bluuebunny/crossref_metadata_2025 huggingface dataset:
ESR Study of Stereospecific Proton Transfer in Irradiated Crystals of l-Alanine
Authors: Miyagawa Ichiro , Tamura Naoyuki , Cook J. W.
Published: February 2004

Crystals of l-alanine irradiated at 80°K were studied with ESR technique. It was found that the proton transfer, which had originally been proposed by Sinclair and Hanna, was stereospecific: The produced species was found to be O(1)−/CH3HCNH3+—Ċ\O(2)–H, and no evidence for its chemically equivalent species O(1)–H/CH3HCNH3+—Ċ\O(2)− was detected. This stereospecific proton transfer was interpreted on the basis of a quantum-tunneling model, which was found to account for the observed result satisfactorily. A new sample cavity was developed. This cavity has a device which enables one to orient an irradiated crystal to any desired direction, even at 80°K.
Mass-Spectrometric Study of the Photoionization of C2F4 and CF4
Authors: Walter T. A. , Lifshitz C. , Chupka W. A. , Berkowitz J.
Published: February 2004

Photoionization-efficiency curves for CF3+ from CF4 and for the parent ion and selected fragment ions from C2F4 are reported for the energy region from onset of ionization to about 20 eV. The ionization-efficiency curves for both parent and fragment ions from C2F4 demonstrate a number of very pronounced autoionization peaks. Appearance potentials are made more reliable by using a cooled ionization chamber to remove most of the thermal vibrational energy of the molecules. From the difference between the appearance potentials of CF+ and CF3+ from C2F4, it is concluded that I.P.(CF) = I.P.(CF3) + 0.06 eV. Therefore the I.P.(CF) = 9.23 ± 0.08 eV can be calculated from the I.P.(CF3) = 9.17 ± 0.08 eV derived in this paper. The onset of CF3 from CF4 is asymptotic, and there is no clear threshold. An upper limit for this threshold was set at 15.35 eV.
Explicitly Correlated Wavefunction for LiH by Perturbation Theory
Authors: Goodisman Jerry
Published: February 2004

Start with a local one-electron Hamiltonian and construct a determinantal wavefunction from its eigenfunctions. Taking this as zero-order function, calculate the first-order correction by perturbation theory. This reduces to several two-electron problems, approximate solutions to which may be found variationally, using trial functions involving interelectronic coordinates explicitly with no necessity for evaluation of multielectron integrals. An exception to this is discussed and dealt with. The energy through second order may be calculated as a sum of pair contributions. For LiH at 3.02a0, calculations with screened nucleus and another zero-order potential are performed. It is shown that this energy can be as good as that from the best variational calculations. Problems of convergence are discussed.
Molecular Association and Molecular Rotation in Liquids
Authors: Anderson J. E.
Published: February 2004

This article concerns the effect of molecular association on the rotary motions of molecules in the liquid state. It is found that two different types of association can be distinguished: (1) In some instances, association involves the formation of polymolecular aggregates, or complexes, that move as a unit. (2) Alternatively, association may involve only correlations in the positions of different molecules, and it may have little effect on molecular motion. The difference between these two cases is analyzed. NMR spin–lattice relaxation studies of various chloroform systems are offered to illustrate these effects. Some of the experimental results suggest that molecular rotation takes place by large-angle jumps rather than by small diffusive steps against a viscous force.
Entropic and Energetic Aspects of Chemical Bonding; Monotonicity of Relation between ΔS° and ΔH°
Authors: Thorn R. J.
Published: February 2004

Within the presently developed phenomenological basis for thermodynamics, no relations are formulated between the change in energy for a chemical reaction at 0°K and the change in the structurally relevant conjugate, the entropy or partition function, at some finite temperature. An investigation of the monotonic characters of the thermodynamic functions associated with the structure functions for pure phase spaces, and of the empirically observed correlations between ΔS and ΔH0 in a large number of cases, evolves a principle of sufficiently equivalent configurations: For a sequence of reactions, order→disorder, in which all the significant configurations of the reactants in the sequence are sufficiently equivalent, and in which all the significant configurations of the products in the sequence are sufficiently equivalent, ΔS is a non-decreasing function of ΔH0 such that a branch can occur at a low virtual temperature with negative curvature, and a branch can occur at high virtual temperature with positive curvature. By scaling exponentially the structure functions for a sequence, one can suggest a correspondence with the linear relations between ΔS and ΔH which are observed frequently for reactions involving organic compounds with varying substituents. The formalism discussed constitutes an “equation of state” for chemical reactions. Thus ΔS = ΔS[ΔH(σ), Δp(σ), ΔN(σ)] in which σ represents a structural parameter.
Cross Sections for the Alkali-Metal–Halogen Molecule Reactions: Cs with I2
Authors: Brodhead D. C. , Davidovits P. , Edelstein S. A.
Published: February 2004

The reaction cross section of alkali-metal atoms with halogen molecules is obtained by a direct measurement of the alkali-atom decay rates. The alkali atoms are produced in the presence of a known amount of halogen molecules, by photodissociating an alkali halide salt with a short pulse of uv light. The alkali atoms react with the halogen molecules and the decay is monitored by observing the transmission of alkali-atom resonance light through the vapor. Since the halogen density is known, the reaction cross section can be computed from the decay rate. Using this method we studied the reaction Cs+I2→CsI+I. The cross section for this process is 180 ± 25 Å2.
Calculated Paramagnetic Mössbauer Spectra of Spin-12> Iron Salts
Authors: Lang George , Oosterhuis W. T.
Published: February 2004

