Ion-cluster

There has been much activity in the shidy of photodissociation of cluster ions, dating back to the 1970s when it was realized that most ions in the earth s lower atmosphere were heavily clustered [7, 35, 36],... 

These days, remarkably high-resolution spectra are obtained for positive and negative ions using coaxial-beam spectrometers and various microwave and IR absorption teclmiques as described earlier. Infonnation on molecular bond strengths, isomeric fonus and energetics may also be obtained from the teclmiques discussed earlier. The kinetics of cluster-ion fonuation, as studied in a selected-ion flow tube (SIFT) or by high-pressure... 

Photoelectron spectra of cluster ions yields cluster-bond strengdis, because each added ligand increases the bindmg energy of the extra electron in the negative ion by the amount of the ligand bond strength (provided the bond is electrostatic and does not appreciably affect the cln-omophore ion) [116]. 

Mass spectra from a carbon cluster ion source show strong magic numbers at C, and C d[136]. This led to the... 

More complex ions are created lower in the atmosphere. Almost all ions below 70-80 km are cluster ions. Below this altitude range free electrons disappear and negative ions fonn. Tln-ee-body reactions become important. Even though the complexity of the ions increases, the detemiination of the final species follows a rather simple scheme. For positive ions, fomiation of H (H20) is rapid, occurring in times of the order of milliseconds or shorter in the stratosphere and troposphere. After fomiation of H (H20), the chemistry involves reaction with species that have a higher proton affinity than that of H2O. The resulting species can be... 

Farrar J M 1993 Eiectronic photodissociation spectroscopy of mass-seiected ciusters soivation and the approach to the buik Cluster Ions ed C Y Ng and i Provis (New York Wiiey)... 

Viggiano A A, Arnold S T and Morris R A 1998 Reactions of mass selected cluster ions in a thermal bath gas Int. Rev. Phys. Chem. 17 147-84... 

Castleman A W and Mark T D 1986 Cluster ions their formation, properties, and role in eluoidating the properties of matter in the oondensed state Gaseous Ion Chemistry and Mass Spectrometry ed J FI Futrell (New York Wiley)... 

There are otlier teclmiques for mass separation such as tire quadmpole mass filter and Wien filter. Anotlier mass spectrometry teclmique is based on ion chromatography, which is also capable of measuring tire shapes of clusters [30, 31]. In tills metliod, cluster ions of a given mass are injected into a drift tube witli well-defined entrance and exit slits and filled witli an inert gas. The clusters drift tlirough tills tube under a weak electric potential. Since the... 

The reactivity of size-selected transition-metal cluster ions has been studied witli various types of mass spectrometric teclmiques [1 ]. Fourier-transfonn ion cyclotron resonance (FT-ICR) is a particularly powerful teclmique in which a cluster ion can be stored and cooled before experimentation. Thus, multiple reaction steps can be followed in FT-ICR, in addition to its high sensitivity and mass resolution. Many chemical reaction studies of transition-metal clusters witli simple reactants and hydrocarbons have been carried out using FT-ICR [49, 58]. 

Metal-carbide clusters are relevant to the fonnation of both endohedral fullerenes and carbon nanotubes [1351. There also exists a class of apparently stable metal-carbide cluster ions, = Ti, V, Cr, Zr and Hf), called... 

Hydrogen-bonded clusters are an important class of molecular clusters, among which small water clusters have received a considerable amount of attention [148, 149]. Solvated cluster ions have also been produced and studied [150, 151]. These solvated clusters provide ideal model systems to obtain microscopic infonnation about solvation effect and its influence on chemical reactions. 

Parent D C and Anderson S L 1992 Chemistry of metal and semimetal cluster ions Chem. Rev. 92 1541... 

Alford J M, Weiss F D, Laaksonen R T and Smalley R E 1986 Dissociative chemisorption of H2 on niobium cluster ions. A supersonic cluster beam FT-ICR experiment J. Rhys. Chem. 90 4480... 

