bluuebunny/crossref_metadata_2025 huggingface dataset:
Theoretical Investigations on the Light Scattering of Spheres. XVI. Range of Practical Validity of the Rayleigh Theory
Authors: Heller Wilfried
Published: January 2005

The errors committed on using the Rayleigh equations of light scattering at finite α values were evaluated numerically for spherical nonabsorbing particles using exact Mie data as the reference. The errors considered are Δα, Δα′, Δτ, and ΔI. Considering an error of 2% as the tolerable maximum, the upper limiting particle diameters which may be evaluated by means of the Rayleigh equations are, expressed in units relative to the wavelength (in the medium) used, 0.124 and 0.207 at m=1.00 and 1.30, respectively. These data which apply to the use of lateral scattering differ little from the limiting data obtained for diameters derived from turbidity. The errors committed on evaluating turbidity or lateral scattering from the Rayleigh equations are distinctly larger at identical true α values, and at identical m values. The interesting fact that the Rayleigh equations perform better the larger m—as long as m<∼1.8—opens up the possibility of using these equations for the evaluation of relative large particle diameters provided m is sufficiently large. Thus at m=1.63±0.2, particle diameters, dimensionally one-third the wavelength in the medium, are obtainable from the Rayleigh equations with 100% theoretical accuracy. This `.second'' range of validity of the Rayleigh theory appears to be of major meteorological and astrophysical interest.
Elementary Rates of Decomposition of the Homologous Series Ethyl through 2-Octyl Radicals
Authors: Pearson M. J. , Rabinovitch B. S.
Published: January 2005

The rates of decomposition of the secondary alkyl radicals 2-butyl, 2-pentyl, 2-hexyl, 2-heptyl, and 2-octyl were measured by an internal comparison method at 300°K. Activation to a level around 45 kcal mole−1 was by addition of H atom to the appropriate α-olefin. The validity of an assumption of invariance of thermochemical parameters, including the bond-dissociation energy D[3(—C)—(4—C)] for the higher members of the radical series, was established by measurements made with 5-Me-2-hexyl radicals. No evidence was found for any significant amount of H migration and isomerization of any of these excited radicals.

Together with earlier work, measurements now exist for the homologous series ethyl through 2-octyl radicals.

Theoretical rate constants agree well with the experimental values. Our earlier experimental verification for relatively smaller molecules that all vibrational and internal rotational degrees of freedom must be treated as active is now extended to the largest member of this series. Within the accuracy of the test provided by this work, intramolecular energy relaxation is also confirmed to be effectively random even for the highest member. The data illustrate the effect on rates of quantum-statistical weight changes due to structural increments in the series.
Energy of Excimer Luminescence. III. Group Theoretical Considerations of Molecular Exciton and Charge Resonance States
Authors: Azumi Tohru , McGlynn S. P.
Published: January 2005

The excimer formed by two identical molecules of D2h or D6h point groups is discussed group theoretically. The manner in which excimer geometry influences configuration interactions between molecular exciton states and charge-resonance states, and the conditions necessary to resonance stabilization of the ground state are delineated. The polarizations of the transitions between the ground state and the various excited excimer states and of that between two excimer excited states are discussed. Some computational results for the D6h benzene excimer are presented.
Secondary Isotope Effects on Amplitudes of Molecular Vibrations
Authors: Bartell L. S.
Published: January 2005

Secondary isotope effects on amplitudes of bond oscillations in harmonically vibrating polyatomic molecules have been studied using normal coordinate theory. Morino's scheme for circumventing the L matrix by expanding the normal coordinate mean-square amplitude matrix in integral powers of the Λ matrix is extended and found to lead to some simple and useful inequalities. Upper and lower limits of bond amplitudes are established which are rigorously independent of masses of atoms other than the atoms in the bond. It is shown that the upper limit of secondary mass dependency vanishes with increasing temperature much more rapidly than does the primary mass dependency.

Even at absolute zero, secondary isotope effects on bond amplitudes are found to be relatively very much smaller than secondary isotope effects on bond frequencies. Numerical results of ``exact'' and various approximate approaches for calculating root-mean-square amplitudes are presented for the C–I bonds in CH3I and CD3I, and for the C=C bonds in C2H4 and C2D4. The smallness of secondary isotope effects on amplitudes indicates that their coupling with Morse bond asymmetry is not a major source of some recently reported secondary isotope effects on bond lengths.
On the Use of Double-Irradiation Methods for the Assignment of High-Resolution NMR Spectra with Repeated Spacings
Authors: Hoffman Ragnar A. , Gestblom Bo , Rodmar Sören , Forsén Sture
Published: January 2005

An analysis of double-resonance experiments on pseudo-AX systems (i.e., pairs of doublets, the four transitions of which form a closed polygon in the energy-level diagram) based on the formalism of Freeman and Anderson, is presented.

