bluuebunny/crossref_metadata_2025 huggingface dataset:
Oxidation of Carbon Monoxide Mixtures with Added Ethane or Azomethane Studied in Incident Shock Waves
Authors: Izod T. P. J. , Kistiakowsky G. B. , Matsuda S.
Published: February 2004

CO/O2/Ar mixtures of varying composition containing small concentrations of ethane or azomethane were investigated in incident shock waves at about 5.0× 1017 particle/cc total concentration. The reaction was followed by measuring the infrared emissions from CO2 and CO for about 1700-μ sec particle time over a temperature range 1400–2200°K. For all mixtures, the rate of CO2 production initially increases exponentially and then becomes constant after several percent conversion. The observed [CO2]- time profiles were compared to those obtained by numerical calculation. For the CO/O2Ar mixtures containing either ethane or azomethane it was possible to describe the observations quantitatively in terms of a mechanism with the following main reactions (rate constants are in units of cubic centimeters/particle·second): CO+O2→CO2+O,   k1=2.0× 10−11exp(−60 000/RT), C2H6+M→2CH3+M,   k2=4.0× 10−3exp(−88 000/RT), CH3+O2→ CH2O+OH,   k4=2.0× 10−12exp(−12 500/RT),  CH3+O→ CH2O+H,   k5=5.75× 10−11exp(−3 200/RT), CH2O+O→ CO+H+OH,   k6=1× 10−10, CO+OH→ CO2+H,   k7=1.5× 10−12exp(−1 000/RT), H+O2→ OH+O   k8=4.2× 10−10exp (−16 790/RT), in addition to several relatively unimportant reactions involving chain carriers, O2 and C2H6. The values for k1, k5, and k8 were taken from the literature and the others were determined by finding the best fit of the [CO2]− time profiles to the experimental data.
Barriers to Linearity in Triatomic Molecules. I. Development of a Curvilinear Quantum Mechanical Model Appropriate for Large Amplitude Bending Motion in Triatomic Molecules of C2ν Symmetry
Authors: Brown Farrell B. , Charles Nina G.
Published: February 2004

A classical kinetic energy expression is developed for a nonlinear triatomic molecule of C2ν symmetry with two degrees of freedom. These are changes in the valence angle plus K-type rotation about the molecular z axis whose moment vanishes as the molecule becomes linear. The bonds are considered rigid, and the z axis is assumed fixed in space, but no other assumptions are made; in particular, neither small amplitude vibrations nor a nearly linear equilibrium configuration is assumed. The quantum mechanical operators are obtained and vibration-rotation eigenvalues are obtained for two cases: (a) rectilinear motion applicable only to small deviations from a nearly linear equilibrium geometry and (b) curvilinear motion applicable to any bending amplitude or any equilibrium geometry. The former case follows as a special condition of the latter case. For each kinematic model the wave equation is solved using potential functions identical in form, and the results illustrate the fallacy of placing the entire burden of unevenly spaced vibrational levels upon the potential energy expression. Furthermore, it has been demonstrated that eigenvalues can be obtained from a five-term recursion relation which arises in the solution for case (b).
Infrared and Raman Spectra of Single-Crystal α-Lead Azide
Authors: Iqbal Zafar , Garrett W. , Brown Chris W. , Mitra S. S.
Published: February 2004

The polarized transmission infrared spectra between 400 and 4000 cm−1 and the He–Ne laser excited Raman spectra between 30 and 1500 cm−1 of an oriented single crystal of α-lead azide (PbN6), have been measured and the long-wavelength vibrational modes have been assigned by factor-group analysis. The observed splittings are in essential agreement with the reported space group D2h16− Pnma. The Raman-active lattice modes are observed in the frequency range 30–210 cm−1. The appearance of peaks in the 1330–1360−cm−1 region due to the symmetric stretching vibration of the azide ion, in both the infrared and Raman spectra, confirms the presence of fairly asymmetric azide ions in the lattice. A probable relationship between a component of the bending mode frequency of the azide ion and the thermal instability of α-lead azide and related metal azides is pointed out.
Far-Infrared and Raman Spectra of Hexachloro Salts of Tetravalent Neptunium
Authors: Berringer B. W. , Gruber J. B. , Loehr T. M. , O'Leary G. P.
Published: February 2004

The far-infrared and Raman spectra have been analyzed for the following compounds: dicesium neptunium hexachloride Cs2NpCl6, ditetramethyl ammonium neptunium hexachloride [(CH3)4N]2NpCl6, and ditetraethyl ammonium neptunium hexachloride [(C2H5)4N]2NpCl6. Infrared studies on polycrystalline samples were carried out at room temperature and 98°K. Single-crystal Raman spectra were recorded at room temperature. Far-infrared absorption peaks were found as follows: Cs2NpCl6−265, 117, and 58 cm−1; [(CH3)4N]2NpCl6−259, 116, and 65 cm−1; and [(C2H5)4N]2NpCl6−259, 117, and 59 cm−1. Observed Raman spectra were found as follows: Cs2NpCl6−310 and 128 cm−1; [(C2H5)4N]2NpCl6−301 and 123 cm−1. An interpretation of the observed spectra was made. The interaction force constants necessary to describe the observed spectrum are the Np–Cl stretch, K; the Cl–Np–Cl bend, H; the nonbonded Cl–Cl stretch, F; the interaction, k, between two Np–Cl stretches on opposite sides of the Np atom; and an angle-angle interaction, h, between angles at right angles to each other which share a common bond. The spectrum of the complex NpCl6−2 in each salt can be described by a given set of octahedral force constants, calculated using the Wilson FG matrix technique and a Urey-Bradley potential. The Cs2NpCl6 spectra are described by force constants K=1.31 mdyn/Å, H=0.053 mdyn/Å, F=0.061 mdyn/Å, k=0.40 mdynÅ, and h=0.015 mdyn/Å. The [(CH3)4N]2NpCl6 and [(C2H5)4N]2NpCl6 salts can be described by the force constants K=1.271 mdyn/Å, H=0.053 mdyn/Å, F=0.05 mdyn/Å, k=0.38 mdyn/Å, and h=0.015 mdyn/Å. The spectrum calculated using these parameters agrees to within 1% of the observed spectrum.
Vibrational assignments and torsional barrier heights of the dimethylhalosilanes
Authors: Durig J. R. , Hawley C. W.
Published: February 2004

