Isotope Shifts of Nitrogen around 800 nm

The Doppler-limited absorption spectra of ¹⁴N and ¹⁵N atoms were measured around 800 nm using concentration modulation spectroscopy to study their isotope shifts. The nitrogen atoms were generated by discharging molecular nitrogen buffered with helium in a homemade discharge tube. The isotope shifts of four multiplets (3s⁴P_J→3p⁴D_J^o, 3s⁴P_J→3p⁴P_J^o, 3s²D_J→5s²P_J^o, and 3p²P_J^o→5s²D_J^o) were measured and their J-dependent specific mass shifts were observed and discussed.     

Kinetic study of electronically excited silicon atoms,Si(3p2(1S0)), by time-resolved attenuation of atomic resonance radiation

The collisional behaviour of electronically excited silicon atoms in the 3p²(¹S₀) state, 1.909 eV above the 3p²(³P₀) ground state, is investigated by time-resolved attenuation of atomic resonance radiation at λ = 390.53 nm (4s(¹P^o₁)←3p² (¹S₀)). The optically metastable Si(3¹S₀) atoms were generated by the repetitive pulsed irradiation of SiCl₄ and their decay monitored in the presence of added gases. Absolute quenching rate constants (k_Q, cm³ molecule^?1 s^?1, 300 K) are reported for the following collision partners: He (?1.3 × 10^?15), SiCl₄ ((9.1 ± 1.4) × 10^?11), O₂ ((1.5 ± 0.2) × 10^?11) and N₂O ((4.3 ± 0.4) × 10^?11). The results for O₂ and N₂O are compared with analogous data reported hitherto for Si(3p²(³P_J)) and with those for the other np²(¹S₀) states of the group IV atoms C, Ge, Sn and Pb. The rate data for the silicon atoms are considered in terms of the nature of the potential surfaces arising from symmetry arguments based on the weak spin orbit coupling approximation.     

The collisional behaviour of the spin orbit states of the lead atom,Pb(63P1,2), studied by time-resolved attenuation of atomic resonance radiation

A kinetic study of lead atoms in the spin orbit states, Pb(6³P₁) and Pb Pb(6³P₂), 0.969 and 1.320 eV, respectively, above the 6³P₀ ground state, has been carried out by atomic absorption spectroscopy. The electronically excited lead atoms were generated by the pulsed irradiation of lead tetraethyl and monitored photoelectrically by time-resolved attenuation of resonance radiation. The decay of the two atomic states has been studied in the presence of He, Ar, H₂, D₂, N₂, O₂, CO, NO, CO₂, N₂O, CH₄, C₂H₄, C₂H₂ CF₄, SF₆, and PbEt₄, and rate constants for the collisional quenching by these gases are reported. The resulting data are compared with those for the deactivation of other atomic spin orbit states of comparable energy. In general, the higher energy state, Pb(6³P₂), is found to be deactivated more rapidly. It would appear that the magnitude of the electronic energy to be transferred on collision governs the rates of quenching, at least where a weak interaction potential is involved, and that for most gases, deactivation of Pb(6³P₂) proceeds via Pb(6³P₁).     

Fine structure of As−

The energies of the As^? fine structure components 4p^{4 3} P ₁ and 4p^{4 3} P ₀ have been determined relative to the 4p^{4 3}P₂ ground state by using photodetachment electron spectroscopy. Fine structure splittings of ΔE(³ P ₁ ? ³ P ₂) = 125(3) meV and ΔE(³ P ₀ ? ³ P ₂) = 166(5) meV have been obtained. It is the first experimental determination of the energy of the J = 1 level and an improvement of the accuracy for the J = 0 level. Previous isoelectronic extrapolations are consistent with the experimental values.     

