bluuebunny/crossref_metadata_2025 huggingface dataset:
Microwave Spectrum, Dipole Moment, and Barrier to Internal Rotation of Fluoral
Authors: Woods R. C.
Published: January 2005

About 700 transitions have been measured and assigned in the microwave spectrum of the ground vibrational state and first excited torsional state of natural and deuterated trifluoroacetaldehyde. Most of these lines occurred as doublets due to tunneling through the barrier to internal rotation of the trifluoromethyl group. The splittings of these doublets were used in conjunction with a recently published computer program to compute independent values of the barrier in the ground state of the normal isotopic species and the excited states of both isotopes. The final averaged barrier estimate is 885±75 cal/mole, the first such value of a three-fold barrier of a CF3 group to be obtained from microwave splittings. This barrier is considerably lower than that (1150 cal/mole) for acetaldehyde. In general the fit with a rigid—rigid model is good but not perfect. The dipole components are estimated to be μ = 0.15 D and μb = 1.64 D. Two novel techniques employed in the assignment of the very intense and rich fluoral spectrum were the assignment, by least-squares polynomial curve fitting, of a Q-branch series of quite high J values as the initial step in solving the spectrum, and the application of the double resonance technique to the location of the weak R-branch spectrum of the excited state.
Experimental Free-Induction-Decay Shapes and Theoretical Second Moments for Hydrogen in Hexagonal Ice
Authors: Barnaal D. E. , Lowe I. J.
Published: January 2005

The results of NMR free-induction-decay shape measurements for protons in single crystals and polycrystals of hexagonal ice are reported. The second moments of the corresponding absorption line are derived from empirical fits of the free-induction-decay shapes. Theoretical values for these second moments are computed for several models of the hydrogen lattice, taking into account the effect of vibrations and librations. There is good agreement between the measured and computed second moments, implying that high-frequency proton tunneling is not present.
Rapid Calculation of Electron Scattering Factors
Authors: Peacher Jerry L. , Wills John G.
Published: January 2005

The phase amplitude method is used to reduce the radial Schrödinger equation to two separate differential equations, one for the phase and one for the amplitude. These functions are both smooth as opposed to the rapidly oscillating solution of the radial Schrödinger equation for electron energies in the kilovolt range. The partial-wave phase shifts were obtained rapidly by integrating the differential equations for the phase and amplitude numerically. Hartree—Fock and Thomas—Fermi—Dirac fields were used in the calculation. Results for argon and uranium are given in order to compare with previous results. It was found that the WKBJ approximation to the partial-wave phase shift is a good approximation for the energies used in electron diffraction. This rapid method of computing electron-scattering factors will make routine analysis of electron diffraction data more rapid as well as more exact.
Crossed Molecular Beam Reactions of Tritium Bromide
Authors: Martin L. Robbin , Kinsey James L.
Published: January 2005

A radioisotope detection method was successfully employed to determine the product distribution in crossed molecular beam experiments. Angular distributions of the atomic tritium product were measured for the reactions K+TBr→KBr+T and Cs+TBr→CsBr+T. The measured distributions correspond to ``backward'' scattering (χ≃π) of the potassium bromide relative to incoming potassium in the center-of-mass coordinate system for both reactions, i.e., the reactions are rebound reactions.
Raman Spectrum of Crystalline Benzene
Authors: Gee A. Roger , Robinson G. Wilse
Published: January 2005

Data are presented for the Raman spectrum of benzene and perdeutero-benzene at 77° and 2°K, with a resolution of 0.65 cm−1. Splittings are detected for all Raman-active degenerate vibrations but for none of the nondegenerate vibrations, with the possible exception of ν5(b2g) in C6H6. Interaction matrix elements are found for three degenerate bands where splittings seem to be uncontaminated by site-group splitting. Comparison is made between the present data and the recent calculations of Harada and Shimanouchi. Extension of the calculation to include intermolecular carbon—hydrogen interactions is indicated by the data.
Frictional Behavior of Polystyrene
Authors: Cowie J. M. G. , Cussler E. L.
Published: January 2005

The frictional coefficients of three fractions of polystyrene, each of sharp molecular-weight distribution, have been determined both from diffusion and sedimentation velocity experiments in cyclohexane at 35°C and in cyclohexane at 25°C. The coefficients obtained from the two methods agree within experimental error. These results have been correlated with light-scattering measurements to provide more accurate values of the ``universal constant'' ψ, the ratio of the intrinsic frictional coefficient to the root mean square of the radius of gyration. For cyclohexane at 35°C, the θ temperature, ψ was found to have an average value of 12.9, in close agreement with the theoretical value 12.74 for impermeable coil. For cyclohexene at 25°C, however, ψ was found to have an average value of 14.0. This result conflicts with existing theories, which predict that ψ should decrease in better solvents.
Mechanisms of Energy Transfer Involving Trivalent Eu and Nd
Authors: Van Uitert L. G. , Dearborn E. F. , Rubin J. J.
Published: January 2005

The mechanism of energy transfer between Eu and Nd and the migration of excitation between Eu ions in the Na0.5(Y, Eu, Nd)0.5Wo4 tungstates and (Y, Eu, Nd)2O3 sesquioxides are examined. Transfer from Eu to Nd appears to be predominately by dipole—dipole interactions. At high Eu concentrations energy may migrate between exchange coupled Eu ions, however, the migration requires thermal activation.
Orientation-Averaged Amplitude of the One-Quantum Term in the Neutron Scattering Law for Molecular Gases
Authors: Carpenter John M.
Published: January 2005

