bluuebunny/crossref_metadata_2025 huggingface dataset:
Finite Nuclear Mass Effects on the Centrifugal Stretching Constant in H35Cl
Authors: Herman R. M. , Asgharian A.
Published: January 2005

It is suggested that the existing discrepancy between the experimentally determined H35Cl energy-level constant Y02 and its value, as predicted through Dunham's theory, represents a deviation from Born—Oppenheimer behavior. Relationships between 1Σ-state molecular energy-level constants, corrected to take account of deviations from Born—Oppenheimer behavior, are then used in a recalculation of the Dunham theoretical value for Y02. The discrepancy is not removed through the present calculation, however. The fractional difference between the Dunham values with and without corrections for deviations from Born—Oppenheimer behavior is −0.29×10−3, as opposed to the fractional difference (0.649±0.065)×10−3 between the experimental and (uncorrected) Dunham theoretical values. The importance of the present calculation to an accurate spectroscopic determination of the velocity of light is indicated.
Iterative Mapping of Phase-Shift Space to Potential Space in Molecular-Beam Scattering
Authors: Olson R. E. , Mueller C. R.
Published: January 2005

An iterative mapping procedure has been developed which correlates variations in the scattering phase shifts to intermolecular potential changes. Although a point-by-point potential is generated, a six-parameter potential form has been assumed for convenience in the generation of the phase shifts via the JWKB approximation. The method has been texted using standard phase shifts to ascertain the inaccuracies to be expected with potential variations. From the calculations, the accuracy of the potential points generated in the mapping is limited only to the technique used to fit them and is found independent of the bowl shape.
Electronic Spectrum of Ethylene Single Crystal; Search for the Olefin Mystery Band
Authors: Lubezky A. , Kopelman R.
Published: January 2005

Ethylene single crystals have been grown as uv specimens. The near-uv spectrum (2000–2500 Å) consists of a number of bands quite analogous to the π—π* (N–V) transition in the gas-phase molecule. No drastic perturbations are observed. No additional electronic transition (e.g., CH*—π, n—π*) is observed in this region, in spite of the relaxation of selection rules in the crystalline site (Ci). Thus, if the ``mystery'' band (6 eV) exists at all, its excited state is most likely either a triplet state or a Rydberg-type state (or a combination of both).
Kinetic Theory of Dense Fluid Mixtures. II. Solution to the Singlet Distribution Functions for the Rice—Allnatt Model
Authors: Wei Ching Cheng , Davis H. Ted
Published: January 2005

The Rice—Allnatt theory of dense fluids has been extended to binary mixtures. It is shown that the linearized Rice—Allnatt equation for the singlet distribution function is a linear integral equation of the second kind. Moreover, it is shown that a simple modification of the Rice—Allnatt equation, the modification being of the same order of approximation as those utilized in deriving the equation, results in a linear equation admitting mass, momentum, and kinetic energy as homogeneous solutions, thus allowing the local hydrodynamic variables to be completely specified by the zero-order solution to the integral equation.

The singlet distribution functions are solved, and the binary diffusivity, thermal diffusion ratio, and kinetic contributions to thermal conductivity and viscosity are obtained.
On the Absence of Isotope Effects in the Absence of Force Constant Changes
Authors: Stern Marvin J. , Wolfsberg Max
Published: January 2005

Calculations have been carried out to demonstrate that there is usually very little quantum-mechanical contribution to an isotope effect on a rate (equilibrium) in the absence of force constant changes, between reactant and transition state (product), at the position(s) of isotopic substitution. The usual upper limits to the deviations of such secondary isotope effects [(k1/k2)(ν1L‡/ν2L‡)−1 or K1/K2] from unity, at room temperature, have been estimated to be 1.5% per α deuterium, 0.2% per β deuterium, and even less for heavy-atom isotopes or for deuteriums further removed from the reaction site. Some exceptional circumstances under which there may be large ``no-force-constant-change'' isotope effects have been found. However, usually it is quite proper to interpret the existence of sizable quantum-mechanical isotope effects as indicative of force constant changes at the isotopic position(s).
Discussion of the Destruction of Diatomic Bonds in Molecular Crystals by Pressure
Authors: Raich J. C.
Published: January 2005

In this paper a model of metallic binding proposed by Raich and Good is applied to estimate the pressure necessary to destroy the directional character of the chemical bonds in molecular crystals.
Simplified Considerations of the Onsager Symmetry in the General Diffusion Equation of Nucleation Theory
Authors: Lothe Jens
Published: January 2005

The general diffusion equation describing the time development of an ensemble, such as naturally encountered in nucleation, is simply the master equation of irreversible statistical mechanics, and it is well known that the coefficients obey the Onsager symmetry. However, the standard proofs of the symmetry are quite involved and consider the entire ensemble as one system with a huge number of degrees of freedom. It is shown that, with a proper definition of drift velocity, one can use the simpler method of considering the fluctuations in only one element of the ensemble as a function of time, just as one does in the simpler phenomenological linear theory of irreversible thermodynamics. Finally, the connection between the diffusion coefficients for the ensemble and macroscopically observable regression rates is briefly discussed.
Resonances in Inelastic Electron Scattering from H2
Authors: Menendez M. G. , Holt Helen K.
Published: January 2005

