2p 2s Research Articles

Two-photon coherent spectroscopy of ultracold Li atoms

Our work is devoted to theoretical study of the two-photon coherent spectroscopy of 7Li atoms continuously cooled in a magneto-optical trap (MOT) on the 2S–2P transition. The ultracold atoms are transferred to highly excited Rydberg states in a two-step coherent excitation process by red and UV lasers. The red laser is detuned by -600 MHz from 2S–2P transition frequency and UV laser frequency detuning is scanned in the vicinity of +600 MHz from 2P-nS(D) transition where n∼40-100 is principal quantum number. The fluorescence signal on the 2P–2S cooling transition makes it possible to obtain a two-photon absorption spectrum. Atom-field interaction is considered in the simple three-level approximation involving a density matrix formalism. It is shown that the effect of the MOT beams on the shape of the two-photon absorption line can be taken into account by an appropriate change in the 2S–nS(D) coherence decay rate.

First-principles Study of Structural Properties of MgxZn1-xO ternary alloys

First-principles calculations have been carried out to investigate the structural and electronic properties of MgxZn1-xO ternary alloys. The calculations are performed using the full potential linearized augmented plane wave (FP-LAPW) method within the density functional theory(DFT). We conclude that the structural properties of these materials, in particular the composition dependence on the lattice constant and the band gap is found to be linear. The a-axis length in the lattice gradually increases, while the c-axis length decreases with the increase in Mg doping concentration, and be corresponded with the Vegard's law linear rule. The lattice parameters of the MgxZn1-xO ternary alloys are consistent with experimental data and other theoretical results. We found in the conduction band portion, the Mg 2p 2s states are moved to high energy region as the Mg content increases, so the band gap increases.

Supramolecular copper halide networks using the coordinative flexibility of the cyclo-P 2S 3 middle deck in (C 5Me 5) 2Mo 2P 2S 3: Phosphorus versus sulfur coordination

Reaction of solutions of [ Cp 2 ∗ Mo 2P 2S 3] ( 1; Cp ∗ = η 5-C 5Me 5) in CH 2Cl 2 with solutions of CuHal (Hal = Cl, Br, I) in CH 3CN gave after slow diffusion the novel coordination polymers [ Cp 2 ∗ Mo 2P 2S 3(CuCl) 4] ( 2), [ Cp 2 ∗ Mo 2P 2S 3(CuBr) 3] ( 3) and [ Cp 2 ∗ Mo 2P 2S 3(CuI) 3] ( 4). The products were characterized by elemental analysis, 31P magic angle spinning (MAS) NMR spectroscopy and single-crystal X-ray crystallography. The solid-state structures of 2 and 3 are composed of two-dimensional polymeric networks, whereas that of 4 contains parallel stacks of one-dimensional ribbons. In all cases the planar cyclo-P 2S 3 middle deck of the organometallic building block 1 provides one or two P atoms of the PS dumbbells along with the singly bridging sulfur atom as coordination sites for the various copper halide subunits. The assignment of P atoms follows from the correlation of 31P MAS NMR spectra with X-ray crystallographic data. In all compounds the distribution of main group atoms in the cyclo-P 2S 3 middle deck is different from that previously found in the starting material 1.

Synthesis and second-order optical nonlinearity of DAMS/Mn 2P 2S 6 intercalated materials by ion exchange method

Intercalated hybrid materials alternating optical nonlinear organic chromophores and inorganic Mn 2P 2S 6 layers were obtained by ion exchange method. The Mn 2P 2S 6 powder was synthesized by solution-state combined solid-state method, which benefited for MPS 3’s mass production. The reaction between Mn 2P 2S 6 layers and inserted chromophores was intensified by UV–visible spectroscopy. It was indicated that Mn 2P 2S 6 powders after solution-state combined solid-state method was single crystalline and DAMS molecules self-assembled in the layers of Mn 2P 2S 6 to form J-aggregates. Second-harmonic generation (SHG) of DAMS/Mn 2P 2S 6 thin films was observed by Maker fringe measurement. The DAMS/Mn 2P 2S 6 intercalated material was well formed by ion exchange method.