Two-photon induced fluorescence and resonance-enhanced ionization of sulfur atoms

Two-photon induced fluorescence and resonance-enhanced photoionization have been observed in atomic sulfur originating from both the ³P_2,1,0 and the ¹D₂ states. Sulfur atoms are generated by the sequential multiphoton dissociation of CS₂ at probing wavelengths. The two-photon absorption process involves the 3 ³P_2,1,0 → 4 ³P_2,0,1 or the 3 ¹D₂ → 4 ¹F₃ transitions with resolution of the individual J″ → J′ transitions in most cases. Intensities of the 3³P_J″ → 4 ³P_J′ transitions have been compared with Hartree-Fock calculated transition probabilities from the analogous transitions in atomic oxygen. Photoionization is observed in a three-photon (two to resonance) ionization originating from the ³P_2,1,0 and the ¹D₂ states. Induced fluorescence is observed at 167 and 180 nm which is dipole-allowed radiation from the intermediate ³S⁰₁ and ¹D⁰₂ states, respectively.     

Crystal and molecular structure of guanidinium hexatungsto-bis(p-aminophenylarsonate) tetrahydrate,[C(NH2)3]4[p-NH3C6H4As)2W6O25]·4H2O

The crystal structure of a new type arylarsonic polytungstate [C(NH₂)₃]₄[p-NH₃C₆H₄As)₂W₆O₂₅]·4H₂O was determined by single-crystal X-ray diffraction analysis. It belongs to triclinic, space group \[ P\bar 1 \], with cell dimensions a = 12.863(3), b = 18.912(3), c = 21.383(4) Å α = 91.14(2)°, β = 93.65(3)°, γ = 92.25(3)°, V = 5185.9 ų, Z = 4, D_c = 2.753 g/cm³. The intensity data were collected on an Enraf-Nonius CAD4 diffractometer with Mo K_α radiation. The positions of all tungsten and arsenic atoms were determined by direct method. The other non-hydrogen atoms were revealed by difference Fourier synthesis. The structure was refined by fullmatrix least-squares procedure to a final R value of 0.070. The crystal structure contains two similar but nonidentical molecules. Two similar anions consist of a ring of six WO₆ octahedra, which are connected with one face-sharing, two corner-sharings and three edge-sharings, and two p-aminophenylarsonic tetrahedra capped above and below the ring. In each WO₆ ring, four tungsten atoms, which are joined with edge-sharing oxygen atoms, are almost coplanar, while the two others, which are joined with face-sharing oxygen atoms, protrude out of the ring towards the same side. The two arsenic atoms in each anion are not equivalent in their bonding manner. In each anion, all non-hydrogen atoms of each organic group are in the same plane. Each molecule contains one anion, four C(NH₂)₃+ cations and four water molecules. There are many hydrogen bonds between cations and anions throughout the whole crystal. The amino groups can accept protons, so that the charge of the resulting anion decreases and [(RAs)₂W₆O₂₅]^4- type complexes are formed.     

Experimental and theoretical cross sections for photoionization of metastable Xe*. (6s 3 P 2, 3 P 0) atoms near threshold

Using high resolution laser photoelectron spectrometry we have determined absolute cross sections σJ ₀ J ₁ and the electron angular distribution parameter for one photon ionization of metastable Xe^*(6s ³ P _J0, J ₀ = 2, 0) atoms to the resolved Xe₊ (² P _J1, J ₁ = 3/2, 1/2) ion states at several wavelengths near threshold. For comparison with the present and future experimental data we have calculated partial cross sections and ß-parameters for photoionization of Xe^*(6s ³ P _J0, J ₀ = 2, 0) and of the analogous alkali atom Cs(6s) over the photoelectron energy range (0–5) eV. We have used both a term-dependent Pauli-Fock (PF) approach and a configuration interaction method involving Pauli-Fock atomic orbitals (CIPF). Through the PF method we include relativistic effects on the atomic orbitals; the CIPF method was designed to take into account the important electron correlation effects which are found to be essential for obtaining good agreement between the theoretical and experimental results.     

