Ionized clusters

Fig. 8. Mass spectrum, with background subtracted, of pbo-toionized (Cfto) Rbv clusters containing both singly and doubly ionized species tbe solid line connects peaks belonging to groups of singly ionized clusters with a fixed value of n. Note tbe dominant peaks corresponding to (C (,Rb, ) Rb and (QoRb,.,) Rb2 (marked...

Fig. 9. Mass spectra of singly (top) and doubly (bottom) ionized Cf2)Li,. clusters note tbe prominent features at x = 7 for singly ionized and x = 8 for doubly ionized clusters and at X = 12 in both spectra.

Isao Yamada, Ionized-Cluster Beam Deposition... 

K. Fukushima, G. H. Takaoka, J. Matsuo, and 1. Yamada, Effects on CO oxidation activity of nano-scale Au islands and Ti02 support prepared by the ionized cluster beam method, Japan. J. Appl. Phys. Part 1—Regul. Pap. Short Notes Rev. Pap. 36(2), 813-818 (1997). 

Finely divided 2.0- to 5.0-nanometer Au particles were 69 prepared in an ionized-cluster-beam time-of-flight mass spectrometer system... 

The main characteristics of the various titanium oxide catalysts used in this chapter are summarized in Table 1. Titanium oxide thin film photocatalysts were prepared using an ionized cluster beam (ICB) deposition method [13-16]. In ICB deposition method, the titanium metal target was heated to 2200 K in a crucible and Ti vapor was introduced into the high vacuum chamber to produce Ti clusters. These clusters then reacted with O2 in die chamber and stoichiometric titanium oxide clusters were formed. Tlie ionized titanium oxide clusters formed by electron beam irradiation were accelerated by a high electric field and bombarded onto the glass substrate to form titanium oxide thin films. 

Ions and ionized clusters ejected from a surface during ion bombardment are detected with a mass spectrometer. Surface chemical composition and some information on bonding can be extracted from SIMS ion fragment distributions. 

Ammonia is well known to be a strong nucleophile. The nucleophilic substitution reactions in the ionized clusters of X-benzene (X = F, Cl) have been widely studied (Brutschy 1989, 1990 Brutschy et al. 1988, 1991 Mayeama and Mikami 1988, 1990, 1991 Riehn et al. 1992). All these experiments clearly show a specific behaviour not encountered in the hydroxylic solvents depending on the substituted aromatic and the cluster size, two types of substitution reaction can be detected. The first type leads to ionic amines by substitution of X by the -NH2... 

Of considerable interest in recent years has been the study of weakly bound van der Waals molecules (clusters) produced in expanding jets. It was expected that upon ionization the nascent cluster ion should undergo de-clustering, i.e. decompose into a smaller ion and neutral molecular constituents (the solvent molecules). In contrast, numerous examples have been reported of reactive processes within the ionized clusters which involve extensive bond reorganization and which can be rationalized in terms of intramolecular ... 

The time evolution of the phenol O—D distance between the phenolic oxygen and the deuterium and the D-Ow distance between the deuterium and the oxygen of the nearest water molecule in the neutral (left panel at the bottom) and ionized clusters (right panels) is shown in Figure 5-6. 

The time evolution of the O—D and D—Ow distances in the ionized clusters is also shown in Figure 5-6 (A-H right panels). In contrast with the neutral system, significant changes of the distances can be observed. These variations describe the occurrence of proton transfer from the phenolic moiety to water and also recombination of the transferred proton with the phenoxy moiety. As expected, the PT dynamics is dependent on the initial configuration. 

Figure 5-6. Time evolution of the O—D distance (full lines) between the phenol oxygen and the deuterium and the D—Ow distance (dotted lines) between the PhOD deuterium and the oxygen of the nearest water molecule in the neutral (left panel at the bottom) and ionized clusters (A-H right panels). The t = 0 time corresponds to the ionization of the [C5H5OD—(IhOb cluster at different (A-H) equilibrium configurations. The snapshots show for each trajectory the structure of the [C HsOD—(fyO) ] cluster corresponding to the configuration where the O—D and D—Ow distances are the same before the first PT following ionization...