Fine and hyperfine structure of P-wave levels in muonic hydrogen

Corrections of order α5 and α6 are calculated for muonic hydrogen in the fine-structure interval ΔEfs = E(2P3/2) − E(2P1/2) and in the hyperfine structure of the 2P1/2-and 2P3/2-wave energy levels. The resulting values of ΔEfs = 8352.08 µeV, ΔẼhfs(2P1/2) = 7819.80 µeV, and ΔẼhfs(2P3/2) = 3248.03 µeV provide reliable guidelines in performing a comparison with relevant experimental data and in more precisely extracting the experimental value of the (2P–2S) Lamb shift in the muonic-hydrogen atom.

Thermal diffusivity and critical behaviour of uniaxial ferroelectric Sn 2P 2S 6

The anisotropy in the thermal diffusivity of uniaxial ferroelectric Sn 2P 2S 6 has been measured as a function of temperature using ac photopyroelectric calorimetry. The second-order ferroelectric transition has been studied in order to ascertain the mechanisms which could explain the anomaly in specific heat through the study of the inverse of the thermal diffusivity. Landau model, as well as critical models considering the different roles of fluctuations of the order parameter and crystalline defects, are considered. Though in the ferroelectric phase the Landau model can mainly explain the anomaly in the physical properties, the fittings for the paraelectric phase show that it is necessary to take into account the influence of both fluctuations and defects to account for the results.

Nonstationary photocurrent and pyroelectric response in aged Sn 2P 2S 6 films

The photoelectric and pyroelectric properties of Sn 2P 2S 6 films were studied by a dynamic method under excitation by periodic rectangular laser beam pulses ( λ = 6328 Å). In this case, an appearance of the nonstationary photoelectric response in the films under visible light irradiation (extrinsic excitation) was observed. It was found that temperature dependence of the unsteady current is connected to features of spontaneous polarization behaviour in Sn 2P 2S 6 thin films. A nature of the nonstationary photoelectric response existence due to an electric field of the potential barrier near an interface is discussed.

Synthesis of σ-π-phosphinidene sulfide complexes [Mn 2(CO) n(μ-η 1,η 2-P(NR 2) [dbnd]S)] ( n = 8, 9) via direct sulfuration of electrophilic μ-phosphinidenes and photochemical transformation to a trigonal prismatic Mn 2P 2S 2 cluster

The μ-phosphinidene complexes [Mn 2(CO) 8{μ-P(TMP)}] ( 1) (TMP = tetramethylpiperidyl) and [Mn 2(CO) 8{μ-P(N i Pr 2)}] ( 2) react with elemental sulfur to form rare phosphinidene sulfide complexes [Mn 2(CO) 9{μ-η 1,η 2-P(TMP) S}] ( 3) and [Mn 2(CO) 8{μ-η 1,η 2-P(N i Pr 2) S}] ( 4), respectively. Photolysis of 3 results in the unprecedented conversion to [Mn 2(CO) 6(μ-{κPκ 2S} 2-(TMP)(S)P–P(S)(TMP)] ( 5), which contains a novel 10-electron donor diphosphene disulfide ligand (TMP)(S)P–P(S)(TMP).

Synthesis and vibrational spectrum of potassium (18-crown-6) hexathiodiphosphate(V) acetonitrile solvate, [K(18-crown-6)] 2 [P 2S 6]·2 CH 3CN

The potassium crown-ether thiophosphate, [K(18-crown-6)] 2 [P 2S 6]·2 CH 3CN, has been obtained by the reaction of K 2P 2S 6 with 18-crown-6 in acetonitrile. The title compound adopts a molecular array of [K(18-crown-6)] 2 [P 2S 6] wherein two K(18-crown-6) units are linked by the P 2S 6 group. FT-Raman and FT-IR spectra of the title compound have been recorded and interpreted, especially with respect to the P 2S 6 group and in comparison to the few known metal meta-thiodiphosphates.

Synthesis and characterization of a family of two related quaternary selenides: Na 8Eu 2(Si 2Se 6) 2 and Na 9Sm(Ge 2Se 6) 2

