Collision-energy-resolved penning ionization electron spectroscopy of HCOOH, CH3COOH, and HCOOCH3 by collision with He*(2(3)S) metastable atoms

Penning ionization of formic acid (HCOOH), acetic acid (CH3COOH), and methyl formate (HCOOCH3) upon collision with metastable He*(2(3)S) atoms was studied by collision-energy/electron-energy-resolved two-dimensional Penning ionization electron spectroscopy (2D-PIES). Anisotropy of interaction between the target molecule and He*(2(3)S) was investigated based on the collision energy dependence of partial ionization cross sections (CEDPICS) obtained from 2D-PIES as well as ab initio molecular orbital calculations for the access of a metastable atom to the target molecule. For the interaction potential calculations, a Li atom was used in place of He*(2(3)S) metastable atom because of its well-known similarity in interaction with targets. The results indicate that in the studied collision energy range the attractive potential localizes around the oxygen atoms and that the potential well at the carbonyl oxygen atom is at least twice as much as that at the hydroxyl oxygen. Moreover we can notice that attractive potential is highly anisotropic. Repulsive interactions can be found around carbon atoms and the methyl group.     

Anisotropic interaction and stereoreactivity in a chemi-ionization process of OCS by collision with He*(2(3)S) metastable atoms

Ionic-state-resolved collision energy dependence of Penning ionization cross sections for OCS with He*(2(3)S) metastable atoms was measured in a wide collision energy range from 20 to 350 meV. Anisotropic interaction potential for the OCS-He*(2(3)S) system was obtained by comparison of the experimental data with classical trajectory simulations. It has been found that attractive potential wells around the O and S atoms are clearly different in their directions. Around the O atom, the collinear approach is preferred (the well depth is ca. 90 meV), while the perpendicular approach is favored around the S atom (the well depth is ca. 40 meV). On the basis of the optimized potential energy surface and theoretical simulations, stereo reactivity around the O and S atoms was also investigated. The results were discussed in terms of anisotropy of the potential energy surface and the electron density distribution of molecular orbitals to be ionized.     

Production of a spin-polarized,metastable He(23 S) beam for studies in atomic and surface physics

This beam was developed as a target for a crossed-beam electron-atom scattering experiment on the interaction of a polarized spin-1/2 electron with a polarized spin-1 atom. In the future this beam will be used in “Spin-Polarized Metastable Atom Deexcitation Spectroscopy” (SPMDS) for studying ferromagnetic surfaces without and with adsorbate layers. We use a discharge source for producing a beam of metastable helium atoms, a permanent sextupole magnet with a central stop at its exit for selecting He(2³ S) atoms in the Zeeman substatem _s =+1, a zero-field spin flipper for reversing the atomic beam polarization with respect to a magnetic guiding field, and a Stern-Gerlach magnet for analyzing the atomic polarization. At a distance of 90 cm beyond the exit of the sextupole, in the “interaction region” of an experiment, the polarized beam has a circular cross section of about 6 mm FWHM and a particle density of 1 · 10⁷ atoms/cm³. The reversible spin polarization was determined asP=0.90±0.02. A possible contamination of the beam with metastable singlet atoms is included within this value; the ground-state He atoms are not considered to be part of the polarized beam. An observed contamination with long-lived Rydberg atoms can easily be destroyed by applying a high electric field.     

Use of spin-labelling techniques to probe the dynamics of He(23 S) deexcitation at solid surfaces

Spin labelling techniques, specifically the use of electron-spin-polarized He(2³ S) metastable atoms coupled with energy-resolved spin analysis of the ejected electrons, are used to investigate the dynamics of He(2³ S) deexcitation at solid surfaces. Data for a clean Au(100) surface are presented that show that deexcitation occurs exclusively through resonance ionization followed by Auger neutralization. The electrons involved in Auger neutralization are observed to be correlated in spin and possible reasons for this are discussed. Results obtained at Xe and NO films adsorbed on cooled Au(100) and Cu(100) substrates, respectively, show that He(2³ S) metastable atom deexcitation is analogous to gas-phase Penning ionization. Detailed differences are apparent that can be attributed to effects associated with the underlying substrate and interactions involving neighboring atoms in the film.     