The amplitude of the one-quantum term in the scattering law for coherent scattering of neutrons by molecular gases is calculated using a generating-function approach. The phase factor exp (iκ·b) is averaged jointly with the amplitude factor (κ·γν) (κ·γν′), as opposed to the more common technique of approximating the joint average by the product of the average of each factor. Results of example calculations show that the correction is of the same magnitude as the result of the conventional calculation.
Surface Dye Sensitization. II. Sulfur
Authors: Ing S. W. , Chiang Y. S.
Published: January 2005

Surface dye sensitization of polycrystalline orthorhombic sulfur has been observed. The dyes used for the sensitization were rhodamine B and pinacyanole. Maximum enhanced photoresponse occurred in the wavelengths from 4500 to 6000 Å. Quantum efficiencies up to slightly over 10−2 have been measured. The observed photocurrents corresponded to electron injection from the sulfur—dye interface into the sulfur.
Theoretical Investigations of Translation—Rotation Energy Transfer: (H2, He) and (D2, He) Systems
Authors: Raff L. M.
Published: January 2005

The classical analysis of translation—rotation energy transfer in (H2, He) and (D2, He) systems is reported. The accurate, a priori potential surface obtained by Krauss and Mies has been employed in a generalized, three-body Monte Carlo calculation to obtain, as a function of temperature, relaxation times and collision numbers for the 0→2 and the 2→0 rotational transitions in both H2 and D2. A negative dependence upon temperature is obtained in each case. The relaxation times for the 0→2 transition in H2 range from 7.725×10−8 sec at 100°K to 3.491×10−8 sec at 700°K. For the 2→0 deexcitation the corresponding values are 9.00×10−8 and 4.30×10−8 sec. When a van der Waals attraction term, whose magnitude is estimated from PVT data, is added to the Krauss—Mies surface, the values for the 0→2 transition decrease to 3.1×10−8 sec at 100°K and 2.0×10−8 sec at 700°K. Corresponding decreases occur for the 2→0 transition. Calculated relaxation times for D2 are 50%—100% smaller than those obtained for H2. These results are in satisfactory agreement with available experimental data and appear to be more accurate than previous theoretical results.

The energy-transfer mechanism has been investigated and found to be smooth and continuous with transfer occurring in about 10−13 sec. The most favorable approach angle for transfer is found to be about 60°.

Two other empirical potential surfaces have been employed to estimate the effect of potential well depth and the assumption of pairwise additivity of molecular potentials. It is found that as the well depth increases, the relaxation time decreases in a manner previously predicted by Parker. The assumption of pairwise additivity is found to yield results for the relaxation times which are low by about a factor of 2. The magnitude of this error, coupled with calculations employing off-center, pairwise potentials, indicates that the repulsive centers in H2 are located about 0.16 Å from the nuclei.
Theory of the Far-Ultraviolet Spectrum of Polypeptides in the β Conformation
Authors: Rosenheck K. , Sommer B.
Published: January 2005

The electronic excited states in polypeptides of the β conformation corresponding to the lowest energy π—π* transition are derived from molecular-exciton theory. Transition energies are calculated in the monopole—monopole approximation, and the results are compared with polarized film spectra obtained in the present study, as well as with experimental data of other investigators. It appears that either parallel sheets or mixtures of parallel and antiparallel sheets are present in poly-L-lysine solutions and films.
On the Equation of State of the Rigid-Disk Fluid
Authors: Young David A. , Rice Stuart A.
Published: January 2005

The modified Yvon—Born—Green (YBG) equation of Rice and Lekner is solved for a system of rigid disks. The equation of state calculated from the solutions of the modified YBG equation is in nearly perfect agreement with the molecular-dynamics data of Alder and Wainwright up to p/ρkT=4.78, which is the Kirkwood limit for the stability of the fluid phase.
LEED Studies of the Adsorption Systems W(100) +N2 and W(100) +N2 +CO
Authors: Estrup P. J. , Anderson J.
Published: January 2005

Low-energy electron-diffraction (LEED) techniques have been used to study the room-temperature interaction of nitrogen with a tungsten (100) surface. Adsorption to saturation results in the formation of a c(2×2)—N structure in which half of the surface sites are occupied, and coverage determinations show the adsorption to be atomic. The complete c(2×2) structure lowers the work function of the surface by 0.65 eV. Rapid desorption occurs at temperatures above ∼1200°K and gives only a single β peak.

