The microwave spectrum of the unsymmetrical conformation of 1-chloro-2-methyl propane

The microwave spectrum of 1-chloro-2-methyl propane has been recorded and lines assigned to ³⁵Cl and ³⁷Cl species in the unsymmetrical conformation. The rotational and distortion constants in MHz are: C₄H₉³⁵Cl, A = 7527.05, B = 2146.21, C = 1793.59, Δ_JK = 4.15 × 10^?3, δ_j = ?8.0 × 10^?5; C₄H₉³⁷Cl, A = 7524.40. B = 2091.73, C = 1755.54, Δ_JK = 2.5 × 10^?3, δ_j = 2.0 × 10^?4.     

Calculations of Jahn-Teller coupling constants in the weak-field basis via the angular overlap model: a simple operator equivalent technique

Within the framework of the angular overlap model the matrix elements of the linear Jahn-Teller operator may easily be calculated in the weak-field basis in terms of simple operator equivalents. The method is applied to the calculation of the 〈M_J|?V/?Q|M_j〉 matrix elements for the |LSJMj〉 ground states of t^x species (x = 1) ? 13) in )^* symmetry.     

Microwave spectrum and substitutional structure of CH2DF

Forty-two transitions of the microwave spectrum of CH₂DF have been observed in the region between 75 and 450 GHz. The measurement of both a-type and b-type transitions makes possible the analysis of the spectrum and the accurate calculation of the rotational constants (in MHz): = 119 675.0535 ± 0.074, = 24 043.4415 ± 0.072, ? = 22959.3732 °0.072, °j = 0.049371 ±0.00011, °_jk = 0.34268 ±0.0006, 2_k = 3,3774 ± 0.0035, δ _j = 0.002329 ± 0.000045, δ_k = 0.0687 ± 0.036. These constants, in combination with the results of earlier work on the symmetric speci r_s structure calculation based entirely on high-accuracy microwave data. The structural parameters are r_CH = 1.100 Å, r_CF = 1.383 Å, and ∠HCH = 110° 37'.     

Distorted-wave calculations for the three dimensional chemical reaction H + H2(v ⩽ 2, j = 0) → H2(v′ ⩽ 2, j′, mj) + H

Calculations of the vibrational—rotational product state population distributions and differential cross sections for the chemical reaction H + H₂(v ? 2, j = 0) → H₂(v′ ? 2, j′, m_j) + H have been carried out on the Porter—Karplus potential energy surface. The vibrationally-adiabatic-distorted-wave (VADW) method has been used. The relative rotational product distributions, differential cross sections and the helicity m_j, dependences of these quantities for the v = 0 reaction agree well with accurate close-coupling results. The absolute integral cross sections are considerably smaller than the accurate quantum values, however. The calculations for the v = 1 reaction agree with the findings of previous sudden quantum, limited close-coupling and quasiclassical theoretical studies and experiments that product H₂(v′ = 1) is more likely to be produced than H₂(v′ = 0). For the reaction with v = 2, it is found that at high translational energies product H₂(v′ = 2) is favoured over H₂(v′ = 1) or H₂(v′ = 0). The VADW differential cross sections for the v = 1 and v = 2 reactions have a similar shape to those of the v = 0 reaction, with backward peaking when summed over all m_j states. The relative rotational distributions for the v = 2, j = 0 → v′ = 2, j and v = 1, j = 0 → v′ = 1, j reactions are also similar to those obtained for the v = 0, j = 0 → v′ = 0, j reaction, with low rotational excitation.     

Calculation of the hyperfine spectrum for H2Ne,H2Ar,H2Kr dimers.

The weakly bound dimers H₂Ne, Ar, Kr are treated such that the H₂, rotation (quantum number j) remains unperturbed except for orientational effects. The orientation of the ortho H₂(j = 1) is mainly influenced by the anisotropic forces between the dimer constituents. We develop a method which allows to extract from a measured hyperfine dimer transition the value of a simple molecular parameter containing mainly the strength of the anisotropic interaction sandwiched between the dimer-stretch vibrational eigenfunctions. An analytic expression is derived permitting an easy comparison between measurements and results from simple model potentials. In addition, where necessary due to the existence of quasi-bound states, the influence of continuum states can be properly taken into account, by our method.     