{Sn(9)[Si(SiMe(3))(3)](2)}(2-): A Metalloid Tin Cluster Compound With a Sn(9) Core of Oxidation State Zero

The disproportionation reaction of the subvalent metastable halide SnCl proved to be a powerful synthetic method for the synthesis of metalloid cluster compounds of tin. Now we present the synthesis and structural characterization of the anionic metalloid cluster compound [Sn(9)[Si(SiMe(3))(3)](2)](2-)3 where the oxidation state of the tin atoms is zero. Quantum chemical calculations as well as M?ssbauer spectroscopic investigations show that three different kinds of tin atoms are present within the cluster core. Compound 3 is highly reactive as shown by NMR investigations, thus being a good starting material for further ongoing research on the reactivity of such partly shielded metalloid cluster compounds.     

Electron-impact ionization of the metastable Mg(...2p63s3p3P0,2) atoms

Electron-impact ionization of Mg atoms from metastable states was investigated. The method and tech-nique of crossed atomic and electron beam studies are described. The value of the total ionization cross section from the 3s3p ³P_j metastable states for 4... 21 eV incident electron energy was determined. It was found that ionization cross sections from the metastable and ground states differ considerably. This is mainly due to the different mechanisms of ion formation from the metastable and ground states. The results obtained are compared with those calculated in the classical mechanics binary approximation.     

Molecular beam kinetics: The excitation function of the reaction Xe(3P0,2) + Br2 → XeBr* + Br

Fast beams of metastable xenon atoms, Xe(³P_0,2), have been generated by combining the high speed rotor technique with electron bombardment excitation. In a crossed-beam apparatus, the excitation function σ(E_t) of the reaction Xe(³P_0,2) + Br₂ → XeBr* + Br has been measured. The results show a close similarity to the behaviour of the alkali metal atoms, with which the metastable rate gas atoms have been previously compared.     

(EnH2)2Ge2S6的合成与结构表征

用溶剂热方法制备了(EnH2)2Ge2S6单晶.单晶X射线衍射分析结果表明,(EnH2)2Ge2S6属单斜晶系,P2(1)/n空间群,晶胞参数a=0.67125(5)nm,b=1.12290(4)nm,c=1.07518(4)nm,β=92.288(2)°,Z=2.利用DSC及TG分析研究了其热稳定性,结果表明,该化合物在200℃以下能够稳定存在.     

Fullerene-like (IF) Nb(x)Mo(1-x)S2 nanoparticles

IF-Mo1-xNbxS2 nanoparticles have been synthesized by a vapor-phase reaction involving the respective metal halides with H2S. The IF-Mo1-xNbxS2 nanoparticles, containing up to 25% Nb, were characterized by a variety of experimental techniques. Analysis of the powder X-ray powder diffraction, X-ray photoelectron spectroscopy, and different electron microscopy techniques shows that the majority of the Nb atoms are organized as nanosheets of NbS2 within the MoS2 host lattice. Most of the remaining Nb atoms (3%) are interspersed individually and randomly in the MoS2 host lattice. Very few Nb atoms, if any, are intercalated between the MoS2 layers. A sub-nanometer film of niobium oxide seems to encoat the majority of the nanoparticles. X-ray photoelectron spectroscopy in the chemically resolved electrical measurement mode (CREM) and scanning probe microscopy measurements of individual nanoparticles show that the mixed IF nanoparticles are metallic independent of the substitution pattern of the Nb atoms in the lattice of MoS2 (whereas unsubstituted IF-MoS2 nanoparticles are semiconducting). Furthermore the IF-Mo1-xNbxS2 nanoparticles are found to exhibit interesting single electron tunneling effects at low temperatures.     

