Light emission from sputtered aluminum atoms and ions produced by ion bombardment

Photon emission originating from sputtering of a polycrystalline aluminum surface under 1–10 keV ion (H⁺, He⁺, Ar⁺, Kr⁺ and Xe⁺) bombardment has been studied. Measured photon emission yields from the 3d ²D_3/2 resonance transition of sputtered excited Al atoms and calculated nuclear stopping powers are compared. The results demonstrate that elastic collisions play a major role in photon emission. Moreover, measurements of photon intensity as a function of the distance from the target surface show that decays of sputtered excited ions Al⁺ and Al²⁺ are faster than decays of excited Al atoms, and less affected by cascade repopulation and de-excitation of fast ions.     

Evaporation kinetics of tetraalkylammonium ions from charged formamide drops

The rate of ion evaporation from the surface of electrically charged liquid drops may be inferred from observations of the minimum drop charge q present on drops of a given radius R. This critical relation q(R) is measured here from the fossil solid residues left by the drops after complete solvent evaporation. We obtain mobility distributions of singly charged clusters formed by charge-reduced electrosprays of tetra-n-alkylammonium salts (C(n)()H(2)(n)()(+1))(4)N(+) (n = 2-10) dissolved in formamide. These distributions exhibit modulated structures, with each wave being associated with an initial charge state of the clusters prior to charge reduction, from which critical q(R) relations follow. For n from 4 to 7, the behavior is weakly dependent on the length of the alkyl chain. Above n = 7, there is a marked increase in solvation energy of the alkylammonium ions, but drop curvature effects contribute a compensating reduction of the energy barrier for ionization. This curvature effect increases monotonically with n and is probably associated with surface activity. Few clear modulations are seen for n < 3, perhaps because of the decreased role of surface activity in transferring solute into very small drops during the Coulombic breakup of larger drops. For this reason, extension of this technique to small inorganic salts is problematic.     

Structural aspects of aqueous tetraalkylammonium salt solutions

Various thermodynamic and spectroscopic investigations on aqueous tetraalkylammonium salt solutions are reviewed from a structural viewpoint. At present, it is not yet clear what kind of water structure is formed around the alkyl groups of the large cations. However, the importance of cosphere overlap and ion-ion interaction (cation-anion, cation-cation, cation-anion-cation, etc.) in determining the solution properties are emerging more clearly. In this regard, model calculations based on the approach of Friedman and his coworkers are expected to be of considerable value.This paper was presented at the symposium, The Physical Chemistry of Aqueous Systems, held at the University of Pittsburgh, Pittsburgh, Pennsylvania, June 12–14, 1972, in honor of the 70th birthday of Professor H. S. Frank.     

Light emission from excited molecules sputtered from chemisorption layers on silicon

Light emission from excited molecular fragments sputtered by a 10 ke V Kr⁺ ion from a silicon surface with chemisorbed oxygen, nitric oxide, water, ammonia, methanol and methyl mercaptan has been obsreved. The fragments which have been identified are SiH, OH, NH, CH and possibly SiO and SiS.     

Influence of tetraalkylammonium ions on structure of nonaqueous solvents

Summary The half-wave potentials of the redox system [Co(en)₃]³⁺/[Co(en)₃]²⁺ have been influenced by the tetraalkylamonium cation of the supporting electrolyte used. This was explained with the specific interactions (solvation) of the tetraalkylamonium ion with the nonaqueous solvent.

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Einfluß von Tetraalkylammoniumionen auf die Struktur nichtwäßriger Lösungsmittel (Kurze Mitt.)

Zusammenfassung Das Halbwellenpotential des Redoxsystems [Co(en)₃]³⁺/[Co(en)₃]²⁺ wird von Tetraalkylammonium-Ionen des Stützelektrolyten beeinflußt. Dies wird durch die spezifischen Wechselwirkungen (Solvatation) der Ionen mit dem nichtwäßrigen Lösungsmittel erklärt.