Resonance structure in the electron scattering from H2 has been observed in two inelastic channels corresponding to excitation to the first and second vibration levels of H2(X1Σg+). An overlapping of resonances due to at least two H2− states lying between 11 and 13 eV is apparent. The structure in the inelastic channels is compared to the observed resonance structure in the transmission channel. The resonances are found to affect the inelastic channels more strongly than the transmission channel. The excitation function for direct vibrational excitation to the v=1 level was measured near threshold and found to increase approximately linearly in this region.
Morphology of Ice Dendrites
Authors: Lindenmeyer C. S. , Chalmers Bruce
Published: January 2005

The morphology of ice crystals produced in supercooled aqueous solutions is described. A freely growing ice dendrite in distilled water propagates in the 〈112̄0〉 direction and has the shape of a very thin flat sheet. The first examples of dendrites which grow in an irrational crystallographic direction, best described as 〈112̄Z〉, have been produced in aqueous solutions. The value of Z has been found to vary between 0 and 0.35, depending upon amount of supercooling, the solute, and solute concentration. Growth of ice upon a substrate is of a very complex nature with numerous grain boundaries and a varying orientation relative to the substrate.
On the Activation Energies of Diffusion
Authors: Lielmezs J. , Watkinson A. P.
Published: January 2005

The self-diffusional activation energies of liquid ethane have been calculated. In accordance with Dienes' suggestions, the effective activation energy depends nonlinearly upon the temperature. The Gibbs free-energy change is found to be a strong function of temperature going through a pronounced maximum in the close vicinity of the critical point.
Statistical Thermodynamics of Polymer Solutions. V. Interactions between Geometrically Dissimilar Polymer Chains in a Poor Solvent
Authors: Casassa Edward F.
Published: January 2005

By the standard perturbation technique of Zimm, the second virial coefficient A2 is calculated in the ``double-contact'' approximation for mixtures of two polymers in a single solvent. The two solute molecules are alike chemically, but they differ in size (molecular weight) and/or geometry (in the sense of straight-chain, branched, or closed-ring architecture). From investigation of a number of pairs of species, some tentative generalizations emerge on limiting behavior for A2 small but positive, i.e., near, but above, the theta temperature. If the two polymer molecules have exactly the same structure and differ only in size (e.g., two straight chains of different molecular weight, two ring molecules of different weight), the virial coefficient, as measured by either osmotic pressure or light scattering, is always a monotone function of the proportions of the two components in the mixed solute; but when the models are different, there can exist a range of relative molecular weights of the two solutes within which A2 passes through a maximum as a function of composition. A minimum is never found.
Solvent Effects on Geminal H–H Couplings: A New Method for Determining Signs of Coupling Constants
Authors: Smith Stanford L. , Cox Richard H.
Published: January 2005

Solvent-dependent variations of geminal coupling constants have been observed in styrene oxide, styrene sulfide, 1,4-diphenylazetidinone, and 4-methyl−1,3-dioxolane. These data, in conjunction with previously reported observations, suggest that Jgem always becomes more negative in the absolute sense in solvents having higher dielectric constants. The reaction field of the solvent seems to be the primary causative factor. The magnitude of the effect is shown to depend on the orientation of the dipole moment of the solute molecule with respect to the H–C–H plane. Qualitative theoretical considerations support the existence of a direct correlation between the observed changes and the absolute sign of Jgem and suggest that the magnitude of the change in Jgem also depends on the relative magnitude of the hyperconjugative contribution to Jgem.
Qualitative Aspects of Resonances in Electron—Atom and Electron—Molecule Scattering, Excitation, and Reactions
Authors: Taylor Howard S. , Nazaroff George V. , Golebiewski A.
Published: January 2005

A qualitative description of various types of resonant states of atoms and molecules is given. The classification is seen to be useful in explaining and discussing experimental phenomena. It is found that, as in nuclear physics, atoms and molecules exhibit both single-particle and core-excited resonant states. A general quasistationary method is presented which can be used to calculate the energies of the resonant states from intuitively selected trial functions. The Feshbach technique is used for formal justification of this method, and the relation of the quasistationary method to other published resonance calculations is discussed. Experiments are suggested to test the ideas presented.
ESR Study of Irradiated Pyridine
Authors: Tsuji Kozo , Yoshida Hiroshi , Hayashi Koichiro
Published: January 2005

Pyridine and pyridine-d5 were irradiated with electrons in the solid state at −196°C. After the irradiation, ESR spectra were measured over a temperature range from −196°C to their melting points. For pyridine, a triplet spectrum (separation of 30 G) with a quartet substructure (separation of 4.3 G) was observed at −196°C. It was assigned to cation radicals[Complex chemical formula]The triplet spectrum disappeared at elevated temperatures and an eight-line spectrum (separation of 12 G) was observed at −90°C which was assigned to free radicals[Complex chemical formula]After the disappearance of these radicals at −65°C, a singlet spectrum (ΔHmsl of 15 G) was observed and disappeared at about −50°C. It was assigned to pyridyl radicals. The radicals produced in the irradiated pyridine-d5 had the same nature as those observed in irradiated pyridine.
Quantum Theory of Interference and Polarization of Stark—Zeeman Lines in Molecules
Authors: Chiu Ying-Nan
Published: January 2005

With special emphasis on the application to transitions between the rovibronic states of molecules, general formulas for the polarization and for the intensity inclusive of interference of multipole emission between Stark—Zeeman levels are derived. The derivation makes use of angular momentum method for molecules and irreducible spherical tensor operators for the interaction of radiation and matter.