The method of calculating paramagnetic Mossbauer spectra is discussed. Only d-electron contributions are considered, and infinitely long relaxation time is assumed. Spectra in zero field and for small applied fields transverse to the gamma beam are presented for the following low-spin ferric cases: cubic symmetry, positive axial field, negative axial field, a field of rhombic symmetry, and an isolated | 3z2 − r2 〉 electron. It is shown that some of the results can be applied to fast relaxing paramagnets under conditions of large H / T.
WKB Solution of Inversion Problems for Potential Scattering
Authors: Miller William H.
Published: February 2004

The construction of a local, not necessarily monotonic, potential is given in the WKB approximation for the two following sets of “input” information: (1) the phase shift as a function of impact parameter (or orbital angular momentum) at one energy; (2) the phase shift as a function of energy for one value of l, plus the eigenvalues of the potential for this same l. It is also shown that in the high-energy WKB approximation (Eikonal approximation) the energy dependence of the total cross section can be inverted to obtain the potential. Procedures for constructing the classical deflection function (or, equivalently, the phase shift as a function of impact parameter) from the observed differential cross section are also discussed.
Optical Phonons and Phase Transitions in the Ammonium Halides
Authors: Perry C. H. , Lowndes R. P.
Published: February 2004

The external optical phonon modes in the ammonium and deuteroammonium halides have been studied through their intrinsic phase transitions in the temperature range 4–290°K using infrared and Raman techniques. The number of infrared and Raman active modes are in agreement with group theoretical predictions for the phases II, III, and IV, with the exception that no measurable anisotropic splitting of the out-of-phase mode in the tetragonal phase was observed in the infrared spectra. Whilst the frequency of the infrared reststrahlen modes showed only small discontinuities with temperature as the phase transitions were traversed, the phonon lifetimes of these modes showed distinct increases as the temperature was lowered through each phase transition. Estimates of the intrinsic ionic distortion present in NH4Cl and NH4Br are given. The compressibilities of NH4Cl and NH4Br at 4°K are calculated to be 3.86 × 10−12 and 6.79 × 10−12 cm2 dyn−1.
Kinematic Model for Reaction. II. Ion–Molecule Reactions Involving H2 and D2
Authors: George Thomas F. , Suplinskas Raymond J.
Published: February 2004

The kinematic model for atom–diatom reactions is extended to include ion–molecule reactions. In the extended model, reactants approach each other up to the point of contact along trajectories and with a relative velocity determined by the potential acting between them. After contact, energy and momentum transfers among the three particles are calculated assuming hard-sphere interactions; reaction probabilities are assigned on the basis of the results of the kinematic analysis. Reaction cross sections are calculated for the Ar+ + H2 and Ar+ + D2 systems for Ar+ energies in the ranges 20–200 eV and 10–100 eV, respectively. Good agreement with experiment is obtained. The model predicts a small isotope effect favoring the reaction of Ar+ with D2 over H2 when compared at the same relative energy. Some qualitative features of the N2+ + D2, H2 reactions are shown to be consistent with the kinematic considerations of the model.
Photoisomerizations of Photochromic Anils
Authors: Potashnik Ruth , Ottolenghi Michael
Published: February 2004

The spectra and photochemistry of the different isomers of some anils of salicylaldehyde and hydroxynaphthaldehyde were investigated over a range of solvents and temperatures. By running flash experiments in fluid solutions it was shown that both intramolecularly H-bonded enol (E) and cis-keto (QA) tautomers yield the trans-keto isomer (QC) as a common photoproduct. In a rigid paraffin glass only the E→QC, but not the QA→QC, photoisomerization can be induced. Two previous suggestions for the mechanism of anils photochromism (i.e., the E→QC conversion) were re-examined in terms of the experimental data. It is concluded that neither is applicable in its original form. The dark QC→E relaxation in low-polarity systems was investigated and was shown to proceed via dimer intermediates. The flash photolysis of a keto dimer (QB) was also studied. Excitation of QB leads to dissociation to enol monomers. An additional path is the formation of a short-lived transient, presumably an excited triplet of the pair.
Tracer Diffusion and Shear Viscosity in the Liquid–Liquid Critical Region
Authors: Leister Harry M. , Allegra Joseph C. , Allen Guy F.
Published: February 2004

Tracer diffusion coefficients of 3-methylpentane in mixtures of 3-methylpentane–nitroethane have been measured over the entire concentration range above the critical temperature in the range 0.04° ≤ T − Tc ≤ 9.5°C using the diaphragm cell technique. No anomaly was detected. The shear viscosity coefficients were measured across the concentration range for temperatures 0.004°C ≤ T − Tc ≤ 13.5°C by a capillary viscometer. The excess viscosities are compared with the predictions of the Fixman theory and the theory of Kadanoff and Swift. Very close to the critical point the weak divergence predicted by the second theory is observed while at larger values of ΔT Fixman's prediction seems adequate.
Evidence for Structure in Plastics from Light Scattering
Authors: Romberger A. B. , Eastman D. P. , Hunt J. L.
Published: February 2004

Measurements of the indices of refraction at 6328 Å of polymerized methyl, ethyl, and butyl methacrylate (PMMA, PEMA, PBMA) as a function of temperature show a discontinuity in the slopes at the glass–rubber transition temperature. A similar discontinuity appears in the hypersonic speeds, obtained as a function of temperature from Brillouin shift measurements and the indices of refraction. From considerations involving the annealing process as seen in the index of refraction, the enhancement of the Rayleigh scattering, the large Landau–Placzek ratio, and the pronounced Krishnan effect (unequal depolarization of the horizontal and vertical components of 90° scattered light for horizontally polarized incident light), one concludes that the polymerization process freezes into the plastic shear and compressional strains that are only partially relieved by annealing.
Viscous Liquids and the Glass Transition: A Potential Energy Barrier Picture
Authors: Goldstein Martin
Published: February 2004

