Photodissociation kinematics. II. Laboratory angular distributions of a hydride model system and the kinematic isotope effect

In the study of photodissociation processes, a theoretical framework of the laboratory angular distributions of photofragments has been firmly established. Numerical calculations of

, which is the radial-rotational coupling coefficient in a quantum-mechanical center-of-mass to laboratory-frame transformation, are implemented in this report. The general behavior of

as a parametric function of l, l₁, l₂ and x is explored. To illustrate the calculation of the laboratory angular distributions in a photodissociation process, a hydride model system is chosen. The parametric dependences of the photofragment's angular distribution on the initial linear momentum, recoil momentum and the angular momentum of the repulsive state are demonstrated in these numerical calculations. The laboratory angular distributions of photodissociated hydrogen and deuterium atoms exhibit a kinematic isotope effect.     

Analysis of kinetic models for the tunnel electron transfer reactions. Reaction kinetics for various radial and angular dependences of the tunneling probability

A new version of the “stepwise” approximation used in kinetic models for the long range electron transfer reactions is suggested. Using this approach the effects on the kinetics of these reactions of such factors are examined as a more complicated dependence (compared to the commonly used exponential one) of the tunneling probability, w, on the distance between the reagents as well as the angular dependence of w. For many practically important situations taking account of the above factors is shown to have no significant effect on the form of the reaction kinetics for both the pairwise and random spatial distributions of the reagents. However, the relations between the parameters a_ef and ν_cf in the expression for the tunneling distance R* = ₂¹a_ef In ν_cft, which can be determined from the experimental kinetics, and similar theoretical parameters ν_o and a that are involved in the expressions for w are found to be different for various types of the radial and the angular dependences of w. It is shown that when the orbitals between which the electron transfer takes place are located at sites removed from the geometric centers of the reactants the values of ν_ef can exceed by many orders of magnitude the characteristic frequency of the electron movement in molecules ν_e ≈ 10¹³ s^?1.     

Rotation of small molecules in liquids. A free-volume model combining collective and collisional effects

The rotational correlation times of C₂D₂ and CO₂ in liquid n-heptane were determined by infrared spectroscopy as a function of temperature. On the basis of the present and other preceding data we propose an interpretation of the rotational motion of small molecules in inert solvents. In this free-volume model the probe molecule is able to rotate freely during a time interval x and is in hydrodynamic interaction with the solvent during the rest (1 ? x). The correlation time of the angular momentum τ_J is, under these conditions, simply given by a linear relation τ_J = x(τ_J)_coll + (1 ? x)(τ_J)_hydro. This model fits very well the experimental data with a value of x consistent with its physical definition.     

Monte Carlo simulation of RRKM unimolecular decomposition in molecular beam experiments. V. product ox angular and energy distributions from O(3P)+X2 (X = Br,I)

Statistical simulation was applied to the unimolecular decomposition of the collision complexes formed in the crossed beam experiments on O(³P) + Br₂ by Fernie et al. and O(³P) + I₂ by Durkin et al. The simulation procedure used the fundamentals of RRKM theory and included exact angular momentum conservation. The impact parameter distributions were varied to obtain the best fits. Good agreement with experimental laboratory angular distributions measured with O atoms seeded in both He and Ne was found for impact parameter distributions which were peaked at quite small values, in most cases between 2 and 3 Å. Product OX molecules were found to be rotationally excited and inverted with a mean rotational energy close to twice the value expected without angular momentum restrictions. The differences found between the calculated and the experimental angular distributions do not support any assumptions about osculating or short-lived complexes. The normal exoergicity ΔD₀ of 27 kJ/mol for the O + I₂ reaction agrees well with the experiments by Dunkin et al.     