Density functional calculations on triply excited states of lithium isoelectronic sequence

Triply excited states of many-electron atomic systems are characterized by the presence of strong electron correlation, closeness to more than one threshold, and degeneracy with many continua; therefore, they offer unusual challenges to theoretical methodologies. In the present article, we computed with reasonable accuracy all the n=2 intrashell triply excited states (2s²2p ²P; 2s2p^{2 2}D, ⁴P, ²P, ²S; and 2p^{3 2}D, ²P, ⁴S) of three-electron atomic systems (Z=2, 3, 4, 6, 8, 10) by using a density functional formalism developed recently in our laboratory, based on the nonvariational Harbola–Sahni exchange potential in conjunction with a parametrized local Wigner and Lee–Yang–Parr correlation potentials. Nonrelativistic energies and densities are obtained by solving a Kohn–Sham-type differential equation. The calculated results are compared with available experimental and other theoretical data. The 2p³(⁴S)→1s2p²(⁴P) transition wavelength for the isoelectronic series is also computed. The overall good agreement of our results with the literature data indicates the reliability of the present density functional methodology for excited states of many-electron systems. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 65 : 317–332, 1997     

Collisional behaviour of electronically excited silicon atoms,Si(3p2(D1D2)), by atomic absorption spectroscopy

The collisional behaviour of electronically excited silicon atoms in the optically metastable 3p²(¹D₂) state (0.781 eV) is investigated by time-resolved resonance absorption in the ultraviolet. Si(3 ¹D₂) was generated by the repetitive pulsed irradiation of SiCl₄ at λ > 165 nm in a flow system, and monitored by attenuation of resonance radiation at λ = 288.16 nm (4s(¹P⁰₁) ← ep²(¹D₂)) using signal averaging. Absolute second-order rate constants (k_R, cm³ molecule^?1 s^?1, 300 K) are reported for the gases: H₂[(8.1 ± 1.5) × 10^?11], O₂[(2.3 ± 0.4) × 10^?11], He (? 10^?15) and SiCl₄ [(2.9 ± 0.4) × 10^?10]. These results are compared with the analogous data reported hitherto for Si(3³P_J) and Si(3 ¹S₀). Those for H₂ and O₂ are discussed within the context of symmetry arguments on the nature of the potential surfaces involved using the weak spin orbit coupling approximation. Finally, pulsed stimulated emission operating on the transition Si(3P²)(¹So → ¹D₂) (λ = 1.0995 μ) was not detected in high energy pulse experiments using a confocal cavity, despite the population inversion between Si(3 ¹S₀ and Si(3 ¹D₂) observed by resonance absorption following the photolysis of SiCl₄.     

Atom Exchange Versus Reconstruction: (GexAs4−x)x− (x=2, 3) as Building Blocks for the Supertetrahedral Zintl Cluster [Au6(Ge3As)(Ge2As2)3]3−

The Zintl anion (Ge₂As₂)^2? represents an isostructural and isoelectronic binary counterpart of yellow arsenic, yet without being studied with the same intensity so far. Upon introducing [(PPh₃)AuMe] into the 1,2‐diaminoethane (en) solution of (Ge₂As₂)^2?, the heterometallic cluster anion [Au₆(Ge₃As)(Ge₂As₂)₃]^3? is obtained as its salt [K(crypt‐222)]₃[Au₆(Ge₃As)(Ge₂As₂)₃]?en?2 tol ( 1 ). The anion represents a rare example of a superpolyhedral Zintl cluster, and it comprises the largest number of Au atoms relative to main group (semi)metal atoms in such clusters. The overall supertetrahedral structure is based on a (non‐bonding) octahedron of six Au atoms that is face‐capped by four (Ge_xAs_4?x)^x? (x=2, 3) units. The Au atoms bind to four main group atoms in a rectangular manner, and this way hold the four units together to form this unprecedented architecture. The presence of one (Ge₃As)^3? unit besides three (Ge₂As₂)^2? units as a consequence of an exchange reaction in solution was verified by detailed quantum chemical (DFT) calculations, which ruled out all other compositions besides [Au₆(Ge₃As)(Ge₂As₂)₃]^3?. Reactions of the heavier homologues (Tt₂Pn₂)^2? (Tt=Sn, Pb; Pn=Sb, Bi) did not yield clusters corresponding to that in 1 , but dimers of ternary nine‐vertex clusters, {[AuTt₅Pn₃]₂}^4? (in 2 – 4 ; Tt/Pn=Sn/Sb, Sn/Bi, Pb/Sb), since the underlying pseudo‐tetrahedral units comprising heavier atoms do not tend to undergo the said exchange reactions as readily as (Ge₂As₂)^2?, according to the DFT calculations.     