Expressions are given for the transition frequencies and the transition probabilities in the general case. It is demonstrated that double irradiation may lead to the collapse of a repeated interval under comparatively general conditions and that double irradiation may alternatively lead to enlargement of the doublet splitting in spin systems which are not ideal for ``decoupling'' experiments.

The collapse or the enlargement of (repeated) doublet splittings may be used to establish the correct level arrangement in a general spin system. As illustrative applications of these methods, the ABX spectra of 5-methylthio-2-thiophenethiol and trans-cinnamaldehyde have been studied experimentally. In 5-methylthio-2-thiophenethiol selective ``decoupling'' and selective enlargement as well as general double irradiation experiments were performed and it was shown that the sign of the side-chain coupling JSH−3 is opposite to that of the ring-coupling constant J34. The implications of this result with regard to the mechanism of long-range thiol proton spin couplings are indicated.

In trans-cinnamaldehyde selective enlargement of an unresolved repeated spacing was produced in order to corroborate the earlier result that the two vicinal couplings in the side chain carry the same sign.
Recombination of Oxygen Atoms at High Temperatures as Measured by Shock-Tube Densitometry
Authors: Kiefer John H. , Lutz Robert W.
Published: January 2005

The rate of recombination of oxygen atoms has been measured by shock-tube x-ray densitometry in the range 1500°—2800°K. Mixtures of ozone, oxygen, and argon or krypton were driven with helium in a shock tube and density records obtained for each experiment.

Within 2 μsec after the arrival of the shock wave the ozone had decomposed leaving an excess of oxygen atoms. The oxygen-atom concentration is subsequently determined by the density of the gas, and the recombination rate is obtained from the gradual decrease in density.

The reaction O+O+O2→ lim k42O2is the dominant reaction in this system, and its rate, defined by the equation d[O2]/dt=k4[O]2[O2] is found to be k4=(6.81±0.54)×108(2200/T)(1.22± 0.53) liter2/mole2·sec. This result is in close agreement with that found by Rink from dissociation experiments.
On the Origin of Spin-Hamiltonian Parameters
Authors: McWeeny R.
Published: January 2005

The various coupling constants which appear in the phenomenological spin Hamiltonian for an atom or molecule can, in principle, be determined from a knowledge of the electronic wavefunction. It is difficult to obtain a physical picture of their origin and interrelationship because of the complexity of the many-electron wavefunction. The problem may be greatly simplified by introducing certain standard density functions, of which the ``spin density'' is the most familiar. Only three types of function are required, all with a physical meaning which is readily visualized. Their significance in determining spin-Hamiltonian parameters is discussed and illustrated with reference to (i) hyperfine coupling (contact and dipole—dipole), (ii) nuclear spin—spin coupling, (iii) electron spin—spin coupling, (iv) g values.
Use of 1s Gaussian Wavefunctions for Molecular Calculations. I. The Hydrogen Atom and the Hydrogen Molecule Ion
Authors: Sambe Hideo
Published: January 2005

The 1s, 2s, 2p, 3s, 3p, 3dz, and 3dxy hydrogen-atom wavefunctions were expanded with linear combinations of 1s Gaussian functions of the form exp(—ar2), centered at different points in space to give the proper orbital symmetry. Energy values of −0.499999, −0.124630, −0.124947, −0.055170, −0.055460, −0.055450, and −0.055527 a.u. were found for 1s, 2s, 2p, 3s, 3p, 3dz, and 3dxy functions, respectively.

Trial functions for the 2Σg+ and 2IIu states of the hydrogen molecule ion were constructed from the 1s Gaussian expansion functions of 1s and 2p hydrogen-atom wavefunctions, introducing an effective charge and a polarization parameter which are closely related to the distortion of an atomic orbital in molecule formation. The trial functions, which have two nolinear parameters, give total energy errors of 0.055% and 0.16% at the equilibrium internuclear distance for the 2Σg+ and 2IIu states, respectively, of the hydrogen molecule ion.