Results are made applicable to linearly polarized radiation with any arbitrary orientation (specified by three Euler angles) of the polarization and propagation vectors with respect to the space-fixed axes. These higher multipole interference effects in a resolved molecular Stark—Zeeman line serve as an extension of the pioneer works on atomic Zeeman transitions of Van Vleck and others. The formulas are tabulated in terms of their dependence on reduced rovibronic matrix elements and their rotational and angular dependence. For the latter dependence that involve products of Clebsch—Gordon coefficients and products of rotational matrices we give explicit examples up to electric and magnetic octopole radiation. Rotation matrices of the third rank, some of which are needed in transitions involving octopole, are computed and tabulated. For the former dependence, general line strengths of linear molecules and rovibronic matrix elements are given with all dependence on rotational wavefunction evaluated, for any Hund's Case a states inclusive of the hypothetical Σ2s+1Ω±(a) states, singlet Case b states, and doublet Σ±(b) states. For diatomic molecules of half-integral spin (even multiplicity), general Case a and b state wavefunctions are constructed, their symmetry under inversion and selection rules are derived. Specific examples are given of the magnetic-dipole—electric-quadrupole radiation in ∏2,412(a)−∏2,412(a) and ∑2±−∏2,434(a) transitions, and of the electric-dipole—magnetic-quadrupole—electric-octopole radiation in ∏2,4,632(a)−∏2,4,632(a) transitions. Attention is called to the existence of cross terms which make the formulas dependent on different Λ-doubling components and hence on the ``Kronig reflection'' symmetry specified by a (±) sign.
Theoretical Studies of Transannular Interactions. II. The Triplet States of the Paracyclophanes
Authors: Hillier Ian H. , Glass Leon , Rice Stuart A.
Published: January 2005

The triplet transition energies of benzene dimers at different inter-ring separations have been calculated, and the results used to interpret the phosphorescence spectra of the paracyclophanes. The transannular interaction is reflected in the energy of both the ground and excited states of the dimer. In the calculation of the latter, the configuration interaction of neutral-exciton and charge-transfer states is taken into account. The results of the calculation, which predict the lowest dimer state to be of benzene 3p parentage, are discussed in relation to the phosphorescence of [2,2] and [4,4] paracyclophane, which spectra are also reported in this paper. Good agreement between the calculated and observed transition energies is found.
Analysis of the v1 and v2 Fundamentals in Deuterium Sulfide
Authors: Miller R. E. , Eggers D. F.
Published: January 2005

The fundamental infrared spectra of gaseous deuterium sulfide have been measured with several grating instruments. The spectra have been analyzed, with the aid of computer programs, to give rotational constants and band centers. For the latter we find v1=1896.38 and v2=855.5 cm−1; very little evidence of v3 was detected. Both bands show a strong intensity anomaly, similar to that of hydrogen sulfide; a classical centrifugal distortion theory, previously applied to it, accounts for the anomaly in deuterium sulfide also. The effect of centrifugal distortion on the energy levels was computed by the Kivelson—Wilson method.
Physical Properties of Aromatic Hydrocarbons. I. Viscous and Viscoelastic Behavior of 1:3:5-Tri-α-Naphthyl Benzene
Authors: Plazek Donald J. , Magill Joseph H.
Published: January 2005

The torsional creep and creep recovery behavior of amorphous 1,3,5-tri-α-naphthyl benzene was studied, while at metastable equilibrium density, along a specified glassy volume—temperature line, and during isothermal volume contraction below the conventional glass transition temperature Tg. Dilatometric measurements confirmed the conventional Tg to be 69°C. The viscosity measurements of Magill and Ubbelohde were extended from 185°C to below Tg, covering viscosity values from 10−1 to 1016 P. In a region of time scale the mechanical response was found to be dominated by Andrade creep. The retardation spectrum found was over 9 logarithmic decades wide in contrast to reportedly narrow spectra exhibited by other liquids with similar molecular weights. A steady-state compliance Je of 2.6×10−10 cm2/dyn at 64.2°C was measured. Although compliances as low as 8×10−11 cm2/dyn were measured, no time-independent glassy compliance Jg could be ascertained. Free-volume theory was found applicable to all measurements made below 120°C. The occupied volume v0 was deduced to be temperature insensitive.
Ternary Excess Enthalpies in Simple Reciprocal Fused-Salt Mixtures. III. Effect of Ionic Size
Authors: Meschel S. V. , Toguri J. M. , Kleppa O. J.
Published: January 2005

Calorimetric measurements are reported on the enthalpies of mixing in the reciprocal system Ag+–Cs+–NO3−–Cl− at 350° and in the systems Li+–Cs+–Cl−–Br−, Na+–Rb+–Cl−–Br, and Na+–Cs+–Cl−–Br− at more elevated temperatures. These results, when compared with data for the binary systems involved, permit an evaluation of the ternary excess enthalpies.

