Absolute cross sections for electron impact ionization of Ag2

The previously measured relative cross section function for electron impact ionization (EII) of neutral Ag₂ has now been calibrated quantitatively by combining the electron impact ionization with in situ non resonant two photon ionization (NR2PI). By comparing the NR2PI saturation intensities measured for Ag ₂ ⁺ and Ag⁺ with the corresponding EII intensities, the ratio between the electron impact ionization cross sections (EIICS) of neutral Ag₂ and Ag was determined to be σ_Ag2/σ_Ag=1.53 for an electron energy of 46 eV. This result agrees well with the geometricn ^2/3-rule \((\sigma X_n \sim n^{2/3} )\) commonly proposed for the dependence of the EIICS of clustersX _n on the cluster sizen.     

Electron impact and single photon ionization cross sections of neutral silver clusters

Neutral silver atoms and small clusters Ag _n (n=1...4) were generated by sputtering, i.e. by bombarding a polycrystalline silver surface with Ar⁺ ions of 5 keV. The sputtered particles were ionized by a crossed electron beam and subsequently detected by a quadrupole mass spectrometer. In alternative to the electron impact ionization, the same neutral species were also ionized by single photon absorption from a pulsed VUV laser (photon energy 7.9 eV), and the photoionization cross sections were evaluated from the laser intensity dependence of the measured signals. By in situ combining both ionization mechanisms, absolute values of the ratio σ _e (Ag _n )/σ _e (Ag) between the electron impact ionization cross sections of silver clusters and atoms could be determined for a fixed electron energy of 46 eV. These values can then be used to calibrate previously measured relative ionization functions. By calibrating the results using literature data measured for silver atoms, we present absolute cross sections for electron impact ionization of neutral Ag₂, Ag₃ and Ag₄ as a function of the electron energy between threshold and 125 eV.     

Micro-Raman Spectroscopy of Nanostructured Silver Sulfide

Nanostructured silver sulfide powder with an average particle size of about 45 nm, an acanthite α-Ag₂S monoclinic structure (space group P2₁/c), and nonstoichiometric composition Ag_1.93S has been synthesized by the chemical deposition method. The silver sulfide nanopowder has been studied by Raman spectroscopy. According to the Raman scattering data, heating the nanopowder with high-power laser radiation in air leads to photoinduced decomposition of the Ag_1.93S nanopowder to give silver metal. The Raman spectrum of the silver sulfide nanopowder shows a series of bands in the low-frequency range from 90 to 260 cm^–1 associated with vibrations of silver atoms, Ag–S bonds, and symmetric Ag–S–Ag longitudinal modes. Raman spectroscopy confirmed an acanthite monoclinic structure of synthesized silver sulfide nanopowder.     

Characterization of the fluxes of neutral and positively charged clusters (Agn and Agn+; n≤4) produced by argon ion sputtering of silver

The emission of neutral and positively charged silver clusters during sputtering of a polycrystalline silver target by 5 keV Ar⁺ ion bombardment has been studied and the sputter ejected silver flux has been characterized. As a result, the silver flux is found to be strongly dominated byneutral clusters rather than cluster ions. The contribution of neutral clusters in the overall silver flux decreases rapidly and monotonically with increasing cluster size n and decreases, in addition, with decreasing bombarding energy. The well known alternation of the secondary ion intensities of Ag _n ⁺ as a function of cluster size (higher intensities for odd n) is found to be correlated with the effective ionization potentials of the corresponding sputtered neutral clusters.     

Synthesis and crystal structure of the mixed-ligand coordination silver polymer [Ag(CH<Subscript>3</Subscript>SO<Subscript>3</Subscript>)(2,3-Et<Subscript>2</Subscript>Pyz)] · H<Subscript>2</Subscript>O

The coordination polymer [Ag(CH₃SO₃)(2,3-Et₂Pyz)] · H₂O (2,3-Et₂Pyz is diethylpyrazine, C₈H₁₂N₂) was synthesized and its crystal structure was determined. The crystals are triclinic, space group P \(\bar 1\), a = 7.212(1)Å, b = 8.446(1) Å, c = 11.394(1) Å, α = 107.58(1)°, β = 100.35(1)°, γ = 99.52(1)°, V = 632.7(1) ų, ρ_calc = 1.875 g/cm³, Z = 2. In this structure, pairs of silver atoms are linked by bridging methanesulfonate anions CH₃SO ₃ ^? into dimeric units Ag₂(CH₃ SO₃)₂. The distance between the silver atoms in this dimer is 5.16 Å.In addition to two oxygen atoms of the CH₃SO₃ ligands, the Ag⁺ ion coordinates two nitrogen atoms of the neutral ligand 2,3-Et₂Pyz. As a result, polymeric chains [Ag(Et₂Pyz)] _∞ ⁺ are formed along the [100] vector, which are associated in pairs by methanesulfonate anions into infinite columns. Water molecules form H-bonds with oxygen atoms of adjacent CH₃SO ₃ ^? anions.     