Kinetic study of N2(B3Πg, υ) quenching by laser-induced fluorescence

The quenching kinetics of N₂(B³Π_g, υ) have been determined in a low-pressure flow system in the absence of N atoms. Individual vibrational levels of the B state were populated by laser pumping (first-positive bands) of N₂(A³Σ_u⁺) molecules. The latter were created upstream by energy transfer from Ar metastable atoms.     

Collision-energy-resolved Penning ionization electron spectroscopy of p-benzoquinone: study of electronic structure and anisotropic interaction with He(*)(2 (3)S) metastable atoms

Collision energy dependence of partial ionization cross sections (CEDPICS) of p-benzoquinone with He(*)(2 (3)S) metastable atoms indicates that interaction potentials between p-benzoquinone and He(*)(2 (3)S) are highly anisotropic in the studied collision energy range (100-250 meV). Attractive interactions were found around the C==O groups for in-plane and out-of-plane directions, while repulsive interactions were found around CH bonds and the benzenoid ring. Assignment of the first four ionic states of p-benzoquinone and an analogous methyl-substituted compound was examined with CEDPICS and anisotropic distributions of the corresponding two nonbonding oxygen orbitals (n(O) (+),n(O) (-)) and two pi(CC) orbitals (pi(CC) (+),pi(CC) (-)). An extra band that shows negative CEDPICS was observed at ca. 7.2 eV in Penning ionization electron spectrum.     

Collision-energy-resolved Penning ionization electron spectroscopy of bromomethanes (CH3Br, CH2Br2, and CHBr3) by collision with He*(2(3)S) metastable atoms

Ionization of bromomethanes (CH3Br, CH2Br2, and CHBr3) upon collision with metastable He*(2(3)S) atoms has been studied by means of collision-energy-resolved Penning ionization electron spectroscopy. Lone-pair (nBr) orbitals of Br4p characters have larger ionization cross sections than sigma(C-Br) orbitals. The collision-energy dependence of the partial ionization cross sections shows that the interaction potential between the molecule and the He*(2(3)S) atom is highly anisotropic around CH3Br or CH2Br2, while isotropic attractive interactions are found for CHBr3. Bands observed at electron energies of approximately 2 eV in the He*(2(3)S) Penning ionization electron spectra (PIES) of CH2Br2 and CHBr3 have no counterpart in ultraviolet (He I) photoionization spectra and theoretical (third-order algebraic diagrammatic construction) one-electron and shake-up ionization spectra. Energy analysis of the processes involved demonstrates that these bands and further bands overlapping with sigma(C-Br) or piCH2 levels are related to autoionization of dissociating (He+ - Br-) pairs. Similarly, a band at an electron energy of approximately 1 eV in the He*(2(3)S) PIES spectra of CH3Br has been ascribed to autoionizing Br** atoms released by dissociation of (unidentified) excited states of the target molecule. A further autoionization (S) band can be discerned at approximately 1 eV below the lone-pair nBr bands in the He*(2(3)S) PIES spectrum of CHBr3. This band has been ascribed to the decay of autoionizing Rydberg states of the target molecule (M**) into vibrationally excited states of the molecular ion. It was found that for this transition, the interaction potential that prevails in the entrance channel is merely attractive.     