It is found that these excess enthalpies are all negative and of an order of magnitude consistent with the predictions of quasichemical theory. This suggests that they in the main are due to deviations from random mixing of the ions. The deviations from quasichemical theory show a nearly linear correlation with the difference in ionic size of interchangeable ions in the mixture.
Theoretical Study on Single, Double, and Triple Bonds between Nitrogen Atoms
Authors: Gotoh Haruo , Nagahara Shigeru , Sawai Kisaku
Published: January 2005

Using the general theory proposed by Nagahara the characteristics of the single, double, and triple bonds between nitrogen atoms are studied systematically. The adiabatic potentials formed by these bonds are calculated quite nonempirically by treating the problems as those of electronic structures of hypothetical diatomic molecular systems, =N–N=, –N=N–, and N≡N, where ``open bonds'' represent each suitable atomic orbital associated with all possible spin configurations.
Normal-Coordinate Analyses of Hydrogen-Bonded Compounds. V. The Enol Forms of Acetylacetone and Hexafluoroacetylacetone
Authors: Ogoshi Hisanobu , Nakamoto Kazuo
Published: January 2005

The infrared spectra of the enol forms of acetylacetone, hexafluoroacetylacetone, and their deutero analogs have been measured from 4000 to 70 cm−1. Normal-coordinate analyses have been carried out to estimate the force constants as well as to make theoretical band assignments. The bands at ∼2750, 1460, 945, and 230 cm−1 of nondeuterated acetylacetone have been assigned to the vibrations originating in the O–H···O system. The corresponding force constants are: O–H stretching, 4.00; O–H···O in-plane bending, 0.05; OH···O stretching, 0.30 mdyn/Å. Similar calculations have also been carried out for hexafluoroacetylacetone and its deutero analog. The effect of the substituent on the chelate ring has been discussed by comparing the results obtained for these two molecules.
Effect of Intra-Atomic Correlation on Long-Range Intermolecular Forces: An Exactly Soluble Model
Authors: Kestner Neil R.
Published: January 2005

Using a model system composed of two two-electron atoms whose electrons are bound to the nucleus by Hooke's law forces (of force constant k) but which interact within an atom with one another as A1(x1x2+y1y 2+z1z2), the appropriate crystal-field term to define the components of 1/r12 for this problem (A1 is a constant), the long-range R−6 interaction is exactly −3/(k+A1)R236. Polarizability of these ``atoms'' is 2/(k+A1). Thus the relative contribution of intra-atomic correlation to the R−6 coefficient is related to polarizability calculated with and without correlation (A1=0) as [α(A1≠0)/α(A1=0)]32. This predicts reasonable values for the corrections in Be, He, and even Ne or Ar interactions. The energy through fourth order is also calculated based on a perturbation due to intra- and interatomic correlations,−(3/k32R6)[1−32(A1/k)+(15/8)(A1/k)2+···].Most of the fourth-order energy contributions (proportional to A12) arise from three-electron correlations. The results are also compared with real systems such as He, Be, and Ne.
Stress-Optical Coefficient of Poly-(dimethylsiloxane) Networks
Authors: Nagai Kazuo , Ishikawa Toshihide
Published: January 2005

An expression in matrix form for the optical anisotropy ΔΓ of Kuhn's random link (an equivalent to the stress-optical coefficient) of two-repeat polymers is derived, based on the additivity principle of bond polarizabilities and the rotational-isomeric-state approximation. The interdependence of neighboring-bond rotations is taken into account.

Stress-optical data of poly-(dimethylsiloxane) networks are analyzed by assuming rotational states to be three in number, i.e., trans (T), gauche (G), and gauche prime (G′). It is found that semiquantitative agreement is achieved by assuming EG>0 and Δαe>0. Here EG is the energy of the gauche conformation relative to that of the trans, and Δαe=(α1−α2)Si–O−(α1−α2)C–Si+(α1−α2)C–H is the ``effective'' anisotropy of the Si–O bond. A harmonized choice of values of θ(G) the internal-rotational angle for the gauche conformation, and ω1, the supplement to ∠SiOSi, is needed for interpretation of two items of ΔΓ/Δαe and 〈r2〉/nb2, the latter being the characteristic ratio for the unperturbed dimension. Definite conclusion could not be obtained about to what extent the GG′ conformations for neighboring bonds are suppressed.
Far-Infrared Spectrum and Hindering Potential of Deuterium Peroxide
Authors: Hunt Robert H. , Leacock Robert A.
Published: January 2005

The hindered-rotation motion in the deuterium peroxide molecule is investigated through a study of the far-infrared absorption of the vapor. A 1-m focal-length vacuum grating spectrometer was used to scan the region from 20 to 400 cm−1 with an average resolution of 0.4 cm−1. Seven perpendicular-type hindered-rotation bands characterized by prominent Q branches and unresolved P- and R-branch structure are observed in the spectrum. The band centers are located at 1.88, 42.3, 123.5, 136.8, 206.7, 250.9, and 302.6 cm−1. From these it is determined that, relative to the ground state, the first five excited hindered-rotation states are at 1.88, 208.6, 250.9, 387.7, and 511.2 cm−1.

A theory of internal rotation, developed for an earlier application to the far-infrared spectrum of hydrogen peroxide, is applied to the D2O2 spectrum. In this theory the only internal degree of freedom is the dihedral angle x defining the relative position of the two OD groups. The Hamiltonian is put in the form H (asymmetric top) +H (internal rotation), where the inertial coefficients are functions of the internal angle x. A three-parameter hindering potential is assumed, V(x)=V1cosx+V2cos2x+V3cos3x and the internal-rotation wave equation is solved numerically by computer to obtain the potential parameters which reproduce the internal-rotation energy eigenvalues. In the semirigid model adopted, the effective hindering potentials, bond lengths, and bond angles of H2O2 and D2O2 differ slightly. The data do not yield a complete set of effective bond lengths and angles for D2O2, but the product of the OD distance and the sine of the OOD angle is found to be 0.01 Å smaller than its H2O2 counterpart. As a result, the inertial parameter in the internal-rotation wave equation is 2% larger than is predicted from the H2O2 data. Using this adjusted inertial parameter, the hindering potential V(x)=994cosx+641cos2x+55cos3x provides a good fit to the D2O2 data. For this potential function the cis and trans potential barrier heights are 2470 and 377 cm−1, respectively, and the potential minima are 110.8° from the cis configuration. These parameter values are similar to the corresponding H2O2 values of 2460 cm−1, 386 cm−1, and 111.5°.
Mass-Spectrometric Studies at High Temperatures. XI. The Sublimation Pressure of NdF3 and the Stabilities of Gaseous NdF2 and NdF
Authors: Zmbov K. F. , Margrave J. L.
Published: January 2005

A mass spectrometer has been used to study the sublimation of NdF3 and gaseous equilibria involving NdF3, NdF2, NdF, Nd, BaF, and Ba.