ESR-spectrum of silver atoms stabilized in gamma-irradiated aluminium silicate modified by nickel

ESR technique was used to study the effect of conditions chosen to prepare samples to obtain and stabilize silver atoms forming under the action of⁶⁰Co -irradiation at 77 K in aluminium silicate modified by nickel and containing silver ions. The use of¹⁰⁹Ag isotope made it possible to detect two types of silver atoms Ag_I and Ag_II in -irradiated aluminium silicate modified by nickel and containing silver ions introduced by various techniques. The parameters of the ESR-spectrum of the silver particles under study have been determined and their thermal stability has been investigated.     

Unusual coordination in a silver thionate complex. Synthesis,structural characterization and theoretical calculations of dinuclear and polynuclear silver(I) thiosaccharinates with pyridine and 1,10-phenanthroline

Treatment of Ag₆(tsac)₆ (tsac = thiosaccharinate anion) with pyridine (py) and 1,10-phenanthroline (o-phen) each affords two novel silver(I)-thiosaccharinate complexes: dinuclear [Ag₂(tsac)₂py] (1) and polynuclear [Ag(tsac)(o-phen)]_n (2). Both crystal structures have been determined by X-ray diffraction and spectroscopic structural analysis (IR and Raman, UV–Vis, ¹H and ¹³C NMR) have also been made for both compounds. Thermal stability analysis (TGA and DTA) of complex 1 are used to confirm the strength of the pyridine coordination to the silver ion. The molecular structure of complex 1 shows some astonishing characteristics. The two silver atoms are in different environments: one of them is surrounded by two S atoms, while the other completes its coordination sphere by three N atoms, two from the thiosaccharinate anions and the third from a pyridine molecule. The short Ag(1)–Ag(2) contact distance, 2.9681(8) Å, indicates an interaction between the two silver metal atoms exists. Complex 2 shows a thiosaccharinate molecule bridging two silver atoms through the exocyclic S atom while the o-phenanthroline ligand is coordinated as a bidentate N,N chelate, forming a polynuclear chain. Quantum chemical calculations confirm the argentophilic character of the Ag–Ag interaction in complex 1, and its structure and vibrational assignments were correlated and confirmed theoretically.     

Neutralization and matrix deposition experiments on mass-selected silver atoms and clusters

A new apparatus for depositing intense beams of neutral, mass selected metal clusters in rare gas matrices or on a solid surface has been constructed. Metal cluster cations, produced by Ar⁺ sputtering, may be energy analyzed and then mass selected in a quadrupole mass filter. The clusters are neutralized by low energy electrons and then co-deposited with a rare gas on a 4 K sapphire window. Matrix samples were interrogated in situ by UV-optical absorption spectroscopy. Good quality neutral Ag spectra were obtained following a 30 min. Kr deposition of a ca. 2.5 nA cm^?2 beam of Ag⁺. Line strength measurements imply matrices containing about 10¹³ atoms cm^?2, corresponding to a neutralization efficiency of about 50%. Preliminary experiments on Ag ₂ ⁺ yielded only Ag spectra, but with a lesser yield, perhaps indicative of incomplete fragmentation.     

Mass-spectrometric study of the formation of silver nanoclusters in polyether media: 2. Fast atom bombardment and modeling

Within the problem of the synthesis of silver nanoclusters and nanoparticles in polyether media, systems containing silver nitrate AgNO₃ and low-molecular-weight polyethers, poly(ethylene glycol) PEG-400 or oxyethylated glycerol OEG-5, were studied by fast atom bombardment (FAB) mass spectrometry. The formation of stable clusters of polyether oligomers (M _m ) with silver cations M _m · Ag⁺ was shown, in agreement with the previous data of laser desorption/ionization. Quantum-chemical DFT calculations have shown that the M _m · Ag⁺ clusters are stabilized by wrapping of the polyether chain around the silver cation with the cation coordinating ether oxygen atoms. Silver nanoclusters were not found in the FAB mass spectra of liquid systems, but Ag _n ⁺ clusters were detected for silver nanoparticles separated from the reaction medium. No products of chemical transformations of PEG-400 or OEG-5 were observed by FAB. A plausible mechanism of the reduction of silver cations involving nitrate anions is discussed.     

