The magic number nine-atom alkali halide cluster ion. Is the nine-atom planar structure the most stable?

The question of whether the cubic structures proposed for the alkali halide cluster ions are the most stable has been re-examined. Geometry/energy optimization calculations were performed on other candidate structures for the [M(MX)₄]⁺ species. The square-planar structure was found to be more than 3 eV lower in energy than a proposed quasi-octahedral structure. The relative energies of the square-planar and other structures for a series of nine-atom alkali halide cluster ions are found to correlate with published experimental data.     

Evidence for the direct ejection of clusters from alkali-halides during laser vaporization

We have studied the formation of clusters of alkali halides during laser vaporization. Measurements of the abundances of cluster ions produced by several different source configurations indicate that clusters are ejected directly from the source sample and do not necessarily grow from an atomic or molecular vapor. Using samples consisting of mixed alkali halide powders, we have found that unalloyed clusters are easily produced in a source that prevents growth from occurring after the clusters leave the sample surface. Melting the sample or encouraging growth after vaporization lead to the production of alloyed cluster species. We also obtain information about the relative binding energies for substituted halogen ions bound to alkali halide clusters.     

Investigation of the relative stability of positive alkali halide cluster ions generated by fast atom bombardment

The stabilities of alkali halide cluster ions [M(MX)_n]⁺ (M ? Li, Na, K, Rb, Cs; X ? F, Cl, Br, I) have been studied by measuring the fragment ion yields following dissociation of the ions in the second field free region of a ZAB-2F mass spectrometer. Extractable cluster ions were observed for certain values of n. It was found that the stabilities of the neutral fragment species formed are also of importance in determining the fragmentation rates. Possible configurations of M and X in the stable ions are discussed.     

SCF calculations of the interactions of alkali and halide ions with the mercury surface

From extensive ab initio calculations on the interactions between mercury clusters and alkali and halide ions we have derived analytical pair-potential functions for the interaction between the ion and an extended mercury (111) surface. A novel correction scheme is proposed in order to reduce the shortcomings of cluster model. A preferred adsorption above the twofold bridge site was found for Li⁺ and Na⁺ and above the threefold hollow site for all other ions. The ab initio results have been fitted to analytical functions that can be used in computer simulations.     

Quantized hydration energies of ions and structure of hydration shell from the experimental gas-phase data

With previous data on alkali metal and halide ions included [Rais, J.; Okada, T. Anal. Sci. 2006, 22, 533], we analyzed rather broad data on ionic hydration from the point of view of gaseous cluster energetics. We have now added alkaline earth cations, Zn(2+), H(+), OH(-), Cu(+), Ag(+), Bi(+), Pb(+), and alkylammonium cations. The present analysis revealed the octa-coordinated nature of alkaline earth cations, which is not fully pronounced for Be(2+) and Zn(2+), existence of Eigen protonium complex, which is trigonally hydrated, and particular property of the first OH-, H(2)O cluster. Whereas these findings are generally in accordance with theoretical model calculation studies, we have foreseen in addition tetrahedral hydration for halide anions and Rb(+) and Cs(+), as well as for alkylammonium ions. The obtained picture of the quantized solvation of ions is mirrored in the ionization potentials of outer electrons of pertinent atoms. This is a second independent phenomenon, and together, they invoked a common pattern formation ("Aufbau") obeying tetra- and octa-coordinated principles.     

The possibilities for glassy clusters: (KCl)32

The (KCl)₃₂ cluster is used as a model system to study the possibilities for clusters to exhibit amorphous or glassy solid forms. The problem has two aspects: first, whether the potential surface of the cluster supports a myriad of locally stable, disordered structures, the ensemble of which would constitute the glassy state, and second, whether an ensemble of amorphous clusters can be prepared under laboratory conditions. Molecular dynamics studies give an emphaticyes to the first issue, and an equally emphaticno to the second, for cooling rates up to 10¹² K/s, a thousand-fold faster than the fastest rates yet reported. However, if the long-range Coulomb interaction of the ions is replaced by a shielded Coulomb (Debye or Yukawa) potential, the secondary minima are sufficiently stabilized and the saddles, sufficiently high, that disordered equilibrium structures can be reached by cooling at fast, but still conceivably attainable rates. The implication is that while alkali halide clusters probably cannot form glasses, binary clusters with shorter-range forces, such as those of II–VI and III–V compounds, probably can form glasses. The highly disordered structures of (KCl)₃₂ are perhaps the most disordered forms yet seen for solid matter.     

Ions interacting in solution: Moving from intrinsic to collective properties

A crucial determinant of Hofmeister effects is the direct interaction of ions in solution with the charged groups on the surface of larger particles. Understanding ion–ion interactions in solution is therefore a necessary first step to explaining Hofmeister effects. Here, we advocate an approach to modeling these types of properties where state of the art Ab Initio Molecular Dynamics (AIMD) simulation of ions in solution is used to establish benchmark values for the intrinsic properties of ions in solution such as solvation structures and ion–ion Potentials of Mean Force (PMFs). This information can then be combined with, or used to parametrize and improve, reduced models, which use approximations such as the continuum solvent model (CSM). These reduced models can then be used to calculate collective and concentration dependent properties of electrolyte solution and so make accurate predictions about complex systems of relevance for direct applications. We provide an example of this approach using AIMD calculations of the sodium chloride PMF to calculate osmotic coefficients of all 20 alkali halide electrolytes.     