The collisional quenching of electronically excited tin atoms Sn(51D2) by time-resolved atomic absorption spectroscopy

Electronically excited tin atoms Sn(5¹D₂), 1.068 eV above the 5³P₀ ground state, have been generated by the pulsed irradiation of tin tetramethyl and monitored photoelectrically in absorption by time-resolved attenuation of atomic resonance radiation at λ=285.06 nm [Sn((5d³F₂⁰) ← (5p^{2 1}D₂))]. Deactivation rate constants are reported for the quenching of Sn(5¹D₂) with a range of collision partners and the resulting data are compared with those for analogous states within group IV, namely, C(2¹D₂) and Pb(6¹D₂). The data are discussed in terms of correlations based on both the weak and strong spin orbit coupling approximations.     

Synthesis,crystal structures and physical properties of two terephthalate-bridged copper(II) and nickel(II) complexes

Two ₂-terephthalate (tp) bridged complexes, [Cu₂(tp)(pren)₄](ClO₄)₂ (pren = 1,3-diaminopropane) (1) and [Ni₂(tp)(pren)₄(Him)₂](ClO₄)₂ (Him = imidazole) (2), have been synthesized and characterized by X-ray single-crystal structural analysis. In the discrete dinuclear [Cu₂(tp)(pren)₄]²⁺ cation of complex (1), each Cu^II atom has a square-pyramidal geometry, being coordinated by four nitrogen atoms (avg. 2.031 Å) from two pren ligands at the basal plane and one oxygen atom [2.259(3) Å] from a bis-monodentate tp group at the axial position. In the discrete dinuclear [Ni₂(tp)(pren)₄(Him)₂]²⁺ cation of complex (2), each Ni^II center is coordinated by five nitrogen atoms [Ni—N 2.069(3)–2.109(2) Å] from one Him group and two pren groups, and completed by one oxygen atom [Ni—O 2.138(3) Å] from a bis-monodentate tp group to furnish a distorted octahedron. Magnetic susceptibility studies show that the pair of metal atoms, although being separated by >11.5 Å, exhibit weak intramolecular antiferromagnetic interactions in complexes (1) (g = 2.07 and J = –3.4 cm^–1) and (2) (g = 2.10 and J = –0.7 cm^–1). The electrochemical behaviors of the complexes have also been studied by cyclic voltammogram processes.     

1H and 13C NMR study of α-acetylenic PIII and PIV derivatives. Signs and magnitudes of J(P?C) and J(P?H)

All J(P? H) and J(P? C) values, including signs, have been obtained in acetylenic and propynylic phosphorus derivatives, R₂P(X)? C?C? H and R₂P(X)? C?C? CH₃ (X ? oxygen, lone pair and R ? C₆H₅, N(CH₃)₂, OC₂H₅, N(C₆H₅)₂, Cl) from ¹H and ¹³C NMR spectra. In P^IV derivatives the following signs are obtained: ¹J(P? C)+, ²J(P? C)+, ³J(P? C)+, ³J(P? H)+, ⁴J(P? H)? . Linear relations are observed between ¹J(P? C), ²J(P? C) and ³J(P? C) versus ³J(P? H), indicating that these coupling constants are mainly dependent on the Fermi contact term, though the other terms of the Ramsey theory do not seem to be negligible for ¹J(P? C) and ²J(P? C). In P^III derivatives these signs are: ¹J(P? C)- and +, ²J(P? C)+, ³J(P? C)-, ³J(P? H)-, ⁴J(P? H)+. Only ³J(P? C) and ³J(P? H) reflect a small contribution of the Fermi contact term while in ¹J(P? C) and ²J(P? C) this contribution seems to be negligible relative to the orbital and/or spin dipolar coupling mechanisms.     