With simultaneous adsorption of N2 and CO the adsorbed species interact to give a series of LEED patterns, none of which can be formed by the individual gases. CO adsorption on the c(2×2)—N structure causes the ½½ diffraction spots to disappear and raises the work function to +0.30 eV above that of the clean surface. Subsequent heating of the saturated surface produces a ¼-order LEED pattern. From these results it is concluded that the interaction of CO gives rise to a new binding state β* for nitrogen.
Atomic Radial Distribution in Amorphous Selenium by X-Ray and Neutron Diffraction
Authors: Henninger E. H. , Buschert R. C. , Heaton Leroy
Published: January 2005

The atomic radial distribution in amorphous selenium at room temperature was determined independently from x-ray and neutron-diffraction patterns. Correction techniques were applied to reduce spurious oscillations in the distribution. The two si(s) intensity functions are in good agreement, and both methods show peaks in the radial distribution at 2.33, 3.7, 4.6, 5.8, and 7.(3) Å. The intensity patterns show no appreciable damping out of intensity peaks even at the experimental limit of s=13. This behavior results from the presence of short and well-defined interatomic distances in amorphous selenium. The intensity function can largely be accounted for by considering only two interatomic distances between the first and second nearest neighbors along the c-axis chain structure of hexagonal crystalline selenium. Thus, the spiral chain structure persists in the amorphous state with nearly unchanged geometry out to second neighbors, but in random orientations.
Scaled-Particle Methods for a Hard Convex-Body Fluid
Authors: Ritchie A. B.
Published: January 2005

Using the methods of Reiss et al. in the evaluation of the radial distribution function for a hard-sphere fluid, an equation of state can be derived for a fluid of hard bodies of any convex geometry. The equation of state is derived for CCl4, and the compressibility factor plotted versus the reduced volume. Expressions for the expansivity, isothermal compressibility, and enthalpy of vaporization are derived. Preliminary calculations show numerical improvement for β and ΔHvap. Reiss' expansivity has an incorrect temperature coefficient; this dependence is correct in the convex-body representation.
Determination of Electron and Molecular Radial Distribution Functions for Liquid Carbon Tetrachloride by X-Ray Diffraction
Authors: Gruebel Robert W. , Clayton Glen T.
Published: January 2005

X-ray diffraction patterns obtained from liquid carbon tetrachloride along the vapor pressure curve at temperatures of 25°, 51.8°, and 115°C were used to calculate the corresponding electronic and molecular radial distribution functions. The electronic distribution functions show peaks at 1.81 and 2.92 Å, and the areas associated with these peaks are in good agreement with those reported by Bray and Gingrich and Eisenstein. The difference between the observed peak areas and the theoretical areas at room temperature was investigated. Because there has been little experimental information available concerning the molecular distribution in polyatomic liquids in which all the constituent atoms have considerable scattering power, the most significant result of this work is the calculation of molecular radial distribution functions for liquid carbon tetrachloride. Peaks were observed in the molecular distribution functions at 3.95, 6.4, and 12.4 Å at all three temperatures. These peaks decreased in amplitude and increased in breadth and the number of molecules represented by these peaks decreased as the temperature increased. Ideal peak calculations were used in all area assignments.
Pressure-Induced Rotational Quadrupole Spectra of HCl and HBr
Authors: Weiss Shmuel , Cole Robert H.
Published: January 2005

Spectra of pure HCl and HCl–SF6 mixtures were taken in the range 350 to 520 cm−1, and of HBr, HBr–SF6, HBr–CF4 in the range 310 to 470 cm−1. For the mixtures, clearly defined peaks are observed at frequencies in these regions for the ΔJ=2 selection rule of quadrupole-induced dipole absorption, direct dipole intensities being much weaker. Calculated molecular quadrupole moments from integrated intensities are QHCl=5.8×10−26 esu·cm2 and QHBr=5.5×10−26 esu·cm2.
Covalency Effects in the Calculation of the g Factor of Hydrogen Atoms in CaF2
Authors: Blum Haywood
Published: January 2005

The positive g shift of hydrogen atoms, interstitial in CaF2, is explained by the inclusion of small amounts of covalent bonding. The calculation predicts an optical transition in the visible, which may have already been observed.
Inversion of Velocity-Averaged Differential-Cross-Section Data to an Intermolecular Potential
Authors: Luoma J. R. , Mueller C. R.
Published: January 2005

Utilizing generating functions, a method was constructed that retrieved the intermolecular potential from non-velocity-selected elastic-scattering data. These generating functions were tested and found to be a slowly varying function of the potential, thereby making them available for use in a linearized Taylor series expansion technique, coupled with a least-squares procedure, that inverted elastic-scattering data. The sensitivity of the averaged differential cross section to the form of the potential was noted.
Point-Group Selection Rules and Polarization for an Alternative Singlet—Triplet Transition Mechanism
Authors: Chiu Ying-Nan
Published: January 2005

A radiative transition mechanism which involves the direct interaction between the electron spin and the radiation field is studied in detail in the limit of small spin—orbit coupling. In this mechanism, the odd-parity, spin-dependent multipoles of the lowest order, the spin—electric dipole and the spin—magnetic quadrupole, are considered as alternative operators for the usual spin—orbit assisted electric-dipole operator in singlet—triplet transitions. It is shown that, although these two spin-dependent spherical operators transform very differently in the three-dimensional rotation group, they contribute comparably to the radiative transition and they must be considered together to preserve the transverse nature of light. For applications to (plane) polarized light spectroscopy in oriented molecular crystals, expressions of these spin-dependent spherical operators are found in terms of the quadratic products of the Cartesian coordinates x, y, and z with the spin components Sx, Sy, and Sz. The explicit forms of the transition operators for propagation of light and polarization along x, y, or z directions are tabulated. The selection rules of the coordinate part of these operators are illustrated for the D6 point group. The selection rules of the spin part are given for the ``uncoupled'' spin quantized with respect to the principal molecular axis or with respect to an external magnetic field. General formulas for deriving the angular distribution of intensity are given in terms of rotation matrices. Specific formulas for the angular dependence and polarization of the ``direct'' phosphorescence from each and all of the three triplet components via this mechanism are derived. These are expressed in terms of the cosine of Euler angles [open phi] and ψ and functions of reduced rotation matrices. The explicit values of these functions of reduced rotation matrices in terms of the Euler angle θ are tabulated. The tabulation is extended for possible use in transitions involving symmetry-adapted spin wavefunctions and transitions in systems with any (lower than axial) point-group symmetry.
Cavity Concept in Dielectric Theory
Authors: Linder Bruno , Hoernschemeyer Donald
Published: January 2005