Studies in cluster ion formation. Part I. Fast atom bombardment mass spectrometry of tetraalkylammonium halides: Factors influencing cluster ion size and stability

Positive and negative ion fast atom bombardment mass spectra of tetraalkylammonium halide salts (NR₄X, where X = Cl, Br, I and NR₄ = NMe₄, NEt₄) have been studied and intense cluster ion formation has been observed. The cluster ion intensity distributions were found to show enhancements at certain cluster numbers (n). The negative cluster ions of NMe₄X salts showed anomalous ion intensity regions, which differed from both the positive cluster ions of all NR₄X salts and also the corresponding negative clusters of NEt₄X salts. The influence of anion and cation size on cluster ion formation and abundances has been studied and it has been established that smaller anion and cation size favours the formation of larger cluster ions. The possible structures of the cluster ions exhibiting relative increased stabilities are discussed.     

Structural electric dipole in small ionic nanocrystals

We present the results of gas phase electric dipole measurements for a series of M₁₈X₁₇ alkali–halide clusters. This cluster has a large structural dipole, which is due to the periodic arrangement of the ions in the nanocrystal and is directly related to the size of the particle. Experimental values are compared to the prediction of a Born Mayer model and to ab initio calculations. The results for the various salts are reproduced by our calculations.     

Quantum chemical studies of the chemisorption of water and of unhydrated and hydrated halide ions on mercury

Local structures on electrode interfaces can be explored by quantum chemical investigation of medium-sized systems consisting of a cluster of substrate (metal) atoms, one or several solvent molecules, and/or at least one ion to be adsorbed at the interface. For the study of water adsorption and halide ion adsorption (unhydrated as well as hydrated) on a mercury surface, we have used the standard CNDO method together with geometrical optimization of the atom positions.In this paper, the following topics have been treated: (a) adsorption of a single water molecule in different positions on a close-packed plane cluster of seven mercury atoms; (b) adsorption of unhydrated halide ions (Cl^?, Br^?, I^?) in the “on-top” or hollow position on the mercury surface; (c) adsorption of monohydrated halides on the mercury surface. Further studies including solvation by six water molecules are discussed.The calculations provide information about minimum-energy geometries, energetic data, and local charges. Furthermore, they allow some conclusions about water mobility and reorientation on a close-packed metal surface, water orientation under the combined influence of an adsorbed ion and the metal surface, and trends of charge distribution in the halide series to be drawn. Calculations are critically discussed in the light of experimental and other quantum chemical data.     

Reactions of mercury-like ions in potassium halide lattices

Cadmium and zinc enter the alkali halide matrices as M²⁺ ions and exhibit characteristic absorption bands in the uv. Often these divalent species aggregate to form dimers (and polymers). After additive coloration of the doped single crystals, reduction occurs and monovalent monomers or dimers, and neutral atomary centers are formed. The monovalent dimers exhibit a broad ESR signal with a g value of ∼2.2.     

Relations between thermodynamic,physical and structural properties of alkali halides at their melting points

Linear relations of the general form Λ = a + mτ have been presented to describe the connection between the characteristic energetic and geometric parameters of alkali halides at their respective melting points. Inference has been made that these presented relations may be associated with the structure of the alkali halide liquids.     

Role of halide ions and temperature on the morphology of biologically synthesized gold nanotriangles

In this paper, we demonstrate the effect of halide ions on the formation of biogenically prepared gold nanotriangles using the leaf extract of lemongrass (Cymbopogon flexuosus) plant. We have also studied the effect of halide ions on the morphology of biogenic nanotriangles. It has been shown that iodide ions have a greater propensity to transform flat gold nanotriangles into circular disk-like structures as compared to other halide ions. The study also suggests that the presence of Cl- ions during the synthesis promotes the growth of nanotriangles, whereas the presence of I- ions distorts the nanotriangle morphology and induces the formation of aggregated spherical nanoparticles. The change in the morphology of gold nanotriangles has been explained in terms of the ability of the halide ions to stabilize or inhibit the formation of (111) faces to form [111] oriented gold nanotriangles. Last, we have also shown that the temperature is an important parameter for controlling the aspect ratio and the relative amounts of gold nanotriangles and spherical particles. The results show that, by varying the temperature of reaction condition, the shape, size, and optical properties of anisotropic nanoparticles can be fine-tuned.     

Stable clusters in the condensed state and some possibilities for gas phase clusters

The classical naked cluster ions of the post-transition elements that are stable in solid compounds and their lower charged analogues observed in mixed metal beams reflect the reduced number of good bonding orbitals. New cluster ions of indium that are hypoelectronic (fewer than 2n+2 skeletal bonding electrons) because of distortions or the bonding of heterometal atoms within the clusters are described. A large family of new, orbital-rich clusters of the group III and IV transition metals sheathed by halide are all centered by a wide variety of heteroatoms. Factors in their stability, possible analogous naked cluster targets, and some calculations are considered.     

