Reactive scattering of alkali dimers: K2 + HgCl2, HgBr2, HgI2

Angular distribution measurements of KX reactive scattering of a potassium dimer K₂ beam by mercuric halide molecules HgX₂ are reported. All the reactions exhibit strong forward peaking in the centre of mass differential cross sections and large total reaction cross sections Q_r ～ 150 Ų. However, there is substantial backward peaking ( forward peak) for HgBr₂, HgI₂. Despite the direct stripping dynamics, both alkali atoms of the K₂ dimer become bound alkali halide molecules in most (perhaps all) reactive collisions. A major fraction of the reaction exoergicity is disposed into vibrational excitation of the product KX molecules. A mechanism involving a first electron jump in the entrance valley and a second electron jump in the exit valley of the potential surface is suggested to explain the rapid transfer of both K₂ valence electrons.     

Reactive scattering of oxygen atoms: O+I2, ICl,Br2

Angular and velocity distribution measurements of IO reactive scattering from crossed beams of O atoms and halogen molecules I₂, ICl are reported. Angular distribution measurements are reported for BrO from O + Br₂. The O atom beam was generated at ～350 K from a microwave discharge source and the halogen molecule beam from a supersonic nozzle source at ～380 K. The product time-of-flight distribution was recorded at each laboratory scattering angle by a mini-computer. The scattering data are found to be in excellent agreement with the RRKM-AM model of reactive scattering via a long-lived collision complex. The observation of IO product from O + ICl identifies the complex with a bound O-I-Cl triplet state, previously observed for O-Cl-Cl in matrix isolation studies, as proposed by Herschbach. The maximum centrifugal barrier B _m′ for dissociation of the long-lived complex can be accurately determined, particularly for O + I₂. The B _m′ values indicate that both the entrance and exit valleys of the potential energy surface are governed by centrifugal barriers in the region of long-range van der Waals potentials. The comparatively small reaction cross section (e.g. Q ～ 2 Ų for O + Br₂ from discharge flow measurements) is attributed primarily to an orientation requirement for reaction. The RRKM-AM model indicates a ‘tight linear’ transition state for dissociation of the O-I-I complex, corresponding to significant long-range IO orienting forces in the exit valley of the potential energy surface.     

Quantum-mechanical high temperature Equation of state: Perturbation theory with finite range Kac potential

Angular distribution measurements of reactive scattering of a supersonic potassium atom beam by a series of halogen and halomethane molecules are reported with initial kinetic energies E ～ 5–6 kcal mol^-1. Differential reaction cross sections for I₂, IBr, CH₂I₂ show decreased wide-angle scattering and decreased total reaction cross sections compared with thermal energies. The differential reaction cross section for CHI₃ is peaked in the forward direction (?=0°) but that for CBr₄ peaks sideways at ? ～ 40°. The variation in reaction dynamics is correlated with the potential energy curves of halomethane molecules and their anions as indicated by dissociative thermal electron attachment experiments.     

Structural studies of tetrachloride liquids

The differential cross-sections for neutron scattering from liquid carbon tetrachloride have been measured with the TSS instrument at the Harwell Electron Linac. Data were taken at seven different scattering angles for a wavelength range of 0·2–3·5 Å. The observed diffraction patterns at high momentum transfer (> 8–30 Å^-1) have been analysed in terms of the molecular form factor f ₁(Q). It was found that the oscillation amplitudes could be satisfactorily described only by introducing an energy-dependent term into the Debye-Waller factors of the form factor. The f ₁(Q) data were fitted with a four-parameter function for measurements at scattering angles of 150°, 90° and 58°. The carbon-chlorine bond length parameter was accurately defined in all cases and had a mean value of 1·766 ± 0·002 Å. The inclusion of an anharmonicity constant in the form factor gave an improved χ²-fit to the data with an increased value of 1·770 ± 0·002 Å for the bond length. The results are in excellent agreement with other measurements and show the importance of pulsed neutron techniques for molecular structure studies of disordered materials.     

Equation of state and thermal expansivity of LiF and NaF

The high-pressure and high-temperature behaviors of LiF and NaF have been studied up to 37 GPa and 1000 K. No phase transformations have been observed for LiF up to the maximum pressure reached. The B1 to B2 transition of NaF at room temperature was observed at ～28 GPa, this transition pressure decreases with temperature. Unit-cell volumes of LiF and NaF B1 phase measured at various pressures and temperatures were fitted using a P–V–T Birch–Murnaghan equation of state. For LiF, the determined parameters are: α₀ = 1.05 (3)×10^?4 K^?1, dK/dT = ?0.025 (2) GPa/K, V ₀ = 65.7 (1) Å³, K ₀ = 73 (2) GPa, and K′ = 3.9 (2). For NaF, α₀ = 1.34 (4)×10^?4 K^?1, dK/dT = ?0.020 (1) GPa/K, V ₀ = 100.2 (2) Å³, K ₀ = 46 (1) GPa, and K′ = 4.5 (1).     

