Ultrahigh-resolution Spectroscopy Research Articles

Ultrahigh resolution mass spectrometry

The integration of soft ionization technologies and ultrahigh resolution FTICR mass spectrometry (Fourier transform ion-cyclotron MS) has enabled the examination of molecules, directly from mixtures, with ultrahigh mass resolution and sub-ppm mass accuracy. This ability to observe structure and reactivity aspects of intact (macro)molecules has, in particular, contributed to the molecular-level characterization of complex matrices, for example novel materials and biological and biogeochemical samples. Here, thousands of molecular formulae can be determined in a single measurement directly from mixtures. The exceptional performance of ultrahigh-resolution FTICR mass spectroscopy in the characterization of complex systems suffers much less from the detrimental effects of intrinsic averaging, which is a characteristic of most other methods of organic structural spectroscopy. This novel information-rich and direct perception has the potential to entirely change the way we address the molecular-level analysis of complex materials, systems, and processes in general, thereby opening novel perspectives in data-driven systems biology and “omics” approaches. The inauguration of Europe’s first 12 Tesla FTICR mass spectrometer at the GSF National Research Center for Environment and Health provided the opportunity to hear expert views on novel research dedicated to the molecular-level characterization of complex systems. A dozen presentations organized in four sessions were delivered during the “First International Symposium on Ultrahigh-Resolution Mass Spectrometry for the Molecular Level Analysis of Complex (BioGeo)Systems”, held at the GSF on November 6 and 7, 2006 (www.gsf.de/FTMS2006). In session one, General Foundations of FTICR Mass Spectrometry, Alan G. Marshall (National High Magnetic Field Laboratory, Tallahassee, USA) provided a wide-ranging overview about the currently available opportunities of FTMS in molecular-resolution analysis: High-field Fourier transform ion cyclotron resonance mass spectrometry: a platform for “omics”. Then, Eugene N. Nikolaev (Institute of Biochemical Physics, Moscow, Russian Federation) investigated the complex trajectories of ions in FTMS cells: The new possibilities in ion clouds dynamic simulation using supercomputers. Application to FTICR and quadrupole devices. Arnd Ingendoh (Bruker Daltonics, Bremen, Germany) provided an overview about current and foreseeable trends in modern mass spectrometry: Mass spectrometry and beyond—new areas of applications. Session two, From Biological Chemistry to Chemical Biology, focused on life sciences applications. Jeremy K. Nicholson (Division of Surgery, Oncology, Reproductive Biology and Anaesthetics, Imperial College, London, UK) produced a comprehensive assessment about integrated views in “omics” sciences (Metabonomics and top-down systems biology: from personalized healthcare to molecular epidemiology) and Hannelore Daniel (Technical University Munich, Weihenstephan, Germany) complemented this interesting and versatile perspective with The bottom-up approach: from individual genes to the systems biology level of nutrition. Michael Sattler (European Molecular Biology Laboratory, Heidelberg, Germany and GSF Research Center for Environment and Health) illustrated the power of modern NMR methods capable of producing well resolved three-dimensional structures of large biomolecules including description of dynamics and reactivity: NMR to study molecular recognition and dynamics of biomacromolecules. Session three, Novel MS Approaches in Biochemistry and Medicine, illustrated novel MS approaches by Gary Siuzdak (Scripps Center for Mass Spectrometry, La Jolla, USA): Novel mass-based approaches to proteomics and metabolomics and advanced carbohydrate analysis by Jasna Peter-Katalinic (Institute fur Medical Physics and Biophysics, Munster, Germany): Requirements on FTICR mass spectrometry for glycomics in structural biology and medicine. Session four, Repetitive and Non-Repetitive Complex Systems, focused on proteome and complex biogeochemical mixture analysis. Michael Przybylski (Department of Chemistry, University of Konstanz, Germany) elucidated aspects of advanced protein analysis High resolution FTICR mass spectrometry and affinity-proteomics: powerful tool for elucidation of antigen-antibody recognition structures and vaccine development in molecular immunology and complex biogeochemical materials and William T. Cooper (Department of Chemistry and Biochemistry, FSU, Tallahassee, USA) provided insights into the structure, synthesis and degradation of natural organic matter: Insights into organic chemistry of the natural environment; FTICR mass spectrometry of really complex mixtures. Norbert Hertkorn (GSF Institute of Ecological Chemistry, Neuherberg, Germany) described the specific utility and complementarity of NMR and mass spectrometry in the analysis of complex biogeochemical systems: Mapping the molecular compositional space with mass spectrometry, and Philippe Schmitt-Kopplin (GSF Institute of Ecological Chemistry, Neuherberg, Germany) provided a comprehensive assessment of biogeochemical analysis with a variety of current examples: Molecular-level analysis of non-repetitive structures in biogeosystems. To recognize the importance of the technique and provide the reader of the journal Analytical and Bioanalytical Chemistry with a perspective of the current trends in FTICR mass spectrometry, this special issue on “Ultrahigh Resolution Mass Spectrometry” was prepared to include research, perspective, and review articles from experts in the field. This special issue reflects the wide scope of current FTICR mass spectrometry utilization in the analytical characterization of natural products, biomolecules and biogeochemical mixtures, hyphenation of separation and mass spectrometry, and integration of spectroscopy and separation in the molecular-level characterization of complex systems. At this point, we would like to thank all the authors for their high-quality articles, all referees for the rapid evaluations.