The extension of this procedure to polyatomic molecules is discussed, and the simplicity of the required integrals and the small number of nonlinear parameters for the procedure are emphasized.
On the Importance of the Polarization Energy in Inelastic Ion—Molecule Collisions
Authors: Shin Hyung Kyu
Published: January 2005

By evaluating the vibrational transition probability for the collision between an ion and molecule, the importance of the polarization energy due to the static charge on the ion and the dipole moment induced on molecule is discussed. The final expression for the de-excitation probability per unit time shows that the polarization energy plays a leading role in bringing two particles closer so that the resulting interaction may become a hard, ``close-in'' collision and that the inclusion of this attractive energy significantly increases the efficiency of the vibrational energy transfer.
Group Moment Interpretation of the Infrared Intensities of Crystalline n-Paraffins
Authors: Snyder R. G.
Published: January 2005

The infrared intensities of bands in the spectra (3000–700 cm−1) of the crystalline n-paraffins n-C4H10 through n-C8H18 have been measured and interpreted using a group moment model. In this model intensities are expressed in terms of dipole moment derivatives with respect to group coordinates, i.e., coordinates describing the motions of CH3 and CH2 groups. In spite of a severe limitation in the accuracy of the measured intensities caused by preferred orientation in the polycrystalline films, a good correlation between calculated and observed intensities has been obtained.
Third Virial Coefficient of Polymer Solutions
Authors: Yamakawa Hiromi
Published: January 2005

The osmotic third virial coefficient A3 of solutions of linear chain polymers is calculated using the random flight model. Some preliminary comments are given somewhat in detail on the approximations introduced, and the theory is developed in the two-parameter scheme. First, the perturbation theory is presented with a revision of the result obtained by Stockmayer. An approximate closed expression for A3 is then derived applying a variational method as used in the previous paper on the second virial coefficient A2, the procedure being equivalent to the coupling-parameter method. Evaluation is performed by introduction of approximations similar to the Casassa—Markovitz approximation in their theory of A2. It is shown that the dimensionless quantity A3/A22M with the polymer molecular weight M becomes zero at the theta point and has the asymptotic value of 0.753 for high-molecular-weight polymers in good solvents if the third-power law equation of Fixman is assumed for the expansion factor of the polymer. The values of A3/A22M are somewhat larger than the corresponding values predicted by Stockmayer and Casassa. A comparison of the theory with experiment is made for polystyrene fractions in toluene and polyisobutylene fractions in cyclohexane, and an agreement between the theoretical and observed values of A3/A22M is discussed.
Magneto-Optical Rotation of Transition-Metal Complexes
Authors: Lin Sheng-Hsien , Eyring Henry
Published: January 2005

The Faraday rotations of certain tetrahedral and octahedral transition-metal complexes are examined by using Kramers' equation from the viewpoint of the crystal-field theory.
Dissociative Ionization of Molecules by Rare-Gas Ion Impact
Authors: Maier William B.
Published: January 2005

Reactions of rare-gas ions with N2O, C2H2, C2H4, and D2 are studied, and cross sections are given for primary-ion energies below 120 eV. These cross sections are compared for qualitative differences. Most of the reactions have rather sharp onsets, and a semiempirical formula is fitted to the data near the apparent threshold energy. The results of this investigation show that useful information about bond energies can be obtained from ion-molecule reactions. The data are consistent with D(H2C=CH2)=8.11 +0.10−0.18 eVand thus with D(CH–H)=3.99 +0.05−0.09 eV,although smaller values of D(H2C=CH2), and thus larger values of D(CH–H), cannot be entirely excluded. The results indicate that ion-impact methods may possess inherent advantages over electron-impact methods in certain cases; for example, the present data show that the electron-impact appearance potential of C2H3+ from C2H4 is certainly 0.3 eV and probably 0.6 eV larger than the true threshold energy. The threshold behavior of an endothermic charge-transfer process Kr++D2→D2++Kr is studied, and the cross section for this reaction is comparable in size to many of the other endothermic reactions observed, despite the fact that kinetic energy of the colliding particles must be converted into electronic energy for the reaction to proceed.
Desorption of He and 14CO2 from Micas
Authors: Brandt W. W. , Hattori M. , Sreenivasan V. R.
Published: January 2005