The infrared and Raman spectra of dimethylfluoro-, dimethylbromo-, dimethyliodo-, and dimethyldiiodosilane have been recorded from 4000 to 33 cm−1 and assignments are proposed for all the fundamental vibrations. The far infrared spectra and low frequency Raman spectra were recorded from 350 to 33 cm−1 for dimethyldifluoro-, dimethylchloro-, dimethyldichloro-, dimethyldibromo-, and dimethylsilane. The methyl torsional modes are assigned at 189, 156, 192, 173, 160, 178, 170, and 152 cm−1 for dimethylfluoro-, dimethyldifluoro-, dimethylchloro-, dimethylbromo-, dimethyldibromo-, dimethyliodo-, dimethyldiiodo-, and dimethylsilane, with corresponding barriers to internal rotation of 2.39, 1.70, 2.56, 2.07, 1.81, 2.18, 2.02, and 1.51 kcal/mole, respectively.
Molecular beam kinetics: Long-lived collision complexes in reactions of K, Rb, and Cs with SnCl4 and SF6
Authors: Riley S. J. , Herschbach D. R.
Published: February 2004

Velocity distributions of reactive scattering from crossed thermal beams of K, Rb, or Cs and SnCl4 or SF6 have been measured over a wide angular range. A kinematic transformation of the data to the center-of-mass coordinate system provides contour maps of the differential reaction cross sections. The cross sections show approximately symmetrical forward-backward peaking with respect to the initial relative velocity vector and very low product translational energy. These features indicate the reactions proceed via formation and decay of a collision complex that persists for many vibrational periods and at least several rotational periods. The observed product angular and velocity distributions are shown to be consistent with a simple transition-state theory developed from the RRKM treatment of unimolecular decomposition. For the SnCl4 reactions, the cross sections give evidence of two distinct decay modes, one consistent with formation of alkali chloride and the other a much heavier alkali compound, probably the alkali chlorostannite, MSnCl3. The latter mode accounts for ∼13 of the reactive scattering for the K case, ∼14 for Rb, and ∼15 for Cs.
Band strengths for electric dipole transitions from ab initio computation: Lio (X 2Π −X 2Π), (A 2Σ+−A 2Σ+), (X 2Π − A 2Σ+); AlO (X 2Σ+−X 2Σ+), (A 2Π −A 2Π), (X 2Σ+−A 2Π), (B 2Σ+−B 2Σ+), (X 2Σ+−B 2Σ+)
Authors: Yoshimine M. , McLean A. D. , Liu B.
Published: February 2004

Intensity relations in diatomic molecule spectra are reviewed and computationally useful expressions given for band strengths and band oscillator strengths in terms of electronic expectations values, which are the normal output of ab initio calculation. Calculations of these properties are reported for 7Li16O and 27Al16O. With very accurate X 2Π and A 2Σ+ LiO wavefunctions, band strengths and band oscillator strengths for all transitions involving ν,′ ν″ up to four are given, both within and between the electronic states. Results, given as band strengths (band oscillator strengths), are X 2Π −X 2Π 0–1 band, 0.038 a.u. (2.4× 10−6). A 2Σ+ −A 2Σ+ 0–1 band, 0.029 a.u. (3.7× 10−5); and X 2Π −A 2Σ+ 0–0 band, 6.4× 10−4a.u. (1.1× 10−6). Similar data are presented for the X 2Σ+ and A 2Π states of 27Al16 0 using wavefunctions of comparable quality. The dipole moment in the X 2Σ+ state is shown to be essentially constant over the range of nuclear vibration in the lowest vibrational levels. Results, given as band strengths (band oscillator strengths), are X 2Σ+ − X 2Σ+ 0–1 band, 2.1× 10−5 a.u. (3.1× 10−8); A 2Π −A 2Π 0–1 band, 0.035 a.u. (2.0× 10−5); X 2Σ+−A 2Π 0–0 band, 0.0158 a.u. (6.8× 10−5). Adjusting this last band oscillator strength by use of the observed rather than the computed energy separation of the X 2Σ+ and A 2Π states increases it from 6.8× 10−5 to 1.2× 10−4. Finally more limited and less accurate calculations on the B 2Σ+ state of 27Al160, give the estimates B 2Σ+ − B 2Σ+ 0–1 band, 0.08 a.u. (1× 10−4) and X2 Σ+ − B 2Σ+ 0–0 band, 1.8 a.u. (0.07).
Theory of electron affinities of small molecules
Authors: Simons Jack , Smith Wesley D.
Published: February 2004

