Gas phase clusters

Spence T G, Trotter B T, Burns T D and Posey L A 1998 Metal-to-ligand charge transfer in the gas phase cluster limit J. Phys. Chem. A 102 6101... 

Metal-metal distances in supported metal clusters (e.g., It4, nearly 2.70 A) determined by EXAFS spectroscopy essentially match those in coordinatively saturated clusters of the same metal (e.g., Ir4(CO)i2). These distances are about O.2-O.3A greater than the metal-metal distances in the free (gas-phase) clusters (e.g., It4, 2.44 A) [32]. Similar results have been determined for supported OS5C [33] and Rhe [28,29]. 

Termath, V., Sauer, J., 1997, Ab Initio Molecular Dynamics Simulation of H502+ and H703+ Gas Phase Clusters Based on Density Functional Theory , Mol. Phys., 91, 963. 

Gas-phase metal oxide cluster cations have become increasingly interesting because of the possibility that a controlled reaction of size selected clusters might shed some light on condensed-phase catalysts. The possibility of producing small clusters in the condensed phase from deposition of gas-phase clusters has also been a driving force in the study of the reactivity of gas-phase ions. 

Semiclassical techniques like the instanton approach [211] can be applied to tunneling splittings. Finally, one can exploit the close correspondence between the classical and the quantum treatment of a harmonic oscillator and treat the nuclear dynamics classically. From the classical trajectories, correlation functions can be extracted and transformed into spectra. The particular charm of this method rests in the option to carry out the dynamics on the fly, using Born Oppenheimer or fictitious Car Parrinello dynamics [212]. Furthermore, multiple minima on the hypersurface can be treated together as they are accessed by thermal excitation. This makes these methods particularly useful for liquid state or other thermally excited system simulations. Nevertheless, molecular dynamics and Monte Carlo simulations can also provide insights into cold gas-phase cluster formation [213], if a reliable force field is available [189]. 

Finally we note that all the aspects of gas-phase clustering and the relations to solvation phenomena have been discussed in detail by Kebarle in a recent authoritative review article 145h... 

Atomic and molecular clusters have been studied for more than fifty years, but the last two decades have seen an increasing interest in new experimental methods for cluster production and analysis. The development and improvement of cluster sources lie at the focal point of the technological advances achieved in the study of gas phase clusters. For what concern the molecules of biological interest, the production and analysis of these molecules both isolated or complexed is made... 

A large number of different sources are available for the production of gas phase clusters, each one having features suitable for particular experimental goals. These include the cluster size range obtainable, versatility in terms of composition, charge and intensity, and the internal temperature of the produced clusters. 

In another DFT study devoted to the reaction mechanism of FeIV=0-catalyzed hydroxylation of L-Phe, the gas-phase cluster model was based on the X-ray crystal structure of the catalytic domain of hPAH containing ferric iron (hPAH-Fe111) (PDBid 1PAH (97)) (119). The water molecule distal to His290 was replaced by the oxo-ligand and only ligands of the first coordination sphere were included in the model. The amino acid residues were truncated in the model to include the side chains only. This model was also used as the QM part in a QM/MM study of the hydroxylation of L-Phe. In the latter study, the MM part included the complete catalytic domain (119). 

Our recent DFT investigations of the AAH catalytic cycle (121-123) will be the main focus of the discussion to come. The gas-phase cluster model that constitutes the starting point for these studies is based on the X-ray crystal structure of the catalytic domain of hPAH in binary complex with the cofactor (hPAH-Fe11-BH4) (PDBid 1J8U) (98). The active site iron and the six ligands,... 

As a result, some approaches to computing dispersion energy have involved using either experimental or theoretical data for gas-phase clusters to estimate the strength of dispersion interactions between different possible solute and solvent functional groups. However,... 

Dissociation energies play a singular role in characterizing gas-phase clusters, since they uniquely determine whether the global minimum has been found. Indeed, agreement between calculations and measurements for any other quantity (e.g. mobility, photoelectron spectrum, or ionization... 

One of the most complete studies of chiral self-recognition concerns serine. The experimental studies carried out on hydrogen-bonded gas phase clusters, provide useful data to be compared with theoretical results, as in general, the latter are... 

V. Termath, J. Sauer, Ab initio molecular dynamics simulation of H502+ and H7C>3+ gas phase clusters based on density functional theory. Mol. Phys. 91, 963-975 (1997)... 

Although gas phase clusters can be generated by a number of techniques, adiabatic expansions are the most widely utilized method for the generation of vdW clusters. A wealth of information regarding the energetics, dynamics, and structures of clusters has been recently obtained due to the availability of many new and improved experimental techniques. Although a number of spectroscopic techniques have been utilized in investigating vdW clusters, mass spectrometry (MS) is extensively employed for the study of clusters, as it enables size selective... 

Mass spectrometric investigation of gas phase clusters has come to play a significant role in cluster research because it is presently the only technique that allows size-dependent analysis of cluster beams. We anticipate that, in the near future, CMS studies utilizing tandem mass spectrometric techniques will be invaluable in confirming the importance of metastable decompositions and in determining the factors responsible for the enhanced intensities of various ions in the CMS. Such an instrument is currently under construction in our own labs, and we should soon have the ability to perform collision-induced dissociation studies on large vdW clusters. 

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