Neutral Metal Atoms Research Articles

HEAVY-METAL RING BAGS METAL ATOM

CHEMISTS have uncovered an unusual example of host-guest behavior in the form of a six-membered heterocyclic metal ring that traps and releases a neutral palladium atom. The research introduces heavy-metal heterocycles as a new class of compounds, and in reversibly trapping a neutral metal atom, the researchers add to the diversity of host-guest interactions ( J. Am. Chem. Soc., DOI: 10.1021/ja205515u). A team led by Richard D. Adams of the University of South Carolina, Columbia, and Michael B. Hall of Texas A&M University developed a process to make metallaheterocycles by linking heavy transition metals with heavy main-group bridging ligands such as diphenylantimony and diphenylbismuth and explained the nature of the host-guest binding. When the researchers took a three-membered Re 2 Sb heterocycle they made and heated it with a palladium catalyst, the Re 2 Sb ring dimerized to form a six-membered Re 4 Sb 2 heterocyclic ring. Under certain reaction conditions, the Re 4 Sb 2 ring trapped an unadorned pall...

Catechol Redox Induced Formation of Metal Core−Polymer Shell Nanoparticles

A novel strategy was developed to synthesize polymer-coated metal nanoparticles (NPs) through reduction of metal cations with 3,4-dihydroxyphenylalanine (DOPA)-containing polyethylene glycol (PEG) polymers. Catechol redox chemistry was used to both synthesize metal NPs and simultaneously form a cross-linked shell of PEG polymers on their surfaces. DOPA reduced gold and silver cations into neutral metal atoms, producing reactive quinones that covalently cross-linked the PEG molecules around the surface of the NP. Importantly, these PEG-functionalized metal NPs were stable in physiological ionic strengths and under centrifugation, and hold broad appeal since they absorb and scatter light in aqueous solutions.

A crossed photon–atom beam method for absolute measurement of total photoionization cross sections on isolated metal atoms: Measurements on Ba and Eu atoms

A crossed photon-atom beam apparatus has been constructed for absolute measurement of total photoionization cross sections of isolated and neutral metallic atoms. The main purpose is to establish the technique which can be used as widely as possible for the metallic elements. Using this apparatus, measurements on Ba and Eu atoms have been made at selected energies in their 4d giant resonance regions 110–140 eV and 140–180 eV, respectively. A monochromatized synchrotron radiation was used as a light source. The target-atom density in the interaction section was determined with accuracy of 9% using the accumulation rate of metallic atoms on a quartz crystal sensor and the average velocity of the atoms obtained by a time-of-flight method combined with a pulsed electron gun. The number of photons was determined with use of a double-ion chamber preferably. The entire systematic errors have been estimated to be 20% for Ba and 27% for Eu. The comparison of the measured cross-section values with previous experimental and theoretical results is reasonable, indicating that the crossed photon–atom beam method is fairly promising technique.

Adsorption of M Species and M2 Dimers (M = Cu, Ag, and Au) on the Pristine and Defective Single-Walled Carbon Nanotubes: A Density Functional Theory Study

We studied the adsorption of neutral M, charged M, and M2 dimers (M = Cu, Ag, Au) on the pristine single-walled carbon nanotubes (SWNTs) as well as on the Stone−Wales and vacancy sites by means of the B3LYP/6-31G (d,p) hybrid density functional method. Our results for neutral metal atoms on the pristine and defective SWNTs agree very well with previous periodic calculations. The binding affinity trend of metal species toward the pristine and defective SWNTs is in the order of M+ > M− > M. This implies that the transfer of electron density between metal species and the nanotubes, the electrostatic attraction, and the Pauli repulsion play an important role in the M−SWNT system. From the Mulliken population analysis, the transfer of electron density induces a positive charge of the metal species and a negative charge of the carbon atoms of nanotubes. As far as the adsorption energy is concerned, the metal species are likely to deposit on the defect site, particularly on the vacancy site, rather than on the pristine tube. To explore the reactivity of the M−SWNT complexes which can serve as a gas sensor as well as a catalyst, the interaction between a CO molecule and a metal atom deposited on the atomic vacancy was also examined. We also found that the adsorption energy per atom decreases from the metal atom to metal dimers in line with the fact that metal−metal cohesion dominates over metal−SWNT interaction. Finally, based on calculated interaction energies, dimerization of adsorbed atoms on the defect sites is not particularly favored compared to dimerization on the pristine tube except for that of Ag and Au atoms on the vacancy site.