A statistical formulation is presented for the reaction and cavity-field response functions of an isotropic nonpolar substance. It is shown that the reaction-field approach can be made consistent to a good approximation with statistically calculated fields by a reasonable choice of the cavity radius a. The cavity radius is a complicated function of density, temperature, and molecular parameters and, in first approximation, is given by expression a−3= ∫ 0∞3r−4ρ(r)dr,where ρ(r) is the radial distribution function. The value of a3 computed for liquid Xe from x-ray scattering data according to the latter formula is found to be equal to ½σ3, where σ is the Lennard-Jones collision diameter; this value is in very good agreement with the Böttcher—Onsager value for a3 calculated on the basis of the macroscopic dielectric constant and polarizability of the free molecule. The dielectric and statistical reaction and cavity-field functions are compared and discussed.
Thermodynamics of M-Center Formation
Authors: Zahrt John D. , Scott Allen B. , Coker E. H.
Published: January 2005

The equilibrium between F centers and M centers in additively colored KCl was studied at temperatures between 60° and 130°C. The M-center concentration at equilibrium varied approximately as the square of the F-center concentration, verifying the stoichiometric equation: 2F=M.At 60°C, the equilibrium constant was 1.7×10−19 cm3. ΔH°=−4.1 kcal/mole, and ΔS°=−98 cal/deg, for the standard state one center/cm3. ΔS° agrees with that calculated from the configurational entropy, i.e., R ln(6/N), where N is the concentration of negative-ion sites.
Benzene-d6 Photosensitized Isomerization of 2-Butene
Authors: Sigal Paul
Published: January 2005

Further study of the benzene-d6 photosensitized isomerization of 2-butene indicates that the intersystem crossover process is either collision dependent or has a rate constant which is a function of the vibrational level of the singlet species.
Cyclohexanethiol and 2,4-Dimethyl−3-thiapentane: Molecular Vibrations, Conformational Analyses, and Chemical Thermodynamic Properties
Authors: Scott D. W. , Crowder G. A.
Published: January 2005

Statistical thermodynamic treatments were made of the conformational energetics of the cyclohexanethiol and 2,4-dimethyl−3-thiapentane molecules. For cyclohexanethiol, there are 24 conformations that arise from the chair—skew-boat and equatorial—axial equilibria of the frame and different orientations of the thiol group. The equatorial-chair conformation is the most stable; the axial-chair conformation has about 1.1 kcal/mole greater energy. For 2,4-dimethyl−3-thiapentane, six conformations could arise from different orientations of the isopropyl groups; however, only a d—l pair that involves no methyl—methyl interaction between the isopropyl groups has appreciable stability. Vibrational assignments needed for each compound were obtained by interpreting the molecular spectra for the vapor, liquid, and crystal states with the guidance of force-constant calculations. Tables of the chemical thermodynamic properties were compiled.
Geometry and Vibrational Spectra of the Alkaline-Earth Dihalides. I. MgF2
Authors: Mann D. E. , Calder G. V. , Seshadri K. S. , White David , Linevsky M. J.
Published: January 2005

The infrared spectra of vaporized MgF2 isolated at liquid-hydrogen temperatures in both argon and krypton matrices are reported. Six major regions of absorption have been found, viz., 240, 450, 477, 483, 740, and 840 cm−1. On the basis of corresponding matrix spectra of nMgF2, 26MgF2 and a 1:1 mixture of nMgF2–26MgF2, it is possible to demonstrate unequivocally that the 240-, 477-, 740-, and 840-cm−1 absorptions are due to molecular species containing one magnesium atom. The 450- and 483-cm−1 features are clearly attributable to polymeric species. From the magnitude of the measured isotope shifts the 740-cm−1 and 477-, 240-, and 840-cm−1 absorptions have been assigned to MgF and v1, v2, v3 of MgF2, respectively. The observation of v1 shows that MgF2 is bent. The higher resolution and precise frequency measurement employed in this work have been used to calculate the apex angle. This lies on the range 145° to 160° the most probable value being 150°.
Statistical Aspects of Autoionization Lifetimes
Authors: Klots Cornelius E.
Published: January 2005

Long-lived, parent-molecule negative ions can serve as convenient prototypes for the autoionizing species frequently postulated in radiation chemistry. Recent measurements of the rates of formation and autoionization of a number of such ions are discussed. The assumptions involved in the derivation of electron affinities from the measurements are found to be identical with those inherent in unimolecular decomposition theory. Implications for photo- and radiation chemistry are noted.
Infrared Spectrum and Internal-Rotation Barrier of Nitroethylene
Authors: Loos K. R. , Günthard Hs. H.
Published: January 2005