Xenon-plasma-light low-energy ultrahigh-resolution photoemission study ofCo(S1−xSex)2(x=0.075)

We have performed low-energy ultrahigh-resolution photoemission spectroscopy on $\mathrm{Co}{({\mathrm{S}}_{1\ensuremath{-}x}{\mathrm{Se}}_{x})}_{2}$ $(x=0.075)$ to elucidate the bulk electronic states responsible for the ferromagnetic transition. By using a newly developed plasma-driven low-energy xenon (Xe) discharge lamp $(h\ensuremath{\nu}=8.436\phantom{\rule{0.3em}{0ex}}\mathrm{eV})$, we clearly observed a sharp quasiparticle peak at the Fermi level together with the remarkable temperature dependence of the electron density of states across the transition temperature. Comparison with the experimental result by the $\mathrm{He}I\ensuremath{\alpha}$ resonance line $(h\ensuremath{\nu}=21.218\phantom{\rule{0.3em}{0ex}}\mathrm{eV})$ indicates that the sharp quasiparticle is of bulk origin and is produced by the Fermi-level crossing of the Co $3d$ ${e}_{g\ensuremath{\downarrow}}$ subband.

Interplay of Superconductivity and Rattling Phenomena inβ-PyrochloreKOs2O6Studied by Photoemission Spectroscopy

The electronic structure near the Fermi level (EF) of the beta-pyrochlore superconductor KOs2O6 is studied using laser-excited ultrahigh-resolution photoemission spectroscopy. The superconducting gap clearly opens across the superconducting transition (Tc=9.6 K), with the strong electron-phonon coupling value of 2Delta(0)/k B Tc>or=4.56. A fitting analysis identifies clear anomalies at Tp=7.5 K in the temperature dependencies of the superconducting gap size and the quasiparticle relaxation lifetime. These anomalies and the fine spectral structures arising from phonons suggest that the existence of the rattling behavior of K ions significantly affects the superconductivity in KOs2O6.

Anomalous absorption of light under nonresonance conditions

The absorption spectrum of a weak probe field in atomic vapours of rubidium, cesium and samarium in the presence of a strong field is studied theoretically. It is shown that away from resonance with an atomic transition, the probe radiation may have an anomalously high absorption coefficient (several times higher than the resonance value) in an anomalously narrow spectral range. The ultranarrow resonance in the probe-field absorption line wing is not related to any real transitions in the atom. Its position is determined by detuning from resonance frequency and by the strong-field intensity. It is shown that for identical frequencies of the strong and probe waves, the resonance can be recorded by using weak magnetic fields. The effect can be applied in the ultrahigh resolution spectroscopy and for precision measurements of the magnetic field strength.