The growth of ionic crystals based on the halogenation of copper cluster anions

We investigated the halogenation reactivity of copper cluster anions produced via a magnetron-sputter source after introduction into a fast-flow tube reaction apparatus simultaneously with chlorine gas. Interesting cluster products corresponding to [Cu(n)Cl(n+1)](-) (n = 1-6) were observed with notable stability, and the mass distribution of these clusters exhibits an exponential decay with increasing values of n. Reaction kinetics analysis is provided on the gas-phase reactivity of copper cluster anions with chlorine. First-principle calculations suggest a series of cubic-like structures for these species similar to the structure of alkali halide clusters due to their similar electronic configurations. These structures act as a starting point in the formation of ionic crystals.     

样品价态对激光气化产生Cu/Cl团簇的组成和稳定性的影响

研究团控的形成条件、形成机理是目前团簇科学中的一个热点领域［‘］．产生气相团簇的方法主要有Knudsen高温炉扩散法、粒子溅射法、激光气化／分子束法、直接激光气化法·因为不需要另加缓冲气体，直接激光气化法【刀具有对体系真空要求较低，装置简单，容易和飞行时间质谱结     

Structural and dynamic properties of concentrated alkali halide solutions: a molecular dynamics simulation study

The physicochemical properties of alkali halide solutions have long been attributed to the collective interactions between ions and water molecules in the solution, yet the structure of water in these systems and its effect on the equilibrium and dynamic properties of these systems are not clearly understood. Here, we present a systematic view of water structure in concentrated alkali halide solutions using molecular dynamics simulations. The results of the simulations show that the size of univalent ions in the solution has a significant effect on the dynamics of ions and other transport properties such as the viscosity that are correlated with the structural properties of water in aqueous ionic solution. Small cations (e.g., Li+) form electrostatically stabilized hydrophilic hydration shells that are different from the hydration shells of large ions (e.g., Cs+) which behave more like neutral hydrophobic particles, encapsulated by hydrogen-bonded hydration cages. The properties of solutions with different types of ion solvation change in different ways as the ion concentration increases. Examples of this are the diffusion coefficients of the ions and the viscosities of solutions. In this paper we use molecular dynamics (MD) simulations to study the changes in the equilibrium and transport properties of LiCl, RbCl, and CsI solutions at concentrations from 0.22 to 3.97 M.     

UV laser-induced desorption mechanism analyzed through two-layer alkali halide samples

Time of flight-mass spectrometry (TOF-MS) is used to analyze positive and negative desorbed ions generated by UV laser ablation of several alkali (X) halide (Y) salts. Most of the observed desorbed cluster ions have the structure (XY)(n)X(+) or (XY)(n)Y(-). Their desorption yields decrease as exp(-kn), where k approximately 2 for both series, suggesting that the neutral component (XY)(n) plays the dominant role in the desorption process. Mass spectrum measurements were performed for compound samples in which two salts (out of CsI, RbI, KBr, KCl and KI) are homogeneously mixed or disposed in two superposed layers. The detection of small new ion species and large cluster ions of the original salts supports the scenario that the uppermost layers are completely atomized while deep layers are emitted colder and fragmented: It is proposed that ns-pulsed laser induced desorption of ionic salts occurs via two sequential mechanisms: (1) ejection of cations and anions in the hot plume, followed by recombination into new cluster ions and (2) ejection of relatively cold preformed species originated from deep layers or from periphery of the irradiated region.     

Solvation structures of iodide on and below a surface of aqueous solution studied by photodetachment spectroscopy

We investigated solvation structures of I(-) on and below a surface of an aqueous solution by photodetachment spectroscopy. An aqueous solution of an alkali halide was introduced to the vacuum as a continuous liquid flow (liquid beam), and the liquid beam was irradiated with a UV laser pulse. The intensity of electrons emitted from the surface by the laser excitation was measured as a function of wavelength (photodetachment spectroscopy), and we obtained absorption spectrum of I(-) on and below the solution surface. From the absorption spectrum, we found that I(-) starts to appear on the solution surface as the bulk NaI concentration increases. Similar concentration dependence was observed for the KI solution. We also found that I(-) located inside the solution is pushed to the surface, when NaCl is added to the solution. These changes are explained in terms of the difference in the polarizability of halide ions.     

Solvothermal Synthesis and Crystal Structures of Alkali Molybdates

Within the frame of systematic morphological studies concerning the solvothermal formation of nanoscale and microscale molybdenum oxides from the interaction of a molybdenum‐based precursor such as MoO₃⋅2 H₂O with ionic additives such as alkali and earth alkali halides, we studied – with the aim to elaborate preparative guidelines – the influence of the precursor structure and the alkali halide upon the crystal structure of the emerging alkali polymolybdates in terms of solvothermal fields and high‐throughput solvothermal techniques. The discussion of the resulting crystal structures revealed a structure‐directing potential of the alkali cations that was explored for the synthesis of new mixed alkali polymolybdates.