The rates of desorption of He from various micas have been measured over an extended temperature range, using a sensitive small mass spectrometer. Below 500°C, the desorption probably involves many individual processes, each characterized by a different effective rate coefficient. As a consequence, the over-all desorption rates are seemingly temperature independent. At elevated temperatures, the desorption rates correspond more closely to a single diffusion process, and are distinctly temperature-dependent. On the basis of electron microscopic results and approximate estimates of the total amount of He evolved from various specimens, it is concluded that the high-temperature process consists of the permeation of silicate sheets of a thickness intermediate between the individual structural ``parcels'' and the macroscopic sheets. The desorption of 14CO2 was followed by a tracer technique and interpreted as a surface process. Approximate 14CO2 transmission rates through mica sheets finally were measured and ascribed to flow through defect pores of submicroscopic dimensions.
Appraisal of the FOPIM Fast-Converging Perturbation Method
Authors: Robinson Peter D. , Huntington John H. , Hirschfelder Joseph O.
Published: January 2005

The practicality of the first-order perturbation-iteration method (FOPIM) is appraised. After the first iteration, the expectation value of the energy is given by a nonanalytic function of the perturbation parameter λ. The asymptotic expansion of this function gives the energy accurately up to O(λ8). The convergence of the asymptotic expansions is discussed. Two examples are considered: a perturbed ground-state hydrogen atom, and a perturbed ground-state linear harmonic oscillator.
Condensation of Supersaturated Vapor
Authors: Stachórska Danuta
Published: January 2005

A formula for the current of drops for the case of the condensation on ions was derived using Frenkel's method. An approximate formula for the time of condensation, i.e., the time elapsed from the beginning of supersaturation up to its complete disappearance, was developed. This time was read from the oscilloscope record of temperature versus time for the expansion in the Wilson chamber. Experiments confirmed the theoretical formula. A rather complicated equation expressing the dependence of the mass of condensed vapor on time was established. It requires a numerical solution.
Ferroelectric Field of BaTiO3 as Measured by Electron Diffraction
Authors: Yamaguchi S.
Published: January 2005

The electrostatic field in a BaTiO3 crystal given by orientation of the ferroelectric domains is measured by observing the dielectric relaxation in terms of electron diffraction. This field amounts to about 200 kV/cm along the [210] axis.
Deduction of the Zero Differential Overlap Approximation from an Orthogonal Atomic Orbital Basis
Authors: Fischer-Hjalmars Inga
Published: January 2005

The validity of the zero differential overlap approximation is investigated by means of a systematic expansion in terms of a parameter of the order of magnitude of a typical overlap integral between neighboring atoms. The terms of the Fock operator in a basis of orthogonal atomic orbitals can be arranged after different orders of the parameter. It is demonstrated that, by inclusion of second-order terms, the conditions imposed by the zero differential overlap approximation are automatically fulfilled. Moreover, all the basic integrals are shown to be transferable in the first order and all but W in the second order. The connection with the ω technique in the Hückel method is also given. A numerical application has been made to ethylene and benzene.
Electronic Absorption Spectra of Square-Planar d8 Complexes in Different Crystal Environments
Authors: Day P. , Orchard A. F. , Thomson A. J. , Williams R. J. P.
Published: January 2005

Polarized crystal spectra of K2PdCl4 and K2PtCl4 have been measured at room temperature and interpreted by means of a vibronic intensity-borrowing mechanism. Single-crystal spectra of Magnus's green salt, Pt(NH3)4PtCl4, and its methylamine analog have also been measured, together with the powder spectra of a wide range of related salts. The visible absorptions are assigned to d—d transitions within axially perturbed anions, while a new infrared band in Magnus's green salt is identified with an intermolecular electron-transfer transition.
Absorption Spectra and Electrical Resistivities of Some Anomalously Composed Thiazine—Quinone Complexes
Authors: Matsunaga Yoshio
Published: January 2005

Dibenzo[c,d]phenothiazine has been found to form a 2:1 complex with 2,3-dichloro-5,6-dicyano-p-benzoquinone and a 3:2 complex with the dibromo analog. The complexes exhibit resistivities of about 17 and 240 Ω·cm at 20°C, respectively. Since the infrared spectra indicate the presence of the semiquinone ion instead of the quinone molecule, the ground state of the complexes is characterized as essentially dative. The appearance of an electronic absorption band in the infrared region is noted in the anomalously composed complexes but not in the 1:1 complexes and is attributed to the interaction between the cationic radical and the neutral donor molecule.
Ionization Potentials and Autoionization Levels of Methyl, Ethyl, n-Propyl, and n-Butyl Free Radicals by an Energy-Calibrated Molecular Orbital Method
Authors: Melton Charles E. , Joy Hubert W.
Published: January 2005

