Size-selected clusters cluster selection

Buck U, Gu X, Lauenstein C and Rudolph A 1988 Infrared photodissociation spectra of size-selected (CHjGH) clusters from / = 2 to 8 J. Phys. Chem. 92 5561... 

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. 

Infrared spectroscopy is the workhorse in this field, because it can quickly provide dynamical details, discriminate between different cluster sizes and phases [40], and sample a wide spectral range. It often yields valuable feedback for quantum chemical calculations. In contrast to some action spectroscopy techniques, IR absorption spectroscopy is not intrinsically size-selective. All cluster sizes generated in the expansion are observed together, and indirect methods of size assignment are needed. 

U. Buck and I. Ettischer, Vibrational predissociation spectra of size selected methanol clusters New experimental results../. Chem. Phys. 108, 33 38 (1998). 

Tada, M. and Iwasawa, Y. (2009) Model Systems in Catalysis From Single Crystals and Size Selected Clusters to Supported Enzyme Mimics (ed. R.M. Rioux), Springer, in press. 

Hanmura, T. Ichihashi, M. Kondow, T. Reaction of Benzene Molecule on Size-Selected Nickel Cluster Ions. J. Phys. Chem. A 2002, 106, 4525-4528. 

A survey of the studies of metal-catalyzed acetylene cyclotrimerization on single-crystal, supported, and bimetallic catalysts is available.539 A new study with size-selected Pdn clusters found that clusters as small as Pd7 are able to induce benzene formation at 157°C.540... 

Using photoelectron detection in a femtochemistry arrangement, we studied size-selected clusters of ionic systems, covering the transition from gas phase to condensed phase dynamics [6]. We investigated the solvent effect on Oj dissociation dynamics, and observed... 

Microscopic Friction and Solvation in Barrier Crossing Isomerization of Stilbene in Size-Selected Hexane Clusters, A. A. Heikal, S. H. Chong, J. S. Baskin, and A. H. Zewail, Chem. Phys. Lett. 242, 380 (1995). 

We have discussed recent computational and spectroscopic results on the photoinduced hydrogen transfer and proton transfer chemistry in hydrogen-bonded chromophore-solvent clusters. The interplay of electronic spectroscopy of size-selected clusters and computational studies has led to a remarkably detailed and complete mechanistic picture... 

The Buck method is most useful for medium sized clusters, and in experiments that do not attempt detailed photochemical studies of the size selected clusters. High resolution spectroscopy of the selected clusters is impractical because the number per quantum state is small, due to the many occupied ro-vibrational... 

Messerli, S., Schintke, S., Morgenstern, K., Sanchez, A., Heiz, U., and Schneider, W.-D., Imaging size-selected silicon clusters with a low-temperature scanning tunneling microscope. Surf. Sci. 465,331 (2000). 

Size selected clusters from molecular beams deposited on planar 2-dimensional (2-D) supports [ 1 ]... 

This combined theoretical-experimental approach shows the potentiality of generating defective surfaces to modify the chemical activity of supported nanoaggregates for catalytic applications. It also shows the importance to obtain an atomistic control on the species deposited on the smface for the proper characterization of their activity. Through a specifically designed experimental apparatus which makes it possible to deposit size-selected metal clusters it has become possible to study the properties of a supported cluster as a function of its size. This opens new, unprecedented perspectives for the understanding of size-dependent activity and selectivity of a supported metal catalyst. To reach this ambitious goal theory plays a role which cannot be overlooked. 

Huisken, R, Kaloudis, M., and Kulcke, A., Infrared spectroscopy of small size-selected water clusters, J. Chem. Phys. 104, 17-25 (1996). 

Most investigations of photoinduced electron transfer have been performed in condensed phases. Much less is known about conditions that permit the occurrence of intramolecular ET in isolated (collision-free) molecular D-A systems. A powerful method for this kind of study is the supersonic jet expansion teehnique (which was originally developed by Kantrowitz and Grey in 1951 [66]) combined with laser-induced fluorescence (LIF) spectroscopy and time-of-flight mass spectrometry (TOF-MS). On the other hand, the molecular aspects of solvation can be studied by investigations of isolated gas-phase solute-solvent clusters which are formed in a supersonic jet expansion [67] (jet cooling under controlled expansion conditions [68] permits a stepwise growth of size-selected solvation clusters [69-71]). The formation of van der Waals complexes between polyatomic molecules in a supersonic jet pro-... 

An example of a size-selecting cluster source is depicted in Fig. 16.1 [11]. A laser ablates a metal target, generating gas-phase metal atoms. Clusters then form in an aggregation tnbe that allows rough control of cluster size due to the inert gas flow rate, pressure and length of the channel. 

Fig. 16.1 A typical experimental set-up for a size selection cluster source. Reproduced from [11]. Copyright 2006 Springer...

Following the TPR experiments discussed earlier, Judai et al. examined the reaction between CO and NO on size-selected Pd clusters using a pulsed molecular beam [73]. In these experiments, CO and N formation are monitored when a constant pressure of 5 x 10 mbar of CO is maintained in chamber while delivering 100 ms pulses of NO (equivalent to an effective pressure of 1 x 10 mbar) to the surface of the sample held at a constant temperature. Although TPR experiments indicated a... 

Future Experiments Involving Size-Selected Clusters... 

Clearly, size-selected cluster catalysts will play a key role in the future of model catalysis and will be an important tool in developing a detailed understanding of size effects in catalysis. Improvements in characterization under reaction conditions are needed to study the stability of these systems. In addition, exciting new possibilities for examining the effects of surface loading (number density) and alloy composition exist which will drive the field forward in the next decade. 

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