EPR of dynamic Jahn-Teller distortion in CuII doped magnesium Tutton's salt

The dynamic Jahn-Teller distortion in single crystals of Cu^II doped magnesium Tutton's salt, MgK₂(SO₄)₂·6H₂O was studied by EPR spectroscopy. The directions of the g tensor axes were found to coincide with those of A at room temperature as well as at 113 K and were correlated with the MgO directions in the lattice. Two spatially distinct sites of copper were detected in the crystal. The g and A values were also calculated from the polycrystalline samples at various temperatures. A d_x²-_y² ground state has been assigned for Cu^II, as in the isomorphous zinc Tutton's salt. The Silver and Getz model was applied to understand the dynamics of Jahn-Teller (JT) activity. The system was found to undergo dynamic JT distortion at all temperatures. At low temperatures, the [Cu(H₂O)₆]²⁺ ion has three possible degenerate vibronic states corresponding to three possible directions for the long axis of the octahedron. The energy separations between the three inequivalent JT valleys were estimated as δ_1,2 = 90 and δ_1,3 = 370 cm⁻¹. The lattice strain parameter V₂ and the JT stabilization energy E_JT were also estimated as 19,140 and 1030 cm⁻¹ respectively. From the E_JT value, the JT distortion present in the system was classified as a case of “strong” coupling.     

Close-coupling elastic and inelastic integral and differential cross sections for Li+ + H2 collisions

The quantum mechanical close-coupling formalism is applied to the study of elastic and rotationally inelastic Li⁺ + H₂ collisions making use of the Kutzelnigg-Staemmler-Hoheisel potential energy surface. Integral and differential cross sections for j = 0 → 0 and j = 0 → 2 are obtained in the collision energy range 0.2 to 0.9 eV and for j = 1 → 1 and j = 1 → 3 at 0.6 eV. A rainbow structure is observed in both the elastic and inelastic angular distributions and a quenching of the fast oscillations is found in the cross sections for j = 1 initially compared to the case j = 0 initially. At 0.6 eV. the calculated quantum mechanical angular distributions are compared to those from a classical trajectory calculation using the same surface and to the experimental ones. The dynamics of rotational excitation in the Li⁺ + H₂ system is contrasted to rotational excitation in systems for which the atom-diatom interaction is predominantly repulsive.     

Neutron diffraction experiments on CsCrI3 at 300, 77, and 1.2 K

CsCrI₃ has been investigated by neutron powder diffraction at room temperature and 77 and 1.2 K. It undergoes a phase transition at 150 K due to the cooperative Jahn-Teller effect. The high-temperature form, α-CsCrI₃ (hexagonal, space group $\text{P6}{}_3\text{mmc}\text{, a = 8.127(1)}$Å, c = 6.944(1)Å, Z = 2), adopts the BaNiO₃ structure with a local Jahn-Teller distortion. The low-temperature form, β-CsCrI₃ (orthorhombic, space group Pbcn, a = 8.102(1)Å, b = 13.792(1)Å, c = 6.900(1)Å, Z = 4), has a structure not yet been reported for a Jahn-Teller distorted BaNiO₃ structure. It is shown that the low-temperature form can be derived from the BaNiO₃ structure by means of a canting of triangles, formed by the three common I^? ions of two adjacent CrI₆^4? octahedra. The magnetic structure of β-CsCrI₃ at 1.2 K is found to consist of an antiparallel sequence of ferromagnetic (0 0 1) planes with a magnetic moment in the ∥1 0 0∥ direction of 3.16 μ_B.     

Phase equilibria and crystal structures of complex oxides in systems La-M-Fe-O (M = Ca or Sr)

Phase equilibria in systems La-M-Fe-O (M = Ca or Sr) at 1100° in air were studied. The homogeneity ranges and structures of solid solutions La_{1 ? x} M _x FeO_{3 ? δ} (0 ≤ x ≤ 0.3 for M = Ca and 0 ≤ x ≤ 0.8 for M = Sr), Sr_{2 ? y} La _y FeO_{4 ? δ} (0.8 ≤ y ≤ 1.0), and Sr_{3 ? z} La _z Fe₂O_{7 ? δ} (0 ≤ z ≤ 0.2) were determined using X-ray powder diffraction. The structural parameters of complex oxides were refined using the full-profile Rietveld technique. Correlations between the unit cell parameters and the compositions of solid solutions were derived. Isobaric/isothermal phase diagrams were constructed for systems La-M-Fe-O (M = Ca or Sr) at 1100°C in air.     