In this paper, the equations-of-motion method, which has been successfully applied to the prediction of electronic excitation energies, is used to derive a physically clear and computationally tractable theory of molecular electron affinities. The contributions to the calculated electron affinities made by the ion-neutral correlation energy difference and by the Hartree-Fock energy change can be computed separately in this theory. In addition, the change in the correlation energy of the parent molecule's electrons, which is caused by adding an ``extra'' electron, can be quantitatively assessed. The physical content of this theory is discussed in considerable detail, and a connection is made with the many-body Green Function theory. The technique is shown to have important advantages over the variational wavefunction approach, the most attractive feature being the small size of the matrices occurring in computational applications.
Microwave-infrared double resonance of CH4 using 3.39μ He–Ne laser line
Authors: Curl R. F. , Oka T.
Published: February 2004

The rotational transition between the F1(2) and F2(2) components of the 67 v3 = 1 level of CH4 has been observed at 6895 MHz by double resonance experiments in the 3.39 μm He–Ne laser cavity. When the microwave radiation is applied the Lamb dip signal is observed to decrease markedly in size because of the double resonance coherence splitting phenomenon. A double resonance signal is also observed over the Doppler width of the CH4 absorption because the population shift caused by the microwave transition reduces the saturation of the CH4 absorption by the laser. The frequency of the transition was measured as 6895.3 ± 0.3 MHz.
Two-phonon infrared absorption spectra in crystalline carbon dioxide
Authors: Dows David A. , Schettino Vincenzo
Published: February 2004

A theory of two-phonon states appropriate to vibrational excitations in molecular crystals is presented. ``Phonon'' is taken to mean any vibrational excitation, external or internal to the molecules of the crystal. The theory includes general values of the wave vector. Possible mechanisms for the interaction of the two-phonon states with radiation are considered and expressions for the intensity of infrared absorption developed. Experimental results are presented for infrared absorption measurements on thin and thick films of polycrystalline carbon dioxide at low temperature. Transitions involving molecular fundamentals of the major constituent (12CO2) and of isotopic impurities and involving two- or multiphonon absorption are observed. The latter include transitions to states involving simultaneous excitation of two internal vibrations as well as excitation of one internal and one lattice vibration. Dispersion curves and densities of states are obtained for two internal molecular fundamentals coupled by dipole-dipole interactions, and comparison with one-phonon transition regions is made. Two-phonon densities of states and intensities of absorption to continua in the ν3+ν1,ν3+2ν2 (3600 cm−1) and ν2+ν1,ν2+2ν2 (2000 cm−1) regions are calculated and are in reasonable agreement with experiment.
Integral equation approach to liquid crystals
Authors: Workman Harry , Fixman Marshall
Published: February 2004

A formal description of angular correlations in fluids is presented. The method of functional Taylor expansion is used to formulate expressions for correlation functions. An approximate potential for rodlike particles, a generalized Ornstein-Zernike equation, and a generalized Percus-Yevick equation are used in the calculation of anisotropic-isotropic transition properties of liquid crystals. It is shown that a purely repulsive potential and the Percus-Yevick equation lead to a description of the anisotropic-isotropic transition that can never agree with the experimentally observed properties.
Hyperfine interactions and electron spin distribution in triplet state phenanthrene
Authors: Frosch R. Peter , Goncalves Antonio M. Ponte , Hutchison Clyde A.
Published: February 2004

The anisotropic proton hyperfine interactions with the electrons of the triplet state phenanthrene molecule in diphenyl single crystals at ∼ 77°K were measured by electron paramagnetic resonance spectroscopy. The distribution of spin in the triplet state phenanthrene molecule was deduced from these measurements and compared with theoretical estimates of the spin densities for triplet state phenanthrene, phenanthrene negative ion, and phenanthrene positive ion.
Velocity distribution measurements of 0.06–1.4 eV argon and neon atoms scattered from the (111) plane of a silver crystal
Authors: Subbarao R. B. , Miller D. R.
Published: February 2004

Velocity distribution and out-of-plane density distribution measurements are reported in detail for 0.6–1.4 eV argon and neon atoms scattered from the (111) plane of single silver crystals. Incident energies were selected to probe the regime of epithermal scattering where significant changes in scattering direction were previously found to occur. Velocity and density distributions are combined and integrated to yield total transfer coefficients. The change in scattering direction is found not to be related to a transition to structure scattering but rather to a decrease in normal momentum transfer as the total scattering becomes more elastic. Structure scattering effects are more apparent in differential momentum transfer data which show a transfer of momentum from normal to tangential components, in agreement with calculations by McClure. The width of the scattering would therefore be a better parameter to indicate structural effects. An anomaly in the direction of energy transfer also appears which suggests that energy may be transferred from the crystal to the gas even though the mean incident energy may be greater than the mean lattice energy. In general the qualitative results of McClure for differential momentum transfer and of Oman for integrated transfer characteristics of the specific argon-silver interaction appear to be substantially correct.
Modifications of the particle-in-a-box model for the electronically excited state of solvated halide ions
Authors: Roberts Joe L. , Chakrabarty M. R. , Stevens C. D.
Published: February 2004