Collisional deactivation Of Ca(4p3PJ) by barium atoms

Collisional deactivation of Ca(4p³P_J by barium atoms proceeds with a thermal cross section of 0.26±0.02 nm² at 850 K. No evidence for the corresponding deactivation of electronically excited Ca(4p³P_J) by Ca(4s¹S_o) was obtained. The optical lifetime of Ca(4p³P_J) was measured to be 0.33 ± 0.03 ms, in good agreement with previous studies.     

CpPEt2As4—An Organic‐Substituted As4 Butterfly Compound

Cp^PEt₂As₄ (Cp^PEt=C₅(4‐EtC₆H₄)₅) ( 1 ) is synthesized by the reaction of Cp^PEt. radicals with yellow arsenic (As₄). In solution an equilibrium of the starting materials and the product is found. However, 1 can be isolated and stored in the solid state without decomposition. As₄ can be easily released from 1 under thermal or photochemical conditions. From powder samples of Cp^PEt₂As₄, yellow arsenic can be sublimed under rather mild conditions (T=125 °C). A similar behavior for the P₄‐releasing agent was determined for the related phosphorus compound Cp^BIG₂P₄ ( 2 ; Cp^BIG=C₅(4‐nBuC₆H₄)₅). DFT calculations show the importance of dispersion forces for the stability of the products.     

Reaction rate studies of atomic germanium (3P0,1) and silicon (3PJ) with various oxidizers

The gas phase reactions of Ge(³P_0,1) and Si(³P_J) with O₂, NO and N₂O have been studied in a flow tube system at 350 K. Atomic Ge and Si were produced by flowing GeH₄ and SiH₄ through a hollow cathode discharge. The subsequent disappearance of the Ge and Si atoms was followed with atomic absorption spectroscopy. Rate constants were determined for the reactions at 4 and 5 torr pressures.     

Ein cyclisches Arsinoschwefeldiimid als intramolekularer Brückenligand: Synthese und Röntgenstrukturanalyse von Os3(CO)10[μ-(t-Bu)As(NSN)2As(t-Bu)]

A Cyclic Arsino Sulfur Diimide as an Intramolecular Bridging Ligand: Synthesis and X-Ray Structure Analysis of Os₃(CO)₁₀[μ-(t-Bu)As(NSN)₂As(t-Bu)] The eight-membered sulfur diimide heterocycle (t-Bu)As(NSN)₂As(t-Bu) ( 8 ) can be incorporated into a trinuclear carbonylosmium cluster either as a mono- or as a bidentate ligand. Reaction of the kinetically labile acetonitrile complex Os₃(CO)₁₁(CH₃CN) with 8 in CH₂Cl₂ solution leads to a monosubstituted derivative of Os₃(CO)₁₂ of composition Os₃(CO)₁₁[(t-Bu)As(NSN)₂As(t-Bu)] ( 9 ) which still contains one uncoordinated arsenic atom; addition of a second [Os₃(CO)₁₁] fragment to 9 was not observed. However, Me₃NO-induced substitution of a carbonyl group in 9 results in coordination of the ligand 8 to the triosmium cluster through both arsenic atoms. The structure of the product Os₃(CO)₁₀[μ-(t-Bu)As(NSN)₂As(t-Bu)](10)¹ was determined by an X-ray structure analysis. I n the triangulo-triosmiumcarbonyl cluster 10 , the ligand 8 occupies two equatorial positions at two adjacent osmium atoms, being coordinated through the arsenic atoms with O s ? As distances of 2.403(1) Å The cluster molecule 10 possesses a 2-symmetry of crystallographic origin. The [Os₃(CO)₁₀] fragment and the eight-membered heterocyclic ligand are not changed significantly in their structures as compared with Os₃(CO)₁₀ and free 8 , respectively. Nevertheless, coordination of 8 imposes its lower 2-symmetry upon the [Os₃(CO)₁₀] fragment. The reduction of mm2- to 2-symmetry (C_2v to C₂) for the cyclic arsino sulfur diimide 8 is more pronounced in the complex 10 than in the free state. The As …? As distance in 10 (8.878(4) A) is considerably enlarged its compared to 8 (3.683(1) Å).     