High-resolution ARPES study of many-body interactions in high-Tc cuprate superconductors

We report our recent ultrahigh-resolution angle-resolved photoemission spectroscopy (ARPES) results on several hole- and electron-doped high-Tc cuprate superconductors. We have studied the momentum and temperature dependence of the kink in the dispersion near the Fermi level and its “magnetic isotope effect” in hole-doped superconductors. The momentum dependence of pseudogap and superconducting gap has been studied for electron-doped superconductors. All the experimental results unambiguously indicate that the magnetic interaction is essential in characterizing the electronic structure and the superconductivity.

Sr87Lattice Clock with Inaccuracy below10−15

Aided by ultra-high resolution spectroscopy, the overall systematic uncertainty of the $^{1}S_{0}$-$^{3}P_{0}$ clock resonance for lattice-confined $^{87}$Sr has been characterized to $9\times10^{-16}$. This uncertainty is at a level similar to the Cs-fountain primary standard, while the potential stability for the lattice clocks exceeds that of Cs. The absolute frequency of the clock transition has been measured to be 429,228,004,229,874.0(1.1) Hz, where the $2.5\times10^{-15}$ fractional uncertainty represents the most accurate measurement of a neutral-atom-based optical transition frequency to date.

Anomalous Quasiparticle Lifetime and Strong Electron-Phonon Coupling in Graphite

We have performed ultrahigh-resolution angle-resolved photoemission spectroscopy on high-quality single crystals of graphite to elucidate the character of low-energy excitations. We found evidence for a well-defined quasiparticle (QP) peak in the close vicinity of the Fermi level comparable to the nodal QP in high-T(c) cuprates, together with the mass renormalization of the band at an extremely narrow momentum region around the K(H) point. Analysis of the QP lifetime demonstrates the presence of strong electron-phonon coupling and linear energy dependence of the QP scattering rate indicative of a marked deviation from the conventional Fermi-liquid theory.

Performance of an ultrahigh resolution cylindrical grating monochromator undulator beamline

An ultrahigh resolution and high-flux undulator beamline U9-CGM, with a cylindrical grating monochromator and covering an energy range from 5to100eV, has been constructed. Two separate entrance slits are included to provide different incident angles, hence to optimize the overall performance. This beamline delivers an average photon flux of 6×1010photons∕s with the entrance and exit slit openings at 10μm. An energy resolving power of 110 000 with a photon flux of 1×1010photons∕s was obtained at 16eV with the 1800line∕mm grating and at 64eV with the 1600line∕mm grating, with the entrance and exit slit openings at 3 and 5μm, respectively. A differentially pumped gas cell is used to attenuate high-order light by up to four orders of magnitude. This beamline will be a powerful tool for research in ultrahigh resolution spectroscopy of atoms, molecules, and condensed matter.

Laser-excited ultrahigh-resolution photoemission spectroscopy of borocarbide superconductor RNi2B2C (R = Y and Er)

We present laser-excited ultrahigh-resolution photoemission spectroscopy of YNi2B2C and ErNi2B2C. The extremely high energy resolution enables us to discuss the superconducting (SC) gap function of YNi2B2C and to measure the density of states which is coexisted between superconductivity and antiferromagnetism in ErNi2B2C. For YNi2B2C, s+g-wave SC gap symmetry cannot reproduce the experimental data, implying importance of taking the complicated electronic structures into consideration. For ErNi2B2C, the observed coherent peak is very broad and finite density of state exists at Fermi level.

