Angle-resolved Auger spectrum of the N₂ molecule

Angle-resolved Auger electron spectra of N2 have been measured with good statistics at photon energies corresponding to the π* resonance and the σ* shape resonance, below and above the N 1s threshold, respectively. Angular anisotropy is observed in both cases, but disappears as expected far above threshold. Satellite Auger transitions also show some angular anisotropy close to the N 1s threshold. This is attributed to the creation and decay of conjugate shakeup initial states, which have non-ground-state symmetry

Core Hole Double-Excitation and Atomiclike Auger Decay in N₂

Core hole decay spectra of the free N2 molecule show evidence for hitherto unobserved molecular resonances both below and above the K-shell photoionization threshold. Based on earlier calculations they are assigned to doubly excited neutral states which could not be seen below threshold in recent high resolution absorption spectra because of the more intense core-to-Rydberg excitations. By calculating the Auger spectrum of core-excited nitrogen atoms, we show that the features are atomiclike

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

High-resolution C 1s photoelectron spectra of methane

The C 1s partial photoionization cross section and photoelectron angular distribution of methane (CH4) have been measured with high-energy resolution between threshold and 385 eV photon energy. From the analysis of the vibrational fine structure on the C 1s−1 photoelectron line a vibrational energy of 396±2 meV and an equilibrium bond length of 1.039(±0.001) Å for the CH+4 ion have been determined. The lifetime broadening was found to be 83(±10) meV. The weak feature in the photoabsorption cross section just above threshold does not influence the vibrational fine structure in a way typical for a shape resonance. We therefore suggest that it is due to doubly excited states of the type C (1s)−1(Val)−1(Ryd)1a(Ryd)1b, an assignment which is supported by recent Auger decay studies. Measurements of the shakeup structure revealed six satellite lines, one of which increases strongly in intensity at threshold, thus pointing to the existence of a conjugate shakeup process

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

Variation of Cross-Section Enhancement in Decay Spectra of CO under Resonant Raman Conditions

We have measured participator and spectator decay at several photon energies within the range of the lifetime-broadened first vibrational component of the C 1s→π* resonance in CO. From the branching ratios it is evident that the resonant enhancement is different for single-hole and two-hole–one-electron states: The maximum in the resonant intensity peaks at different photon energies. It now becomes necessary to calculate energy-dependent transition matrix elements within the lifetime-broadening range

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