Electron spectroscopy using excited atoms and photons VI. Penning ionization of HCN and some related compounds

The He*(2¹S, 2³S) Penning ionization electron spectra of HCN, (CN)₂, CH₃CN, BrCN and ICN are compared to the corresponding 584 Å photoelectron spectra. Large differences are observed for the relative populations of the ionic states of the various molecules when Penning ionization is compared to photoionization. For these molecules, the ratio of the normalized relative populations of states corresponding to removal of π bonding and nitrogen lone pair electrons is significantly greater for 584 Å photoionization than for He*(2³S) Penning ionization. Some unidentified chemi-ionization processes are observed for (CN)₂, BrCN and ICN.     

Extended X‐ray absorption fine structure and multiple‐scattering simulation of nickel dithiolene complexes Ni[S2C2(CF3)2]2n (n = −2, −1, 0) and an olefin adduct Ni[S2C2(CF3)2]2(1‐hexene)

A series of Ni dithiolene complexes Ni[S₂C₂(CF₃)]₂ⁿ (n = ?2, ?1, 0) ( 1 , 2 , 3 ) and a 1‐hexene adduct Ni[S₂C₂(CF₃)₂]₂(C₆H₁₂) ( 4 ) have been examined by Ni K‐edge X‐ray absorption near‐edge structure (XANES) and extended X‐ray absorption fine‐structure (EXAFS) spectroscopies. Ni XANES for 1 – 3 reveals clear pre‐edge features and approximately +0.7 eV shift in the Ni K‐edge position for `one‐electron' oxidation. EXAFS simulation shows that the Ni—S bond distances for 1 , 2 and 3 (2.11–2.16 Å) are within the typical values for square planar complexes and decrease by ～0.022 Å for each `one‐electron' oxidation. The changes in Ni K‐edge energy positions and Ni—S distances are consistent with the `non‐innocent' character of the dithiolene ligand. The Ni—C interactions at ～3.0 Å are analyzed and the multiple‐scattering parameters are also determined, leading to a better simulation for the overall EXAFS spectra. The 1‐hexene adduct 4 presents no pre‐edge feature, and its Ni K‐edge position shifts by ?0.8 eV in comparison with its starting dithiolene complex 3 . Consistently, EXAFS also showed that the Ni—S distances in 4 elongate by ～0.046 Å in comparison with 3 . The evidence confirms that the neutral complex is `reduced' upon addition of olefin, presumably by olefin donating the π‐electron density to the LUMO of 3 as suggested by UV/visible spectroscopy in the literature.     

Reactive scattering of alkali dimers K2 + I2, CH2I2, CHI3, CBr4

Angular distribution measurements of KX reactive scattering of a potassium dimer K₂ beam by I₂ and by a series of halomethane molecules are reported. The K₂ + I₂ reactive scattering is similar to that previously observed for K₂ + Br₂. The predominant reaction path yields K + KI + I with the K and KI product recoiling in the forward direction. However, the forward peak of the KI differential cross section is lower than that for K from K₂ + I₂ and is broader than that observed for KBr from K₂ + Br₂. This is attributed to slow dissociation of the I ₂ ^- ion formed in the electron jump mechanism previously proposed for K₂ + Br₂. In the halomethane reactions, both alkali atoms of the K₂ dimer become bound alkali halide molecules in all reactive collisions, despite the direct dynamics of the corresponding supersonic K atom reactions. Thus, these reactions provide compelling evidence for a second electron jump mechanism, previously proposed for the reactions of K₂ dimers with polyhalide molecules. The differential cross sections for the K₂ dimer plus halomethane reactions indicate an osculating collision complex with a lifetime at least comparable to its rotational period, perhaps much longer. This reaction complex is identified with the doubly ionic state formed by the second electron jump transition.     