The infrared spectra of nitroethylene-d0 and 1-nitroethylene-d1 have been obtained in the vapor phase over the range 4000–70 cm−1. All fundamental frequencies have been observed and the NO2 torsion was located at 103 and 95 cm−1 for the d0 and d1 isotopes, respectively. The barrier to internal rotation has been calculated to be 6510±280 cal/mole for H2CCHNO2 and 5960±280 cal/mole for H2CCDNO2 using the ``semirigid'' model with a V2(1-cos2φ) potential. A normal-coordinate analysis has been carried out in order to clarify the nature of the fundamental vibrations. It shows that there is considerable mixing between the symmetry coordinates in the normal modes. The existence of this interaction indicates that the common assumption that the torsional mode is decoupled from the other modes of the same symmetry, the semirigid model, does not appear to be valid here. The effect of this on the barrier height is discussed.
Energy Transfer in Solution between UO22+ and Eu3+
Authors: Kropp John L.
Published: January 2005

Energy transfer from UO22+ to Eu3+ has been observed in several solutions. Quantitative data for the quenching of UO22+ fluorescence at various [Eu3+] and the corresponding build up of Eu3+ fluorescence has been obtained in D2O solutions. Rate constants for the transfer of energy from UO22+ to Eu3+ are derived, the value is determined to be about 107M−1·sec−1. This value is less than the diffusion-controlled reaction rate. The low value can be related to mutual ion—ion repulsion.
Thermal-Diffusion Column Transport Coefficients for Isotopically Substituted Methane
Authors: Rutherford W. M.
Published: January 2005

Thermal-diffusion column transport coefficients were measured for isotopically substituted methane in a 7.32-m hot-wire column. At wire temperatures of 320° and 480°C, measured values of the convective and diffusive remixing coefficients were in agreement with values obtained by numerical integration, specifically for methane, of the equations of the theory of the thermal-diffusion column. Measured values of the initial transport coefficient were consistent with the thermal-diffusion factor measurements of Nier.
On the Perturbation—Variation Calculation of Spin—Spin Coupling Constants
Authors: Schaefer Jacob , Yaris Robert
Published: January 2005

The use of the perturbation—variation method to calculate spin—spin coupling constants is examined. It is shown that the use of trial functions with δ-function singularities leads to ambiguous results (this ambiguity is explicitly exhibited for HD). With the ambiguity removed a calculation of JHD is performed using correlated ground-state and trial wavefunctions. It is concluded that convergence is slow.
Flash Photolysis and Time-Resolved Mass Spectrometry. I. Detection of the Hydroxyl Radical
Authors: Meyer Richard T.
Published: January 2005

Improved techniques of flash photolysis and time-resolved mass spectrometry have been applied for the first time to the detection of a transient, reactive free radical. The hydroxyl radical has been observed simultaneously with the formation of water in the nitrogen dioxide sensitized reaction between hydrogen and oxygen. In addition, the effect of added oxygen and total pressure upon the induction periods for hydroxyl formation is correlated with the temperature dependence of concomitant flash heating. It is concluded, in agreement with the literature, that an increase in flash intensity leads to reaction acceleration through an increased initial supply of oxygen atoms.
Theory of Collision-Broadened Ion Cyclotron Resonance Spectra
Authors: Beauchamp J. L.
Published: January 2005

A formalism for calculating collision-broadened ion cyclotron resonance spectra is developed in detail. The Boltzmann transport equation describing the time variation of the arbitrary function of ion velocity X (v) is extended to include resonant charge transfer. Then with X (v) =v and X (v) =v2, equations describing, respectively, the velocity and energy of an average particle are developed. The solution of these equations is used to obtain the power absorption of the ions from the observing radio-frequency electric field.

The effects of collisions are treated in terms of specific ion—molecule interactions. The equations of motion for a mixture of ions, A and B, are coupled by the collision term which accounts for the charge-transfer process A++B⇄A+B+. As numerical examples the collision frequencies are evaluated for the rare gases and used to calculate absorption spectra for Ar+ in Ar and mixtures of He and Ne isotopes. The formalism permits the straightforward examination of the effects of electric-field strength, pressure, and temperature on the line shapes.
Optical Spectra of Orientationally Disordered Crystals. I. Theory for Translational Lattice Vibrations
Authors: Whalley E. , Bertie J. E.
Published: January 2005

There is a class of crystals in which the molecules are arranged on or near regular positions in space, but are irregularly oriented. The irregular orientation of the molecules frequently perturbs only slightly the translational lattice vibrations of the crystal, that would be perfectly periodic if the irregular orientation were absent. For a first approximation, then, the crystal can be considered to have mechanically regular vibrations. In particular, any normal vibration can be described in terms of a wave vector k that is the wave vector of the dominant Fourier component of the vibration. The irregular orientation of the molecules will cause the dipole-moment change due to a displacement of a particular molecule to depend in magnitude and direction upon its own orientation and upon the orientation of its neighbors. The crystal is thus in a sense electrically irregular.

The theory of the optical spectra due to the translational lattice vibrations of these mechanically regular, electrically irregular crystals is discussed assuming that the translational and rotational vibrations are not coupled. All the vibrations are active in both infrared and Raman spectra, and to a first approximation, for a crystal with only one nearest-neighbor central interaction, the intensity of absorption or of Raman scattering by any particular normal vibration of the crystal that is active only because of the irregularity of the orientations (there may, of course, be vibrations that are active in the absence of electrical irregularity) is proportional to the square of its frequency. For more realistic models, the relationship is more complicated. The optical spectra of these crystals provides, therefore, information about the spectrum of lattice vibrations. In particular, features in the optical spectrum probably arise mainly from features in the vibrational spectrum, and it may be possible to identify corresponding features.