ChemInform Abstract: Laser Multiphoton Ionization and Photoelectron Spectroscopy of Co(CO) 3NO and Fe(CO)5

Laser multiphoton dissociation‐resonance‐enhanced multiphoton ionization (MPD‐REMPI) and time‐of‐flight photoelectron spectra (TOF‐PES) of Co(CO)3NO and Fe(CO)5 have been obtained in the range 445–455 nm. The only ions produced by the pulsed dye laser are Co+ and Fe+. Transitions observed in the MPD‐REMPI spectra are assigned to resonant states of the neutral atoms. Final states of the atomic ions are determined from the TOF‐PES spectra. The multiphoton dissociation process produces metal atoms in a broad distribution of states, ranging in energies up to 33 000 cm−1 for Co, and 32 000 cm−1 for Fe. The most intense REMPI lines are associated with low‐lying electronic states (<8500 cm−1 for Fe and Co). By tuning the laser to appropriate wavelengths, neutral metal atoms in selected electronic states may be ionized. At most laser wavelengths, the atomic metal ions are formed in a distribution of states, only some of which are consistent with preservation of the core configuration of the Rydberg intermediate i...

Crystal field splitting on D↔S transitions of atomic manganese isolated in solid krypton

Narrow excitation features present on the [Ar]3d64s1aD(J=9∕2−1∕2)6←[Ar]3d54s2aS1∕26 transitions of manganese atoms isolated in solid Kr are analyzed within the framework of weak crystal field splitting. Use of the Wp optical lineshape function allowed identification of multiple zero-phonon lines for individual spin-orbit J states of the a aD6←aS6 transition recorded with laser-induced excitation spectroscopy. Excellent agreement exists between the predicted crystal field splitting patterns for the J levels of the aD6 state isolated in the «red» tetravacancy site of solid Kr. The tetrahedral crystal field of the «red» trapping site splits J&amp;gt;3∕2 levels of the aDJ6 and aD7∕24 states by approximately 30cm−1. This report represents the first definitive evidence of crystal field splitting, induced by the weak van der Waals interactions between a neutral metal atom and the rare gas atoms surrounding it in a well-defined solid-state site.

Experimental and theoretical study on activation of the C–H bond in pyridine by [Mm]− (M = Cu, Ag, Au, m = 1–3)

Activation of the C-H bond of pyridine by [M(m)](-) (M = Cu, Ag, Au, m = 1-3) is investigated by experiment and theory. Complexes of coinage metal clusters and the pyridyl group, [M(m)-C(5)H(4)N](-), are produced from reactions between metal clusters formed by laser ablation of coinage metal samples and pyridine molecules seeded in argon carrier gas. We examine the structure and formation mechanism of these pyridyl-coinage metal complexes. Our study shows that C(5)H(4)N bonds to the metal clusters through a M-C sigma bond and [M(m)-C(5)H(4)N](-) is produced via a stepwise mechanism. The first step is a direct insertion reaction between [M(m)](-) and C(5)H(5)N with activation of the C-H bond to yield the intermediate [HM(m)-C(5)H(4)N](-). The second step is H atom abstraction by a neutral metal atom to yield [M(m)-C(5)H(4)N](-).

First observation of micrometeoroid differential ablation in the atmosphere

Every day, billions of microgram‐sized‐extraterrestrial particles enter and ablate in the upper layers of the Earth's atmosphere, depositing their mass in the mesosphere and lower thermosphere (MLT). This evaporated meteoric mass is the source of global layers of neutral metal atoms, sporadic E layers of metal ions, and meteoric smoke particles. Because their kinetic energy is insufficient to produce detectable optical emissions, these particles can only be observed using sensitive radars, which detect the plasma (i.e., electrons) either immediately surrounding the meteoroid (head‐echo), or left behind along its path (trail‐echo). Here we show that observed short‐scale temporal features in the radar returned signal from the meteor head‐echo are explained by differential ablation of the chemical constituents. These results represent the first observation of this mass‐loss process, indicating that this is the main mechanism through which the meteoric mass of micron‐sized particles is deposited in the MLT.