The sublimation pressure of NdF3 is given by the equation logPatm=[−(1.873±0.025)×104/T]+8.03±0.17,where 1383°<T<1520°K. The heat of sublimation of NdF3 at 1448°K is 85.7±1.1 kcal mole−1.

Studies of the equilibria among gaseous species over the mixtures Nd+BaF2 and Nd+NdF3 yielded the heats of atomization of NdF3(g) and NdF2(g) and the heat of dissociation of NdF(g). The standard heat of formation of NdF3(s) is −399±10 kcal mole−1.
Hydroxyl as a Defect of the Perovskite BaTiO3 Lattice
Authors: Coufová Pavla , Novák Josef , Hlasivcová Nataša
Published: January 2005

The hydroxyl group as a defect in inorganic crystals of more complicated structure has thus far received little attention. Most publications deal with water-soluble substances. A more detailed study of the OH group has been made for rutile and anatase single crystals. The present paper investigates the hydroxyl group as anionic part in the Perovskite lattice. Results of ir spectroscopy and chemical analysis are compared with the data obtained on rutile.
Shape of the Coexistence Curve of an Analytical Fluid in the Critical Region
Authors: Barieau Robert E.
Published: January 2005

For an analytical fluid it is shown that the relationship between coexisting phases is given by a3=−a1(1+Ma1),where a3=(ρliq/ρc)−1,a1=(ρgas/ρc)−1,M=−4/15−13(paat/pat)+15(paaaa/paaa),p=(P/Pc)−1,and p with subscripts indicates partial derivatives of p evaluated at the critical point

Coexisting phases as a function of temperature are given by a1=(3Mpatt/paaa)−(−6patt/paaa)12,a3=(3Mpatt/paaa)+(−6patt/paaa)12,where t=(T/Tc)−1.

The reduced rectilinear diameter is given by [(a3+a1)/2]+1=1+(3Mpatt/paaa).

The reduced slope of the reduced rectilinear diameter is given by 12[d(a1+a3)/dt]=3Mpat/paaa.
Acceptor Action of Alkali Metals in II—VI Compounds as Detected by Electron Spin Resonance Techniques
Authors: Dieleman J. , de Jong J. W. , Meijer T.
Published: January 2005

Experiments were performed to decide whether the introduction of alkali metals into II—VI compounds gives rise to the appearance of acceptor levels. In comparison with single crystals, powder samples are in most cases purer and it is much easier to dope powders rapidly and reproducibly. For that reason polycrystalline materials were used in this investigation. In order to obtain a quick and decisive answer to the above-mentioned question we used electron spin resonance techniques to study the influence of alkali metals on the Fermi level position in these samples. This requires at least one indicator, the presence of which can readily be detected by the employed techniques. For that purpose Fe was chosen since the valence change of divalent Fe to trivalent Fe, caused by the introduction of lower-lying acceptors, is easily detected at 77°K due to the appearance of the electron spin resonance signal of the trivalent Fe. The use of Fe as an indicator has the additional advantage of setting an upper limit to the depth of the acceptors introduced by the alkali metals, since the position of the Fe level is quite accurately known.

If no acceptors were introduced the Fe was found to be introduced in the divalent form under the preparation conditions chosen and no resonance of trivalent Fe was detected. The simultaneous introduction of the alkali metals Li or Na in ZnS, CdS or ZnSe caused the appearance of resonances due to trivalent Fe. These results unequivocally show that these alkali metals introduce acceptor levels into the lattices investigated. The upper limit to the acceptor depth (optically, with respect to the valence band) are 1.4 eV for cubic ZnS, 1.3 eV for hexagonal CdS, and 1.1 eV for cubic ZnSe. The increase in the amount of Fe that is converted to the trivalent form by the introduction of the alkali metals on going from ZnS to CdS or ZnSe is discussed and explained in terms of the decreasing energy needed to ionize the electron from Fe centers into the conduction band.
Appraisal of Some One-Center Calculations for the Neon- and Argonlike Series of Molecules
Authors: Hake R. B. , Banyard K. E.
Published: January 2005

The united-atom (UA) method and the self-consistent-field one-center-expansion (OCE) treatment have been applied recently to the study of neonlike and argonlike molecules, namely, HF, H2O, NH3, NH4+, CH4, HCl, H2S, PH3, PH4+, and SiH4. In the present article, the values of physical properties predicted by each method are compared with the corresponding experimental quantities. For each molecule, comparisons with experiment have been made for the molecular energy, theoretical bond lengths, ``breathing'' force constants, and, for NH3 and PH3, the proton affinities. The radial density distribution of electrons, determined by us from the published OCE wavefunctions, has been used to calculate the coherent x-ray scattering factor for the gaseous state of each molecule. The electron densities were also used to determine the purely diamagnetic contribution χr to the total molar magnetic susceptibility. A comparison was made with the corresponding UA results and with the available experimental quantities. From the trend shown by the relationship between the theoretical and ``experimental'' values for χr, it was possible, for a molecule with Td symmetry, to suggest a range of values for the diagonal components (gjj″) of the electronic contribution (g″) to the molecular rotational gyromagnetic tensor (g). Hence, for SiH4, it was suggested that −1.48 < gjj″ < −1.31. No experimental value for this quantity is known by the authors.

