Coherent states molecular clustering

Dynamics. Cluster dynamics constitutes a rich held, which focused on nuclear dynamics on the time scale of nuclear motion—for example, dissociahon dynamics [181], transihon state spectroscopy [177, 181, 182], and vibrahonal energy redistribuhon [182]. Recent developments pertained to cluster electron dynamics [183], which involved electron-hole coherence of Wannier excitons and exciton wavepacket dynamics in semiconductor clusters and quantum dots [183], ultrafast electron-surface scattering in metallic clusters [184], and the dissipahon of plasmons into compression nuclear modes in metal clusters [185]. Another interesting facet of electron dynamics focused on nanoplasma formation and response in extremely highly ionized molecular clusters coupled to an... 

A microwave pulse from a tunable oscillator is injected into the cavity by an anteima, and creates a coherent superposition of rotational states. In the absence of collisions, this superposition emits a free-mduction decay signal, which is detected with an anteima-coupled microwave mixer similar to those used in molecular astrophysics. The data are collected in the time domain and Fourier transfomied to yield the spectrum whose bandwidth is detemimed by the quality factor of the cavity. Hence, such instruments are called Fourier transfomi microwave (FTMW) spectrometers (or Flygare-Balle spectrometers, after the inventors). FTMW instruments are extraordinarily sensitive, and can be used to examine a wide range of stable molecules as well as highly transient or reactive species such as hydrogen-bonded or refractory clusters [29, 30]. 

Third, the notion (and reality) of such structural infractions as twins and coherent intergrowths - as is seen by Yacaman et al. in a 923-atom nanoalloy of AuPd [35] - is meaningless in our molecular bimetallic nanoparticles. In the nanoaUoys of Yacaman et al. [35, 42] and others [43], one may discern directly, by aberration-corrected electronic microscopy, thin bands of hexagonal close-packed and face-centered cubic packed sheets. In a typical molecular nanoparticle of the kind that we have studied (also by aberration-corrected electron microscopy [39]), it is directly established (in line with theoretical predictions [44]) that a single bimetallic cluster of RUj Pt does indeed possess molecular character. Furthermore, when six or more such clusters coalesce into larger entities containing ca 200 atoms they adopt the regular crystalline, and faceted state of a bulk metal. 

The characterization of structure and dynamics in metal carbonyl cluster chemistry has understandably been based around single-crystal X-ray diffraction and NMR spectroscopic studies, respectively. As has been shown in the earlier part of this chapter, these sources of data can be used in conjunction to provide a coherent picture of the possible molecular configurations of a given species and the processes by which they interconvert, at least in favorable cases. In general however, it is not possible to determine the geometric structures of these species in solution, nor to obtain direct experimental evidence to confirm that the same structure(s) obtain in solution as in the solid state. Fortunately the rebirth and exploitation of X-ray absorption spectroscopy (XAS) and in particular the application of synchrotron X-ray sources and improved methods of data analysis to EXAFS (Extended X-ray Absorption Eine Structure) spectroscopy has provided exactly this sort of experimental evidence. In this section we provide selective coverage of such work as relates to the structure and dynamics of metal carbonyl clusters. 

In the previous sections we have shown how it is possible to obtain a coherent generalization of the coupled-cluster theory to the description of the ground state properties of molecular solutes. In this section we will show how a similar generalization can be obtained for the EOM-coupled cluster theory, for the description of the excited states properties of solvated molecules. 

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