Depletion kinetics of low-lying states of tungsten in the presence of NO,N2O,and SO2

The gas-phase reactivities of W(a⁵D_J, a⁷S₃) with N₂O, SO₂, and NO in the temperature range of 295–573 K are reported. Tungsten atoms produced by the photodissociation of W(CO)₆. The tungsten atoms were detected by a laser-induced fluorescence technique. The removal rate constants for the 6s²5d⁴ a⁵D_l states were found to be pressure dependent for all of the reactants. Removal rate constants for the 6s¹5d⁵ a⁷S₃ state were found to be fast compared to the a⁵D_J states and often approached the gas kinetic rate constant. The reaction rates for all the states were found to be pressure independent with respect to the total pressure. Results are discussed in terms of the different electronic configurations of the states of tungsten © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 367–375 1997     

Analysis of autoionizing Rydberg series Cu I 3d 9 4snl with the multichannel quantum defect theory

Using atomic beam technique, a combination of collisional and laser excitation, and photoion detection, autoionizing Cu I states in the region of the ionization limits Cu II 3d ⁹ 4s(^3,1 D) were investigated. In spite of the complicated structure of the signals due to the four different ionization limits³ D ₃,³ D ₂,³ D ₁ and¹ D ₂ and the large number of possible (LSJ)-states, which can be reached by this experimental technique, the majority of the signals could be attributed to definite Rydberg series 3d ⁹ 4s(³ D ₃,³ D ₂,³ D ₁,¹ D ₂)nl (LSJ). Perturbations were analyzed by the three- and four-channel quantum defect theory and by Hartree-Fock calculations. General formulas for the calculation of the photoionization cross section by the four-channel quantum defect theory in the case of two closed and two open channels are given.     

Structural and Spectroscopic Investigations of the 1:1 Complex between Europium Nitrate and a Tetraoxadiaza Macrocycle

The crystal and molecular structure of dinitrato(1,7,10,16-tetraoxa-4,13-diazacyclooctadecane)europium(III) nitrate, ([Eu(NO₃)₂(C₁₂H₂₆N₂O₄)]NO₃) has been determined from single-crystal X- ray diffraction: a = 12.567(3), b = 11.585(3), c = 16.354(5) Å, β = 112.45(2)°, space group P2₁/n, Z = 4. The structure consists of discrete dinitrato complex cations and of nitrate anions. The Eu(III) ion is 10-coordinate, bonding to the six donor atoms of the macrocycle and to four O-atoms of the two bidentate nitrates. The mean distances are Eu? O(ether) = 2.60(2), Eu? O(NO₃) = 2.47(3) and Eu? N = 2.62(2) Å. The metal site has an approximate C₂ symmetry. The IR and Raman spectra show the presence of an ionic and of two bonded bidentate nitrates. These latter have a different v₁-v₄ splitting, which reflects their dissymmetrical bonding. Luminescence spectra have been recorded at 296, 77, and 4 K by laser-excitation techniques. One sharp ⁵D₀←⁷F₀ transition was observed and almost all the sublevels of the ⁷F_J manifold could be identified. The interaction between a sharp distribution of the phonon states (especially between 950 and 1200 cm^?1) and the electronic ⁷F₂ sublevels results in the presence of several satellite lines accompanying the ⁵D₀→⁷F₂ transition. In MeCN solutions, both luminescence and conductivity data point to the presence of the [Eu(NO₃)₂(2,2)]⁺ cation.