Although it is seen that the OCE results are, in most instances, superior to the results obtained from the UA approximation, the latter method still provides very useful results with comparatively little computation.
Chemical Activation and Nonequilibrium Unimolecular Reactions of C2H5Cl and 1,2-C2H4Cl2 Molecules
Authors: Hassler J. C. , Setser D. W. , Johnson R. L.
Published: January 2005

A gas-phase chemical activation technique employing the H and Cl abstraction reactions by methylene from chloromethanes has been developed for the production of chloroethanes in the energy range between 85 and 95 kcal mole−1. In this paper the results from the reaction of methylene with chloromethane are reported. The abstraction reactions serve as a clean source of methyl and chloromethyl radicals; combination of these radicals at 25°C produces C2H5Cl and 1,2-C2H4Cl2 at energies near 90 kcal mole−1. Since the critical energy for the unimolecular HCl elimination reactions is about 55 kcal mole−1, the molecules will react by this pathway unless deactivated by collisions with the bath molecules. By studying the system in the appropriate pressure ranges, the nonequilibrium rate constants were measured at 25°C as 3×109 and 1.8×108 sec−1 for C2H5Cl and 1,2-C2H4Cl2, respectively.
Multiple-Scattering Treatment of Low-Energy Electron-Diffraction Intensities
Authors: McRae E. G.
Published: January 2005

A theory of intensities in the diffraction of low-energy (≲100-eV) electrons by crystals is formulated on the basis of Lax's multiple-scattering equations. The formulation is self-consistent and is thus applicable regardless of the magnitude of the atomic-scattering factor.

The qualitative conclusions of the theory are discussed in detail with reference to simplified model crystals. The theory predicts that the reflectivity curves (reflectivity associated with a given beam versus electron energy) should show two types of peaks in addition to the ordinary Bragg peaks: (a) a resonance peak in the specular reflectivity curve; (b) secondary Bragg peaks in all reflectivity curves. The resonance peak is predicted at an energy just below that of the first appearance of a nonspecular beam. It derives from multiple scattering in a single atom layer and is associated with a resonance (zero and phase discontinuity) in the effective field. The secondary Bragg peaks are predicted at energies given by conditions similar in form to the ordinary Bragg condition. They derive from multiple scattering between atom layers and are associated with the interference between four or more plane wave components of the effective field. Both types of peaks are prominent only when the atomic-scattering cross section is large. All qualitative results are illustrated by an exact numerical application to a model crystal of isotropic (s-wave) scatterers.

The relationship with existing theories is discussed. It is shown that the conventional modified kinematical approach to low-energy electron diffraction is a limiting case that is approached when inelastic scattering is dominant. It is also shown that when certain assumptions are introduced, the most important being that of neglecting intralayer multiple scattering and the ``two-beam'' assumption, the theory reduces to the Darwin dynamical theory.
Numerical Calculation of the Energy and Wavefunction of the Ground State of Beryllium
Authors: Kotchoubey A. , Thomas L. H.
Published: January 2005

An algorithm for the numerical calculation of the energy and wavefunction of the lowest state of the beryllium atom has been developed and used on the IBM 7090/94 computer systems.

The method is variational in nature. Its object is to find the solution of proper symmetry of the time-independent, nonrelativistic Schrödinger equation for the beryllium atom, for which the energy is a minimum (most negative). The wavefunction in configuration space is expanded in terms of a sum of products of one-electron functions of a complete basis set. These basis functions are chosen to be hydrogenlike functions, all with the same exponential factor. The sum is truncated, and the coefficients are adjusted to minimize the energy, subject to the condition that the function has the symmetry required for a singlet state. Rotational symmetry conditions are also used, to restrict the function to correspond to an S state, thus decreasing the number of coefficients that must be evaluated. The coefficients of the expansion are determined by an iterative procedure rather than by direct solution of the variational equations. Two parameters are introduced in the algorithm. One is the result of transforming the Schrödinger equation to have a discrete spectrum, in which the eigenvalue of least magnitude corresponds to the lowest energy. The other parameter is introduced in order to shift the eigenvalue spectrum and increase the separation between the smallest eigenvalue and the next smallest, thus improving the convergence of the iteration process.