In this work, two related quaternary rare earth selenide phases were synthesised using the molten flux method. Na 8Eu 2(Si 2Se 6) 2 crystallizes in C2/ m with cell parameters a = 7.0898(10) Å, b = 12.228(2) Å, c = 7.9499(11) Å, β = 107.427(2)° and V = 657.6(2) Å 3 ( Z = 1). This structure comprises layers of [Eu 2(Si 2Se 6) 2] 8− that are in the (1 1 0) planes; each contains ethane-like (Si 2Se 6) 6− units oriented along c, or perpendicular to the planes. This phase is reminiscent of the family of M 2P 2S 6 well-known layered phases and we prepared the series where the main group metal was Si or Ge and the chalcogen was Se or Te. Na 9Sm(Ge 2Se 6) 2 is a related structure, also crystallizing in C2/ m with cell parameters a = 7.9158(15) Å, b = 12.244(2) Å, c = 7.1048(13) Å, β = 106.99(1)° and V = 658.6(2) Å 3 ( Z = 1). This structure comprises layers of [Sm 2(Ge 2Se 6) 2] 9− similar to the selenosilicate yet contains ethane-like (Ge 2Se 6) 6− units oriented along a, i.e. parallel to the layers. We have investigated the family of solids changing the chalcogen atoms (S, Se and Te) and evaluating how the structure changes with chalcogen and with the tetrelide atom (Ge, Si). In addition to single crystal diffraction studies, Raman, diffuse reflectance UV–vis and photoluminescence measurements (for Eu phases) have been used to characterize these compounds.

Ultrasonic and piezoelectric studies of new layered ferroelectric compounds of Sn 2P 2S 6 family

Ultrasonic and piezoelectric studies of two-dimensional layered crystalline structures of MM 1P 2X 6 (M,M 1 = Cu, In, Sn, Cr; X = S, Se) are presented in this contribution. It was shown, that such materials: CuInP 2S 6, CuCrP 2S 6 and CuInP 2Se 6 undergo phase transitions (PT) and exhibit piezoelectric effect in low temperature phases. Anomalies of ultrasonic velocity and attenuation at phase transitions have been observed in these materials. Measurements of temperature dependencies of ultrasonic velocity and attenuation revealed the first order phase transition at T c ≈ 312 K in CuInP 2S 6; two successive phase transitions at T c1 ≈ 180 K and T c2 ≈ 145 K in CuCrP 2S 6; and two phase transitions at T c1 ≈ 235 K and T c2 ≈ 228 K in CuInP 2Se 6.

Trends in the band structures of the group-I and -II oxides.

Measured and calculated band structures for the six lightest group-I and -II oxides are reported. Band structures have been measured using electron momentum spectroscopy, a technique that maps the ground-state occupied orbitals resolved both in energy and momentum. Measurements are compared with first-principles calculations carried out within the linear combination of atomic orbitals approximation using both Hartree-Fock (HF) and density functional (DFT) methods. Three DFT functionals are used representative of the local density approximation, the generalized gradient approximation, and a hybrid method incorporating exact exchange. The calculated O 2p bandwidths and O 2p-2s band gaps generally scale linearly with the inverse of the oxygen-oxygen separation squared, but consistently show an anomaly at Li(2)O. These trends, including the anomaly, are also observed in the experimental data. HF calculations consistently overestimate the oxygen 2p-2s band gap by almost a factor of two. Measured band gaps lie within the range of the three DFT functionals employed, with evidence that the description of exchange becomes more important as the cation size increases. Both HF and DFT calculations overestimate the oxygen valence bandwidths, with DFT giving more accurate predictions. Both observed and calculated bandwidths converge as the cation size increases, indicating that exchange-correlation effects become less important as the metallic ion becomes larger.

Electronic structure and chemical bonding of phosphorus-contained sulfides InPS 4, TI 3PS 4, and Sn 2P 2S 6

The electronic structure of phosphorus-contained sulfides InPS 4, Tl 3PS 4, and Sn 2P 2S 6 was investigated experimentally with X-ray spectroscopy and theoretically by quantum mechanical calculations. The partial densities of electron states calculated with the ab initio multiple scattering FEFF8 code correspond well to their experimental analogues—the X-ray K- and L 2,3-spectra of sulfur and phosphorus. The good agreement between theory and experiment was also achieved for K-absorption spectra of S and P in the investigated sulfides. In spite of the difference in the crystallographic structure of InPS 4, TI 3PS 4, and Sn 2P 2S 6 that influence the form of K-absorption spectra, the electronic structure of their valence bands are rather similar. This is due to the strong interaction of the P and S atoms, which are the nearest neighbors in the compounds studied. The electron densities of p- and s-states of phosphorus are shifted by about 3 eV to lower energies in comparison to the analogous electron states of sulfur. This is connected with the greater electro-negativity of sulfur, and is confirmed by the calculated electron charge transfer from P to S.