Structure and Properties Characteristic of Dimeric Silver(I) Complex: Dinuclear Bis(O,O′-Diphenyldithiophosphato)bis(1,10-phenanthroline) Ag(I)

The complex bis(O,O-diphenyldithiophosphato)bis(1,10-phenanthroline) silver(I), Ag₂[(PhO)₂PS₂]₂(Phen)₂, has been synthesized and structurally characterized. Its crystal structure has been determined by X-ray crystallography. It crystallizes in the monoclinic system, space group P2₁/c, with unit cell parameters a = 11.140(2) Å, b = 10.044(2) Å, c = 23.006(6) Å, = 113.36(3)° V = 2363.1(9) ų, _calcd = 1.600 g/cm³, and Z = 4 for R ₁ = 0.0961. The coordination geometry of each Ag atom, by two N atoms from 1,10-phenanthroline ligand and by two S atoms from two O,O-diphenyldithio phosphate anions, is that of a tetrahedron. The two diphenyldithiophosphato ligands each bridge two silver atoms to form an eight-membered Ag₂S₄P₂ ring, while the 1,10-phenanthroline molecule coordinates to a silver atom to complete the local tetrahedral geometry. The Ag···Ag separation is 3.185(2) Å. The data of elemental analysis, IR and UV-vis spectroscopies are in good agreement with the crystal structure. The thermal gravimetry data indicate that there are two decomposition steps with one intense endothermical peak and one weak exothermical peak. The final product of the thermal decomposition is AgS.     

Four- and five-coordinate metal atoms in a supramolecular polymeric assembly of silver(I) with (4-methyl-2-quinolylthio)acetate

The coordination compound [Ag₂L₂(H₂O)₂] · ₂H₂O (I), L = C₁₂H₁₀NO₂S has been synthesized by the reaction of AgNO₃ with 4-methyl-2-quinolylthioacetic acid (HL) preliminarily neutralized with an equimolar amount of NBu₄OH. Its crystal structure has been determined, and luminescence properties have been studied. Crystals of I are monoclinic, space group C2/_c, _a = 31.239(6) Å, _b = 12.056(2) Å, _c = 16.846(3) Å, β = 122.17(3)°, V = 5370.4(2) ų, ρ_calc = 1.861 g/cm³, Z = 16. The structure is formed by two crystallographically nonequivalent silver atoms Ag(1) and Ag(2) and two tridentate bridging ligands L coordinated through the S, N, and O atoms. These atoms, together with water molecules, form the coordination environments of the metal atoms with CN = 5 and 4, respectively. The Ag⁺ ions and the tridentate ligands form infinite [Ag₄L₄]_n bands extended in the [001] direction. The presence of outer-sphere water molecules involved in O–H···O hydrogen bonding is responsible for the formation of a supramolecular framework structure. The photoluminescence spectrum of compound I shows two bands at ~450 and ~485 nm corresponding to the blue spectral range.     

Kinetics of electrochemical reactions on the Ag(Hg)/Ag4RbI5 interface

The electrochemical behaviour of the Ag(Hg)/Ag₄RbI₅ interface is investigated by a potentiostatic pulse method. It is found that the rate-determining step of the electrode reaction is electron transfer with an exchange current density of 68 mA cm^–2 and a transfer coefficient of approximately 0.45. The order of the electrochemical reaction for silver oxidation is estimated from polarization investigations of silver amalgam in various concentrations. From this it is deduced that the mercury is ionized and is implanted in the electrolyte together with silver under anodic polarization: 15Ag+85Hg–100e^–→15Ag⁺+85Hg⁺. From comparison of the electrochemical behaviour of the Ag(Hg)/Ag₄RbI₅ and Ag/Ag₄RbI₅ interfaces it is concluded that the rate of anodic silver dissolution on the Ag/Ag₄RbI₅ interface is limited by crystallization effects. Electronic Publication     

Synthesis, crystal structure, and luminescent properties of a silver(I) perrhenate complex with phenazine