Using a 20-function basis, corresponding to eight s states and four p states, an energy of −14.6533 a.u. was found for the lowest state of beryllium. This value is an upper bound to the true eigenvalue of the Schrödinger equation, and has a relative error of about 0.10% with respect to the experimental estimate of the true eigenvalue.
Microwave Spectrum, Molecular Structure, Dipole Moment, and Ring-Bending Vibration of 1,3,2-Dioxaborolane
Authors: Hand J. H. , Schwendeman R. H.
Published: January 2005

Transitions in the microwave spectrum have been assigned for three vibrational states of 1,3,2-dioxaborolane, three vibrational states of the 4,4,5,5-tetradeutero species, two vibrational states of the 4-13C species, and the ground state of the 10B-substituted species. The vibrational states have been assigned as the v=0, v=1, and v=2 states of the lowest-energy ring vibration. The vibration is symmetric to 180° rotation about the b inertial axis and is hindered by a small barrier in the planar configuration of the molecule. Bond distances and bond angles are as follows: CC=1.541, CO=1.438, BO=1.368 Å, OBO=114.2°, BOC=107.3°, and OCC=104.9°. The dipole moment is 2.28 D, and the quadrupole coupling constants are χaa=−0.67, χbb=−2.41, χcc=3.08 Mc/sec.
Evidence for Thermal Hydrogen-Atom Reactions in Irradiated Gaseous HCl
Authors: Davidow R. S. , Lee R. A. , Armstrong D. A.
Published: January 2005

The addition of SF6, which is known to have a high cross section for reaction with thermal electrons, reduces the hydrogen yield from irradiated gaseous HCl to G(H2) = 3.9. The yield of hydrogen from pure HCl is G(H2) = 8.0 and the reduction of 4.1 G units achieved by the SF6 is within experimental error equal to Gionization for the system. Both Cl2 and Br2 cause a greater reduction to a residual or ``unscavengable'' hydrogen yield, GH″, of 2.2±0.2 G units. In the case of Cl2 this value is within experimental error independent of temperature over the range −79° to 23°C. The addition of Cl2 to SF6—HCl mixtures of a composition such that virtually all electrons are scavenged by SF6 causes a reduction from the SF6 plateau to the same residual yield observed with Cl2 and Br2 alone. This reduction may be attributed to a competition between Cl2 and HCl for thermal H atoms, which are formed in processes not involving thermal electrons as direct precursors. A competition kinetic study gave the following values of kH+HCl/kH+Cl2: 8.7±0.5×10−3 at 23°C; 7.5±0.5×10−3 at 1°C; and 1.6±0.5×10−3 at −77°C. The values at 23° and 1°C are in good agreement with recent experimental values of this ratio obtained by other methods. Possible origins of the thermal hydrogen atoms and the residual hydrogen yield are discussed.
Absorption Spectrum of Mn2+ in KCl
Authors: Mehra Anjani , Venkateswarlu Putcha
Published: January 2005

The absorption spectrum of an Mn2+-doped KCl crystal has been measured at room temperature. The observed bands are assigned as transitions from the 6A1(S) ground state to various excited quartet levels of a Mn2+ ion in a cubic crystalline field. The observed band energies are fitted with four parameters B, C, Dq, and α and the values obtained for the parameters in cm−1 are B=760, C=2955, Dq=590, and α=76.
Correction of Configuration-Interaction Wavefunctions by Perturbation Theory
Authors: Adams William H.
Published: January 2005

It is shown that a natural choice of the zeroth-order Hamiltonian for a configuration-interaction or a multiconfigurational self-consistent-field wavefunction, has interesting implications for the Rayleigh—Schrödinger perturbation corrections to the wavefunction and the energy of a system. In particular it is shown that the odd-order corrections to the energy vanish. In addition we demonstrate two other properties of the perturbation expansion based on a projection operator definition of the zeroth-order Hamiltonian.
Calculated Ion Distributions in a Helium Negative Glow
Authors: Hurt W. B.
Published: January 2005

The spatial distributions of helium atomic and molecular ions in the negative glow are calculated assuming that both ions diffuse away from the cathode, that atomic ions are simultaneously being converted to molecular ions, and that both ions are being destroyed by recombination. Different assumptions are made relating the charge distributions to the intensity distributions with the result that a consistent diffusion—collisional—radiative recombination model best satisfies the experimental observations.
Equations for a One-Component Lattice Gas with ``Ising'' Interaction
Authors: Czerwonko Jerzy
Published: January 2005

The thermodynamical properties of a lattice gas, the atoms of which interact according to their mutual orientations, are described. We obtain the expressions for the thermodynamical potential, mean value of energy, the average number of particles, and average orientations by means of the variational method of Bogolubov. It has been shown that in this case there exists a phase order-disorder transition, the temperature of which has been calculated.
Theory of Phase Transitions in Solid Heavy Methane
Authors: James Hubert M. , Keenan Thomas A.
Published: January 2005

It is the purpose of this paper to explain the existence of three solid phases in CD4, and to predict the molecular ordering in each phase, by straightforward deduction from a reasonable assumption concerning the orientational coupling of the molecules. Molecular and lattice vibrations are neglected, the crystal being treated as an f.c.c. array of spherical rotators carrying distributions of charge with tetrahedral symmetry. It is assumed that the dominant term in the orientational coupling of the molecules is their electrostatic interaction, of which only the octopole-octopole interaction of next neighbors is retained in the calculation. The magnitude of the effective octopole moment is the only disposable constant in the theory. The statistical calculation is based on a classical version of the self-consistent field idea; neglect of quantum effects makes the results inapplicable to CH4, which shows large isotope differences from CD4. The conditions for self-consistency in the theory appear as a family of integro-functional equations, one for each molecule in the crystal. These are brought into convenient form by introduction of tetrahedral harmonics and associated tetrahedral rotator functions. The consistency equations are first solved for the cases in which the orientational distribution function is the same for all molecules in the crystal. There exist three distinct solutions of this type, in which all molecules are subject to identical orienting fields with symmetries T, C2, or D3, respectively. More general solutions are then found, for which the molecules are not all equivalent, but may be freely rotating, or in orienting fields of symmetry T, C2, or D3. The consistency relations state restrictions on the distribution of such molecules in the crystal lattice, and fix the strengths of the orienting fields; they can be satisfied only for small numbers of molecules in a crystal cell. An apparently exhaustive tabulation is made of all solutions with low free energy. Three of these minimize F in some temperature range, and describe stable phases. At the lowest temperatures the stable phase has tetragonal symmetry Vd, with all molecules oscillating about equivalent equilibrium orientations. As T rises this undergoes a first-order transformation to a phase with octahedral symmetry O, in which one molecule in four rotates freely, surrounded by a shell of oscillating next neighbors. At higher temperatures this undergoes a transformation (described by the theory as of second order) to an orientationally disordered phase. If the molecular octopole moment is assigned the magnitude 0.504×10—24 electron cm3 needed to make the predicted upper transition temperature agree with the 27.1°K observed in CD4, the predicted lower transition temperature is 24.4°K, as against the observed 22.2°K. Predictions of the theory are also in satisfactory agreement with observations on integrated heats of transition, zero-point entropy, and the optical properties of the phases.
Hydrogen→ Deuterium Exchange Reaction in Fibrous Proteins. II
Authors: Fraser R. D. B. , Macrae T. P.
Published: January 2005