Ionization potentials and possible autoionization levels of the methyl, ethyl, n-propyl, and n-butyl free radicals have been calculated with an energy-calibrated molecular orbital method. Molecular orbitals were constructed as a linear combination of 1s hydrogen and 2p carbon atomic orbitals. Autoionization levels were calculated from molecular orbitals constructed to include autoionizing levels of the carbon atom (2p3, 1D, etc.). Two different models of the free radicals were formulated for the calculations, a simple planar model in which the interaction of the atomic orbitals was restricted to adjacent atoms, and a more complicated group model in which the interactions of the orbitals were much less restricted. Calculations in both models were based upon the assumption that the ionization processes are principally controlled by the unpaired carbon 2p electron. Calculated and experimental values are in reasonable agreement over the energy range of the experimental data. The lowest ionization potential of the n-butyl radical is calculated to be lower than the experimental value (8.0 vs 8.6 eV).
Theory of EPR of Ti3+ in Trigonal Environments
Authors: Gladney H. M. , Swalen J. D.
Published: January 2005

For a single d electron in a trigonal environment, the complete ligand-field Hamiltonian, including the interactions with the upper states of the cubic splitting, has been diagonalized in order to re-examine critically the theory of the EPR spectra of various Ti3+ compounds. The compounds for which there are adequate experimental data to justify a detailed discussion of the parametric theory of the electronic structure are titanium in corundum, cesium titanium alum, titanium acetylacetonate, and titanium-doped aluminum trichloride. Only for the first of these is it possible to fit the magnetic properties with crystal-field parameters. In each of the others, covalency is qualitatively indicated, but it is not possible from the present experimental data to give good numerical values either for the trigonal components of the effective potential or for the parameters describing covalency. We suspect that similar uncertainty exists in many of the published interpretations of iron-group compounds.
Comparison of Theories of Heat of Transport and Thermal Diffusion with Experiments on the Cyclohexane—Carbon Tetrachloride System
Authors: Bearman Richard J. , Horne Frederick H.
Published: January 2005

Theories of the heat of transport and the related thermal diffusion factor have been developed previously. In this paper the theories are compared with experimental results. Both theories represent adequate first approximations since they both predict the sign and magnitude of the experimental results without adjustment to experimental transport data.
Vibrational Relaxation of Oxygen by Methane, Acetylene, and Ethylene
Authors: White Donald R.
Published: January 2005

The vibrational relaxation of oxygen containing from ¼% to 2% of CH4, C2H2, and C2H4 has been studied by shock-tube interferometry. From about 450° to 1300°K the vibrational relaxation zone is not affected by chemical reaction, and the observed oxygen relaxation in mixtures containing only small amounts of hydrocarbon may be accounted for by using the standard formula for a binary mixture and assuming the relaxation time in seconds of oxygen dilute in 1 atm of the hydrocarbon to be given by log10τO2–CH4 = 18T—⅓−8.7, log10τO2–C2H2 = 7.5T—⅓−7.3, and log10τO2–C2H4 = −6.92. For higher temperatures, the exothermic reaction may result in a nonlaminar flow behind an aplanar shock, and the relaxation zone then cannot be resolved interferometrically. For still higher temperatures the relaxation zone is again laminar, but the vibrational excitation of O2 is accelerated by concurrent chemical reactions in the induction zone. From the observation at lower temperatures that τO2–CH4<τCH4 and τO2–C2H4<τC2H4 one is led to conclude that at least below 800°K collisions with O2 are more effective in the excitation of CH4 and C2H4 than are self-collisions, and that the excitation of O2 by collision with a hydrocarbon molecule is through a vibrational exchange reaction with the more easily excited hydrocarbon molecule.
Spin Densities in Azo-Type Radical Anions
Authors: Strom E. Thomas , Russell Glen A. , Konaka R.
Published: January 2005

Various methods of calculating 14N hyperfine splittings are compared with the experimental splitting constants observed for benzo[c]cinnoline, trans-azobenzene, and 1,4-dimethyltetrazine radical anions in dimethyl sulfozide [80%]—t-butyl alcohol [20%] solution. The theory of Stone and Maki gives reasonable results although better argument is obtained by use of a modified value for QCNN of 13.8 G.
Shift of the R(0) and P(1) Infrared Lines of HCl Perturbed by Noble Gases
Authors: Ben-Reuven A.
Published: January 2005