Applicability of the Levich Equation for a Two-Phase Solution in the Rotating Disk Electrode System

The mass-transter characteristics of a two-phase system formed by mixing a fixed quantity (20 v/v%) of organic solvent with an aqueous ferricyanide electrolyte solution in an RDE system were studied. The Levich eqution, I₁ = 0.62 nFAC_bD^2/3v^?1/6_ω^1/2, was found to be applicable to the two-phase system with only a minor modification in the angular velocity (ω) at Reynolds numbers between 3–5 × 10⁴. The experimental results indicate that the interfacial tension is the most important variable for the two-phase system. One group of organic solvents with smaller interfacial tension, such as benzene or toluene, needs a modification of the Levich equation by replacing the observed angular velocity (ω_o) with the true angular velocity (ω_t) which was observed to be 1.1 times the observed angular velocity. For the other group with larger interfacial tension, such as n-hexane or cyclohexane, there is no need to modify the observed angular velocity. In other words, the Levich equation may be expressed as I₁ = 0.65 nFAC_bD^2/3v^?1/6ω^1/2 for two-phase solution if the interfacial tension is smaller than 37.0 dyne/cm.     

Thermostable Hemicellulases of a Bacterium,Geobacillus sp. DC3, Isolated from the Former Homestake Gold Mine in Lead,South Dakota

A thermophilic strain, Geobacillus sp. DC3, capable of producing hemicellulolytic enzymes was isolated from the 1.5-km depth of the former Homestake gold mine in Lead, South Dakota. The DC3 strain expressed a high level of extracellular endoxylanase at 39.5 U/mg protein with additional hemicellulases including β-xylosidase (0.209 U/mg) and arabinofuranosidase (0.230 U/mg), after the bacterium was grown in xylan for 24 h. Partially purified DC3 endoxylanase exhibited a molecular mass of approximately 43 kDa according to zymography with an optimal pH of 7 and optimal temperature of 70 °C. The kinetic constants, K _m and V _max, were 13.8 mg/mL and 77.5 μmol xylose/min·mg xylan, respectively. The endoxylanase was highly stable and maintained 70 % of its original activity after 16 h incubation at 70 °C. The thermostable properties and presence of three different hemicellulases of Geobacillus sp. DC3 strain support its potential application for industrial hydrolysis of renewable biomass such as lignocelluloses.     

Fabrication and optical conductivities of strained epitaxial NaxCoO2 thin films: x=0.5, 0.7

Epitaxial γ phase-Na_xCoO₂ thin films were deposited on (001) sapphire by the pulsed laser deposition method. To fabricate epitaxial Na_0.5CoO₂ thin films, we used a solution of iodine-dissolved acetonitrile and obtained an epitaxial Na_0.5CoO₂ thin film with a high crystallinity because of Na deintercalation of epitaxial Na_0.7CoO₂. From the spectroscopic ellipsometry analysis, we obtained the optical constants as well as the optical conductivities for the Na_0.5CoO₂ and Na_0.7CoO₂ thin films. The energy splitting between e_g and a_1g increased because of the structural strain of the Na_0.7CoO₂ thin film. It is inferred that the structural strain is the source for the lower resistivity and the preservation of the strongly correlated system up to 200 K for the Na_0.7CoO₂ thin film. On the other hand, the strain in the Na_0.5CoO₂ thin film was not affected, and the charge-ordering state and the Na content (x=0.5) only cause the charge-ordering state.     

Vibrationa-rotational structure in the angular distribution and intensity of photoelectrons from diatomic molecules. II. H2

Total intensity and angular distribution of photoelectrons ejected from H₂ are calculated for individual vibrational-rotational transitions accompanied by photoionization The relevant transition moment is evaluated in the two-center spheroidal coordinates with varying internuclear distance. The calculations for 584 Å and 736 Å lines are compared with the observed spectra. The theoretical result clearly shows the dependence of the angular distribution on the initial and final vibrational states and the dominance of the rotational transition with ΔJ = 0 over that with |Δ| = 2.     