Previously it has been shown that when α-keratin is reacted with deuterium oxide the peptide hydrogens in the crystalline regions are not replaced by deuterium. In the present contribution it is shown that when the native configuration of this protein is destroyed, for example by stretching or supercontraction, complete replacement is obtained. Neither cleavage of the disulfide linkages nor treatment with acetic acid-d, which reduces the crystallinity appreciably, effects complete exchange in α-keratin and it is presumed therefore that the array of hydrogen bonds in the native monomeric unit is one of high inherent stability. This stability is attributed to its α-helical configuration, cyclic nature, and to interactions between side chains along the area of contact between the helix pair forming the cyclic unit. When collagen is reacted with deuterium oxide complete exchange is rapidly attained and this is correlated with the fact that the hydrated collagen is not appreciably stabilized by side-chain interactions and that the hydrogen bond array is only partially intrahelical.
Structure of Vitreous B2O3·⅓H2O
Authors: Milberg M. E. , Meller F.
Published: January 2005

A boron oxide glass containing 25 mole percent water, corresponding to the formula B2O3·⅓H2O, has been prepared and its structure studied. Diffractometric x-ray scattering measurements have been made for both vitreous B2O3·⅓H2O and vitreous B2O3, and from these measurements radial distribution functions have been computed. Examination of the atomic distribution function of B2O3·⅓H2O and comparison of the electronic distribution functions of B2O3·⅓H2O and B2O3 indicate that the fundamental triangular coordination of vitreous B2O3 is retained in B2O3·⅓H2O, but the network of the latter is somewhat looser than that of the former. It is suggested that while most of the oxygen atoms are shared between boron atoms, some of the oxygens are present in hydroxyl groups or O–H–O hydrogen bonds. The possibility that a small fraction of the boron atoms are coordinated by four oxygen atoms is not completely excluded.
Magnetic Study of the Frozen Products from the Nitrogen Microwave Discharge
Authors: Fontana B. J.
Published: January 2005

Magnetic susceptibility measurements have been made during the condensation at low temperatures of the mixture of atomic and molecular nitrogen produced in a microwave discharge. From the nitrogen atom concentration in the gas reaching the condensing surface and the magnetic measurements on the deposited solid, it is concluded that a concentration of a few tenths of a mole percent N cannot be exceeded in the solid phase. Such concentrations are observed only for relatively brief intervals after which catastrophic recombination occurs. Stable, long-lived concentrations, which account for the previously reported thermal and light emission effects that accompany warmup of such deposits, are estimated to be less than a few hundredths of a mole percent N. Susceptibility measurements are based on calibration with solid molecular oxygen, and the calculation of N atom concentrations assumes that the susceptibility of dilute N atoms in an N2 matrix approximates that of the free gas.
Two-Dimensional Nucleation of Noncoherent Layers
Authors: Sears Gerald W.
Published: January 2005

The kinetics of nucleating noncoherent layers on a parent crystal lattice are considered. The results are applied to perfect crystal growth. It is found that the maximum probability of growing a perfect crystal exists when growth occurs from a parent phase in contact with which the appropriate edge energy for two-dimensional nucleation is least.
Transition from Deflagration to Detonation in Cast Explosives
Authors: Maček Andrej
Published: January 2005

An experiment is described in which velocity and pressure changes during the transition from slow burning to detonation in cast explosives are measured. A simple one-dimensional physical model of explosive burning under confinement is assumed and used, in connection with experimental evidence, as the basis for a calculation of the time and distance necessary to start a shock in a deflagrating solid explosive. The calculated distance of incipient shock formation is 11–15 cm. This result supports the hypothesis that transition from slow burning to detonation is due to a shock which arises spontaneously in a confined burning medium. The nature of the shock-forming pressure pulse, p=p(t), is discussed.
Electron Population Analysis of LiH and HF
Authors: Karo A. M.
Published: January 2005

Following the analysis proposed by Mulliken, SCF LCAO-MO coefficients for LiH and HF are used to obtain qualitative information about the electron distributions in these molecules. Several additional aspects of population analysis are considered: the variation of atomic and overlap populations with internuclear distance and with choice of basis atomic orbitals, and the extent to which CI alters the qualitative description. It is shown that at equilibrium distances the results appear to be qualitatively unchanged by CI but are rather sensitive to the choice of basis functions.