Clustering, measurement

Figure 2 Comparison between the experimental average magnetic moments of Ni clusters measured by Apsel et al.3 (black dots) and the moments calculated by a tight binding method45,4 (light circles). Reproduced with permission from Ref. 44.

Figure 4-19. Resonance-enhanced two-photon ionization spectra of ions issued from fluorobenzene/methanol d4/helium clusters, measured by scanning the laser near the 00 transition of fluorobenzene [0]. Bands [4-6] are due to the FB+(CD3OD)2 precursor which totally fragments, either by evaporation of one methanol-d4 molecule or reaction leading to anisole + DF + CD3OD. Bands [7-9] are due to the 1-3 precursor also losing one CD3OD molecule or reacting. Bands [1-3] are more likely attributed to the 1-1 complex (isomer( ) [1], hot band [2], 0q [3]) (from Brutschy et al. 1991).

Fig. 12.3. a The time-integrated X-ray emission spectrum of laser-irradiated micron-sized Ar clusters measured at an intensity of 1.3 x 1019W/cm2, a pulse duration of 30fs, and a contrast ratio of C = 5 X 10-6. b Enlarged spectrum of a in the vicinity of the Li-like line structure... 

The first reported gas phase electronic spectra of DNA base pairs described hydrogen bond frequencies of GC clusters, measured by REMPI [26], On the one hand these frequencies agreed quite well with theoretical predictions. On the other hand, the six hydrogen bonding modes between two molecules of a given mass are only very weakly dependent on cluster structure and can therefore neither serve as a structural tool nor as a good benchmark for theory. Moreover, REMPI only measures excited state vibrations, while the best calculations apply to the ground state. 

Tartan and Gidaspow (29) have recently developed an experimental kinetic theory based particle image velocity technique for measuring particle and Reynolds stresses in gas-solid risers. They have shown that for gas-solid flow that are two types of turbulence in the risers random oscillations of the individual particles and oscillations of clusters measured by the Reynolds stresses of die particles. Earlier Mudde et al (30) have obtained similar measurements for bubble columns. Pan et al (72) have compared Mudde et al (30) experiments to simulations using the Los Alamos CFD code. Figure 4 shows typical Reynolds stress computations to the experiments. 

Knowledge of one implies knowledge of the other. As sure as Bragg scattering measures the structure of a crystal in q space, so too the structure factor of a cluster measured optically represents the structure cluster in q space. 

The photoabsorption spectrum a(co) of a cluster measures the cross-section for electronic excitations induced by an external electromagnetic field oscillating at frequency co. Experimental measurements of a(co) of free clusters in a beam have been reported, most notably for size-selected alkali-metal clusters [4]. Data for size-selected silver aggregates are also available, both for free clusters and for clusters in a frozen argon matrix [94]. The experimental results for the very small species (dimers and trimers) display the variety of excitations that are characteristic of molecular spectra. Beyond these sizes, the spectra are dominated by collective modes, precursors of plasma excitations in the metal. This distinction provides a clear indication of which theoretical method is best suited to analyze the experimental data for the very small systems, standard chemical approaches are required (Cl, coupled clusters), whereas for larger aggregates the many-body perturbation methods developed by the solid-state community provide a computationally more appealing alternative. We briefly sketch two of these approaches, which can be adapted to a DFT framework (1) the random phase approximation (RPA) of Bohm and Pines [95] and the closely related time-dependent density functional theory (TD-DFT) [96], and (2) the GW method of Hedin and Lundqvist [97]. 

Fig. 5.7. Relative size distribution in terms of potential alpha energy concentration, PAEC, of the unattached radon decay product clusters measured in indoor air.

Figure 5.92. Reflected light image of a defect in cable insulation. The defect appears rougher in texture than the surrounding matrix (dotted outline) (A). Reflected light image of the thick section shown in (A) following three local thermal analysis cluster measurements using SThM (B). Intermittent contact mode AFM phase images of (C) the cross linked PE/EBA matrix and (D) the defect shown in (A). The defect is devoid of discrete EBA phases. The thermomechanical response of the heated probe in contact with the defect (solid curves) and matrix (dashed curves of [A]) are seen to melt at different temperatures (E). (From Bar and Meyers [170] used with permission of the MRS Bulletin.)...

EA s of metal clusters are measured through photoelectron spectroscopy of anionic clusters. Clusters that are just short of a filled shell configuration should have large EA s. This is indeed borne out in experiments. EA s of Cu, clusters measured by Pettiette et al. [21] show sharp drops after N=l, 17, 19, 33, aud 39 (Figure 8.5). These clusters are one electron short of filled shell configurations at Af = 8,18,20,34,... 

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