Three modified particle-in-a-box models for the excited state of the charge-transfer-to-solvent spectra of aqueous halide ions are derived. In two of these (I and II), the halogen atom is represented as a potential well within the box, and its effect on the energy is calculated by first-order perturbation theory. In I, the excited state is the n = 1 level of the box, and in II, the n = 2 level. In the third model (III, the halide atom is represented as a hard sphere. In this extension of the previous model, the thickness of the spherical shell between the hard sphere and the box replaces the radius of the box as the factor that determines the energy of the excited electron. This model is energetically similar to the previous one, but differs from it in that the overlap between the wavefunctions of the ground and excited states can be adjusted by varying the radius of the hard sphere.
Many-body interaction free energy to infinite order. II. Collective behavior
Authors: MacRury T. B. , Linder B.
Published: February 2004

The closed-form expressions for the infinite order free energy, derived in the preceding paper [J. Chem. Phys. 58, 5388 (1973), Paper I] are recast in several different forms which focus on the collective behavior of the many-body system. In particular, it is shown that the present formulation is equivalent to the treatments based on collective modes of motion and to those developed on the basis of time-dependent Hartree theory.
Method of rapidly optimizing bond lengths in all-valence electron SCF-MO calculations
Authors: Hashmall Joseph A. , Raynor Susanne
Published: February 2004

A method for rapidly finding the bond lengths for which all-valence electron SCF-MO methods will give energy minima is presented. The necessary constants for application of this method to MINDO/2 calculations are given and its general utility tested. The results are in excellent agreement with the energies and bond lengths found from true geometry optimization, but require only a fraction of the time.
Neutron quasielastic scattering study of SH− reorientation in the cubic phases of cesium and rubidium hydrosulfide
Authors: Rowe J. M. , Livingston R. C. , Rush J. J.
Published: February 2004

The orientational disorder of the hydrosulfide ions in CsSH (CsCl phase) and RbSH (NaCl phase) has been investigated by quasielastic neutron scattering with high energy resolution (Δ E1/2max=0.25 meV). The experimental results provide a clear demonstration of the theoretically predicted separation of the quasielastic neutron peaks for rotating groups or molecules into unbroadened and broadened components which reflect, respectively, the geometric and time behavior of the rotation. Jump reorientation of the ions between equilibrium directions is established as the dominant mechanism creating the rotational disorder in the hydrosulfides, and both small-step rotational diffusion and quasifree rotation are clearly ruled out. Average residence times between reorientation jumps are derived from comparisons of the experimental results with theoretical calculations based on jump reorientation models, but it is not possible to determine the equilibrium orientation of the SH− ions. Mean-square vibrational amplitudes for the hydrogen atoms are also obtained from the observed integrated intensities of the elastic peaks. The present results are compared in detail with previous lower-resolution neutron results on NaSH and CsSH. It is concluded that in most cases measurements using single crystals will be necessary to establish the details of orientation disorder in solids.
Collision-induced ion pair formation of thallium halides: Threshold behavior
Authors: Parks E. K. , Wagner A. , Wexler S.
Published: February 2004

The threshold laws for direct polar disociation A+BC → A+B++C− and for ion-complex formation A+BC → AB++C− are determined for the collision of Xe and Kr atoms with TlCl, TlBr, and TlI by analysis of the experimental excitation functions presented in the preceding paper. The cross section for direct polar dissociation is parameterized by the expression A(Etot−E0)n/Erel, where Etot and Erel are the total energy and the relative translational energy, respectively, of the reactants, and E0 is the threshold energy. The cross section is averaged over the experimental translational and internal energy distributions, and, for each pair of reactants, E0, n, and A are determined from the best fit to the data. For ion-complex formation, the data are analyzed in terms of a step behavior at the reaction threshold. For the system Xe + TlCl, experimental measurements of the cross section as a function of internal energy are presented, and the relative importance of translational and internal energy in promoting polar dissociation is discussed. It is found that an increment of internal energy is more effective in promoting polar dissociation than an equal increment of translational energy.
Possibility of a diffracted beam in the absence of the corresponding Fourier component of potential in gas-surface scattering
Authors: Goodman Frank O. , Tan Whee-Keng
Published: February 2004

It is shown, with a simple analytical example, that the intensity of a diffracted beam in atom-surface scattering is not necessarily small if the corresponding Fourier component of potential is small. This result contradicts the predictions of the existing first-order theory. An experimental result that higher-order diffracted beams can dominate the scattering while the specular and other lower-order beams can be relatively small, combined with a theoretical result that the Fourier components of potential decrease strongly with increasing order, leads to the conclusion that first-order theory is invalid in general for an interpretation of gas-surface diffraction.
Depolarized Rayleigh scattering and orientational relaxation of molecules in solution. I. Benzene, toluene, and para-xylene
Authors: Alms G. R. , Bauer D. R. , Brauman J. I. , Pecora R.
Published: February 2004

Measurements of orientational relaxation rates of benzene, toluene, and para-xylene in a variety of solvents have been made by depolarized light scattering. A plot of reorientational relaxation time of each solute versus solution viscosity was found to fit a straight line with nonzero intercept. The slopes of the lines are compared with those predicted by the Stokes-Einstein relation.
ESR studies of the triplet state of [n.n] paracyclophanes
Authors: Bramwell Fitzgerald B. , Gendell Julien
Published: February 2004