Cheshnovsky O, Yang S H, Pettiette C L, Craycraft M J and Smalley R E 1987 Magnetic time-of-flight photoeieotron spectrometer for mass-selected negative cluster ions Rev. Sci. Instnim. 58 2131... 

Kaiser B, Bernhardt T M, Kinne M, Rademann K and Fleidenreich A 1999 Formation, stability, and structures of antimony oxide cluster ions J. Chem. Phys. 110 1437... 

A typical FAB mass spectrum of glycerol alone, showing a protonated molecular ion at m/z 93 accompanied by decreasing numbers of protonated cluster ions (m/z, 1 + nx92 n = 2, 3, 4,. ..). 

To aid the evaporation of the droplets, a flow of a gas (often nitrogen) is directed across them. This drying gas helps to reduce the number of cluster ions (Figure 9.3). 

Cluster ion. An ion formed by the combination of two or more molecules of a chemical species, often in association, with a second species. For example, ((HjO) ) is a cluster ion. 

Mass spectral analysis of quaternary ammonium compounds can be achieved by fast-atom bombardment (fab) ms (189,190). This technique rehes on bombarding a solution of the molecule, usually in glycerol [56-81-5] or y -nitroben2yl alcohol [619-25-0], with argon and detecting the parent cation plus a proton (MH ). A more recent technique has been reported (191), in which information on the stmcture of the quaternary compounds is obtained indirectly through cluster-ion formation detected via Hquid secondary ion mass spectrometry (Isims) experiments. 

The predominant species observed in SIMS spectra are singly charged atomic and molecular ions [51], However, inorganic and organic cluster ions can also be formed. If the sample consists of a simple single-component metal, then clusters such as M, M, etc., are observed in addition to M+ [52], Oxidation of the metal results in formation of MO ", MO/, M Oll", etc. The relative yield of MO+ to M+ depends on the bond dissociation energy of the oxide [52], For a two-component, oxidized metal, clusters of the type M/", M N, MjO, and M N O/ are observed [51]. 

Cluster ions are also emitted from organic materials their identity and yield depend on the chemical structure of the materials. Molecular or quasi-molecular ions may be observed as well as other ions that are formed by fragmentation, rearrangement, decomposition, or reaction [52], Several typical ion formation processes are summarized in Table 3 [40]. 

With large organic cluster ions (e.g. Ph4As+) pink 5-coordinate OsNX4 (X = Cl, Br) is obtained. Red OsNI4 is made ... 

The smaller cluster ions 83", 84" and 85 + have been examined by Zakrzewski and von Niessen at the HF/6-3H-G level [82]. The lowest cationic states are predicted to be 82, and A" for 83 (Cyv), 84 (I>4h) and (Cs), respectively. The ionisation processes may result in significant structural relaxation leading to the sequence of states different from that of the vertical states. The calculated lowest adiabatic ionisation energies, using the GI method with a very large ANO basis set, are 9.53, 8.05, and 8.20 eV for 83, 84 and 85 , respectively. 

The mass separated, pulsed, and focused primary ions with the energy of 1 -25 keV, typically liquid metal ions such as Ga, Cs, and O", are used to bombard the sample surface, causing the secondary elemental or cluster ions to emit from the surface. The secondary ions are then electrostatically accelerated into a field-free drift region with a nominal kinetic energy of ... 

In the lower>mass distribution, cluster ions are observed with an interval of An-1, while the high>mass distribution Is characterized by An-2, with only even n values being observed. The low mass distribution is essentially the same in each method, and observation of high-mass clusters has not been reported with direct formation methods. 

The fact that f.a.b.-m.s. can be used to observe cluster ions has been exploited in a study of metal binding to cyclodextrins, and in an investigation of the complexes formed between a 3-O-methylmannose dodecasac-charide and alkyltrimethylammonium ions having decyl and hexadecyl as alkyl chains. In the latter study, the larger organic cation was shown to form the stronger complex. 

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