Synthesis of ditin hexathiophosphate Sn 2P 2S 6 by low-energy ball-milling and monomode microwave

High- or low-energy mechanochemistry is frequently used to synthesize chemical compounds. The present work is devoted to the possible synthesis of ditin hexathiodiphosphate Sn 2P 2S 6 by low-energy ball-milling: first, directly from its atomic components, second, by ball-milling followed by a microwave treatment. Stoichiometric ratio powders were milled by means of 10 steel balls (2.0 g each) under ambient atmosphere for 80 h or so. Afterwards, the samples were studied by X-ray spectroscopy, energy dispersive X-ray spectroscopy, IR and DSC. The resulting diffraction patterns showed the formation of the desired compound. The ball-milled powder was also studied by transmission electron microscopy which revealed its ferroelectric character. Some previous confusing conclusions about the various crystalline forms of Sn 2P 2S 6 are re-examined. With Mn, Fe, Ni or In instead of Sn, no hexathiodiphosphates were formed through direct ball-milling.

Low-energy ball milling associated with a monomode microwave: a new route to synthesize manganese hexathiohypodiphosphate and to intercalate ionic species

To synthesize manganese hexathiohypodiphosphate, stoichiometric mixtures of manganese, red phosphorus, and α-sulfur, together with potassium chloride, underwent low-energy ball milling under ambient conditions followed by exposure to the electromagnetic beam of a monomode microwave. X-ray diffraction patterns show that Mn 2P 2S 6 (structure MI, or H) has formed, as well as small amounts of intercalated KCl [these findings are supported by infrared (IR) observation]. Also some α-MnS have been formed. Electron diffraction patterns show the existence of structure H. They also reveal the emergence of the (up to now hypothetical) orthohexagonal structure and of some «turbostratic» layered material whose nature is not yet understood. Superconducting quantum interference device (SQUID) measurements show a ferromagnetic behavior, which can be assigned to the formation of some manganese monophosphide. Tetraethyl chloride ammonium is then easily intercalated as revealed by X-ray patterns and IR measurements. Finally, it has been shown that all three parameters (ball milling, microwave exposure, and presence of KCl as a catalyst) are necessary to form manganese hexathiophosphate. Filtrations and decantations lead to a pure hexathiophosphate compound.

Synthesis and average and incommensurately modulated crystal structure of 2D-K 3Ce 2P 3S 12

K 3Ce 2P 3S 12, a new thiophosphate of cerium and potassium, has been synthesized for the first time and its average structure solved from single crystal data. A tentative solution for its weakly modulated, incommensurate structure has also been found within a (3+1)D formalism. The average structure of this new, yellow material has monoclinic symmetry, space group C2/ c with the following cell parameters a=20.595(3) Å, b=9.6453(10) Å, c=22.161(4) Å, β=97.360(13) and V=4366.0(19) Å 3 ( Z=8). Its crystal refinement yielded the residual factor R=4.77% for 187 parameters and 3117 independent reflections at a 2 σ( I) level. The two-dimensional structure can be viewed as built upon infinite 1 ∞[Ce 2P 2S 12] 8− chains connected to each other by [PS 4] tetrahedra to form 2 ∞[Ce 2P 3S 12] 3− layers. These corrugated slabs are electrostatically linked by potassium ions. K 3Ce 2P 3S 12 can be considered as a new member of the (K I 4(P 2) VIIIQ −II 6) l(K I 3P VQ −II 4) m(Ln III 4(P 2) VIII 3S −II 18) n(Ln IIIP VQ −II 4) o family (Ln=La, Ce; Q=S, Se) with l=0, m=1, n=0 and o=2 (K I 3Ce III 2P V 3S −II 12). The crystal refinement of the true modulated structure within the (3+1)D formalism (wavevector: q =−0.559(2) a ∗+0.589(3) c ∗ ) yielded the residual factor R=5.66% for 296 parameters and 3583 independent reflections (3117 main reflections and 466 first order satellites). In the aperiodic crystal, the modulation results from the rotation of the [PS 4] tetrahedra and the bicapped [CeS 8] trigonal prisms around the alkali metals.