Structural and transport characteristics of substituted bismuth niobates

The results of studying solid solutions with the composition of Bi₃Nb_{1 ? y} Zr _y O_{7 ± δ}, Bi_2.95Y_0.05Nb_{1 ? y} Zr _y O_{7 ± δ} (y = 0–0.5; Δy = 0.1), and Bi_6.95Y_0.05Nb_{2 ? y} Zr _y O_15.5 (y = 0.1–1; Δy = 0.1) are presented. XRD and electron microscopy with X-ray microanalysis are used to determine the homogeneity regions of solid solutions; crystallochemical parameters are calculated. It is shown that irrespective of the ratio of Bi: Nb, two cubic phases are formed at an increase in the dopant amount. One of these represents a solid solution based on Bi₃NbO₇ (δ-phase) and the second one is a solid solution based on δ-Bi₂O₃ (δ′-phase). Conductivity of sintered samples is studied using the impedance spectroscopy technique. Introduction of yttrium into the bismuth sublattice results in no increase in conductivity of solid solutions, while in the case of the ratio of Bi: Nb = 3: 1, overall conductivity of solid solutions is somewhat higher at similar dopant concentrations.     

Cathodic materials for intermediate-temperature solid oxide fuel cells based on praseodymium nickelates-cobaltites

A unique combination of methods (TPD of O₂, thermogravimetry, isotopic heteroexchange of oxygen in different modes) was used to carry out detailed studies of oxygen mobility and reactivity in mixed praseodymium nickelates-cobaltites (PrNi_{1 ? x} Co _x O_{3 + δ}) and their composites with doped cerium dioxide (Ce_0.9Y_0.1O_{2 ? δ}) as promising cathodic materials stable towards the effect of CO₂ in the intermediate-temperature region. It is shown that in the case of composites of PrNi_{1 ? x} Co _x O_3+δ-Ce_0.9Y_0.1O_{2 ? δ} synthesized using the Pechini method and ultrasonic treatment, stabilization of the disordered cubic perovskite phase due to redistribution of cations between the phases provides high oxygen mobility. Preliminary results on tests of cathodic materials of this type supported on planar NiO/YSZ anodes (H.C. Starck) with a thin layer of YSZ electrolyte and a buffer Ce_0.9Y_0.1O_{2 ? δ} layer showed that power density of up to 0.4 W/cm² was reached in the region of medium (600–700°C) temperatures, which was close to typical values for fuel cells of this type with cathodes based on strontium-doped perovskites and their composites with electrolytes.     

Measurements of the hyperfine dimer spectrum for H2-Ne,H2-Ar,H2-Kr by the magnetic beam renosance technique

Measurements are performed on ortho H₂(I = 1, j = 1, vibrational ground state)-X dimers with X = Ne, Ar, Kr; the dimers H₂-X occur in their van der Waals stretch ground state. The dimer end-over-end rotational states (quantum number L) are investigated for L ?2. The rf hyperfine-transition frequencies are measured, 30 ? v ? 600 kHz. Combining our results with scattering data from the Göttingen group, for H₂Ne the full potential could be described with high accuracy. For the other systems, a simple molecular parameter is derived pertaining to the dimer system. As our spectroscopy mainly permits a sensitive probing of the well region, new scattering data are needed to determine accurate model potentials over the full range.     

Dynamically based fitting law for thermal rate coefficients in rotational relaxation

An earlier analytical, approximative result for the semi-classical, sudden limit of energy dependent j_o → j cross sections of rotational relaxation of homonuclear, diatomic molecules perturbed by an atom has been integrated to obtain dynamical fitting of temperature dependent rate coefficients. The result can be written by using two parameters, k_jjo = [(2j + 1)/(2j_o + 1)] ^1/2a (lj - 1]^?1 ? b), where the parameters a and b are given from the assumed intermolecular potential, The reduced mass for the collisions and the temperature. A comparison with several experimental results proves the validity of the above expression and gives some statements about the intermolecular potentials for the systems considered.     