Limits on the impact parameters occuring in specific K−p interactions at 8.25 GeV/c

We have determined a lower limit of the impact parameter for the reactions associated with the channels K^?p → K^?pπ⁺π^?K^?p → λπ⁺π^?π⁰. The limit was found to be highest for the diffractive parts of the first channel (～ 0.52 fm) and smallest for the forward Λ in the second channel (～0.21 fm).We have also examined the elements of the inverse correlation matrix for the transfer: the off-diagonal elements are small (consistent with zero) for n = 4?7 body products. The log 〈Q_i·Q_j〉 of the correlation matrix as a function of $\text{Гi?jГ}$ falls on a straight line and the eigenvalue λ₁ of the transverse momentum transfer eigenfunction was found to increase slightly from ～0.6 for 4-body to ～0.7 for 7-body products. The 〈cosφ_ij〉 of the Q_i, Q_j shows similar behaviour to the 〈Q_i·Q_j〉     

Perturbation allowed transitions in the infrared spectrum of 14ND3: determination of the K-dependent parameters in the ground state

ABSTRACT

Accurate values of the K-dependent constants ^{( i )} C, ^{( i )} D_K and ^{( i )} H_K in the ground state of ¹⁴ND₃, with i = s, a, have been determined for the first time thanks to the detections of ‘perturbation allowed’ transitions in the ν₁, ν₂, ν₃, ν₄ and 2ν₄ infrared bands. The rotation–inversion and inversion transitions from the literature, together with 7289 ground state combination differences from the infrared vibration–rotation–inversion transitions have been simultaneously analysed. The adopted rotation–inversion Hamiltonian includes distortion constants up to the eighth power and the Δk = ±3 and Δk = ±6 interaction terms. Precise values of the diagonal constants and of the Δk = ±3 interaction coefficients have been obtained. Accurate values of the ground state term values have been calculated for both s and a levels up to J = 21.     

Crystal Structures of Tetrakis‐(4‐chlorophenylthio)‐butatriene and Tetrakis‐(tert‐butylthio)‐butatriene

Tetrakis‐(4‐chlorophenylthio)‐butatriene (3a) and tetrakis‐(tert‐butylthio)‐butatriene (3b) were synthesized, and their crystal structures were determined. The compound 3a is monoclinic, space group P2₁/c, a=6.9785(8), b=8.6803(9), c=22.884(2) Å, β=93.887(6)^o, V=1383.0(3) ų, Z=2. The compound 3b is monoclinic, space group P2₁/n, a=11.0615(6), b=10.8507(4), c=11.2717(6) Å, β =116.427(2)^o, V=1211.5(1) ų, Z=4. The title compounds 3a and 3b reside on an inversion center so that only half of the molecule is crystallographically unique. Both compounds are not planar. The crystal structures of 3a and 3b have cumulated double bonds. The C7–C8–C8ⁱ and C5–C6–C6ⁱ angles that show the linearity in both structures, respectively, are 176.4(3)° in 3a and 175.6(2)° in 3b.     

Investigation of local lattice structure around Cr3+ ions at the trigonal and tetragonal sites in RbCdF3: Cr3+ crystal

The local lattice structure and EPR, optical spectra for Cr³⁺ doped in RbCdF₃ crystal have been studied by diagonalizing the complete energy matrices. The results show that the local structure of the Cr³⁺ ions in RbCdF₃ exhibits a compressed distortion at the trigonal and tetragonal sites. The compressed distortion can be ascribed to the fact that the radius of Cr³⁺ ion is smaller than that of Cd²⁺ ion, and therefore Cr³⁺ ion will draw the fluorin ligands inwards. The variational ranges of the local structural parameters for Cr³⁺ doped in RbCdF₃ crystal R =?1.9491 Å ～?1.9814 Å, θ?= 55.234° ～?55.286° at the trigonal site and R ₁ =?1.8617 Å ～?1.8928 Å, R ₂ =?1.9527 Å ～?1.9851 Å at tetragonal site are obtained respectively, and the EPR and optical spectra agree well with the experimental results.     

A new high-pressure polymorph of Ti2O3: implication for high-pressure phase transition in sesquioxides

The post-corundum phase transition has been investigated in Ti₂O₃ on the basis of synchrotron X-ray diffraction in a diamond anvil cell and transmission electron microscopy. The new polymorph of Ti₂O₃ was found at about 19 GPa and 1850 K, and this phase was stable even at about 40 GPa. A new polymorph of Ti₂O₃ can be indexed on a Pnma orthorhombic cell, and the unit-cell parameters are a=7.6965 (19) Å, b=2.8009 (9) Å, c=7.9300 (23) Å, V=170.95 (15) Å³ at 19 GPa, and a=7.8240 (2) Å, b=2.8502 (1) Å, c=8.1209 (3) Å, V=181.10 (1) Å³ at ambient conditions. The Birch–Murnaghan equation of state yields K ₀=206 (3) GPa and K′₀=4 (fixed) for corundum phase, and K ₀=296 (4) GPa and K′₀=4 (fixed) for the post-corundum phase. The molar volume decreases by 12% across the phase transition at around 20 GPa. The structural identification was carried out on a recovered sample by the Rietveld method, and a new polymorph of Ti₂O₃ can be identified as Th₂S₃-type rather than U₂S₃-type structure. The transition from corundum-type to Th₂S₃-type structure accompanies the drastic change of the form of polyhedron: from TiO₆ octahedron in the corundum-type to TiO₇ polyhedron in the Th₂S₃-type structures.     