Photodissociation and ab initio studies of Mg+(NH3)n, n=1–4: Electronic structure and photoinduced reaction

Photodissociation spectra of Mg+(NH3)n (n=1–4) cluster ions are examined in the wavelength region of 240–1200 nm. From the comparison with the results of ab initio calculations for the structure and the excitation energies of these clusters, the observed absorption bands are assigned to the transitions derived from the P2–2S transition of Mg+ ion. The extensive redshift of the observed spectra is ascribed to the formation of a one-center ion-pair state. In the photolysis of Mg+NH3, NH3+ and Mg+NH2 ions are produced via photoinduced charge transfer and intracluster reaction processes, respectively, in addition to the Mg+ ion generated by the evaporation of ammonia molecules. For n=2, both the intracluster reaction and evaporation are dominant decay processes, while the evaporation is the sole photodissociation channel for larger clusters. The branching fractions of these processes are found to depend strongly on the solvation number n and also on the photolysis wavelength. The energetics and the dynamics of the dissociation processes are discussed in relation to the redox reaction of metal ions.

Explanation of the EPR g factors for Co 2+ impurities in trigonal Cd 2P 2S 6 crystal

By extending the theory of Abragam and Pryce, the formulas of EPR parameters g ∥ and g ⊥ for 3d 7 ion in trigonal octahedral crystals are established from a cluster approach. In these formulas, not only the configuration interaction effect, but also the covalency effect are considered and the parameters related to both effects and the trigonal distortion are determined from the optical spectra and the structural data of the crystal under study. Based on these formulas, the g ∥ and g ⊥ of Cd 2P 2S 6 : Co 2+ crystal are reasonably explained from its structural data. The relationship between the sign of Δ g (= g ∥− g ⊥) and the trigonal distortion (elongated or compressed) of ligand octahedron, which is opposite to that obtained in the previous paper, is given and the results are discussed.

A study of the threshold photoelectron spectra and the photoionisation yield curves of the silicon tetrahalides

The threshold photoelectron spectra and the photoionisation yield curves of SiF 4, SiCl 4 and SiBr 4 have been recorded in the photon energy range 10–240 eV using synchrotron radiation. The outer valence shell photoelectron bands exhibit effects due to spin–orbit splitting and to Jahn–Teller interactions, and vibrational progressions associated with the Jahn–Teller active modes have been observed. The continuous nature of the inner valence shell photoelectron bands and the absence of main-lines demonstrates the importance of electron correlation in redistributing the intensity amongst satellite states. New Rydberg series have been observed in the photoionisation yield curves associated with excitation from the valence shell, and the improved resolution has allowed some earlier assignment discrepancies to be clarified. The threshold photoelectron spectra and ion yield curves recorded at higher energies display features attributable to the Si 2p,2s, Cl 2p and Br 3p shells. The photoelectron spectra have enabled the following splittings to be measured: Si 2p–2s, Si 2p 1/2–2p 3/2, Cl 2p 1/2–2p 3/2 and Br 3p 1/2–3p 3/2, and the corresponding values are 51.21, 0.52, 1.62 and 4.6 eV, respectively. The interpretation of the features observed in the SiBr 4 spectra has been based upon previously reported assignments of similar structure in SiF 4.

The effect of phosphorus on the properties and structure of GeAsS glasses

Stoichiometric Ge-poor (<50% GeS 2) GeAsPS glasses, as well as GeAsPS glasses with a fixed Ge:As:P ratio of 5:1:1 and S contents ranging from 56% to 74%, were synthesized. The compositional dependence of the physical properties and nuclear magnetic resonance (NMR) spectra of the stoichiometric glasses indicates that tetrahedral SPS 3/2 groups constitute the dominant P species. On reducing the S content, the absorption edge of variable S GeAsPS glasses remains constant until S deficits of about 25% are attained. Raman spectra of stoichiometric and S-deficient glasses show bands attributed to As 2P 2S 8 and (As,P) 4S 3 species, respectively, whereas those of variable S glasses with S deficits ⩽15% show a high frequency band indicating the presence of tetrahedral SPS 3/2 groups. NMR spectra of glasses with S deficits of 7–15% are dominated by a 31P resonance at about 117 ppm that is assigned to trigonal PS 3/2 groups. NMR spectra of glasses with S deficits ⩾10% have a 31P resonance near −100 ppm, indicating that tetrahedral SPS 3/2 and trigonal PS 3/2 groups are replaced by species containing P–P and, ultimately, P–(Ge, As) bonds as the S content of these glasses decreases. Comparison of these results with those for GeAsS glasses demonstrates that P–P bonds form preferentially to metal–metal bonds containing either Ge or As, and that P tends to associate with As instead of Ge as next nearest neighbors.