The silver complex with phenazine [Ag(Phz)₂(H₂O)]ReO₄ (Phz is C₁₂H₈N₂) has been synthesized, and its crystal structure has been determined. The crystals are triclinic: space group $P\bar 1$ , a = 9.587(1) Å, b = 10.875(1) Å, c = 11.668(1) Å, α = 104.98(1)°, β = 103.87(1)°, γ = 92.94(1)°, V = 1132.6(2) ų, Z = 2, ρ_calc = 2.160 g/cm³. The structure is composed of the [Ag(Phz)₂(H₂O)]⁺ silver cationic complexes and ReO ₄ ^? anions. The Ag⁺ ion is coordinated by two nitrogen atoms of independent phenazine molecules and the water oxygen atoms and has a T-shaped coordination (Ag-N_av 2.223 Å, Ag-O_w 2.498(8) Å). Phenazine, being an electron-donor ligand, forms columns due to π-π stacking interaction between the aromatic groups. The water molecules form hydrogen bonds with the oxygen atoms of water molecules of neighboring complexes and with oxygen atoms of the ReO ₄ ^? anions.     

Laser photoionization and spectroscopy of gas phase silver clusters

Silver clusters containing up to 40–50 atoms are produced by laser vaporization in a pulsed-nozzle molecular beam source and studied with laser photoionization mass spectroscopy. A variety of Nd:YAG pumped dye laser and UV excimer laser wavelengths are used to achieve ionization. Ionization dynamics are studied by varying the laser wavelength and fluence. Bracketing experiments under single-photon ionization conditions are used to estimate ionization potentials as a function of cluster size. An even-odd ionization potential alternation is observed with odd-numbered clusters (N=3, 5, 7 ...) having lower ionization potentials than adjacent even-numbered species. Shell closings at clusters containing 2, 8 20 and 40 electrons are observed consistent with a one-electron shell model picture of cluster electronic structure. Resonance-enhanced ionization produces a vibrationally resolved spectrum for the trimer, Ag₃, yielding an electronic state assignment and excited state vibrational frequencies. Fragmentation in dimer ionization via theE state at 249 nm establishes the dissociation energy of Ag ₂ ⁺ to be <2.1 eV.     

Stepwise Photoionization of 1,2-Dihydroxybenzene Vapor

The stepwise ionization processes of 1,2-dihydroxybenzene vapor at 315–275 and 266 nm were studied by the techniques of mass spectrometry, total ionization current spectroscopy, and zero electron kinetic energy spectroscopy. A two-step ionization process yielding the molecular ion prevails at a laser intensity up to 10⁷W/cm². As the radiation intensity increases, fragmentation takes place via the dissociation of molecular and fragment ions due to absorption of one additional photon. The formation pathways of principal fragment ions are discussed.     

Coordination silver polymer with the bridging anion of oxadiazolylacrylic acid: Synthesis,crystal structure,and luminescence properties

Metal complex [AgL] (I) is synthesized by the reaction of AgNO₃ with 3-(5-furyl-1,3,4-oxadiazol-2-yl)acrylic acid (HL, C₉H₆N₂O₄), and its crystal structure is determined (CIF file CCDC no. 1426528). The crystals are monoclinic, space group P2₁/n, a = 4.946(1), b = 20.084(1), c = 9.015(1) Å, β = 92.32(1)°, V = 894.482 ų, ρ_calcd = 2.442 g/cm3, Z = 4. In structure I, pairs of centrosymmetric silver atoms are bound by bidentate-bridging oxygen atoms of two anions L into dimeric blocks. The Ag–Ag distance in the dimer is 2.854(1) Å. The coordination sphere of Ag⁺ contains two oxygen atoms, one silver atom, and one nitrogen atom of the diazolyl fragment of the adjacent anion. The coordination polyhedron of Ag⁺ is a strongly distorted tetrahedron. The molecular packing of crystal I is built of infinite ribbons (AgL)n extended along the direction [001]. The photoluminescence spectrum of compound I contains intense bands about 550 nm corresponding to the green spectral range and less intense bands at 425 and 485 nm.     