In addition, these crystals are intermediate between perfect crystals, which are mechanically and electrically regular, and vitreous solids, which are mechanically and electrically irregular. The study of their spectra should therefore provide an approach to understanding the spectra of vitreous phases.
Radiative Recombination of Chlorine Atoms in Shock Waves
Authors: Carabetta Ralph A. , Palmer Howard B.
Published: January 2005

The equilibrium emission behind shock waves in Cl2–Ar mixtures has been measured as a function of temperature, wavelength, and atom concentration. The emission spectrum has been recorded at 2200°K and the absolute rate of emission has been measured in two regions of the visible spectrum. The emission is found to behave in adequate accordance with a theory based on calculation of the equilibrium concentrations of molecules in excited states. However, it is necessary that the radiative lifetime of the 3Π0+u state be considerably shorter than previously thought. It appears to be a few microseconds, i.e., of the same order as the 1Π1u.
Irreversibility in Finite Quantum-Statistical-Mechanical Systems
Authors: Hobson Arthur
Published: January 2005

It is shown that the usual proofs of the quasiperiodicity of isolated, finite quantum-statistical systems, previously thought to be general proofs, are in reality based on the special case of a discrete array. Quasiperiodicity is demonstrated for the analogous special case (the discrete distribution) in classical statistical mechanics. The density-operator formalism is set up for the case of a continuous array. The question of the possibly irreversible behavior of isolated, finite quantum-statistical systems with continuous arrays is investigated. An argument is given indicating that such systems generally behave irreversibly. The situations in classical and quantum statistics then appear to be entirely analogous, since it is well known that isolated, finite classical-statistical systems may, in the case of a continuous distribution (the analog of a continuous quantum-statistical array), behave irreversibly.
Electron Spin Resonance of Manganese in Borate Glasses
Authors: de Wijn H. W. , van Balderen R. F.
Published: January 2005

The ESR spectra of Mn2+ ions have been observed in borate glasses of the composition (MnO)x(B2O3+0.04 K2O)1−x with x from 0.001 up to 0.030. For small concentrations of Mn2+ the central fine-structure transitions (M = +½↔—½), although broadened by the random orientation of small noncubic crystalline fields, show a well-resolved hyperfine structure. In addition to the Δm=0 transitions, ``forbidden'' Δm=±1 have been observed. The spectra prove that the coordination of the O2− ions around the Mn2+ ions is mainly cubic, but that small deformations of the cubic symmetry exist. The deformations vary from ion to ion, and range up to average values of the order of 5% in the interionic distances and 10 deg in the angles. The discussion has been based on a spin Hamiltonian involving an isotropic g factor, fine structure term D, and hyperfine structure term A. The line positions have been calculated up to the third order in D and A. The numerical results are: g=2.002±0.002, | A | /hc= (87–2)×10−4 cm−1, and DAv/hc= (89±10)×10−4 cm−1, the latter value representing an average over all deviations from cubic symmetry.
Structure of Liquids. IV. Direct Correlation Functions of Liquid Argon
Authors: Mikolaj P. G. , Pings C. J.
Published: January 2005

Recently acquired x-ray diffraction data from 13 states of fluid argon were used to compute the direct correlation function, C(r). This function is found to be definitely short range, particularly when compared to the conventional radial distribution function at the same state. Using experimental data and knowledge of the radial distribution function, estimates were also made of the state-dependent behavior of C(r) for radii less than the atomic radius. The median location of the first zero of C(r) is r0=3.39±0.06 Å; this value tends to increase with increasing temperature and with decreasing density. The median location of the maximum in C(r) is rmax=3.84±0.07 Å; this value shows a slight but inconclusive tendency to increase with increasing temperature and to decrease with increasing density. The height of the single maximum varies from 0.8 to 1.3 over the range studied; while there was no observable temperature effect, the peak height tends to decrease as the density is increased. The computed direct correlation functions were used in conjunction with previously calculated radial distribution functions in order to test fundamental hypotheses underlying the derivations of the Percus—Yevick and convoluted-hypernetted-chain integral equations, with the conclusion that these equations have systematic density-dependent defects. The intermolecular potential function was estimated by zero density extrapolation of a potential computed from the PY equation, with results in good agreement with currently accepted values for the pair potential.
Polarizability of the Hydrogen Molecule
Authors: Kol/os W. , Wolniewicz L.
Published: January 2005

A variation perturbation method has been employed to calculate the static dipole polarizabilities of the hydrogen molecule. The wavefunction was represented by an expansion in elliptic coordinates including the interelectronic distance. A 54-term expansion was used for the zero-order wavefunction and 34 terms for the first-order corrections. The polarizabilities computed for several values of the internuclear distance (0.4≤R≤4.0) were averaged for various vibrational and rotational states of H2, HD, and D2. The results are in a satisfactory agreement with the experimental values.
Energy Levels of Sm3+ in LaF3
Authors: Rast H. E. , Fry J. L. , Caspers H. H.
Published: January 2005