Helium states II. Perturbation treatment of the ground state using the coordinates r< and r>

In an attempt to improve upon the convergence properties of the Hylleraas-Scherr-Knight-Midtdal perturbation expansion for the ground-state energies and eigenfunctions of the helium isoelectronic sequence, the term r is included in the zeroth-order Hamil-tonian. This term dominates the usual perturbation r for the ground state of these systems, and by removing it from H⁽¹⁾ we substantially reduce, in some sense, its size. In order to find the exact eigenfunction of the resulting zeroth-order Hamiltonian it was found necessary to include in H⁽⁰⁾ two additional terms involving the delta function δ(r₁ ? r₂) = δ(r_< ? r_>) and one such term in H⁽¹⁾. Approximate first- and second-order eigenfunctions are calculated variationally giving the energies to fifth order. The results are disappointing. The errors in the energies to fifth order for He, Li⁺, and Be²⁺, although quite small, are significantly larger than the corresponding errors in the more conventional perturbation treatment. Reasons for the failure to improve upon the earlier results are discussed. A “paradox” noted some time ago by Snyder and Parr is examined in an Appendix.     

State-selected molecular-beam reaction dynamics of K with HF (υ = 1, j = 5, 6 and 7)

The crossed-molecular-beam method has been used to measure relative integral cross sections σ_r (υ = 1, j; E) of the endothermic (0.75 eV) reaction K + HF (υ = 1, j) → KF + H as a function of both the rotational quantum number j (j = 5, 6 and 7) and the translational energy E (0.55 ? E ? 1.32 eV) of the reagents. The vibrational-rotational (υ, j) states of HF were populated by infrared pumping with the radiation of a properly tuned pulsed chemical HF laser. In addition, relative cross sections with υ = 0 but averaged with respect to the initial rotational-state distribution of the HF molecules were also determined. The results exhibit three remarkable features: (a) σ_r (υ = 1, j; E) rises with increasing j, (b) the steepness of the ascent roughly decreases with increasing E, (c) at E = 0.98 eV reagent vibrational energy is about a factor of 200 more efficient in promoting the reaction than reagent translational energy. An intuitive dynamical model suggests that observations (a) and (b) are to be expected for a reaction governed by a potential-energy surface with a late barrier. This is consistent with the well-known interpretation of large vibrational effects as indicated by result (c).     

Studies on the La2−xSrxNiO4 (0 ⩽ x ⩽ 1) system

A new series of solid solutions of composition La_2?xSr_xNiO₄ (0 ? x ? 1) in which the oxidation state of nickel varies from +2 at x = 0 to +3 at x = 1 has been prepared. All the members of the system crystallize in the tetragonal K₂NiF₄ structure. The tetragonality ratio $\text{c}\text{a}$ shows a maximum at x = 0.5 which is interpreted as arising from a weak cooperative Jahn-Teller distortion due to octahedral site low-spin Ni³⁺ ions. The variation of electrical properties in the system is attributed to changes in electronic configuration of Ni³⁺.     

Features of the Diels-Alder reaction between 9,10-diphenylanthracene and 4-phenyl-1,2,4-triazoline-3,5-dione