     

Adsorption of tetraalkylammonium ions on microporous and mesoporous activated carbons prepared from vinylidene chloride copolymer

The adsorption of tetraalkylammonium ions on microporous (AC-micro) and mesoporous (AC-meso) activated carbons prepared from vinylidene chloride copolymer was investigated. The adsorbed amounts on AC-micro decreased in the order of tetraethyl-, tetrapropyl-, hexadecyltrimetyl-, and tetrahexylammonium bromide. Consequently it is suggested that the pore size of the activated carbon plays an important role in the adsorption. The adsorbed amounts on AC-meso increased with increasing alkyl chain length. In the case of mesoporous activated carbon, hydrophobic interaction between tetraalkylammonium ions and the surface of activated carbons contributes to in the adsorption.     

Formation of C7H7(+) from benzyl chloride and chlorotoluene molecular ions: a theoretical study

The potential energy surface (PES) for the formation of C7H7(+) from benzyl chloride and chlorotoluene ions was obtained by quantum chemical calculations at the B3LYP/6-311+G(3df,2p)//B3LYP/6-31G(d) level. On the basis of the PES, the RRKM model calculations were carried out to predict the rate constants of the dissociations of the molecular ions of o-, m-, and p-chlorotoluene, all of which agreed well with previous experimental results. The kinetic analysis showed that the benzylium ion was the predominant product in the dissociations of the four isomeric molecular ions, below the thresholds of the formation of tolylium ions.     

Formation of molecular halide ions from alkyl-halide clusters irradiated by ps and fs laser pulses

We report on the interaction of alkyl-halide clusters with 35 ps and 20 fs laser pulses at λ = 266, 532, and 1064 nm and 400 and 800 nm, respectively. Particularly, we examine by means of time-of-flight mass spectrometry the intracluster photochemical processes, which give rise to the formation of molecular halogen ions. The efficiency of molecular halogen ion formation is found to depend strongly on the laser wavelength and pulse duration. The ionization/excitation schemes involve in both cases the multiphoton absorption by the clusters and the combined action of the laser and the intracluster electric field. Intracluster energy transfer processes seem to have a significant contribution to the molecular halogen ion formation in the ps domain, while in the fs region, this is probably facilitated by a rescattering process and/or by photon absorption. A physical mechanism for the interpretation of our experimental results is proposed.     

Studies in cluster ion formation. Part II. Concentration and matrix effects on the cluster ions of tetraalkylammonium halide salts

The roles of the matrix and salt concentration on the formation of cluster ions during fast atom bombardment of tetraalkylammonium halide salts have been studied. The occurrence of anomalous ion intensity regions at certain cluster numbers (n) is found to depend strongly on the salt concentration in the matrix. In addition the time-dependent nature of the spectra is examined and cluster ion formation is explained by postulating that equilibrium processes occur during bombardment of the salt solution.     

Electrochemical synthesis of layered manganese oxides intercalated with tetraalkylammonium ions

Thin films of birnessite-type layered manganese oxides with various interlayer spacings have been prepared on a platinum electrode by a one-step electrochemical procedure. The process involves a potentiostatic oxidation of aqueous Mn(2+) ions at around +1.0 V (Ag/AgCl) in the presence of tetraalkylammonium cations with different alkyl chain lengths. X-ray diffraction indicates that the films deposited with tetrabutylammonium (TBA), tetrapropylammonium (TPA), and tetraethylammonium (TEA) ions are composed of a single phase where unhydrated tetraalkylammonium ions are accommodated as a monolayer between manganese oxide layers. The interlayer spacing of the products increases in an order of TEA < TPA < TBA. The film deposited with tetramethylammonium (TMA) is a mixture of two phases relating to hydrated and unhydrated guest cations, the former being predominant probably as a result of less hydrophobic property of TMA compared to that of other tetraalkylammonium ions. The TBA(+)-intercalated Mn oxide film-coated electrode exhibits a good charge/discharge property in a KCl solution between 0 and +0.8 V. In this case, TBA(+) ions between the Mn oxide layers are rapidly replaced with K(+) in solution by ion exchange, accompanying a shrinkage of the interlayer. The incorporated K(+) ions as well as protons play an important role in the electrochemical conversion between Mn(4+) and Mn(3+) in the oxide layer. In the TBACl solution, the interlayer TBA(+) ions can be excluded electrochemically during the positive-going scan, concomitant with the oxidation of Mn(3+) sites. This causes an anodic current and the accompanying shrinkage of the interlayer. On the reverse scan, however, the compressed interlayer does not allow the incorporation of bulky TBA(+) ions from the electrolyte, with virtually no cathodic current observed. Such an obvious difference in electrochemical behavior between the two electrolytes can be recognized by considering that most of the Mn oxide surface is present inside the layered structure, not on the external surface. This indicates that the layered structure is formed over the entire film.     