New layered materials: syntheses, structures, and optical properties of K(2)TiCu(2)S(4), Rb(2)TiCu(2)S(4), Rb(2)TiaAg(2)S(4), Cs(2)TiAg(2)sS(4), and Cs(2)TiCu(2)Se(4)

The new compounds K(2)TiCu(2)S(4), Rb(2)TiCu(2)S(4), Rb(2)TiAg(2)S(4), Cs(2)TiAg(2)S(4), and Cs(2)TiCu(2)Se(4) have been synthesized by the reactions of A(2)Q(3) (A = K, Rb, Cs; Q = S, Se) with Ti, M (M = Cu or Ag), and Q at 823 K. The compounds Rb(2)TiCu(2)S(4), Cs(2)TiAg(2)S(4), and Cs(2)TiCu(2)Se(4) are isostructural. They crystallize with two formula units in space group P4(2)/mcm of the tetragonal system in cells of dimensions a = 5.6046(4) A, c = 13.154(1) A for Rb(2)TiCu(2)S(4), a =6.024(1) A, c = 13.566(4) A for Cs(2)TiAg(2)S(4), and a =5.852(2) A, c =14.234(5) A for Cs(2)TiCu(2)Se(4) at 153 K. Their structure is closely related to that of Cs(2)ZrAg(2)Te(4) and comprises [TiM(2)Q(4)(2)(-)] layers, which are separated by alkali metal atoms. The [TiM(2)Q(4)(2)(-)] layer is anti-fluorite-like with both Ti and M atoms tetrahedrally coordinated to Q atoms. Tetrahedral coordination of Ti(4+) is rare in the solid state. On the basis of unit cell and space group determinations, the compounds K(2)TiCu(2)S(4) and Rb(2)TiAg(2)S(4) are isostructural with the above compounds. The band gaps of K(2)TiCu(2)S(4), Rb(2)TiCu(2)S(4), Rb(2)TiAg(2)S(4), and Cs(2)TiAg(2)S(4) are 2.04, 2.19, 2.33, and 2.44 eV, respectively, as derived from optical measurements. From band-structure calculations, the optical absorption for an A(2)TiM(2)Q(4) compound is assigned to a transition from an M d and Q p valence band (HOMO) to a Ti 3d conduction band.     

Collision-energy-resolved penning ionization electron spectroscopy of phenylacetylene and diphenylacetylene by collision with He*(2(3)s) metastable atoms

Penning ionization of phenylacetylene and diphenylacetylene upon collision with metastable He*(2(3)S) atoms was studied by collision-energy-/electron-energy-resolved two-dimensional Penning ionization electron spectroscopy (2D-PIES). On the basis of the collision energy dependence of partial ionization cross-sections (CEDPICS) obtained from 2D-PIES as well as ab initio molecular orbital calculations for the approach of a metastable atom to the target molecule, anisotropy of interaction between the target molecule and He*(2(3)S) was investigated. For the calculations of interaction potential, a Li(2(2)S) atom was used in place of He*(2(3)S) metastable atom because of its well-known interaction behavior with various targets. The results indicate that attractive potentials localize in the pi regions of the phenyl groups as well as in the pi-conjugated regions of the acetylene group. Although similar attractive interactions were also found by the observation of CEDPICS for ionization of all pi MOs localized at the C[triple bond]C bond, the in-plane regions have repulsive potentials. Rotation of the phenyl groups about the C[triple bond]C bond can be observed for diphenylacetylene because of a low torsion barrier. So the examination of measured PIES was performed taking into consideration the change of ionization energies for conjugated molecular orbitals.     

Metastable 11 K Superconductor Na(1-y)Fe(2-x)As(2)

The topochemical deintercalation of Na(+) ions from solid NaFeAs at room temperature in THF with iodine yields the superconducting phase Na(1-y)Fe(2-x)As(2) (T(c) ≈ 11 K). This metastable iron arsenide decomposes at 120 °C and is not accessible by high-temperature solid-state synthesis. X-ray powder diffraction confirms the ThCr(2)Si(2)-type structure, but reveals very small coherently scattering domains with a mean composition Na(0.9(2))Fe(1.7(1))As(2). HRTEM investigations show crystalline as well as strongly distorted areas with planar defects. The latter are probably due to sodium loss and disorder which is also detected by (23)Na solid state NMR. The (57)Fe-M?ssbauer spectrum of Na(1-y)Fe(2-x)As(2) shows one type of iron atoms in tetrahedral coordination. All results point to one crystallographic phase with very small domains due to fluctuations of the chemical composition. From electronic reasons we suggest the superconducting phase is presumably NaFe(2)As(2) in the ordered fractions of the sample.     