The fluorescence and infrared absorption spectra of Sm3+ in single crystals of LaF3 have been observed and analyzed. Fluorescence was observed in the spectral range of 0.55 to 1.1 μm, and absorption in the region of 0.9 to 10 μm. The intermediate coupling free-ion energy levels of the 6FH multiplets have been calculated from energy matrices including the effects of all the quartet and doublet states of the f5 configuration. The experimentally determined barycenters of the crystalline Stark components have been fitted to a ``free-ion'' calculation of the energy levels in terms of the Slater integrals F2, F4, F6, and spin—orbit parameter ζ4f. A root-mean-square deviation of 12 cm−1 was achieved between the calculated and the observed energies. The wavefunctions are tabulated for Sm3+ in LaF3. Values of F2=356.3 cm−1, F4=55.77 cm−1, F6=4.829 cm−1, and ζ=1151 cm−1 are found to give the best over-all agreement between the observed and the calculated energy levels.
Semiempirical Calculation of Bond Lengths in Cyclopentadienyl Ligands
Authors: Randić M. , Trinajstić N.
Published: January 2005

The main idea of this paper is that in those sandwich molecules where experiment shows that there is a twofold axis of symmetry in the C5H5 part of the sandwich molecule, a reasonable and simple explanation of bond lengths can be given in terms of the flow of electrons from the occupied π molecular orbital of the five-membered ring onto the central metal atom and also from the central metal atom onto the unoccupied molecular orbitals of the ring. By using simple Hückel theory and the assumptions that cyclopentadienyl ligands may be considered as independent systems the bond lengths in several cyclopentadienyl rings in cyclopentadienyl—metal complexes are calculated by considering various donor—acceptor relationships between the ligand and the metal. The results show how bond lengths may be used to give some insight into the bonding in these complexes. There is good agreement between calculation and experiment for several molybdenum complexes indicating that the approach is essentially correct. In other cases the agreement is less satisfactory, showing that different assumptions about the bonding possibly need be considered.
Intermolecular Forces in Globular Molecules. IV. Additive Third Virial Coefficients and Quadrupolar Corrections
Authors: Storvick T. S. , Spurling T. H. , De Rocco A. G.
Published: January 2005

Additive third virial coefficients for a spherical-shell potential have been computed for varying shell sizes corresponding to r0*=1.4, 1.6, 1.8, 2.0, 2.5, 3.0, and 4.0, and a temperature range 0.4<T*<10.0. In addition, the first quadrupolar correction has been computed for this model. The resulting expressions are compared with experiment for seven globular molecules employing force constants deduced independently from second virial data alone. For the simpler substances the spherical-shell and Lennard-Jones (12–6) models are about equally useful in representing the data. For the truly globular molecules, however, the spherical-shell potential is a marked improvement, although Cadd alone is insufficient to represent the data. Corrections for nonadditive forces are discussed briefly and qualitatively. An argument is made to show that such corrections to spherical-shell results for globular molecules can be expected to improve the fit, whereas similar corrections to Lennard-Jones (12–6) may not. For the case of benzene we have estimated the quadrupolar correction to Cadd and shown that its inclusion seems necessary if three-body forces are to improve agreement with experiment.
Infrared Absorption Spectra of the 18O-Labeled Acetylacetonates of Cr(III) and Mn(III)
Authors: Pinchas S. , Silver Brian L. , Laulicht I.
Published: January 2005

The 18O-induced isotopic shifts of the Cr(III) and Mn(III) acetylacetonate (of over 90 at % 18O) infrared absorption bands were measured in the 400–1650-cm−1 region. The hitherto accepted assignments of these bands are discussed in the light of these measurements. It is found that the band at about 1520 cm−1 is due to C=C stretching while that at about 1570 cm−1 has a C=O stretching character. The ∼1425-cm−1 band must be due to the asymmetrical CH3 bending while the one at 661 cm−1 probably belongs to an out-of-plane deformation and that at 590 cm−1 to an M—O stretching.
ESR Spectrum and Structure of O2F
Authors: Adrian Frank J.
Published: January 2005

The electron spin resonance (ESR) spectrum of the dioxygen monofluoride radical (O2F) has been observed in an argon matrix at 4.2°K. The radical was produced by the reaction of O2 with fluorine atoms obtained from the photolytic decomposition of F2. Computer analysis of the spectrum gave the following values for the components of the g factor and fluorine hyperfine-splitting tensors: g1=2.0080, g2=2.0008, and g3=2.0022; A1/h=±288.4, A2/h=∓141.1, and A3/h=∓39.2 Mc/sec. Theoretical considerations suggest that A1 is negative, and that Axis 1 lies along the O–F bond, Axis 2 is perpendicular to the molecular plane, and Axis 3 lies along the O–O bond. The ESR spectrum of O2F was found to contain normally ``forbidden'' lines in which the electron spin transition is accompanied by a nuclear spin flip. These lines may be responsible for some of the complicated changes in the appearance of this spectrum which accompany changes in temperature and matrix. By using the experimental value of g3 to evaluate a critical parameter in a semiempirical molecular-orbital treatment of O2F, values were obtained for the charge distribution and bond order in this radical. The results agree with conclusions drawn from infrared spectroscopy, and suggest that this radical is stabilized by resonance which permits the fluorine to form a weak O–F bond without any loss of the O–O bond strength.
Influence of Torsional Motions on the Quadrupole Resonance Lines of 14N in Piperazine
Authors: Barton B. L.
Published: January 2005