Double helix of the coordination polymer of silver with 1,3-bis(4-pyridyl)propane: Synthesis and crystal structure of [Ag(C<Subscript>13</Subscript>H<Subscript>14</Subscript>N<Subscript>2</Subscript>)](CF<Subscript>3</Subscript>CO<Subscript>2</Subscript>)

The [Ag(Bpp)](CF₃CO₂) complex (Bpp is 1,3-bis(4-pyridyl)propane, C₁₃H₁₄N₂) is synthesized, and its structure is determined. The crystals are monoclinic, space group C2/c, a = 26.169(5), b = 10.521(2), c = 12.906(3) Å, β = 117.99(3)°, V = 3137.7(11) ų, ρ_calcd = 1.775 g/cm³, Z = 8. The structure contains double helices of-Ag-Bpp-Ag-Bpp-cationic chains with a helix period of 21.042 Å. The Ag…Ag distance between a pair of silver atoms from different chains in the helix is 3.201 Å, and the distance between the adjacent helices is 3.279 Å. The silver atom is linked with two bridging nitrogen atoms of two Bpp ligands in an almost linear coordination: Ag-N_avg 2.142 Å; NagN, 171.3(4)°. The CF₃C ₂ ^? anion has a weak contact with the silver ion (Ag…O 2.62(2) Å).     

<Emphasis Type="Italic">In situ</Emphasis> XPS study of the size effect in the interaction of NO with the surface of the model Ag/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/FeCrAl catalysts

The interaction of NO with the surface of model Ag/Al₂O₃/FeCrAl catalysts containing Ag nanoparticles of different size (1 and 3 nm) was studied. The use of the Auger parameter α_Ag (E _b(Ag3d_5/2) + E _kin(Ag MVV)) made it possible to reliably identify the change in the chemical state of silver cluster upon their interaction with О₂ and NO. The oxygen treatment leads to the oxidation of small Ag nanoparticles (1 nm) and formation of AgO _x clusters resulted in the intensive formation of nitrite—nitrate structures on the step of the interaction with NO. These structures are localized on both the silver clusters and Al₂O₃ surface. An increase in the size of Ag⁰ nanoparticles to 3 nm results in an increase in the stability of these structures and impedes the Ag⁰ → AgO _x transition, due to which the formation of surface groups NO₂ ^–/NO₃ ^– is suppressed. The data obtained make it possible to explain the dependence of the activity of the Ag/Al₂O₃ catalysts in the selective reduction of NO on the Ag nanoparticle size.     

Synthesis and crystal structure of [Ag2(μ4-hmt)(NO2)2]n. A two-dimensional network with square cavities self-assembled by hmt (hmt = Hexamethylenetetramine)

AgNO₂ (1 mol) reacts with hexamethylenetetramine (hmt) (1 mol) in MeCN–H₂O to yield a two-dimensional coordination polymer [Ag₂( ₄-hmt)(NO₂)₂]_n with square cavities. The Ag2 atom is located in a linear structure coordination environment with two nitrogen atoms from two hmt molecules respectively. The Ag1 atom is coordinated in a triangular prism surrounded by two nitrogen atoms from two hmt molecules respectively and four oxygen atoms from two NO^– ₂ ions respectively. The four nitrogen atoms of each hmt unit are all connected to Ag^I to form a two-dimensional network.     

Improved detection sensitivity of elements in solids via laser postionization in laser desorption time‐of‐flight mass spectrometry

A newly constructed laser desorption (532 nm, 5 ns) and laser postionization (266 nm, 5 ns) time‐of‐flight mass spectrometer (LD‐LPI‐TOFMS) has been applied for improving the detection sensitivity of elements in solid samples. This method affords to acquire the information of the elemental impurities in solid standards as well as limit of detection (LOD) down to 10⁻⁸ g/g for some elements. Neutral atoms of solids are generated by low‐irradiance laser desorption (< 10⁸ W/cm²), followed by high‐irradiance laser postionization (~ 10⁹ W/cm²) of the desorbed atoms, facilitating to decouple the desorption and ionization processes in spatial and temporal domain. This non‐interacting feature overcomes the discrimination between deteriorating spectral resolution at high irradiance (10⁹–10¹¹ W/cm²) and limited detectable elemental species and high LOD at low or medium irradiance (below 10⁹ W/cm²). The utilization of originally “wasted” neutral atoms by laser postionization will help improve atom utilization and instrumental sensitivity. In this work, getting the utmost out of the consumed neutral atoms instead of an increment in sampling amounts is given attention with high priority for achieving high sensitivity and low LOD, which is especially useful on the occasions where very low sample consumption is desired.