ESR experiments were performed on the triplet state of randomly oriented paracyclophanes in a variety of rigid glasses at temperatures ranging from 103 to 15°K. Spectra were recorded for [2.2]; [3.3]; (4,7,12,15)-tetramethyl [2.2]-paracyclophane and stagger-ring paracyclophane. For all the samples except stagger ring, a four-ringed paracyclophane, only the Hmin feature was observed from which D*, the root-mean-square zero-field splitting, was calculated. For stagger ring the triplet spectrum has two features in the Δ ms= 1 region in addition to the Hmin feature. From these, the zero-field splittings, D and E, were calculated. The triplet spectra for the paracyclophanes show that there is strong transannular interaction with electron delocalization over all benzene rings. There is evidence for strongly coupled intramolecular exciton effects. The effect of increasing the inter-ring separation from [2.2] paracyclophane to [3.3] paracyclophane is to decrease the transannular interaction. The effect of methyl substitution is to increase transannular effects relative to the parent compound. Transannular interactions in stagger ring are greater than in [2.2] paracyclophane despite the increased electron delocalization possible through the introduction of more than two rings. The large value of E for stagger ring represents a significant deviation from axial symmetry for the zero-field-splitting tensor and indicates that the methylene bridges, the methyl substituents, or the ring distortion, may make important contributions to the electronic distribution of the triplet state.
Concerning Cartesian tensors that are invariant under point group transformations. The zero components
Authors: Reznik A. A. , Hollingsworth C. A.
Published: February 2004

A method for obtaining some general results concerning the components of Cartesian tensors that are invariant under symmetry transformations is presented. The type and number of components which must be zero in order for a tensor (of any rank) to be invariant under any of the 32 crystallographic point groups are given.
Equations-of-motion method including renormalization and double-excitation mixing
Authors: Shibuya Tai-ichi , Rose John , McKoy Vincent
Published: February 2004

The equations-of-motion method is discussed as an approach to calculating excitation energies and transition moments directly. The proposed solution [T. Shibuya and V. McKoy, Phys. Rev. A 2, 2208 (1970)] of these equations is extended in two ways. First we include the proper renormalization of the equations with respect to the ground state particle-hole densities. We then show how to include the effects of two-particle-hole components in excited states which are primarily single-particle-hole states. This is seen to be equivalent to a single-particle-hole theory with a normalized interaction. Applications to various diatomic and polyatomic molecules indicate that the theory can predict excitation energies and transition moments accurately and economically.
Planewise summation of point dipole-dipole interactions for some aromatic hydrocarbon crystals
Authors: Philpott Michael R.
Published: February 2004

Lattice sums of point dipole-dipole interactions have been evaluated by the method of planewise summation for wave vectors perpendicular to the (001) plane of aromatic hydrocarbon crystals. The interaction between a plane of dipoles and a single dipole located at the origin is called a plane sum. It is found that the magnitude of plane sums falls off very rapidly with perpendicular distance of the plane from the origin. The contribution from all plane sums not containing the origin is less than 10% of the total lattice sum for naphthalene, approximately 1% for anthracene and phenanthrene, and negligible in the cases of tetracene and pentacene. Some results for L axis dipoles on translationally inequivalent molecules are given below (units cm−1/Å2). I1L,2L(0) is the plane sum for the plane containing the origin, I1L,2L(1) is the nearest neighbor plane sum, and Ewald sum is the infinite crystal lattice sum. CrystalI1L,2L (0)I1L, 2L(1)Ewald sumNaphthalene3333−573219Anthracene2701−202661Tetracene4577−14575Pentacene463104631Phenanthrene424654255It is suggested that the existence of weakly coupled crystal planes simplifies the theoretical treatment of several exciton processes. A brief discussion is given for absorption and reflection spectra, exciton band structure and exciton-phonon coupling.
Some remarks on the calculation and use of retarded and static dipole sums in molecular exciton theory
Authors: Philpott Michael R. , Lee Jo W.
Published: February 2004

Retardation corrections to the static dipole sums used in molecular exciton theory are calculated by an Ewald summation procedure. The corrections are found to be negligible thereby confirming conclusions of several earlier investigations. A description is given of the correct method of using retarded dipole sums in molecular exciton theory and some of the misuses pointed out. The widespread abuse of static dipole sums in molecular exciton theory is discussed and attributed to a misunderstanding of the k=0 selection rule and the shape dependence of static dipole sums.
Critical-point thermodynamics of fluids without hole-particle symmetry
Authors: Widom B. , Stillinger F. H.
Published: February 2004

We have examined an infinite class of fluids which exhibit a liquid-vapor critical point, with regard to corrections to thermodynamic scaling of critical phenomena. These ``penetrable-sphere models'' possess an underlying bilateral symmetry in their equivalent binary fluid mixture versions. After postulating a suitable scaling for these mixtures, we show that the transciption to the penetrable-sphere models produces a generalization of the conventional pure-fluid scaled equation of state. Some leading corrections to the scaled form of thermodynamic properties are derived and tabulated. These corrections are presented in a form that makes no explicit reference to their modelistic source, so in fact they may apply to real substances.
Diffusion of Sr2+ in single crystal MgO
Authors: Mortlock A. J. , Price D. M.
Published: February 2004

Measurements of the diffusion of Sr2+ at tracer concentration in high-purity single crystal MgO have been made over the temperature range from 1000 to 1600°C. After applying a graphical correction for the effects of a short-circuiting diffusion component which is also present, the observed diffusion coefficients, D, applicable to lattice diffusion could be fitted by the equation D=(6.0 ±3.810.7) × 10−4exp[−(2.91 ± 0.13)/kT] cm2/sec, where T is the absolute temperature and k is Boltzmann's constant in electron volts per degree Kelvin. The relation of this result to previously found correlations of the activation energy and frequency factor with the radius of the diffusing ion, r, is examined. It is found that D can be expressed as a rapidly varying function of r and T only over a range of r from 0.3 Å to 1.3 Å. This size effect is discussed in relation to that observed in other ionic solids.
Theory of Zeeman effect for rare earth ions in crystal field with D2 symmetry and application to rare earth garnets
Authors: Kambara T. , Haas W. J. , Spedding F. H. , Good R. H.
Published: February 2004