Circular emission from molecular iodine

The resonance emission from molecular iodine excited by circularly polarised light is circularly polarised. We report the circular emission spectrum of iodine excited by the 5145 A line of Ar⁺. In zero field the prominent rotational triplet and the high energy P,R doublet are strongly circularly polarisation ratios close to theoretical.     

Physicochemical properties of tetraalkylammonium tetraphenylborates and tetraalkylammonium dodecylsulfates

Physicochemical parameters (composition, conventional solubility products, and thermal stability) of ionic associates of tetraalkylammonium dodecylsulfates and tetraalkylammonium tetraphenylborates are determined. The usefulness of these compounds as electrode-active components of membranes in potentiometric sensors that selective to tetraalkylammonium salts is assessed.     

Formation and stability of oxocarbenium ions from glycosides

Structural, protecting group and leaving group effects in the formation of oxocarbenium intermediates were studied in the gas phase. It is found that significant stabilization of oxocarbenium cations is achieved by protecting groups that interact with the cationic center via neighboring group participation despite the electron-withdrawing character of these moieties. On the other hand, ethereal protecting groups do not facilitate the formation of oxocarbenium intermediates. The experimental findings are supported by DFT calculations that show the following order of stabilization by the group adjacent to the cationic center: RCO > SiR(3) > R, where R is an alkyl group. This indicates that the SN1-like mechanism that is commonly proposed for this reaction is not always valid. Moderate leaving group effect is also detected in a series of thioaryl glucopyranosides.     

Doped gelatin films as a model matrix for molecular secondary ion mass spectrometry studies of biological soft tissue

Porcine gelatin films doped with a number of biological compounds at various concentrations and prepared by spin-casting have been used as model biological tissue matrices for studying organic ion emission in molecular secondary ion mass spectrometry. For many compounds, portions of the working curves were found to be linear over several orders of magnitude in concentration. Detection limits for the, analyzed compounds were in the parts per million range for several organic salt compounds but high (0.1 wt%) for others. Owing to the presence of a significant chemical background, the poorest detection limits were generally obtained from compounds with low molecular weights. Secondary ion yield matrix effects, indicated by a reduction in ionization efficiency at higher concentrations, were observed for several organic salt compounds.     

Formation of M+ ions and electronic excitation under fast-atom bombardment conditions by using a liquid matrix

Japan The mechanism for the formation of molecular ions M^+· under fast-atom bombardment (FAB) conditions with a liquid matrix is discussed on the basis of the mass spectra of pyrene, coronene, and fullerene C₆₀ obtained by using electron impact, gas-phase fast-atom bombardment, and gas-phase fast-molecule bombardment techniques. The obtained results suggest that formation of the M^+· ions under FAB conditions is not due to direct collisions between analytes M and fast atoms A, but is due to collision interactions between M and recoiling matrix molecules B or matrix ions. It has been confirmed, furthermore, that the FAB conditions with a liquid matrix are sufficient in energy for formation of singly charged ions M^+· and insufficient for the formation of multiply charged ions M ^z+ (z=2, 3) of pyrene, coronene, and C₆₀.     