Laser-excited ultrahigh-resolution photoemission study of anisotropic s-wave superconductor YNi 2B 2C

We have performed laser-excited ultrahigh-resolution photoemission spectroscopy of Y(Ni 1− x Pt x ) 2B 2C ( x=0.0, 0.2) and numerical simulation using s, anisotropic s and even s+g symmetry to study the superconducting gap anisotropy in borocarbide supercodnuctors. We observed the reduction of gap anisotropy in the x=0.2 sample in comparison to the x=0.0 sample, confirming the anisotropic s-wave gap. We also found that the spectrum of x=0.0 at 3.5 K cannot be fitted well with the s+g-wave symmetry, implying that the s+g symmetry is too simple to describe over all supercodncuting gap electronic structure of borocarbides.

Fermi surface and edge-localized states in graphite studied by high-resolution angle-resolved photoemission spectroscopy

We have performed ultrahigh-resolution angle-resolved photoemission spectroscopy on graphite single crystal (kish graphite). We have successfully determined the electronic band structure in the close vicinity of the Fermi level and found an extremely small hole-like Fermi surface centered at the K(H) point. We also found a weakly dispersive band near the Fermi level around the K(H) point, which is not predicted by the bulk band calculation. The origin of this anomalous feature is discussed in relation to the electronic states characteristic of the stepped surfaces.

Chlorofluoroiodomethane as a potential candidate for parity violation measurements

CHFClI is among the more favorable molecules for parity violation (PV) measurements in molecules. Despite the fact that calculated PV effects are two orders of magnitude smaller than in some organometallic compounds, CHFClI displays interesting features which could make possible a new experimental PV test on this molecule. Indeed, ultrahigh resolution spectroscopy using an ultrastable CO(2) laser is favored by several intrinsic properties of this molecule. For example, the high vapor pressure of CHFClI allows investigation by supersonic beam spectroscopy. Indeed, the spectroscopic constants have been accurately determined by microwave and millimetre wave spectroscopy. This is important for the subsequent selection of an appropriate absorption band of CHFClI that could be brought to coïncide with the absorption of CO(2). Partially resolved (+)- and (-)-CHFClI enantiomers with respectively 63.3 and 20.5% ee's have been recently prepared and analyzed by molecular recognition using chiral hosts called cryptophanes. Finally, the S-(+)/R-(-) absolute configuration was ascertained by vibrational circular dichroïsm (VCD) in the gas phase.

Laser-excited ultrahigh-resolution photoemission spectroscopy of superconducting Na0.35CoO2·1.3H2O

Abstract We have studied the electronic structure near the Fermi level of the layered cobaltate superconductor Na 0.35 CoO 2 ·1.3H 2 O using laser-excited ultrahigh-resolution photoemission spectroscopy (PES). In the normal state, we observed the formation of a pseudogap with an energy scale of ∼20 meV. Across the superconducting transition, we observed the leading-edge shift at 3.5 K compared to that at 10 K, indicating superconducting gap (SC gap) opening having a gap value Δ of 0.5–0.7 meV. The energy scale of the SC gap is ∼20 times smaller than that of the pseudogap, suggesting the existence of competing order parameters at low temperatures.

Ultrahigh-Resolution Photoemission Study ofh-ZrRuP

We have performed ultrahigh-resolution photoemission spectroscopy on the intermetallic superconductor hexagonal h -ZrRuP ( T c = 13 K). We observed the opening of a superconducting gap below T c , and found that the most probable order parameter is s -wave with a gap size (Δ) of 1.8 meV at 6 K. This gap size gives 2 Δ 0 / k B T c ∼3.5, suggesting the weak-coupling nature of the superconductivity in h -ZrRuP. We also observed a pseudogap-like suppression of spectral weight up to ∼45 meV from the Fermi level, indicative of the strong coupling of electrons with phonons and/or the charge density wave fluctuation.