Recent attempts have been made to assess the relative merits of the free volume and entropy theories of viscous flow in glass-forming liquids by accurate measurement of viscosity over wide temperature ranges, and subsequent comparison with the equations derived from these theories. In the author's view, this effort is misguided. The theories are crude and qualitative, and such tests are too stringent. It is better to make qualitative or semiquantitative comparison of a wide variety of physical phenomena; judged by this criterion, the entropy theory appears more successful. It is conjectured that further progress can be made by accepting the crude, naive character of any model we are likely to find tractable for the foreseeable future, and recognizing both the values and limitations of such models. A picture of the flow process in viscous liquids is proposed, in an attempt to answer certain questions about the molecular steps in flow either answered unsuccessfully or ignored by present theories, in the hope that it will lead a model closer to molecular reality but still sufficiently tractable to allow some range of predictive value. The model is based on the idea that in “viscous” liquids (shear relaxation time ≥10−9 sec) flow is dominated by potential barriers high compared to thermal energies, while at higher temperature, this will no longer be true. Certain concepts borrowed from the continuum theory of lattice defects are joined to a qualitative description of viscous flow due to Orowan, to provide a picture which leads to some qualitative predictions about flow and relaxation in the liquid and glassy states.
Heat Capacity, Transformations, and Thermal Disorder in the Solid Electrolyte RbAg4I5
Authors: Johnston W. V. , Wiedersich H. , Lindberg G. W.
Published: February 2004

The heat capacity of RbAg4I5 has been measured in an adiabatic calorimeter between 5 and 340°K. The compound undergoes transformations at 121.8 and at 209°K and exhibits a very sizable configurational heat capacity. The latent heat and entropy changes of the apparently first-order transformation at 121.8°K are 190.9 ± 0.8 cal mole− 1 and 1.568 ± 0.007 cal deg− 1·mole− 1, respectively. The second transformation appears to be of the lambda type. Upper limits to the heat and entropy changes are 225 cal deg− 1 and 1.0 cal deg− 1·mole− 1, respectively. The configurational entropy is 10.81 cal deg− 1·mole− 1 at 300°K. A residual entropy of 2.25 ± 1.6 cal deg− 1·mole− 1 was found. The standard entropy for the compound is 147.07 cal deg− 1·mole− 1. The ΔS°, ΔH°, and ΔG° of formation are 20.55 ± 2.2 cal deg− 1·mole− 1, − 136.2 ± 0.5 kcal mole− 1, and − 142.3 ± 0.1 kcal mole− 1, respectively. The heat capacity is exceptionally high at all temperatures above ∼50°K. This is attributed to a continuously increasing disorder among the silver ions as temperature is increased. A simple model for the disordering process based on incompletely filled sets of silver sites with different energy levels is suggested to account for the residual entropy and excess heat capacity.
Crystal Spectrum of the Rare-Earth Hexahalide Complexes, MCl63−: The Absorption Spectrum of [(C6H5)3PH]3NdCl6
Authors: Gruber J. B. , Menzel E. R. , Ryan J. L.
Published: February 2004

The site symmetry of Nd3+ in single-crystal [(C6H5)3PH]3NdCl6 is predicted by considerations of molar absorptivity, vibronic spectra, and stoichiometry. A calculation of the crystalline-field splitting of 4f3 J levels appears to predict a sixfold octahedral site symmetry with a slight distortion along one of the axes, in agreement with the observed spectrum. In addition, the observed spectrum indicates the occurrence of two slightly inequivalent sites of Nd3+. The effects of the small distortion away from octahedral symmetry and the spectrum due to two inequivalent sites are sufficiently small (5% of the average J-manifold crystalline-field splitting), however, as not to affect a first-order crystal-field analysis of the dominant portion of the spectrum. The crystal-field parameters based on octahedral symmetry, B4 = 282 cm−1 and B6 = 74.7 cm−1, predict a splitting of crystal quantum states in good agreement with experiment.
Oscillatory Normal Stresses in Dilute Polymer Solutions
Authors: Akers L. C. , Williams Michael C.
Published: February 2004

The Rouse–Zimm theories of polymer solution dynamics have been extended to include normal stresses as well as shear stresses and have been evaluated for low-amplitude oscillatory shear. Two normal stress coefficients (ζd, characterizing a displacement function, and ζ*, characterizing the oscillation about the displacement) appear as analogs to the complex viscosity η* for shear stress. Theoretical predictions are compared with data obtained with a Weissenberg rheogoniometer on five dilute solutions of monodisperse polystyrene (M = 1.8 × 106 and 4.1 × 105) in Aroclor 1254. The models are found to describe the measured η* and ζd with equal good success, but uncertainties in ζ* measurements preclude complete verification. Strong evidence is presented to support the model-independent prediction that ωζd = η″.
Crystal Structures of Cubic and Trigonal Yttrium Hypocarbides; A Dimorphically Interphased Single-Crystal Study
Authors: Atoji Masao , Kikuchi M.
Published: February 2004