Zhou, J. K., Takeuchi, M., Zhao, X. S., Ray, A. K. and Anpo, M. (2006). Photocatalytic decomposition of formic acid under visible light irradiation over V-ion-implanted Ti02 thin film photocatalysts prepared on quartz substrate by ionized cluster beam (ICB) deposition method. Catal. Lett. 106(1-2), 67-70. 

Gas phase molecular aggregates that contain acid molecules have been produced with free jet expansion techniques and detected by using electron impact ionization mass spectrometry. The clusters of aqueous nitric acid paralleled many properties of the condensed phase. Multiple nitric acid molecules were found in the clusters that were sufficiently dilute. The acid molecule was absent in the ionized clusters involving HC1 and only water was evident. Experiments also demonstrated the reactivity of ammonia with aqueous nitric acid and sulfur dioxide clusters and of sulfur trioxide with water clusters. The natural occurrence of acid cluster negative ions offers a means to probe the gas phase acid loading of the atmosphere through laboratory and field studies of the ion chemistry. 

When the vapor from a boiling solution of 6M HC1 is expanded, the detected cluster ions lack HC1 as evidenced by the absence of the characteristic m+2 isotope due to Cl. On the other hand, the observed H+(H20)n distribution is noticeably different than that obtained in the expansion of pure water. For instance, the usual prominent discontinuities at H+(H20)4 anc H+(H20)2 are not evident and a slight local minimum in intensity occurs at H+(H20) 3. The indication is that HC1 is initially present in the neutral cluster but that ionization leads to "boiling off" of HC1. The molecular ions H 5C1+ and H C1+ are observed. Expansion of the vapor over NH S also results in an ionized cluster distribution in which one of the expected components, namely H2S, is absent (7 ). Quite unlike the distribution obtained from the expansion of pure ammonia, a strong local minimum similar to the H+(HN03)(H20)n distribution is present. 

For small metal clusters, the core level shifts may be explained by all of the above plus a final state effect, i.e., the charge on the ionized cluster. In an XPS experiment, it is impossible to distinguish between these different phenomena. Therefore, binding energy shifts, or a lack thereof, cannot be taken as evidence for or against an electronic interaction with the metal. 

The first principles molecular dynamics simulation has been applied, based on the linearized-augmented-plane-wave (LAPW) method, to Seg and Seg+ clusters. The equilibrium structures have been obtained for Se8 and Se8+ clusters for the ionized cluster Seg-, a remarkable change from that for the neutral cluster has been found, which reflects the strong electron-lattice coupling in the cluster <1997MI1660, 1997MI75, 1997MI472>. 

The simple model for activation proposed by Whetten et al (2) was later questioned by Smalley and coworkers ".. one wonders how a simple electrostatic model can possibly explain the known sensitivity of H and Ng chemisorption to particular surface geometries, and to the presence of open d orbitals at the reactive site" and they continue by raising the question "Is the correspondence between I.P. and reactivity causal, or casual " (9). To answer this question Smalley et al studied the reactivity pattern of ionized clusters. It turned out that the positive clusters had a very similar reactivity pattern as the neutrals and sometimes reacted with even greater cross sections even though these clusters have a far less tendency to donate eletronic charge to the neutral adducts. This finding is consequently in conflict with the simple electrostatic model of Whetten et al. 

In the present calculations, the geometries of the Zn clusters up to Zn were taken from Ref. (39). The larger clusters are assumed to have simple hexagonal symmetry (hex) or hexagonal close-packed synunetry (hep) with the same bond distances as in the bulk (45). We performed self consistent calculations on both neutral and ionized clusters (ASCF) in order to account properly for relaxation energies. In the case of ions the calculations were carried out using the spin polarized approach. 

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