Photoemission resonant

Mikuushkin V.M., Shnitov V.V., Gordeev Yu.S., Molodtsov S.L., Vyalykh D.V. Photoemission resonance and its decay in the process of destruction of C6o fullerite molecular structure by synchroton irradiation. Fiz.Tv.Tela (in Russian) 2004 46 2233-2237. 

Mayor LC, Taylor JB, Magnano G, Rienzo A, Satterley CJ, O Shea IN, Schnadt J (2008) Photoemission, resonant photoemission, and X-ray absorption of a Ru(ll) complex adsorbed on mtile Ti02 (110) prepared by in situ electrospray deposition. J Chem Phys 129(11) 114701-114709... 

RD Bringans, H Hochst. Photoemission resonance effects in the nitrides of titanium and zirconium. Phys Rev B 30 5416, 1984. 

We consider a general dissipative environment, using a three-manifold model, consisting of an initial ( ), a resonant ( r ), and a final ( / ) manifold to describe the system. One specific example of interest is an interface system, where the initial states are the occupied states of a metal or a semiconductor, the intermediate (resonance) states are unoccupied surface states, and the final (product) states are free electron states above the photoemission threshold. Another example is gas cell atomic or molecular problems, where the initial, resonant, and final manifolds represent vibronic manifolds of the ground, an excited, and an ionic electronic state, respectively. 

Thanks to the extensive literature on Aujj and the related smaller gold cluster compounds, plus some new results and reanalysis of older results to be presented here, it is now possible to paint a fairly consistent physical picture of the AU55 cluster system. To this end, the results of several microscopic techniques, such as Extended X-ray Absorption Fine Structure (EXAFS) [39,40,41], Mossbauer Effect Spectroscopy (MES) [24, 25, 42,43,44,45,46], Secondary Ion Mass Spectrometry (SIMS) [35, 36], Photoemission Spectroscopy (XPS and UPS) [47,48,49], nuclear magnetic resonance (NMR) [29, 50, 51], and electron spin resonance (ESR) [17, 52, 53, 54] will be combined with the results of several macroscopic techniques, such as Specific Heat (Cv) [25, 54, 55, 56,49], Differential Scanning Calorimetry (DSC) [57], Thermo-gravimetric Analysis (TGA) [58], UV-visible absorption spectroscopy [40, 57,17, 59, 60], AC and DC Electrical Conductivity [29,61,62, 63,30] and Magnetic Susceptibility [64, 53]. This is the first metal cluster system that has been subjected to such a comprehensive examination. 

It must be emphasized that these cross sections are only valid for an electron excitation into free-electron like final states (conduction band states with parabolic band shape) and not for resonance transitions as f — d or p - d excitations. If too low excitation energies (< 10 eV, see Table 1) are used in UPS, the final states are not free-electron like. Thus the photoemission process is not simply determined by cross-sections as discussed above but by cross-sections for optical transitions as well as a joint density of states, i.e. a combination of occupied initial and empty final states. 

Resonance photoemission measurements have been recently made for U metal , and show indeed a resonant enhancement of the satelUte at 2.3 eV only for the threshold energy (5 A i2. hv = 94 eV) (Fig. 15). In addition the main peak at Ep shows the expected off-resonance behaviour. Further support for such an interpretation of the satellite is given by the analysis of the photon excited Auger emission. This is shown to be composed of two different bands also separated by 2.3 eV and due to the two screening channels by 5 f or 6 d states ... 

Other resonant photoemission studies for uranium compounds show, regardless of the degree of localization, that suppression (off-resonance) and enhancement (on-resonance) of 5 f emission are always found for hv = 92 and 98 eV, respectively. On the other hand, localized 5f derived structures have been identified at 0.7, 0.9, 1.0 and 1.5 eV for USb, UTe, UPds and UO2 respectively i.e. for compounds in which 5 fs differ considerably with respect to localization. 

The other possible assignment of the 2.3 eV structure to 6d excitation (line II, Ref. 56, 66) cannot be ruled out. Resonant photoemission on Ce compounds ° shows indeed that a resonant enhancement at the 4 d 4 f threshold is not only present for 4f but also for 5 d emission. Thus an easy identification of 4f emission is not possible. Theoretical calculations of the cross section due to resonant enhancement result in a 2 eV shift to lower photon energy for the maximum 5d enhancement compared with the 4f enhancement ... 

In conclusion, the partial localization effects in the valence band spectra of the light actinides, although extremely important if convincingly verified, still need much experimental and theoretical investigation. It is expected that the situation will improve considerably when resonant photoemission studies become available for actinide compounds in which the 5 f and 6 d emissions do not overlap. In addition, theoretical calculations of 5 f and 6 d cross sections near the 5 d threshold will be very helpful. 

The 5 f character of the peak at 1.4 eV in UO2 is evidenced by varying the excitation energy in the UPS/XPS technique, as well as by other techniques such as ARPES and resonant photoemission (see Table 3). 

Struc- Eb eV) ture Occupied states Xps ) BIS ARPES ") UPS/XPS this laboratory" Resonant photoemission ... 

An attempt of identification of 5 f character has been recently reported for UO2 by resonant photoemission of the valence band region with excitation energies of 92 eV (off-resonance) and 98 eV (on-resonance). The core absorption edge used was the 5d ionization threshold, corresponding to a process ... 

Combined with photoemission, DRS provides quantitative data on excitation-luminescence behavior of powdered specimens which can be used to determine photoluminescence quantum efficiencies and the extent of resonant energy transfer among the bulk and surface activators and sensitizers. 

Further evidence for strong mixing of Cu 3d and Cl 3p orbitals is obtained from the resonant photoemission data shown in Figure 22 for (CH NH, ) CuCl (31). In addition to the Cu 3d and Cl 3p... 

Figure 22. Resonant photoemission spectra of the valence band of D,-Cu(II)C1, as the photon energy is tuned through the Cu...

Kimura et al. (1995) reported on an investigation of the electronic structure of 7 3Au3Sb4 (R = La, Ce, Pr) by reflectivity and resonant photoemission spectra. The hybridization between the Ce4f state and the Sb5p state valence band was found to be weak as deduced from the resonant photoemission spectra of Ce3Au3Sb4. This result was found to be consistent with the electronic structure derived from an analysis of the optical data about the energy gap. 

Fig. S a Valence band spectra of Gd C82 (grey) and C82 (black) measured with Al Ka x-rays, b Symbols Gd 4f photoemission after subtraction of the empty C82 C 2s/2p spectrum. The vertical lines are individual components of atomic calculations for a 4f> multiplet, and the solid curve is their broadened sum. c Gd-N4>5 x-ray absorption spectrum (Gd 4d-4f excitations) of Gd C82. The complex lineshape comes from the widely spaced multiplet components resulting from the strong Coulomb interaction between the single hole in the 4d shell and the eight electrons present in the 4f shell in the x-ray absorption final state [see Fig. lc]. The arrows represent the two photon energies used for the data shown in panel d. d Resonant photoemission data of the valence band region of Gd C82 recorded off (hv=137 eV) and on (hv=149 eV) the Gd 4d-4f giant resonance...

Fig. 6 Main picture valence band photoemission spectra of Tm C82 recorded at photon energies across the Tm 4d-4f threshold. The inset shows the Tm-N4 5 x-ray absorption spectrum, indicating the choice of photon energies for the resonant photoemission experiment. The photon energies are (1) 169.4 eV, (2) 173.7 eV, (3) 177.8 eV and (4) 183.9 eV...

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