Ab Initio Investigation of the Microspecies and Energy in Hydrated Strontium Ion Clusters

Quantum chemistry calculations were used to study the structure and energy of strontium (Sr) ion hydrated clusters [Sr(H₂O)_1?25]²⁺. The saturated hydration number of the first hydration layer of Sr²⁺ was 8, and the hydration distance was 2.58 Å. The second hydration layer had 1–9 hydration numbers, and the hydration distance was in the range of 4.4–4.6 Å. This work also developed the relationship between the thermodynamic data (average water binding energy E_n and successive water binding energy ΔE_n,n?1, etc.) of the aforementioned low-energy structure and the hydration structures. The first hydration layer was formed by the strong electrostatic interaction between Sr²⁺ and water molecules, and the decrease in ΔE_n,n?1 was relatively large. Hydrogen bonds were formed between water molecules of the second hydration layer and water molecules of the inner layer, and the decrease in ΔE_n,n?1 was relatively small. When one water molecule was added beyond the second hydration layer, ΔE_n,n?1 was close to the hydrogen bond energy 8.88 kcal/mol (37.1 kJ/mol) of dimer water molecule, indicating that there was very weak interaction between Sr²⁺ and the water molecules beyond the second hydration layer.     

The anharmonic bending vibration of the NaCl dimer

A vibrational analysis of the NaCl dimer at high temperature is performed, with special attention given to a quantum mechanical study of the anharmonic, large amplitude B_1u out-of-plane bending mode. This mode is the primary contributor to the perpendicular amplitude correction K, and the anharmonic, large amplitude K value for the Na—Cl bond is found to be only 0.0002 Å less than the standard harmonic value of 0.0159 Å at 1130 K. This corresponds to an average out-of-plane bending angle α¯ of 10°. The results of a standard ASYM20 harmonic analysis are then applied to extract an approximate r _e(Na—Cl) value for the dimer of 2.514(40) Å, in excellent agreement with the best microwave/ ab initio value of 2.515 Å. Derived non-bonded r _a to r _e corrections are also reasonable, although the nona e bonded distances are best combined to determine the Cl—Na—Cl angle.     

Zerfallende Zustände als physikalisch nichtisolierbare Teilsysteme

Presently the investigations of decaying quantum mechanical systems lack a well-founded concept, which is reflected by several formal difficulties of the corresponding mathematical treatment. In order to clarify in some respect the situation, we investigate, within the framework of nonrelativistic quantum mechanics, the resonant scattering of an initially well localized partial wave packet ϕ_l(r, t). If the potential decreases sufficiently fast for r → ∞, ϕ_l(r, t) can be expressed at sufficiently long time after the scattering has taken place, as ϕ_l(r, t) = I(r, t) + ∑ N_iϕl(K_i, r) exp {–iK_i² t/2M} × Θ(k_i – γ_i – Mr/t), ϕ_l(K_i, r) being the resonant solution with complex “momentum” K_i = k_i – iγ_i. From this heuristic relation one can deduce not only the probability for the creation of unstable particles but also obtain some hints to a connection between decaying states and physically nonisolable partial systems. On the other hand, this connection can perhaps display the inadequacy of attempts which suggest to solve the problem of decaying states within the usual Hilbert space methods.     

Reactive scattering of a supersonic oxygen atom beam O+ICl

Reactive scattering of O atoms with ICl molecules has been studied at an initial translational energy E = 40 kJ mol^-1 using a supersonic beam of O atoms seeded in He and at E = 15 kJ mol^-1 using O atoms seeded in Ne. Velocity distributions of OI product were measured by cross-correlation time-of-flight analysis. Full contour maps of the differential reaction cross-section have been obtained which show peaking almost equally in the forward and backward directions at both initial translational energies. The product translational energy distributions are consistent with a long-lived O-I-Cl collision complex dissociating via a loose transition state. The stability of the O-I-Cl complex is attributed to the low electronegativity of the central I atom compared with the peripheral atoms. This electronegativity ordering rule also determines the stability of the intermediates in the other reactions of oxygen atoms with halogen molecules. The mild peaking of the product angular distributions for O + ICl and IBr indicates that collision complexes have quite modest collision angular momenta L ～ 40 ? corresponding to impact parameters b ～ 1·4 Å and that the angular momentum of the OI molecule in the loose transition state may be approximately half the product orbital angular momentum.     