The Diels-Alder reaction between substituted anthracenes 1a?1j and 4-phenyl-1,2,4-triazoline-3,5 (2) is studied. In all cases except one, the reaction proceeds on the most active 9,10-atoms of substituted anthracenes. The orthogonality of the two phenyl groups at the 9,10-position of diene 1a is found to shield 9,10-reactive centers. No dienophiles with C=C bonds are shown to participate in the Diels-Alder reaction with 1a; however, the reaction 1a + 2 proceeds with the very active dienophile 2,4-phenyl-1,2,4-triazoline-3,5-dione. It is shown that attachment occurs on the less active but sterically accessible 1,4-reactive center of diene 1a. The structure of adduct 3a is proved by ¹H and ¹³C NMR spectroscopy and X-ray diffraction analysis. The following parameters are obtained for reaction 1a + 2 ? 3a in toluene at 25°C: K _eq = 2120 M^?1, ΔH _f ^≠ = 58.6 kJ/mol, ΔS _f ^≠ = ?97 J/(mol K), ΔV _f ^≠ = ?17.2 cm³/mol, ΔH _b ^≠ = 108.8 kJ/mol, ΔS _b ^≠ = 7.3 J/(mol K), ΔV _b ^≠ = ?0.8 cm³/mol, ΔH _r-n = ?50.2 kJ/mol, ΔS _r-n = ?104.3 J/(mol K), ΔV _r-n = ?15.6 cm³/mol. It is concluded that the values of equilibrium constants of the reactions 1a?1j + 2 ? 3a?3j vary within 4 × 10¹?10¹¹ M^?1.     

Kinetics of the Hg(II)/Hg electrode reaction in DMSO solutions of chloride ions

The electrode reaction Hg(II)/Hg in complex chloride solutions with dimethyl sulfoxide as solvent has been investigated at the equilibrium potential by the faradaic impedance method and a cyclic current-step method. The ionic strength was 1 M with ammonium perchlorate as supporting electrolyte, and the temperature was 25°C. Double-layer data have been determined by electrocapillary measurements. From the results of the kinetic measurements at ligand numbers ≤1.1 or ≥2.3 it is concluded that the overall charge transfer proceeds step-wise. The solvated Hg²⁺ and Hg₂²⁺ as well as the complexes HgCl_j^2?j and the dinuclear Hg₂Cl³⁺ contribute to the exchange current density. The rate constant of the step HgCl_j^2?j/ Hg(I) is found to increase with the number of Cl^? coordinated. This increase can be correlated to a decrease in solvation and a lengthening of the Hg?Cl distance. For 1.1 << 2.3, impedance measurements indicate a rate-controlling adsorption step. It is suggested that the uncharged HgCl₂ then forms an adsorbed network on the mercury surface.     

Some models for evaluating the cavity formation energies in liquids

In the mixing process of solutes into solvents, the cavity formation energy is generally introduced into the energy balance. In this study, models for calculating this type of energy are proposed. These models are based on the Hansen's partial solubility parameters δ_d (MPa^1/2) dispersive, δ_p (MPa^1/2) polar and δ_h (MPa^1/2) hydrogen-bonding, and on the internal pressure P_j (J cm^?3) of the solvents.     

Synthesis, structure, and 13C and 31P CP/MAS NMR of the tetraphenylantimony(V) di-iso-propyl phosphorodithioate complex [Sb(C6H5)4{S2P(O-iso-C3H7)2}] and its solvated form [Sb(C6H5)4{S2P(O-iso-C3H7)2}] · 1/2C6H6: An example of the monodentate coordination of dithio ligands

The crystalline tetraphenylantimony(V) O,O′-di-iso-propyl phosphorodithioate complex [Sb(C₆H₅)₄{S₂P(O-i-C₃H₇)₂}](I) and its solvated form [Sb(C₆H₅)₄{S₂P(O-i-C₃H₇)₂}] · 1/2C₆H₆(II) were synthesized. Solid compounds I and II were studied by MAS NMR (¹³C, ³¹P). The ³¹P NMR chemical shift anisotropy ³¹P δ_aniso = (δ _zz ? δ_iso) and asymmetry parameter η = (δ _yy ? δ _xx )/(δ _zz ? δ_iso) were calculated using χ ² plots constructed on the basis of the ³¹P MAS NMR data. The O,O′-di-iso-propyl phosphorodithioate ligands in both complexes are characterized by predominantly the axially symmetric ³¹P chemical shift tensor (for the case δ _zz < δ _xx ≈ δ _yy ) with close values of anisotropy parameters (δ_aniso and η), which reflects their identical S-monodentate structural function. X-ray crystallography showed that II has a trigonal-bipyramidal molecular structure with the uncommon monodentate coordination of the Dtph ligands through an S atom in an axial position of the trigonal bipyramid and the benzene molecule in the outer sphere.