X-ray structure determinations on the cubic YCx (x ≈ 0.3 − 0.7, stable above about 900°C) and the trigonal Y2C (stable below 900°C) have been carried out using a quenched “single crystal” in which a transient state in the midst of the cubic-to-trigonal transition has been arrested. Our “single crystal” is composed of one cubic and four trigonal single crystals, the trigonal c axis being parallel to one of four cubic body-diagonal axes. The cubic structure is of NaCl type with random holes in the carbon-atom sites and with a = 5.115 ± (2) Å for YC0.44. The ordering of the carbon atoms creates the anti-CdCl2-type trigonal Y2C with the yttrium positional parameter z = 0.2585 ± (3) in the hexagonal-based unit cell, a = 3.617 ± (2) and c = 17.96 ± (1) Å, containing three Y2C formula units. Mo Kα x-ray was employed, and consequently the dispersion corrections on the atomic scattering factor of Y amount to 10%–20% of the nondispersion value and are considerably larger than the carbon-scattering factor. The structure analyses with and without the dispersion corrections demonstrate that even these unusually large corrections do not modulate the Y and C positional parameters significantly. The x-ray single-crystal results were further substantiated by the neutron-powder analysis. The present work confirmed unambiguously not only the reported x-ray powder results as well as the neutron-powder data of the isostructural Ho2C, but also yielded the structural parameters with a much higher accuracy, hence providing detailed insights into the chemical-bonding correlation in the order–disorder transition.
Collision Broadening of Rotational Absorption Lines. V. Pressure Broadening of Microwave Absorption Spectra Involving Asymmetric-Top Molecules
Authors: Murphy Joseph S. , Boggs James E.
Published: February 2004

Pressure broadening of microwave absorption spectra by collisions involving asymmetric-top molecules either as absorbing or as perturbing molecules has been investigated within the framework of a pressure-broadening theory presented earlier. Modifications of this theory are required because of the increased mathematical complexity involved in asymmetric-top calculations and because asymmetric-top molecules may have two energy levels spaced relatively close together with all other levels widely spaced. This latter condition may result in saturation of certain energy-level pairs and must be considered for accurate linewidth calculations. The linewidth calculations are found to be in very good over-all agreement with experimental values in most cases, although a few discrepancies occur. Comparison of calculated and experimental linewidth data suggest that H2O and SO2 have quadrupole contributions of about 10%–15% of the observed values while linewidths involving CH2Cl2, CH2CF2, and C2H4O can be explained solely on the basis of dipole–dipole interaction. A value of (2.87 ± 0.10) D·Å was determined for the molecular quadrupole moment of N2 from linewidth data for broadening of the 22,0→31,3 transition of H2O by N2 and appears to be in excellent agreement with the value obtained previously from data for NH3–H2 broadening.
Polarized Laser Raman Studies of Biological Polymers
Authors: Fanconi Bruno , Tomlinson Barrett , Nafie Laurence A. , Small Wallace , Peticolas Warner L.
Published: February 2004

A group-theoretical analysis of the Raman tensor for helical polymers is given and illustrated for the Pauling α helix which possesses 18 residues in five turns. A detailed determination of the polarized Raman spectra is given for oriented α-helical poly-l-alanine fibers and for four polyribonucleotides in solution. Tentative assignments to A, E1, and E2 symmetry are made on certain Raman bands of poly-l-alanine based on the polarization of the Raman light. A detailed comparison of monomer and polymer bands are given for the four polynucleotides. A theory for the angular dependence of Raman light scattered from helical molecules is given.
Lower Bounds and Estimation of Energy Eigenvalues in a Gaussian Basis
Authors: Mazziotti Alexander
Published: February 2004

Lower bounds to the ground-state energy of the helium atom are computed in the Gaussian framework. Comparison is made between the lower bounds obtained using variationally optimized upper-bound wavefunctions and the best lower bounds obtained by complete optimization of all parameters. There is a large improvement in the latter. Conroy's method of estimating eigenvalues is tested for the first time in a Gaussian basis, giving relatively poor results. An alternative method of estimating eigenvalues, based upon the partitioning of spectral impurities, is presented. The results of computations with this method are seen to be quite good.
ESR of 17O-Labeled Nitrogen Dioxide Trapped in a Single Crystal of Sodium Nitrite
Authors: Luz Z. , Reuveni A. , Holmberg R. W. , Silver Brian L.
Published: February 2004

A study is reported of the ESR spectrum of NO2–17O formed by γ irradiation of single crystals of NaNO2–17O at 77°K. Hyperfine splittings due to 14N and 17O were studied as a function of orientation, and the principal values and directions of the hyperfine tensors determined. The results for the nitrogen hyperfine and g tensor agree with those of Zeldes and Livingston. In a general orientation, splittings are observed due to two magntically inequivalent oxygens. The magnitudes of the principal values for the hyperfine tensors of both oxygens are:4.27, 54.90, and 1.74 G. The directions of the largest principal values are in the molecular plane at angles of + 7.5° and − 7.5° to the molecular axis. The results are used to derive values for the MO coefficients of the 4a1 orbital which contains the unpaired electron. An attempt is made to interpret the g tensor in terms of the electronic structure of NO2.
Ionic Collision Processes in Gaseous Mixtures of Oxygen and Nitrogen
Authors: Ryan K. R.
Published: February 2004