Direct observation of superconducting gap in YB 6 by ultrahigh-resolution photoemission spectroscopy

We have performed ultrahigh-resolution photoemission spectroscopy (PES) on superconducting hexaboride YB 6 ( T c = 7.1 K) to investigate the electronic structure in the vicinity of the Fermi level ( E F ). We have succeeded in directly observing the superconducting gap together with a sharp coherent peak in the superconducting state (5 K). From the numerical simulation of the PES spectra by using isotropic Dynes function, we have estimated the size of the superconducting gap to be 0.9 meV, which corresponds to 2 Δ (0)/ k B T c = 3.8 . We found a dip structure around 10 meV with respect to E F in the PES spectrum in the superconducting state. This structure is attributed to the strong coupling feature of electrons with the 10 meV acoustic phonon. These results indicate that YB 6 is categorized into phonon-mediated BCS superconductor in the strong or intermediate coupling regime.

Photoemission Spectroscopic Evidence of Gap Anisotropy in anf-Electron Superconductor

We used low-temperature ultrahigh-resolution (360 microeV) photoemission spectroscopy with a laser as a photon source (Laser-PES) to study the superconducting (SC) gap of an f-electron superconductor CeRu2. The unique combination of the large escape depth expected from the known universal behavior and extremely high-energy resolution has enabled us to directly measure the bulk SC gap of an f-electron superconductor for the first time. The present study provides direct evidence for an anisotropic SC gap in CeRu2, and also demonstrates the potential of Laser-PES in investigating unconventional superconductivity realized in correlated d- and f-electron superconductors.

Laser-excited ultrahigh-resolution photoemission spectroscopy ofNaxCoO2·yH2O: Evidence for pseudogap formation

We have studied the temperature-dependent electronic structure near the Fermi level (EF) of the layered cobaltate superconductor, Na0.35CoO2.1.3H2O, and related materials, using laser-excited ultrahigh-resolution photoemission spectroscopy. We observe the formation of a pseudogap with an energy scale of ~ 20 meV in Na0.35CoO2.1.3H2O and Na0.35CoO2.0.7H2O, which is clearly absent in Na0.7CoO2. The energy scale of the pseudogap is larger than the expected value for the superconducting gap, suggesting an additional competing order parameter at low temperatures. We discuss implications of the pseudogap in relation to available transport and magnetic susceptibility results.

Frequency Measurement of an Ar<tex>$^+$</tex>Laser Stabilized on Narrow Lines of Molecular Iodine at 501.7 nm

A spectrometer for ultrahigh-resolution spectroscopy of molecular iodine at wavelength of 501.7 nm, near the dissociation limit is described. Line shapes about 30 kHz wide half-width half-maximum (HWHM) were obtained using saturation spectroscopy in a pumped cell. The frequency of an Ar/sup +/ laser was locked to a hyperfine component of the R(26)62-0 transition and the first absolute frequency measurement of this line is reported.

Erratum: Electronic structure and superconducting gap of silicon clathrateBa8Si46studied with ultrahigh-resolution photoemission spectroscopy [Phys. Rev. B64, 172504 (2001)

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Para- to antiferro-magnetic phase transition of CeSb studied by ultrahigh-resolution angle-resolved photoemission spectroscopy

Temperature-dependent angle-resolved photoemission spectroscopy has been performed on CeSb to study the origin of its complicated magnetic phase transition. In paramagnetic phase ( T=30 K), we have found that the electronic structure near the Fermi level (E F) consists of the hole-like Sb 5p band at the Γ point and the electron-like Ce 5d bands at the X point. With decreasing temperature across T N ( T N=10 K), both the energy shift and the energy splitting of the bands appear along the ΓX high-symmetry line. While the energy shift of the bands is consistent with the pf mixing model, the energy splitting has not been expected in the model so far. On the other hand, by comparing with the recent calculation based on the pf+dp mixing model, we found a qualitative agreement between the experiment and the calculation. This result suggests the importance of the dp mixing effect to interpret the mechanism of the magnetic phase transition of CeSb.