Das cyclische Thioarsenat(III) (PPh4)2As2S6

The Cyclic Thioarsenate(III) (PPh₄)₂As₂S₆ The reaction of Na₃AsS₄ with tetraphenylphosphonium chloride in ethanol or dimethylformamide proceeds with an intramolecular redox reaction, yielding (PPh₄)₂As₂S₆. According to its X-ray crystal structure analysis (4071 reflections, R = 0.070) the anion consists of a six-membered ring of two As and four S atoms in the chair conformation. The As atoms occupy the ring positions 1 and 3, and each of them has an additional terminal S atom.     

Velocity dependence of the penning ionization cross section of D atoms by He (2 1S) and He (2 3S) atoms

Measurements of the Penning ionization cross section, σ_PI of D atoms by metastable He atoms show that σ_PI for the reaction He (2 ¹S) + D is much larger than σ_PI for He (2 ³S) + D. In the relative velocity range ν_r = (2.3–4.8) × 10⁵ cm/s (0.037–0.163 eV), σ_PI for He (2 ¹S) + D collisions was found to vary as ν_r^?0.33.     

Ge4Br4[Mn(CO)5]4 and Ge6Br2[Mn(CO)5]6: first germanium cluster compounds containing Mn(CO)5 ligands

Cluster compounds of germanium exhibiting germanium-germanium bonds, where the germanium atoms are additionally bound to transition metal ligands, are rare. Here a synthetic pathway to such cluster compounds is described, starting from metastable Ge I halide solutions leading to the two cluster compounds Ge4Br4[Mn(CO)5]4 and Ge6Br2[Mn(CO)5]6, being the first examples of germanium cluster compounds bearing Mn(CO)5 ligands. The Ge6 compound exhibits a novel arrangement of germanium atoms that has not been previously observed in ligand stabilized cluster compounds of germanium, neither with organic nor with transition metal ligands. The bonding situation inside the cluster compounds is discussed, together with a possible reaction pathway that opens the way to metalloid cluster compounds of germanium exhibiting Mn(CO)5 ligands.     

Lifetime and yield of metastable Ar2(+) ions

Ar2(+) ions produced in a cooled supersonic expansion by electron-impact ionization are accelerated at 2.5 keV and kept during few milliseconds inside a linear electrostatic trap. The lifetime of the metastable Ar2(+) ion is determined from the measurement of the rate of the argon atoms escaping the trap. The lifetime and the relative metastable populations are measured as a function of the pressure and temperature in the supersonic expansion, i.e., of the mean cluster size. Possible mechanisms responsible for the metastable formation are discussed.     

Complexes of Co(II) and Zn(II) with N-(Thio)phosphorylthioureas AdNHC(S)NHP(O)(OiPr)2 and MeNHC(S)NHP(S)(OiPr)2

The reaction of the potassium salt of the N-(thio)phosphorylated thioureas AdNHC(S)NHP(O)(OiPr)₂ (HL^I , Ad = Adamantyl) and MeNHC(S)NHP(S)(OiPr)₂ (HL^II ) with Co(II) and Zn(II) in aqueous EtOH leads to [ML^I,II ₂] chelate complexes. They were investigated by UV-vis, ¹H and ³¹P NMR spectroscopy, and microanalysis. The molecular structures of [ML^I ₂] were elucidated by single crystal X-ray diffraction analysis. The metal centers in both complexes are found to be in a distorted-tetrahedral O₂S₂ environment formed by the C=S sulfur atoms and the P=O oxygen atoms of two deprotonated L^I ligands. The photoluminescence properties of [ZnL^II ₂] are also reported.