and experiment disagree in the magnitude of the symmetry breaking: when D + ions are produced with an energy of around 5 eV. This reflects the subleties associated to such simple molecules when exposed to this fine scrutiny.

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Circular dichroism of molecules in the continuous absorption region

Cited by 153 publications

References 9 publications

Circular Dichroism in Core Level Photoemission from an Adsorbed Chiral Molecule

Circular Dichroism in Core Level Photoemission from an Adsorbed Chiral Molecule

Real-space Green's function approach to angle-resolved resonant photoemission: Spin polarization and circular dichroism in itinerant magnets

Circular dichroism in molecular-frame photoelectron angular distributions in the dissociative photoionization ofH2andD2molecules

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