The widely different relaxation times and frequency shifts, observed for the quadrupole resonance lines of piperazine, are treated theoretically as the effects of small-amplitude torsional motions undergone by the molecule. The torsional frequencies and the ratio of relaxation times are calculated.
Infrared Spectrum of Europium Acetylacetonate
Authors: Liang C. Y. , Schimitschek E. J. , Stephens D. H. , Trias J. A.
Published: January 2005

The infrared spectrum of europium acetylacetonate has been observed from 4000 to 200 cm−1 and a normal-coordinate calculation for the in-plane vibrations of the 1:1 single ring complex has been carried out. The Eu–O stretching frequencies are found to be in the region from 400 to 200 cm−1 and the Eu–O stretching force constant is estimated to be about 1.43×105 dyn/cm. The interpretation of the spectrum is discussed generally.
Scattering of X Rays by Liquids with Complex Molecules. The Choice of the Molecular Center
Authors: de Vries Adriaan
Published: January 2005

The formula for the intensity of the radiation scattered by a liquid with complex molecules is discussed. It is shown that the choice of the molecular center is not arbitrary but determined by the condition that the distance between two molecular centers should have no influence upon the orientation of the molecules concerned. Also it is pointed out that Fourier inversion of the intensity formula is not always possible.
Anomalous Specific Heat and Viscosity of Binary van der Waals Mixtures
Authors: Deutch J. M. , Zwanzig Robert
Published: January 2005

This article investigates the behavior of several properties of a model binary van der Waals mixture near the solution critical point. The behavior of the heat capacity is determined from an exact analysis of the partition function. For the shear and bulk viscosity, the time dependence of the currents appearing in the time correlation function formulas is determined from linearized hydrodynamic equations. For the heat capacity and the shear viscosity the results of this model are identical to those originally obtained by Fixman by a different procedure. Comparison is also made with the results obtained by Zwanzig and Mountain for these quantities in a one-component van der Waals system near the liquid—vapor critical point. One finds, in qualitative agreement with available experiments, that the shear viscosity of a binary mixture diverges at the critical point.
Infrared Lattice Vibrations of KNiF3 from Reflection Data at 300° and 90°K
Authors: Balkanski M. , Moch P. , Teng M. K.
Published: January 2005

Elementary group-theoretical considerations predict three infrared-active vibrational modes in KNiF3 which crystallizes with the cubic perovskite structure. Reflectivity measurements at 300° and 90°K, in the spectral range extending from 80 to 600 cm−1, allow the observation of the above three modes corresponding to the wavenumbers: 148, 244, 441 cm−1 for T=300°K and 144, 248, 452 cm−1 for T=90°K. In addition, we observe a side band near 500 cm−1 at 300°K and 520 cm−1 at 90°K.

Assuming that the dispersion can be interpreted in terms of independent damped oscillators, the reflection data have been analyzed using both the Kramers—Kronig relationships and the classical dispersion formula. The intensity of the extra band and some feature of the vibrational absorption spectrum in the visible range suggest that this extra band may arise from a one-phonon process.

The oscillator parameters associated with each observed mode and those deduced from the two methods of analysis are in good agreement with temperature-dependence considerations.
Ionization Cross Sections of the Elements Calculated from Mean-Square Radii of Atomic Orbitals
Authors: Mann Joseph B.
Published: January 2005

Relative ionization cross sections for single ionization by electron impact on free gaseous atoms have been calculated by utilizing a summation of the mean-square orbital radii of outer electrons. A previous calculation of the cross sections by Otvos and Stevenson was in only fair agreement with experimental data due to the use of incorrect mean-square radii, and to the method of summation of electron-shell contributions to the total cross sections. Hartree—Fock calculations of orbital wavefunctions have been carried out for all of the elements. Mean-square radii of atomic orbitals from the Hartree—Fock calculations were corrected approximately for relativistic effects. The ionization cross sections obtained from the summations were normalized at argon and compared with experimental values. The computed maximum cross sections are a considerable improvement over past theoretical values.
Hyperfine Structure in the Solution ESR Spectrum of Di-tert-butyl Nitroxide
Authors: Faber Roger J. , Markley Finley W. , Weil John A.
Published: January 2005

Isotropic splitting constants for 14N, 15N, 13C, and 17O nuclei present in natural abundance in di-t-butyl nitroxide have been measured by electron spin resonance, using benzene solutions at room temperature. The proton hyperfine structure was not resolved, but was estimated from best-fitting computer-simulated spectra. Comparison of computer-simulated single- and double-substitution 13C satellites with the experimental satellites indicates that only six of the eight positions contribute to these satellites.
General Second-Order Perturbation Treatment of σ Spin Densities in Planar, Conjugated π Radicals
Authors: Malrieu Jean-Paul
Published: January 2005

We calculate σ spin density in π planar radicals by a full second-order perturbation treatment, the correlation potential being taken as the perturbation Hamiltonian. This paper allows a clear discussion of the way π inner-shell spin densities contribute to aH splittings and of the type of approximations implied in the use of the simple McConnell relationship with improved π spin densities. We show that second-order contributions to Q constants are at least about one-fourth of the first-order contribution and come from σσ diexcited states. Some new contributions to the ``charge effect'' appear, which are of the same order of magnitude as the previous Colpa—Bolton effect.