Rare earth ions in solids frequently exhibit sharp-line optical spectra. In this paper a part of the theory of the Zeeman effect for the lines is developed, first for a single rare earth ion in D2 symmetry, and secondly for rare earth ions at different inequivalent sites in garnet crystals. The results for the case in which the crystal field and Zeeman splittings are comparable have application for magnetic garnets such as the rare earth iron garnets, while the results for the case where the Zeeman splittings are treated as a perturbation on the crystal field states have application for nonmagnetic garnets such as the rare earth aluminum or gallium garnets. In both cases it is found that when the magnetic field is restricted to the xy plane of the local site coordinate, there exists an antiunitary symmetry operation which simplifies the energy level and transition probability calculations, and which leads to the assignment of a quantum number ζ = ± 1 to the states. There are shown to be two types of states: Type A, for which the assignment of ζ value is not sensitive to the choice of coordinate axes, and Type B states for which it is. It is also shown, in the case of rare earth ions with an odd number of 4f electrons, that the Types of the states are determined by the relative signs of the principal values of the g factors. Furthermore, it is found that the dependence of line intensity on magnetic field direction for A→A and B→B transitions is clearly different from that of A→B and B→A transitions.

Finally, and most important, it is shown that studies of the energies and intensities of the Zeeman lines as a function of magnetic field direction in suitable crystal planes can be used to distinguish between spectra arising from different inequivalent rare earth ion sites in garnets. This result has immediate importance for experimental study of site selectivity problems in garnets, and, when combined with the other conclusions of this work, leads to definite suggestions for experimental determinations of at least some of the details of the states.
Coulomb approximation for multipole polarizabilities and dispersion forces: Analytic static polarizabilities of ground and excited state atoms
Authors: Adelman S. A. , Szabo Attila
Published: February 2004

An analytic expression for the 2j-pole static electric polarizability of an atom is obtained in a Coulomb-like approximation. Core effects are neglected and following Bates' and Damgaard's method for oscillator strengths, the valence orbital is approximated by the asymptotically valid Whittaker function with hydrogenic normalization. Information about the symmetry allowed excited states is introduced via an r−2-type pseudopotential. This simple choice leads to an analytically tractable perturbation equation which is solved by an adaptation of the technique of Schwartz and Tiemann. The effective nonintegral quantum numbers which enter our expression for the polarizability are obtainable from spectroscopic data. Our expression yields very accurate dipole and quadrupole polarizabilities for monovalent ground and excited s-state atoms. Reasonable though somewhat less accurate results are obtained for divalent species and monovalent p-state systems. The method is generalizable to frequency-dependent perturbations.
Matrix reactions of lithium atoms with N2O: Infrared spectra of LiO and Li2O
Authors: Spiker Robert C. , Andrews Lester
Published: February 2004

Simultaneous matrix deposition of Li atoms and N2O at high dilution in nitrogen has produced new infrared absorptions which show appropriate lithium and oxygen isotopic shifts for vibrational assignment to the high temperature molecules LiO and LiOLi, which were observed in earlier evaporative studies. The identification of LiO and LiOLi was confirmed in mixed isotopic experiments. Isotopic assignments to ν3 of Li2O in nitrogen matrices provide data for calculations of the Li–O–Li bond angle which are consistent with a linear molecule, in agreement with the electric deflection and earlier infrared work on Li2O.
Reformulation and extension of Wigner-Witmer and Mulliken's correlation rules for the spin and orbital states of diatomic molecules upon dissociation
Authors: Chiu Ying-Nan
Published: February 2004

Projection operator technique and angular momentum coupling methods are used to construct the eigenfunctions of diatomic molecular states in terms of the eigenfunctions of separate atomic states. The resulting eigenfunctions of the molecular term manifolds contain correct and compatible permutation symmetry and continuous group as well as point group symmetry pertinent to the molecule. These eigenfunctions will, in contrast to molecular orbital description, give the correct states of the atomic dissociation products required in chemical reactions and collisional energy transfer. In the above construction, we elucidate the correlation principle that dictates the nonexistence of two incompatible symmetries for certain states and allows for certain symmetries of the molecular term manifold to arise from given atomic multiplet states. The qualitative aspects of the newly derived correlation rules in simple methematical language are shown to agree with the early works of Wigner-Witmer and Mulliken. These rules are then extended to treat ionic molecular states arising from atomic ions and radicals of variable charge and number of electrons but of the same element. Such ions may be important in ion-molecule reactions and in mass spectrometry studies. The extension as well as quantitative application of the new procedure devised are illustrated by constructing explicitly the eigenfunctions, in Slater determinant forms, of the molecular states that arise from different combinations of O (3Pg, 1Dg, 1Sg), O+ (4Su, 2Du, 2Pu), and O− (2Pu) which have not been considered by early workers. These combinations are shown to exhibit charge-exchange degeneracy in parallel to excitation exchange degeneracy in the study of exciton states.
Infrared study of solid phosphine
Authors: Francia Marie D. , Nixon Eugene R.
Published: February 2004

