Natural widths in open-shell atoms: The K absorption spectrum of atomic oxygen

Total-ion-yield measurements and Hartree-Fock calculations are presented for the 1s→np, n=2 to 5 photoexcitations in atomic oxygen. Energies and relative intensities of the [1s]2s22p4(4P)np and [1s]2s22p4(2P)np series members are determined, and the apparent linewidths are measured. It is shown that natural widths in an open-shell atom can be deduced from an absorption spectrum only with the aid of theoretical input. The linewidth for the six individual components contained in the 1s→2p transition is determined to be 140(9) meV

Natural Widths In Open-Shell Atoms: The K Absorption Spectrum Of Atomic Oxygen

Total-ion-yield measurements and Hartree-Fock calculations are presented for the 1s-- \u3enp, n=2 to 5 photoexcitations in atomic oxygen. Energies and relative intensities of the [1s]2s(2)2p(4)(P-4)np and [1s]2s(2)2p(4)(P-2)np series members are determined, and the apparent linewidths are measured. It is shown that natural widths in an open-shell atom can be deduced from an absorption spectrum only with the aid of theoretical input. The linewidth for the six individual components contained in the 1s--\u3e2p transition is determined to be 140(9) meV

Nonlinear dispersion in resonant Auger decay of H₂O molecules

We have measured the resonant Auger decay spectrum of the water molecule at the oxygen K edge. Strong deviations from the expected linear dispersion of the participator lines (which correspond to single-hole valence states) are observed. In a simplified picture the effect can be attributed to the combined effect of the intermediate- and final-state potential curves

Subnatural Linewidths in Core Level Excitation Spectra

We have measured a core excitation spectrum on the N2 1s→π* transition in which the experimental linewidth is limited by the instrumental resolution rather than by the lifetime of the core hole. The measurement is performed by recording the partial yield of resonant Auger electrons within a fixed kinetic energy window. The factors contributing to the line shape and the general applicability of the method are discussed

Influence of multielectron excitations on the O 1s photoionization in CO₂

High-resolution O 1s photoelectron spectra of the CO2 molecule have been measured in the region of the resonant features above the O K edge. The cross sections and asymmetry parameters were determined for the vibrational components of the O 1s photoelectron line. The vibrational fine structure is completely dominated by the antisymmetric stretching mode, which arises due to vibronic coupling. The O 1s line is accompanied by a rich satellite structure. Auger electron spectra have been measured at the energies of the continuum resonances and used as an indirect probe for multielectron excitations. The shoulder on the low-energy side of the 4σu shape resonance is due to double excitations that decay via spectator processes

Band dispersion in the deep 1s core level of graphene

Chemical bonding in molecules and solids arises from the overlap of valence electron wave functions, forming extended molecular orbitals and dispersing Bloch states, respectively. Core electrons with high binding energies, on the other hand, are localized to their respective atoms and their wave functions do not overlap significantly. Here we report the observation of band formation and considerable dispersion (up to 60 meV) in the $1s$ core level of the carbon atoms forming graphene, despite the high C $1s$ binding energy of $\approx$ 284 eV. Due to a Young's double slit-like interference effect, a situation arises in which only the bonding or only the anti-bonding states is observed for a given photoemission geometry.Comment: 12 pages, 3 figures, including supplementary materia

A setup for studies of photoelectron circular dichroism from chiral molecules in aqueous solution

We present a unique experimental design that enables the measurement of photoelectron circular dichroism (PECD) from chiral molecules in aqueous solution. The effect is revealed from the intensity difference of photoelectron emission into a backward-scattering angle relative to the photon propagation direction when ionizing with circularly polarized light of different helicity. This leads to asymmetries (normalized intensity differences) that depend on the handedness of the chiral sample and exceed the ones in conventional dichroic mechanisms by orders of magnitude. The asymmetry is largest for photon energies within several electron volts above the ionization threshold. A primary aim is to explore the effect of hydration on PECD. The modular and flexible design of our experimental setup EASI (Electronic structure from Aqueous Solutions and Interfaces) also allows for detection of more common photoelectron angular distributions, requiring distinctively different detection geometries and typically using linearly polarized light. A microjet is used for liquid-sample delivery. We describe EASI’s technical features and present two selected experimental results, one based on synchrotron-light measurements and the other performed in the laboratory, using monochromatized He-II α radiation. The former demonstrates the principal effectiveness of PECD detection, illustrated for prototypic gas-phase fenchone. We also discuss the first data from liquid fenchone. In the second example, we present valence photoelectron spectra from liquid water and NaI aqueous solution, here obtained from a planar-surface microjet (flatjet). This new development features a more favorable symmetry for angle-dependent photoelectron measurements