Some collision processes in ionized mixtures of nitrogen and oxygen have been examined in the ion source of a mass spectrometer. Attention was paid to the possible reactions of molecular ions, in excited electronic states, at translational energies below 1 eV. In particular, evidence for the following reactions was sought: O2+a 4Πu+N2→N2++O2, O2+a 4Πu+N2→N2O++O, N2+A 2Πu+O2→N2O++O, O2+a 4Πu+N2→NO2++N. Reaction (a) was found to proceed with a cross section of 38 × 10−16 cm2 at the low-ion energies employed. Evidence was obtained for the production of N2O+ by Reaction (b). Whether or not Reaction (c) proceeds is not made clear in the present experiments. It has been assumed that for ion kinetic energies <1 eV Langevin type capture orbitals control the charge-transfer Reaction (a). Furthermore, for the competitive Reactions (a) and (b), it was found that (a) was far more probable that (b). No reproducible evidence could be found for the production of NO2+ via (d).
Fluorescence Lifetimes of Vibronic States of Benzene in the Vapor Phase
Authors: Nishikawa M. , Ludwig P. K.
Published: February 2004

The time dependence of benzene vapor fluorescence is studied as function of vapor pressure for excitation in the neighborhood of 2600, 2530, and 2470 Å. At pressures above about 20 torr the decay appears exponential and independent of excitation wavelength. At lower pressure, deviations from exponential decay are observed for 2530- and 2470-Å excitation. The decay times obtained under different conditions are combined with steady-state data available in the literature and several rate constants derived. The result is related to discussions of the mechanism of deactivation of excited benzene molecules.
Inversion of the Partition Function: The First-Order Steepest-Descent Method
Authors: Hoare M. R. , Ruijgrok Th. W.
Published: February 2004

This paper explains and advocates the use of a Laplace-transform steepest-descent method for the computation of energy-level densities g(E) by inversion of the partition function. The earlier Lin–Eyring approach, based on the Darwin–Fowler method, is shown to be unnecessarily obscure and in part redundant By use of a much-simpler formulation due to Kubo, it is shown that the first-order steepest-descent approximation to the inversion integral follows straightforwardly from a knowledge of the relevant partition function, its energy, and specific-heat relations. In this way several explicit equations for g(E) and its integral W(E) are derived, including two for anharmonic vibration and internal vibration–rotation. The relationship of the S–D method to Tolman's classical formula is discussed and some thermodynamic implications pointed out. Numerical results agree closely with those obtained by the direct counting of energy levels and, with certain exceptions, the indirect computations of other authors.
Cl+HBr Pulsed Chemical Laser: A Theoretical and Experimental Study
Authors: Airey J. Richard
Published: February 2004

The most powerful and efficient pulsed chemical lasers produced to date have resulted from the simple exothermic reactions between halogen atoms and hydrogen halides. These reactions have been initiated by flash photolysis. One such reaction is Cl+HBr→HCl+Br, − ΔH = 15.5 kcal/mole. A kinetic model has been developed for this laser system which calculates the intensity profile of the laser pulse as a function of time. The input data for the model include estimates of the reaction rate into the zeroth and first vibrational level of HCl and cross sections for collisional deactivation by the different chemical species in the laser medium. The rate of reaction into the second vibrational level of HCl is assumed to be zero. Any small finite rate into the second level would have a negligible effect on the calculated performance of the laser which operates only on the V(1 → 0) fundamental transition of HCl. The theoretical model also requires as input data the photolysis flash intensity profile, the cavity geometry, and the losses. A discussion of the model is given, and a comparison is made between experiment and theory. The model is able to predict quantitative variations of the laser pulse characteristics as a function of flash intensity, cavity losses, and reagent partial pressures. The quantitative calculations are in reasonable agreement with experiment. It is concluded that (a) the most important single contribution to deactivation in the system is HCl (V = 1) + HBr (V = 0) → HCl (V = 0) + HBr (V = 1), and (b) the rate of reaction to produce HCl (V = 1) is at least as large as that to produce HCl (V = 0).
Anomalous Temperature Dependence of the Emission Spectra of 2Cr(en)3Cl3·KCl·6H2O and Cr(en)3Cl3·3H2O
Authors: Flint C. D.
Published: February 2004

The photon-induced luminescence spectra and emission lifetimes of crystalline 2Cr(en)3Cl3·KCl·6H2O (en=ethylenediamine) at temperatures down to 5°K are reported. The E2 → 4A2 emission occurs at 14 880 cm−1 with vibronic structure to lower energy. At temperatures below 200°K accumulation of a new chromium(III) center during illumination partially quenches this emission, and a broader emission band due to transitions within the new chromium center appears at ∼14 500 cm−1. An equilibrium is set up between the number of these centers and the normal chromium sites, the position of the equilibrium being dependent on the temperature and the intensity of the incident light. Below 100°K equilibrium is attained only slowly. Cr(en)3Cl3·3H2O shows similar behavior, but the E–42A2 emission band is not quenched to the same extent. The nature of the new chromium centers and of the various relaxation processes is discussed.
Theory of Excluded Volume in Coiled Polymers: Cumulant Expansion
Authors: Chikahisa Yoshiaki
Published: February 2004

The excluded-volume effect in a randomly coiled polymer is investigated by the method of cumulants. The spatial expansion factor α2 of a polymer chain is expanded in a power series: α2 − 1 =  ∑ n=1∞(− 1)n−1Cnzn, where z is the usual excluded-volume parameter, and a general formula for Cn is given. By means of a “ladder” approximation C4 is calculated to be 1.3438. Contributions of small and giant clusters in a polymer chain to α2 are discussed. The above power series is predicted in the ladder approximation to converge for 0 ≤ z ≤ N, where N is the total number of segments constituting the polymer chain. We are unable, however, to dispose of the possibility that in general Cn for 5 ≤ n ≪ N includes a term proportional to N1/2logN.
Nuclear Magnetic Resonance Spectroscopy of Bicyclobutane
Authors: Wüthrich Kurt , Meiboom Saul , Snyder Lawrence C.
Published: February 2004