Infrared spectra of two crystalline forms of PH3 and PD3 are reported. The modification studied at 35°K displays broad structureless absorption bands but the form below the transition temperature at about 30°K has a complexity of sharp spectral lines. From results of the temperature effect on the spectra and from studies of isotopic impurities in PH3 and PD3 host crystals, the authors speculate that this lower temperature form of phosphine may have a structure with a primitive cell containing as many as 12 molecules occupying six different sets of sites.
Incoherent neutron scattering and molecular reorientations in crystals near Tc
Authors: Michel K. H.
Published: February 2004

The incoherent neutron scattering law is derived for a proton which belongs to a XH4-tetrahedron. Reorientations around threefold and twofold tetrahedral axes are taken into account. The latter process depends on the position of the neighboring tetrahedra. As a consequence the correlation time for the protonic motion is a function of the equilibrium pair correlation. In case of a first order phase transition this collective effect leads to a discontinuous change of the width of the quasielastic line.
Diffusion theory for adsorption and desorption of gas atoms at surfaces
Authors: Pagni Patrick J. , Keck James C.
Published: February 2004

The time evolution of a nonequilibrium ensemble of gas atoms adsorbed on a solid surface is described. Adsorption and desorption rate constants and adatom (adsorbed atom) energy distributions are obtained in the steady state approximation from the appropriate master equation or an equivalent diffusion equation. Energy transition probabilities are obtained from a classical gas-surface collision model using an interaction potential composed of an oscillating harmonic repulsion and a stationary attraction. Calculations have been performed over the following range of similarity parameters: inertia ratio 10−2<μ=mg/ms<2, frequency ratio 1<ν=ωs/ωg<10, and well depth 2<δ=D/kT<100. For ``resonance'' values of the frequency ratio, gas-surface collisions are sufficiently adiabatic that adatom energy distributions are significantly nonequilibrium, and steady state rate constants are depressed below the equilibrium rate constants. Applications include prediction of adsorption and desorption rate constants, sticking and accommodation coefficients, sublimation and condensation rates, and boundary conditions for the Knudsen layer.
Experimental test of classical nucleation theory in a liquid-liquid miscibility gap system
Authors: Heady R. B. , Cahn J. W.
Published: February 2004

The classical formulation of homogeneous nucleation theory has been tested in the methylcyclohexane-perfluoromethylcyclohexane liquid-liquid gap miscibility system. The theory was found to be invalid for temperatures above 35°C. The discrepancy between theory and experiment (critical undercoolings are predicted which are less than those observed) can not be explained by simple modifications of the theory. These results confirm the discrepancy found by Sundquist and Oriani.
Estimate of classical binary collision operator
Authors: Eu Byung Chan
Published: February 2004

The classical binary collision operator T(ε) for a class of nonsingular repulsive interactions is estimated as a function of ε and k, where ε is a parameter with dimension of inverse time and k the wavenumber. It is found that (k|T(ε)|k′) is a smooth bound function of ε and k−k′. The utility of the estimate of T(ε) in the theory of transport processes of classical fluids is discussed especially in connection with the divergence question of the density expansion of the transport coefficients.
Investigation of singlet-triplet transitions by phosphorescence excitation spectroscopy. X A simple α, β-unsaturated ketone
Authors: Jones Claude R. , Kearns David R. , Wing Richard M.
Published: February 2004

X-ray diffraction techniques and Patterson methods have been used to determine the crystal structure of the simple conjugated enone, ketone I. The crystals studied belong to space group P1 with a = 9.365(6), b = 6.578(4), c = 8.321(5), α = 101.70(3), β = 101.55(3), and γ = 101.37(3). Least squares refinement of 836 counter-collected, unique reflections having | F |2>2.5σ(| F |2) led to a final value of the conventional R1 factor (based on F) of 5.8%. The structure consists of rather loosely packed, strain free bicyclic molecules, in which the enone chromophore is planar. Phosphorescence excitation spectroscopy was used to obtain the polarized singlet-singlet and singlet-triplet absorption spectra of oriented crystals. The important results are: (i) The ordering of excited states in this molecule is (n, π*)>1(n, π*)>3(π, π*)3. (ii) Polarization measurements and Franck-Condon considerations indicate that the difference in geometry between the 3(π, π*) state and the gound state is small. (iii) The 1(n, π*) state appears to be the exclusive source of intensity for the origin band of the Tπ,π*← S0 transition. (iv) The Tπ,π*← S0 absorption spectrum indicates that there is extensive vibronic mixing between the 3(π, π*) state and the nearly degenerate 3(n, π*) state. (v) Vibronic mixing is much less important in the emission spectrum. Consequently, the Tπ,π*⇄ S0 absorption and emission spectra are far from mirror-image symmetric, and the observed radiative lifetime of the triplet state is quite different from that computed from the T← S0 absorption. (vi) The polarization of the Tn,π*← S0 transition can be accounted for in terms of spin-orbit coupling between the 3(n, π*) and 1(π, π*) states. (vii) The complete absence of vibrational structure in the Tn,π*← S0 spectrum is attributed to extensive mixing between the 3(n, π*) state and degenerate vibronic levels of the lower lying 3(π, π*) state. (viii) The significant in-plane polarization in the Sn,π*← S0 transition is attributed to perturbations of the planar enone chromophore by out of plane hydrogen and methyl groups which introduce intensity that is in-plane polarized but perpendicular to the C=O axis. (ix) Much of the intensity in the Sn,π*← S0 transition is vibronically induced and polarized along the C=O axis.
Elastic and inelastic scattering of electrons from sodium atoms using Glauber approximation
Authors: Tripathi A. N. , Mathur K. C. , Joshi S. K.
Published: February 2004