The roles of the solute and solvent cavities in charge-transfer-to-solvent dynamics: Ultrafast studies of potasside and sodide in diethyl ether

Although electron transfer reactions are among the most fundamental in chemistry, it is still not clear how to isolate the roles of the solute and solvent in moving charge between reactants in solution. In this paper, we address this question by comparing the ultrafast charge-transfer-to-solvent (CTTS) dynamics of potasside (K(-)) in diethyl ether (DEE) to those of sodide (Na(-)) in both DEE and tetrahydrofuran (THF). We find that for sodide in both DEE and THF, CTTS excitation leads to delayed ejection of a solvated electron that appears with its equilibrium absorption spectrum. This indicates that the ejected electrons are localized in pre-existing solvent traps, suggesting that the structure of liquid DEE is characterized by cavities that are favorably polarized to localize an excess electron, as has been previously shown is the case for liquid THF. We also find that the geminate recombination dynamics following CTTS excitation of sodide in THF and DEE are similar, suggesting that the nature of the CTTS excited states and their coupling to the electronic states supported by the naturally occurring solvent cavities are similar in the two solvents. In contrast, the geminate recombination dynamics of potasside and sodide in DEE are different, with red-edge excitation of the K(-) CTTS band producing a greater number of long-lived electrons than is seen following the corresponding red-edge excitation of the Na(-) CTTS band. This indicates that the CTTS excited states of K(-) are better able to couple to the electronic states supported by the naturally occurring solvent cavities, allowing us to compare the energetic positions of the potasside and sodide ground and CTTS excited states on a common absolute scale. Finally, we also observe a strong transient absorption following the CTTS excitation of potasside in DEE that correlates well with the 766 nm position of the gas-phase potassium D-line. The data indicate that CTTS excitation of alkali metal anions essentially instantaneously produces a gas-phase-like neutral alkali metal atom, which then spontaneously undergoes partial ejection of the remaining valence electron to form a neutral alkali metal cation:solvated electron tight-contact pair.

Endohedral and Exohedral Complexes of T8-Polyhedral Oligomeric Silsesquioxane (POSS) with Transition Metal Atoms and Ions

The equilibrium geometries of the exohedral and endohedral complexes of the polyhedral oligomeric silsesquioxane (POSS) cage (HSiO3/2)8 containing the transition metal atoms or ions Sc0,+, Cr0,+, Fe0,+, Co0,+, Ni0,+, Cu0,+, Zn0,+, Mo0,+, W0,+, Ru0,+, Os0,+ have been investigated at the B3LYP/LanL2DZ levels. All these species form endohedral complexes with the T8-POSS cage except Sc0,+, Mo0, and W0,+. The Mo0 and W0,+ species as well as Cr0,+, Fe0,+, Co0,+, Ni0,+, Cu+, Zn+, Ru0,+, Os0 form stable exohedral complexes. Geometries, electronic properties and ionization potentials were computed. The Si−O and Si−H bond lengths in the cationic endohedral complexes are shorter than in the corresponding complexes of neutral transition metal atoms. The zero-point corrected inclusion energies of the endohedral species X@(SiHO3/2)8 (X = Fe+, Co+, Ni+, Cu+, Os+) are all negative, suggesting that these complexes are more stable than their isolated components. All exohedral complexes have energies that are lower than their corresponding endohedral analogs. Transition metal atom encapsulation raised the HOMO and lowered the LUMO energies, reducing the HOMO−LUMO gaps of every complex compared to that of the pure cage. The HOMO−LUMO gap of the empty cage is 8.1 eV while the endohedral complexes exhibit gaps between 1.2 and 4.96 eV. Insertion of Cr, Fe, Co, Ni, Cu, or Zn into the POSS cage is more favorable in water than in the gas phase. However, insertion of Co+, Ni+, Cu+, or Zn+ into the POSS cage is less favorable in water than in the gas phase. Overall, both the neutral and ionic endohedral transition metal complexes, X@(SiHO3/2)10, (X = Cr0,+, Fe0,+, Co0,+, Ni0,+, Cu0,+, Zn0,+, Ru0,+, Os0,+) appear to be viable synthetic targets.