Geometry,strength of binding and Br2 charge redistribution in the complex OC ··· Br2 determined by rotational spectroscopy

The ground-state rotational spectra of the six isotopomers ¹⁶O¹²C ··· ⁷⁹Br⁷⁹Br, ¹⁶O¹²C ··· ⁸¹Br⁷⁹Br, ¹⁶O¹²C ··· ⁸¹Br⁸¹Br, ¹⁶O¹²C ··· ⁷⁹Br⁸¹Br, ¹⁶O¹³C ··· ⁷⁹Br⁷⁹Br, ¹⁶O¹³C ··· ⁸¹Br⁷⁹Br, were observed by pulsed-nozzle, Fourier-transform microwave spectroscopy. The spectroscopic constants B _O, D _J, χ _aa (Br_i), χ _aa (Br_o), M_bb (Br_i) and M _bb (Br_o), where i = inner and o = outer, were determined for each isotopomer. The complex is linear, with the weak bond between the C atom of CO and Br_i. The rotational constants were used to determine the distance r(C ··· Br_i) = 3.1058Å and to show that the Br—Br bond lengthens by ～0.005–0.01Å on complex formation. The intermolecular stretching force constant kσ = 5.0 Nm^?1 was obtained from D_J and the Br nuclear quadrupole coupling constants were interpreted to reveal that a fraction δ = 0.02 of an electronic charge is transferred from Br_i to Br_o when Br₂ is subsumed into the complex. Properties of the two series OC ··· XY and H₃N ··· XY, where XY = C1₂, Br₂ and BrC1, are compared.     

X‐ray pair distribution function analysis of nanostructured materials using a Mythen detector

Total scattering from nanocrystalline materials recorded on the Australian Synchrotron powder diffraction beamline has been analysed to produce atomic pair distribution functions (PDFs) for structural analysis. The capability of this beamline, which uses the massively parallel Mythen II detector, has been quantified with respect to PDF structure analysis. Data were recorded to a wavevector magnitude, Q, of 20.5 Å^?1, with successful PDFs obtained for counting times as short as 10 s for crystalline LaB₆ and 180 s for nanocrystalline (47 Å) anatase. This paper describes the aspects of a PDF experiment that are crucial to its success, with reference to the outcomes of analysis of data collected from nanocrystalline TiO₂ and microcrystalline LaB₆ and IrO₂.     

The properties of some derivative autocorrelation functions computed with the atom-atom potential

High-resolution quasi-elastic neutron-scattering measurements have been made on two nematogens: DMBCA with a nematic range 108 to 119°C, and 5CB and a tail-deuteriated sample (D5CB), having a nematic range 22·6 to 35·1°C.

Results on 5CB in the crystal phase at ～18°C showed no significant quasielastic broadening, which means that any random motions of the alkyl chain are slower than about 5 × 10⁹ rad s^-1. Measurements were made at a single temperature in the nematic phases on specimens aligned in a magnetic field of 0·25T; for DMBCA with scattering vector Q⊥n (n is the nematic director) and for 5CB and D5CB with Q⊥n and Q∥n and also on the isotropic liquid phase of D5CB at 45°C. Analysis of the coherent scattering from nematic D5CB at Q = 1·2 Å^-1 and 25°C gave an order parameter <P ₂>=0·55, close to the simple mean field value for this temperature. The coherent scattering from DMBCA is too weak to allow this experiment to be performed.

The most remarkable qualitative feature of the results is the close similarity of the scattering law S(Q, ω) for D5CB (and 5CB) with Q⊥n and Q∥n. Analysis of the results in all cases was made using values for the translational diffusion constants measured previously. Corrections for multiple scattering are shown to be important and a single simple model has been devised which fits the line shapes of all the results for D5CB in nematic (Q⊥n and Q∥n) and isotropic liquid phases and DMBCA. The model involves uniaxial rotational diffusion about the long molecular axis m coupled to a displacement along the rotation axis giving a net rotation in a plane whose normal makes an angle ∝ relative to the direction m. Values for the rotational diffusion constant D _rd ns^-1 are as follows: D5CB, 25°C, 6 (∝ ～ 50°); 45°C, 10. DMBCA, 112°C, 16, (all ±10–15 per cent).

The results for D5CB and 5CB are so similar that no additional detailed model fitting was attempted for the fully hydrogenous sample and it is concluded that while the motion of the alkyl tails is freer, the time scale of the motions is not more than about a factor of 2 faster than that of the molecular cores.