A DWBA study of angular distributions for the state-to-state reactive scattering process of F + H2 → HF + H

Based on our earlier three-dimensional DWBA theory, we discuss angular distributions and the roles of various angular momenta. The theory predicts a relatively small number of partial waves, backward scattering, and broadening of angular distributions with increased energy, for the reaction F+ H₂ (v_a = 0, j_a = 0) → HF (v_b = 2 j_b = 0) + H     

The nickel-group IV molecules NiC,NiSi, and NiGe

All electron ab initio calculations have been applied to elucidate the electronic states and the nature of the chemical bonds in the molecules NiC, NiSi, and NiGe. The calculations have revealed that the ground states of all three molecules are¹Σ⁺, but due to the open 3d shell of the Ni atom the molecules have many low-lying electronic states. The NiC molecule is strongly polar, and the low-lying electronic states have been identified as those arising when the angular momenta of the³F_g Ni⁺ ion are coupled to the angular momenta of the⁴S_uC^? anion. The chemical bond in the NiC molecule has triple bond character due to the valence bond couplings between the Ni 4s and 3dπ electrons and theC 2p electrons. The chemical bonds in the molecules NiSi and NiGe are very much alike; they are double bonds composed of oneσ and oneπ bond. Theσ bond is due to the doubly occupied delocalized molecular orbital composed of the Ni 4s orbital and the Si 3pσ or the Ge 4pσ orbital. Theπ bond originates from the valence bond coupling between the localized hole in the Ni 3dπ orbital and the valencepπ electron of Si or Ge.     

Direct observation of the angular distribution of the chemiluminescence from Ba + N2O → BaO + N2

The angular distribution of the chemiluminescent reaction Ba + N₂O → BaO + N₂ has been investigated by photographing directly the chemiluminescence from this reaction in a crossed beam experiment. It was found that the lifetime of the reactively scattered chemiluminescent BaO molecules is sufficiently long (≈ 10^?s δ) to allow the observation of the angular distribution. From the dependence of this distribution on R and ? where R is the distance from the scattering center and ? the laboratory scattering angle, we conclude that under single collision conditions the chemiluminescence arises preferentially from highly excited vibrational-rotational levels of the A′¹ Π state of BaO.     

Probes for narcotic receptor mediated phenomena. Part 31: Synthesis of rac-(3R,6aS,11aS)-2-methyl-1,3,4,5,6,11a-hexahydro-2H-3,6a-methanobenzofuro[2,3-c]azocine-10-ol, and azocine-8-ol, the ortho-c and the para-c oxide-bridged phenylmorphan isomers

Two of the 12 possible oxide-bridged phenylmorphans, were synthesized, rac-(3R,6aS,11aS)-2-methyl-1,3,4,5,6,11a-hexahydro-2H-3,6a-methanobenzofuro[2,3-c]azocine-10-ol (7) (the ortho-c compound), and rac-(3R,6aS,11aS)-2-methyl-1,3,4,5,6,11a-hexahydro-2H-3,6a-methanobenzofuro[2,3-c]azocine-8-ol (8) (the para-c compound). Single-crystal X-ray diffraction studies indicated that the dihedral angle between the least squares planes through the phenyl ring and the atoms C₁, C_11a, C₁₂, and C₃ in the piperidine ring in both 7·CHCl₃ and 8·HBr was 6.9°. The C₁₂-C_6a-C_6b-C_10a torsion angle was found to be 139.3° for both compounds. The angular relationship between the phenolic ring and the piperidine ring in phenylmorphans that interact with specific opioid receptors as agonists or antagonists is of considerable theoretical interest.     

A Novel Alkaliphilic Xylanase from the Newly Isolated Mesophilic Bacillus sp. MX47: Production, Purification, and Characterization

A newly isolated bacterial strain, Bacillus sp. MX47, was actively producing extracellular xylanase only in xylan-containing medium. The xylanase was purified from the culture broth by two chromatographic steps. The xylanase had an apparent molecular weight of 26.4?kDa with an NH₂-terminal sequence (Gln-Gly-Gly-Asn-Phe) distinct from that of reported proteins, implying it is a novel enzyme. The optimum pH and temperature for xylanase activity were 8.0 and 40?°C, respectively. The enzyme activity was severely inhibited by many divalent metal ions and EDTA at 5?mM. The xylanase was highly specific to beechwood and oat spelt xylan, however, not active on carboxymethyl cellulose (CMC), avicel, pectin, and starch. Analysis of the xylan hydrolysis products by Bacillus sp. MX47 xylanase indicated that it is an endo-??-1,4-xylanase. It hydrolyzed xylan to xylobiose as the end product. The K _m and V _max values toward beechwood xylan were 3.24?mg?ml^?1 and 58.21???mol?min^?1?mg^?1 protein, respectively.     