Theoretical study on the structure and formation mechanism of [C6H5Mm]− (MAg, Au; m = 1–3)

The structures and formation mechanisms of the important intermediate phenyl-coinage metal complexes [C(6)H(5)M(m)](-) (M==Ag, Au, m = 1-3) are investigated at B3LYP//6-311G(d, p)/Lanl2dz level using Gaussian 03 program. The adiabatic electron affinity and vertical dissociation energy of [M(m)](-) and [C(6)H(5)M(m)](-) are calculated, which are excellently coincident with the experimental determination. The C(6)H(5) group bonds on metal clusters through M--C sigma bond in the complex [C(6)H(5)M(m)](-). The complexes [C(6)H(5)M(m)](-) (M==Ag, Au; m = 2-3) are generated through a stepwise reaction. The first step is a direct insertion reaction between [M(m)](-) (M==Ag, Au, m = 1-3) and C(6)H(6,) which leads to the generation of intermediate [C(6)H(5)M(m)H](-) (m = 1-3) with the activation and cleavage of C--H bond. The second step is the neutral metal atom abstracting the H atom to yield the product [C(6)H(5)M(m)](-).

Spatially Periodic Formation of Nanoparticles in Metal-Doped Glasses

In the course of reactive diffusion of hydrogen in metal-doped glasses, at some conditions, metallic nanoparticles grow forming quasi-periodic layered structure. We have developed a model defining conditions necessary for the formation of the layered structures. The model indicates relatively narrow range of parameters providing the quasi-periodic growth of the nanoparticles. The layered structure arises at relatively low over-saturation by neutral metal in the diffusion zone, due to the competition of two processes: enrichment of the glass by neutral metal atoms via reducing of metal ions by diffusing hydrogen and depletion of the glass by the metal atoms caused their diffusion to the nanoparticles. The model can be also applied to other situations where reactive diffusion inducing the formation and growth of nanoparticles occurs.

Simultaneous observations of sporadic Fe and Na layers by two closely colocated resonance fluorescence lidars at Wuhan (30.5°N, 114.4°E), China

The focus of this paper is to study the relationship between sporadic Fe (Fes) and Na (Nas) layers through simultaneous and common volume Fe and Na lidar observations. A total of 37 sporadic layering events were identified from one year (195 hours) of observations at Wuhan (30.5°N, 114.4°E), China. Out of the 37 events, 23 (62%) are characterized by the simultaneous formation of Fes and Nas layers. The most prominent feature for each of the 23 events is that the Fes and Nas layers occurred in overlapping altitude ranges and moved following almost the same track. On occasion the Fes and Nas layers exactly simultaneously reached their maximum peak densities at nearly the same altitude. These observational results strongly suggest that Fes and Nas layers are formed via the same or very similar mechanisms. This conclusion contradicts the previous suggestion based on those independent observations of Fes and Nas layers, that the Fes and Nas layers may be formed via different mechanisms. Out of the 37 events, 14 (38%) belong to single‐species sporadic layering events. It is noticed that the formation of each single‐species sporadic atom layer was usually accompanied by a weak density enhancement in the other metal atom. This supports the suggestion that Fes and Nas layers are formed via the same or very similar mechanisms. Both the Fes and Nas layers over Wuhan showed a tendency to strengthen with decreasing occurrence altitude. This tendency is consistent with the earlier Nas layer observations at high and low latitudes. Moreover, it is noticed by comparing the currently available Fes and Nas layer characteristics, which came from the observations at five different locations (including Wuhan) during different periods, that a lower average altitude could link to a higher average peak density and vice versa. The statistics‐based link might perhaps represent a universal feature of sporadic layers. From our simultaneous Fe and Na density data we have found that the undersides of the normal Fe and Na layers follow nearly the exact movements and occur at nearly the same altitude. The normal Fe layer tended to be narrower than the corresponding Na layer nearly at all times, and this difference was generally reflected in the extent of the upper edge of the layer. The nearly persistent underside overlap strongly suggests that on the undersides of these meteoric metal layers there exist some sink mechanisms leading to the concurrent removal of different sorts of free neutral metal atoms.

Comparative spectral analysis of the peculiar red novae V838 Mon and V4332 Sgr in quiescence after their outbursts