The proton and carbon-13 nuclear magnetic resonance spectra of bicyclobutane have been analyzed in detail. The use of information from NMR spectra of bicyclobutane in a nematic solvent permits an unambiguous assignment of all chemical shifts and spin–spin interactions to specific nuclei. Some of the assignments differ from previously published ones. A long-range indirect spin–spin coupling of 5.9 Hz is found between the two exo protons, and an indirect coupling of 16.0 Hz is observed between the exo proton and the carbon-13 to which the other exo proton is bonded.
Collisional Deactivation of O(1S)
Authors: Filseth S. V. , Stuhl F. , Welge K. H.
Published: February 2004

Absolute rate coefficients for the collisional deactivation of O(1S) have been measured for CO2, CO, SF6, O2, H2O, NH3, CH4, C2H4, C2H6N2O, NO, NO2, H2, N2, He, Ne, Ar, Kr, and Xe. The measurements have been made with a lifetime technique in which O(1S) is produced in the photodissociation of CO2 by a pulsed vacuum-ultraviolet light source The rate coefficients were obtained from time-resolved measurements of the intensity of the O(1S → 1D) line at 5577 Å. Deactivation of O(1S) by collision induced radiation has been observed for H2, N2, Ar, Kr, and Xe.
Rare-Gas Scattering from LiF: Correlation with Lattice Properties. II
Authors: Smith Joe N. , O'Keefe D. R. , Palmer R. L.
Published: February 2004

The scattering of thermal energy atomic beams of Ne, Ar, Kr, and Xe from the (001) face of LiF has been studied. Two dominant peaks in the scattering distributions in the plane of incidence are observed: one peak remains fixed with respect to the crystal whereas the position of the other displays a strong dependence on angle of incidence, incident energy, and azimuthal orientation of the target. The former peak is associated with the normal modes of the lattice, in particular with dipole–induced dipole attractive forces produced by longitudinal optical modes in next-nearest-neighbor unlike ion directions. The latter peak is discussed in terms of the surface properties of the crystal, e.g., interaction potential and elastic properties, the latter acting on the transfer of tangential momentum. For Ne, additional peaks occur which arise from diffraction effects. The present results provide additional insight into the phenomenon of preferential scattering reported earlier and strongly emphasize the inadequacies of existing theoretical descriptions of thermal energy atomic and molecular (TEAM) scattering from surfaces, especially when applied to the surfaces of ionic crystals.
Far-Infrared Spectrum and Ring-Puckering Potential of Silacyclopent-2-ene
Authors: Laane Jaan
Published: February 2004

The far-infrared spectrum of silacyclopent-2-ene, CH←CHSiH2CH2CH2, has been recorded, and a series of weak absroption peaks was observed between 120 and 200 cm−1. The absorptions arise from the ring-puckering vibration, and the frequencies fit well with the potential V = 31.45 (Z4 + 2.40Z2) cm−1, where Z is the puckering coordinate in reduced form. In terms of the dimensioned coordinate X, the potential becomes V = 18.51 × 105 X4 + 18.27 × 103 X2. The coefficients of the terms in the potential function are unexpectedly large and show that silacyclopent-2-ene is planar and unusually rigid in that position. Interaction between the silicon d orbitals and the carbon–carbon π bond most likely accounts for the observed results.
Application of the Gaussian-Type Orbitals for Calculating Energy Band Structures of Solids by the Method of Tight Binding
Authors: Chaney Roy C. , Tung T. K. , Lin Chun C. , Lafon Earl E.
Published: February 2004

The 1s, 2s, and 2p Gaussian-type atomic orbitals were used to construct the Bloch functions of the lithium crystal, and the energy band structure of lithium was calculated by the tight-binding method with these Gaussian-type Bloch functions as basis. The results agree well with those of the previous tight-binding calculations in which the Bloch functions were expressed in terms of the Slater-type orbitals. The use of the Gaussian-type orbitals resulted in a great deal of simplification of the computational procedure. It was found that both the very long-range and short-range Gaussian components of the atomic wavefunctions may be removed without affecting the band structure provided that the relative weighting of the remaining Gaussians is readjusted by the variational method.
High-Energy Alkali–Rare-Gas Scattering
Authors: Malerich C. J. , Cross R. J.
Published: February 2004

Absolute total-collision cross sections in the LAB energy range of 6–1000 eV were measured for several alkali-metal–rare-gas systems—Na + Ar, Xe; K + Ne, Ar, Kr, Xe; and Cs + Kr, Xe. The limiting repulsive part of the intermolecular potential was described accurately by an inverse-power law Cr−8, where s varied from 5.75 to 10.75 depending on the system. In the low-energy region the cross sections for the heavier systems show a pronounced rise due to the influence of the attractive part of the potential. In no cases could the cross sections be fitted by a two-term Lennard-Jones potential. A more abrupt transition is required between the inverse-power repulsion and the well region of the potential.
Scattering of 0.06–2.5-eV Neon and Argon Atoms from a Silver (111) Crystal
Authors: Miller D. R. , Subbarao R. B.
Published: February 2004