Relation between the crystal structures of some salts of the type Me(OCOCH3)2 · nH2O and their ability to form mixed crystals or double salts (Me2+ = Mg,Ca, Mn,Co, Ni,Cu, Zn,Cd)

An attempt is made to find the relation between the crystal structures of some salts of the type Me(OCOCH₃)₂ · nH₂O (Me²⁺ = Mg, Ca, Mn, Co, Ni, Cu, Zn, Cd) and their ability to form mixed crystals or double salts by taking into account the difference in the ground-state configurations of the metal (II) ions. Such a treatment is based on the theoretical argument that the formation of isomorphous and isodimorphous mixed crystals occurs when the admixed ion may assume the coordination environment of the substituted ion in the crystal structure of the host salt. Double salts are formed mainly between the acetates of the d⁵, d¹⁰ and p⁶ metal ions, i.e., for ions that allow strong angular deformations of the coordination polyhedra or when at least one of the metal ions meets this condition so that acetate bridge bonding may occur.     

Determination of the perpendicular magnetic parameters for Cu(II) EPR spectra from angular anomalies

A method is outlined to obtain accurate values of g_? and A_? in EPR spectra of Cu(II) compounds, provided that an extra absorption peak due to an angular anomaly can easily be recognized. This method turns out to be useful especially in the case of low resolution and in the presence of a superhyperfine pattern due to the ligands.     

Angular dependent linewidths of ESR spin probes in oriented smectic systems. An application to oriented lecithin—cholesterol multibilayers

A theory, based on the diffusion model of molecular reorientation extended with an orienting potential, is developed for the angular dependence of the ESR linewidths of symmetrical top radicals in oriented smectic liquid crystals. The theoretical results have been compared with linewidth data obtained with the cholestane spin label in oriented multibilayers of equimolar quantities of dipalmitoyl lecithin and cholesterol. For the determiination of the linewidths, the ESR spectra were fitted to a line shape function, which includes unresolved proton hyperfine interactions.From the comparison of theory and experiment the rotational diffusion tensor and order parameter S can be found, giving D_⊥ = 3.4 × 10⁶ s^?1, D|/D_⊥ = 40 and S = 0.86 at 49°C. The high value of D|/D_⊥ indicates a strong anisotropic motion of the cholestane spin label. The order parameter found is in good agreement with the order parameter calculated from the angular dependence of the ESR line positions.     

The Fokker-Planck-Langevin model for rotational brownian motion. IV. Asymmetric top molecules

The general series expansion for the joint angular velocity-orientation conditional probability density for a fluid composed of asymmetric top molecules is derived, and expressions for the reorientational correlation functions, correlation times, spectral densities, and the correlation times relevant to magnetic relaxation via spin-rotation interactions are presented. The reorientational correlation times and spin-rotation functions computed using this Fokker-Planck-Langevin (FPL) model with isotropic friction tensor (τ_x = τ_y = τ_z) are compared with the corresponding times and functions computed with the J-diffusion limit of the extended diffusion (EDJ) model. The models are found to predict significantly different behaviour only in the regime where free rotation and precessional effects become important. The reorientation self- and cross-correlation times are shown to follow Hubbard relations in the limit of short τ_x, τ_y, τ_z. Numerical calculations of the FPL reorientational correlation functions, correlation times and spin-rotation functions show that these properties are sensitive to the anisotropies in the friction tensor in the rotational Langevin equation.     

Laser-assisted (e, 2e) collisions in helium

The influence of a strong laser field on the dynamics of fast (e, 2e) collisions in helium is analyzed in the asymmetric, coplanar geometry. The interaction of the laser field with the incident, scattered and ejected electrons is treated in a non-perturbative way, while the remaining interactions are treated by using first order perturbation theory. Detailed calculations are performed for an incident electron energyE _{k i}=600 eV, an ejected electron energyE _{k B}=5 eV and a scattering angle θ _A =4°. The influence of the laser parameters (photon energy, intensity and direction of polarization) on the angular distribution of the ejected electron is analyzed. We find that in general the triple differential cross sections are strongly dependent on the dressing of the projectile and the target by the laser field.