We analyze spectra of V838 Mon and V4332 Sgr taken in 2004–2005 using the 6 m telescope of the Special Astrophysical Observatory with the UAGS and SCORPIO spectrographs; the spectra have a resolution of 4.6 A and a high signal-to-noise ratio. We confirm that V838 Mon is a spectral binary containing a B3V star and cool oxygen-rich star. We identify AlO, TiO, VO, ScO, BaO, ZrO, and YO molecular bands in the cool star’s spectrum. The TiO absorption band at λ4423 A overlaps the continuum of the hot B3V star, testifying that the hot star and its cool companion form a wide physical pair. Further evidence for the components’ interaction is the presence of forbidden [Fell] lines that become stronger in the blue. We detected significant spectral variability of the cool star during 10 months in 2004. The spectrum of V4332 Sgr in 2005 (11 years after the outburst) contains emission lines of neutral metal atoms and of metal oxides against a photospheric continuum with a blackbody temperature of 2700 K. We identify the AlI, CaI, CrI, MnI, and SrI resonance lines and molecular emission lines of AlO, TiO, and VO, along with numerous emission lines of CrI in the spectrum. The MgI λ4571 A intercombination line is present. The emission lines are formed in a large volume of cool low-density gas. We conclude based on spectroscopy combined with archive photographs and modern CCD photometry that both peculiar red novae were binaries prior to their outbursts, and contained blue hot components that exploded. The secondary of V838 Mon is a hot B3V star, and that of V4332 Sgr is a cool M7 star.

Estimating the Hydration Enthalpies of Neutral Alkali Metal Atoms

Using existing data on the ionization energies of alkali metal atoms in small clusters of water, a thermodynamic cycle is proposed from which the hydration enthalpies of the neutral metal atoms can be estimated. Where comparisons are possible, the results are in reasonable agreement with those obtained using both experimental and ab initio methods. Application of the thermodynamic cycle to neutral alkali metal atoms solvated in ammonia yields solvation enthalpies that are significantly lower than those obtained for water.

Reactions of Neutral Transition Metal Atoms with Small Molecules in the Gas Phase

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Solute size effects on the solvation structure and diffusion of ions in liquid methanol under normal and cold conditions

We have performed a series of molecular dynamics simulations of alkali metal (Li+, Na+, K+, Rb+, and Cs+) and halide (F-, Cl-, Br-, and I-) ions in liquid methanol at two different temperatures to investigate the effects of ion size on the hydration structure and diffusion of ions in methanol under normal and cold conditions. Simulations are also carried out for some of the larger cations such as I+, (CH3)4N+, and (C2H5)4N+ and also neutral alkali metal atoms in methanol at both temperatures. With the increase of ion size, the diffusion coefficients of both positive and negative ions are found to show anomalous behavior. For cations, it is found that the maximum of the diffusion coefficient versus ion size curve occurs at the rather large cation of (CH3)4N+ unlike in water where the maximum occurs at the relatively smaller ion of Rb+. For halide ions, the anomalous behavior, i.e., the increase of diffusion with ion size, continues up to iodide ion and no maximum is observed. These results are in good agreement with experimental observations. The diffusion coefficients of neutral atoms are found to be greater in methanol than that in water and they decrease monotonically with solute size, whereas the diffusion coefficients of the corresponding ions are found to be smaller in methanol. Accordingly, an ion experiences a smaller Stokes friction and a higher dielectric friction in methanol than in water. These contrasting effects are believed to be responsible for the shift of the maximum of ion diffusion toward a larger ion size when compared with similar anomalous size dependence in liquid water.

Electrolyte-as-Cathode Glow Discharge Emission and the Processes of Solution-to-Plasma Transport of Neutral and Charged Species

Emission from an atmospheric-pressure glow discharge with alkali metal chloride solutions used as the cathode was studied. The relation between the discharge emission and the cathode sputtering process leading to the transfer of solution components to the plasma zone was analyzed. It was assumed that the appearance of neutral alkali metal atoms and halogens in the plasma zone is due to the dissociation of halide molecules from a covalently bound state, since the transition to this state becomes possible as a result of excitation of sputtered molecules to high vibrational levels.

Competition between C-C and C-H insertion in prototype transition metal-hydrocarbon reactions.

The competition between C-C and C-H insertion in model transition-metal reactions with cyclopropane and propene (C3H6) was studied as a function of total energy. Insertion of neutral transition metal atoms M (= Y, Zr, Nb, and Mo*) into the C-C bonds of cyclopropane led to formation of MCH2 + C2H4, whereas C-H insertion produced MC3H4 + H2. The measured product branching ratios verify the relative potential energy barrier heights for C-C and C-H insertion predicted by ab initio calculations.

Mechanism of metal cationization in organic SIMS

A scenario of metal cationization in which the organic molecule combines with a neutral excited metal atom is proposed. Ionization of the nascent complex occurs via ejection of an electron during the association process. Electron structure calculations for the model systems C 6H 6+Me (Me=Ag, Cu, Au) using the density functional theory give a strong argument in favor of the proposed mechanism.