Reflected density distributions of argon and neon scattered from the (111) plane of a silver crystal have been examined at incident energies from 0.06 to 2.5 eV. Two regimes of scattering were detected in which the characteristic properties of the reflected distribution, direction and width, reverse their behavior as a function of incident energy. This confirms the recent theoretical work of Oman, wherein he characterizes the two regimes as thermal scattering and structure scattering. The data suggest that, for scattering at incident energy Ei and angle θi, the transition from one type of interaction to the other is characterized by one critical value of Eicosθi. For argon, this critical value is near 0.21 eV and for neon 0.108 eV. At these critical energies the velocities of argon and neon are nearly identical. At a given incident angle, a maximum degree of supraspecular scattering exists, which is less for neon than for argon.
Infrared Study of Liquids. I. The Theory of the ir Spectra of Diatomic Molecules in Inert Solutions
Authors: Bratŏz S. , Rios J. , Guissani Y.
Published: February 2004

A theory is proposed to explain the ir spectra of inert solutions of diatomic molecules. The theory is a stochastic-type theory related to similar theories of the NMR spectra. The vapor-solution band shifts are shown to depend on the difference between the solvent–solute interaction energies of the two vibrational states involved in the transition. The band profiles are basically asymmetrical; nevertheless, symmetric limiting forms exist as well. The theory predicts the existence of a continuous sequence of band forms comprising, among others, the profile with P- and R-type wings, the Lorentzian profile, the Gaussian profile, the Voigt profile, and several sorts of asymmetric profiles. The relation between a given band form and the nature of the dominating relaxation process is discussed.
Density Matrix Study of Atomic Ground and Excited States. I. Beryllium Ground State
Authors: Olympia Pedro L. , Smith Darwin W.
Published: February 2004

Various configuration-interaction wavefunctions for the Be ground state built up from Slater-type orbitals are reported. Their 1- and 2-matrices are examined in detail and compared with those previously reported in the literature. It is shown how the quality of a basis set and the omission of just a few configurations noticeably alter the density matrix structure. Further, it is pointed out that the occupation numbers of some important natural states are in general quite sensitive to the goodness of the wavefunction. In the choice of configurations to be included in a truncated CI expansion over an extended basis set by performing stepwise full CI expansions over small basis sets, the role played by singly excited configurations is emphasized. The use of density matrices as a global representation of the wavefunction is also stressed.
Soft-Sphere Equation of State
Authors: Hoover William G. , Ross Marvin , Johnson Keith W. , Henderson Douglas , Barker John A. , Brown Bryan C.
Published: February 2004

The pressure and entropy for soft-sphere particles interacting with an inverse twelfth-power potential are determined using the Monte Carlo method. The solid-phase entropy is calculated in two ways: by integrating the single-occupancy equation of state from the low density limit to solid densities, and by using solid-phase Monte Carlo pressures to evaluate the anharmonic corrections to the lattice-dynamics high-density limit. The two methods agree, and the entropy is used to locate the melting transition. The computed results are compared with the predictions of the virial series, lattice dynamics, perturbation theories, and cell models. For the fluid phase, perturbation theory is very accurate up to two-thirds of the freezing density. For the solid phase, a correlated cell model predicts pressures very close to the Monte Carlo results.
Mercury P13–1S Transition in Solid Rare Gases
Authors: McCarty M.
Published: February 2004

It is shown that the gross shifts in the spectrum of the Hg P13 ← 1S0 transition of Hg in solid-rare gases can be correlated by considering the difference in the interaction potential between the lattice and the Hg atom in the P13 and S01 states, providing the distortion of the lattice caused by the Hg atom is taken into account. In Ar, Kr, and Xe the spectrum can consist of three separate components. It is quantitatively shown that one of the components arises from relatively isolated Hg atoms while the other two components result from Hg atoms having nearest neighbor Hg atoms.
Distorted Wave Born Series for Rotational Inelastic Scattering
Authors: Roberts R. E. , Ross John
Published: February 2004

The distorted wave Born series is applied to the problem of rotational inelastic scattering of an atom by a diatomic molecule. The formulation is made in the total angular momentum representation, and for the special but important case of an exponential interaction a simple second-order expression for the degeneracy averaged cross section is derived. Numerical results for two intermolecular potentials compare favorably with exact multistate calculations. The analytic results (1) show that differences between exact and DW results do not vanish near threshold, (2) show the applicability of the method to molecules heavier than H2, (3) provide a method of assessing the relative order of contributions from various internal states, (4) provide a method of estimating higher-order terms in the DWB series. The application of the second-order DWB series to problems with different forms of potentials of interaction requires only a single numerical integration.
One-Dimensional Random Lattice Systems Including DNA
Authors: Cohen S. S. , Penrose O.
Published: February 2004

A first-order difference equation is derived in the ratio of successive partition functions along the lattice for one-dimensional lattice systems with a nonconstant 2 × 2 transfer matrix. In the case of DNA, the distribution functions of these ratios are easy to generate. Numerical values for the expected free energy, obtained using unsophisticated computer techniques, are reported. They agree with those given by Lehman et al. to within 2% computational accuracy. The random Ising model is also considered and the DNA generating equations shown to apply in a special case.
Ion–Molecule Reactions Involving N2+, N+, O2+, and O+ Ions from 300°K to ∼1 eV
Authors: Johnsen R. , Brown H. L. , Biondi Manfred A.
Published: February 2004