The Glauber approximation has been applied to study the elastic and the inelastic scattering of electrons from sodium atoms. Adopting a frozen core approximation the total integrated elastic scattering cross section from the ground state of the sodium atoms and the inelastic scattering cross section for the resonance transition (3s-3p) in the sodium atoms are calculated and compared with other theoretical calculations and with the experimental data. With the frozen core assumption and the Glauber approximation, the calculated elastic and inelastic cross sections for the electron sodium atom collisions agree better with experimental data than the results of calculations based on the Born and the close coupling approximations.
Diatomics-in-molecules potential energy surfaces. I. First-row triatomic hydrides
Authors: Tully John C.
Published: February 2004

The diatomics-in-molecules formalism is presented in a way which explicitly accounts for the directional nature of chemical bonding. The method has been used in the simplest reasonable way to obtain ground and excited potential energy surfaces for the molecules BeH2, BH2, CH2, NH2, H2O, and FH2. The results are shown to compare well with experiment and with accurate ab initio calculations, thereby establishing that the range of applicability of the method can be extended to molecules containing p electrons. The outlook for the method is discussed, with emphasis on the construction of potential energy surfaces adequate for the description of molecular collision processes.
Detection, assignment of the microwave spectrum and the molecular Stark and Zeeman effects in CSe, and the Zeeman effect and sign of the dipole moment in CS
Authors: McGurk J. , Tigelaar H. L. , Rock S. L. , Norris C. L. , Flygare W. H.
Published: February 2004

The microwave spectrum of seven isotopic species of CSe has been observed leading to an internuclear distance of d=(1.67647± 0.0002)× 10−8cm. The Stark effect measurements led to an electric dipole moment of | μ |=(1.99± 0.04) D. The molecular Zeeman effect was also observed in CSe leading to the molecular g⊥ value in 12C80Se of g⊥=−0.2431± 0.0016, the magnetic susceptibility anisotropy of χ⊥ − χ∥=(27.8± 1.4)× 10−6erg/G2· mole, and the molecular electric quadrupole moment of Q∥=−(2.6± 1.6)× 10−26esu·cm2. The molecular Zeeman effect was observed in three isotopic species of CS leading to the measurement of the sign of the electric dipole moment of −CS+. The results are compared to similar molecules.
An EPR study of Cr3+:K2SbF5
Authors: Hempel J. C. , Klassen D. , Hatfield W. E. , Dearman H. H.
Published: February 2004

A single crystal X-band EPR study of chromium (III) in the matrix K2SbF5 is reported, and five chromium sites are characterized. Two pairwise related sites with gz=1.9717± 0.0006, gx=gy=1.9744± 0.0006, D=0.2750± 0.0002 cm−1, E=0.00836± 0.00007 cm−1 markedly predominate and can be associated with a six-coordinate species. The optical spectrum of the Cr3+:K2SbF5 system is correlated with the magnetic resonance behavior of the predominating sites with an empirical ligand field calculation assuming D3 symmetry. A site present in very low concentrations can perhaps be associated with a five-coordinate species, a symmetry characteristic of the antimony site in the K2SbF5 matrix.
Determination of cooperativity parameter from hydrodynamic data
Authors: Kumbar Mahadevappa M.
Published: February 2004

The approximations involved in the theory relating the hydrodynamic data, such as viscosity, to the cooperativity of the helix-to-random-coil transition have been examined. The equation relating the viscosity to the cooperativity parameter is written as ([η]/[η]coil)2/3(1−θ)−1=f(Φ)2/3+f(Φ)2/3(2/α2σ)(lh/lc)2×[θ/(1−θ)]3/2, where f(Φ) is a function of the universal constant Φ,θ is the fraction of monomer units in the helical conformation, lh is the length of the monomer unit in helical conformation, lc is the effective length of the monomer units in coiled section, α is the expansion factor due to long-range interactions, σ is the cooperativity parameter, [η] is the intrinsic viscosity of the partially helical polymer, and [η]c is the intrinsic viscosity of the completely disordered random coil. It has been shown that Φ assumes different values for the partially helical polymer chain and randomly coiled chain of the same length. Upon accounting for this factor as well as chain expansion due to long-range interactions, it has been concluded that the cooperativity parameter and hence Δ S remains independent of ionic strength as well as solvent components.
Electronic spectroscopy of highly-polar aromatics.* II. Luminescence of nitroanilines
Authors: Khalil O. S. , Seliskar C. J. , McGlynn S. P.
Published: February 2004

The luminescences of isomeric nitroanilines and their N-methylated derivatives, as observed in glassy media at 77°K, are reported. The o- and m-derivatives fluoresce only. The p-derivatives may fluoresce only, phosphoresce only, or show both a fluorescence and a phosphorescence whose relative intensities are dependent on the polarity of the medium and the exciting wavelength. These p-derivatives which possess the largest ground-state dipole moments exhibit the largest phosphorescence yields; they also exhibit a dependence of φp/φf on excitation energies which lie within the wavelength compass of the lowest-energy absorption band, a ``red-edge'' effect, and different fluorescence and phosphorescence excitation spectra. Some suggestions as to the interpretation of these effects are made.