Inverse velocities of sputtered monatomic ions: Systematics and quantification

The emission of secondary ions of about fifteen different elements, sputtered from Ti-base metal specimens, has been studied by SIMS. Both positive and negative ion yields have been measured at different exit energies up to ca 350 eV. It is found that when the logarithm of ionizability is plotted versus the inverse of the exit velocity, each element suggests a straight line behavior at energies above ca 20 eV. The gradient of the straight line is related to the respective 1st ionization potential (for positive ions) or electron affinity (negative ions). This behavior gives considerable support to the premises of modern theory of ionization in sputtering. Furthermore, the straight line plots for different elements are seen to converge as exit velocity increases; the intercepts at zero inverse velocity are found to be proportional to the respective element concentrations. This in principle offers a means of quantification in elemental analysis by SIMS, a method that does not require any external standards. The usefulness of the new method is demonstrated for ten elements sputtered from two specified titanium-base alloy standards from NIST.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday     

The metastable formation of di-ethylchloronium ions from ethylchloride dimer ions in a seeded molecular beam

Cluster ions of ethylchloride and their dissociation products have been produced in a supersonic expansion of ethylchloride seeded in Ar and energy selected by the threshold photoelectron photoion coincidence (TPEPICO) method. The peak widths of the ion time of flight distribution indicate that all of the clusters are produced by dissociative photoionization of higher order clusters. Thus, trimer ions dissociate to form dimer ions and an ethylchloride monomer. This dimer ion was found to be metastable with respect to the formation of the di-ethylchloronium ion and a chlorine atom. The measured dissociation rate as a function of the dimer ion internal energy was compared to the calculated rates based on the statistical RRKM/QET theory. Good agreement was found when the dimer adiabatic IP was assumed to be 10.2 eV. The Cl loss from the ethylchloride dimer ion is associated with a reverse activation energy of about 0.32 eV.     

Formation of iminium ions by fragmentation of a2 ions

Tandem mass spectrometric experiments have been carried out on the protonated amides H-Gly-Ala-NH2, H-Ala-Gly-NH2, H-Ala-Val-NH2, H-Val-Ala-pNA, H-Leu-Phe-NH2, H-Phe-Leu-NH2, H-Phe-Tyr-NH2 and H-Tyr-Phe-NH2 with particular emphasis on the fragmentation of the isomeric a2 ions derived therefrom. Primary fragmentation reactions of the protonated amides involve formation of the y1" and b2 ions with further fragmentation of the b2 ion to form the a2 ion which fragments to form iminium ions. Collision-induced dissociation studies of the mass-selected a2 ions were carried out. For the Gly-Ala, Ala-Gly and Val-Ala a2 ions, weak signals were observed corresponding to loss of CO from the a2 ion. With the exception of the Gly-Ala, Ala-Gly and Val-Ala a2 ions, both possible iminium ions (a1 and the internal iminium ion) are observed with the most abundant being that formed by proton attachment to the imine of higher proton affinity. The results provide strong support for the recently proposed (El Aribi et al. J. Am. Chem. Soc. 2003; 125: 9229) mechanism of fragmentation of a2 ions which involves elimination of CO from the a2 ion to form a proton-bound complex of two imines. Based on this mechanism ab initio calculations of the total energies of the a2 ions and the transition states for fragmentation have been carried out giving the energy barrier for fragmentation of each a2 ion. The experimental results are interpreted in terms of these energetics data, unimolecular rate constants calculated by using the RRKM theory, and the imine proton affinities.     

Ion-pair induced self-assembly of molecular barrels with encapsulated tetraalkylammonium cations based on a bis-trisurea stave

A bis-trisurea ligand assembles with the tetraalkylammonium halides to form the flat 'stave' structures or 'barrels' that encapsulate multiple R(4)N(+) guests, depending on the size of the halide anion (Cl(-) or Br(-)) and the R(4)N(+) cation.