Several ion–molecule reactions of ionospheric interest have been studied in a drift-tube–mass-spectrometer apparatus for ions of mean energy from thermal energies to ∼ 1 eV. The measured rate coefficients in cubic centimeters/second are N++O2: 5 × 10−10 from 0.039–0.9 eV; N2++O2: 6 × 10−11 at 0.039 eV, decreasing to ∼ 8 × 10−12 at 0.9 eV; O2++NO: 3 × 10−10 from 0.039–1.6 eV; O++CO2: 1 × 10−9 at 0.039 eV, decreasing to 5 × 10−10 cm3/sec at 1.3 eV. The relevance of the first three reactions for the Earth's ionosphere and of the last reaction for the Martian atmosphere is discussed briefly.
Flowing Afterglow Studies of the Reactions of the Rare-Gas Molecular Ions He2+, Ne2+, and Ar2+ with Molecules and Rare-Gas Atoms
Authors: Bohme D. K. , Adams N. G. , Mosesman M. , Dunkin D. B. , Ferguson E. E.
Published: February 2004

The flowing afterglow technique has been used to measure rate coefficients and product channels for the reactions of He2+, Ne2+, and Ar2+ with the rare-gas atoms Ne, Ar, and Kr, and with the molecules NO, O2, CO, N2, and CO2 at 200°K. These reactions are found to proceed principally by asymmetric charge transfer. The experimental results for the reactions of the rare-gas molecular ions with rare-gas atoms indicate a correlation between reaction probability and reaction exoergicity analogous to that observed for asymmetric atomic ion–atomic neutral charge-transfer reactions. The reactions with molecules are found to proceed with unit reaction probability with the exception of the reactions Ar2++O2 and Ar2++NO. The reaction probability for the reactions of the molecular rare-gas ions with molecules is not very sensitive to an energy resonance criterion. Finally, rate coefficients and reaction channels for the reaction of the mixed rare-gas molecular ions HeNe+, ArKr+, and ArCO+ with Ne, Kr, and CO, respectively, are reported.
Sound Velocities in Concentrated Metal–Ammonia Solutions
Authors: Bridges R. , Ingle A. J. , Bowen D. E.
Published: February 2004

The velocity of 10 MHz sound waves in solutions of lithium, calcium and barium in ammonia are presented. The sound velocity in the lithium and calcium solutions exhibits a minimum which had not previously been detected. This minimum is a function of the metal concentration and of the temperature. Previous investigations of the sound velocity in potassium and sodium ammonia solutions did not reveal the presence of such a minimum. It is postulated that the minimum is an indication of compound formation in the solutions. Calculations of the sound velocity for the lithium–ammonia solutions are presented using the scheme of Schroeder and Thompson. Data on the saturation curve of the lithium–ammonia solutions is also presented.
Theoretical Study of the Σ+1, 3Σ+, 3Π, 1Π States of NaLi and the Σ+2 State of NaLi+
Authors: Bertoncini P. J. , Das G. , Wahl Arnold C.
Published: February 2004

Ab initio calculations have been performed for the NaLi molecule at a series of internuclear distances. The Hartree–Fock and extended Hartree–Fock optimized valence configuration (OVC) approximations of Das and Wahl are compared for the Σ+1 ground-state potential curve. In each approximation, the NaLi molecule is found to be bound relative to the separated atoms. The OVC wavefunctions are tabulated as a function of internuclear distance and contour diagrams of the total density for the OVC wavefunction and of the difference densities between the ground-state molecular OVC wavefunction and the atomic and molecular Hartree–Fock wavefunctions are given. The OVC calculations are compared with a further approximation in which Φ0 is frozen to be the Hartree–Fock configuration at each internuclear distance. The comparison suggests that a better approximation would be one in which only the core orbitals are frozen at the Hartree–Fock level and all valence and correlating orbitals optimized to self-consistency. In addition, potential curves for the Σ+3, 3Π, and Π1 states of NaLi and the Σ+2 state of NaLi+ have been computed in the Hartree–Fock approximation. Expectation values of various one-electron operators for all states at each internuclear distance and spectroscopic constants obtained by Dunham analysis of all bound-state potential curves are also reported.
Study of the Reflection Spectrum of Crystalline Anthracene: Evidence for the Existence of Defects
Authors: Morris Graeme C. , Rice Stuart A. , Martin Abraham E.
Published: February 2004

This paper reports the results of a study of the reflection spectrum of crystalline anthracene at 4 and 77°K. At 4°K the reflection spectrum has, on the low-energy side of the transition to the first exciton state, a number of narrow regions of low reflectivity. At 77°K these antireflection lines do not appear. A crystal may be cycled repetitively between 4 and 77°K, reversibly exhibiting this phenomenon. It is argued that the observed antireflection lines are associated with exciton states bound to lattice defects, and that the lattice defects arise because of the inclusion of chemical impurities in the crystal. The observed antireflection lines can be correlated with lines in the low-energy emission spectrum of anthracene; our data are sufficient to resolve some previous difficulties of interpretation in the assignment of the luminescence spectrum. Some aspects of the interpretation of the linewidths and line intensities, and of the relationship between the bound excitons and the free exciton band, are discussed.
Electronic Absorption Spectrum of Ni2+ Doped in NH4Cl Single Crystal
Authors: Narayana P. A. , Venkateswarlu Putcha
Published: February 2004

The absorption spectrum of Ni2+ doped ammonium chloride is studied in the temperature range of 293–77°K. From the observed spectrum it is concluded that Ni2+ goes interstitially. Different possible coordinations at the metal ion site are discussed. It is suggested that the divalent nickel ion has very likely a fourfold chlorine coordination associated with two neutral water molecules at the first-neighbor NH4+ sites along 〈100〉 direction. An abrupt blue shift of about 100–150 cm−1 is observed at 235°K in the positions of the band maxima and is attributed to the anomalous lattice contraction of the host lattice at this temperature.