Adiabatic collisions, in the sense that the magnetic quantum number m is defined with respect to the rotating intermolecular axis, are shown to give a major contribution to the pressure shifts of the R(0) and P(1) lines in the vibration—rotation bands of HCl gas, perturbed by argon and by krypton. The right sign and magnitude of these shifts, however, are reproduced only if the effect of the rotation of the intermolecular axis on the rotational wavefunctions is correctly taken into account. This approximation fails in treating the shifts of the outer lines of the band, where the phase-shift approximation of Ben-Reuven, Friedmann, and Jaffe should apply.
Mass-Spectrometric Study of Photoionization. II. H2, HD, and D2
Authors: Dibeler Vernon H. , Reese Robert M. , Krauss Morris
Published: January 2005

Mass-spectrometric techniques have been used to obtain the photoionization-efficiency curves for H2, HD, and D2 in the energy range 815 to 700 Å (15.2 to 17.7 eV). A qualitative description of the observed autoionization process, based on a theory proposed by Fano, is applied to an analysis of the results.
Measurements of the Viscosity of Parahydrogen
Authors: Diller Dwain E.
Published: January 2005

The coefficient of shear viscosity η of parahydrogen has been measured by the torsional crystal method at temperatures from 14° to 100°K and at pressures up to 345 atm. Twenty compressed fluid isotherms encompass the density range 0.003–0.087 g/cm3 and include the critical region. The precision and accuracy of the measurements is about 0.5%. The temperature dependence of η changes sign at a density approximately twice the critical density. The viscosity at the critical point is estimated to be 35.5±0.5×10−6 g/cm·sec. The viscosity of saturated liquid normal hydrogen is up to 5% greater than that of parahydrogen at the same temperature. Data of this report have been represented within experimental error by an empirical equation of the form η=η0(T)+A(ρ) expB(ρ)/T, where η0(T) is the viscosity in the low-density limit and A(ρ) and B(ρ) are density-dependent coefficients.
Paramagnetic Resonance of Fe3+ in Polycrystalline Ferrichrome A
Authors: Wickman H. Hollis , Klein Melvin P. , Shirley D. A.
Published: January 2005

Polycrystalline samples of iron-containing ferrichrome A, a cyclic hexapeptide obtained from the fungus Ustillago sphaerogena, have been investigated by paramagnetic resonance. Spectra were obtained at several temperatures between 300° and 1°K; a prominent line of 400-Oe width located at g=4.3 was observed at all temperatures, while at 1°K additional resonances at g values of 9.6, 1.3, and 1.0 were observed. The spectra are interpreted by assuming a spin Hamiltonian containing crystal-field terms large compared with the Zeeman splittings; the crystal-field situation is intermediate between the case of axial symmetry, with H=D[Sz2−(1/3)S(S+1)]+gβS·H and a model proposed by Castner, Newell, Holton, and Slichter to explain certain iron resonances occurring at g=4.3, with H=E(Sx2−Sy2)+gβS·H. We have computed g values, energy eigenvalues, and eigenfunctions to be expected for the region between these two extremes, and the results should be useful in interpreting similar spectra due to iron situated in strong crystal fields of low symmetry.
Rectangular Approximation for Concentration-Dependent Sedimentation in the Ultracentrifuge
Authors: Weiss George H. , Yphantis David A.
Published: January 2005

We derive an exact solution to the rectangular approximation of the Lamm equation where s=s0(1—kc). Properties of the solution are examined for approach to equilibrium and for velocity sedimentation.
Thermal Decomposition of ClCN
Authors: Schofield David , Tsang Wing , Bauer S. H.
Published: January 2005

The thermal decomposition of cyanogen chloride was studied in a shock tube, using specific absorption spectroscopy to follow the concentration of CN radicals as a function of time behind the shock wave. This investigation is similar to the previously studied dissociation of cyanogen, but the kinetics are much more complex because of the possibility of reactions involving the unlike radicals CN and Cl.

A mechanism involving six reactions is proposed; these account for all features which characterize the observed results. Values for some ratios of rate constants have been obtained by direct analysis of the CN absorption curves. A method of trial curve fitting using a digital computer was used to deduce the absolute values of the rate constants for the important steps.
Barrier Studies in the Halopropenes. I. The Microwave Spectrum, Barrier to Internal Rotation, Quadrupole Coupling Constants, and Microwave Double-Resonance Spectra of 2-Chloropropene
Authors: Unland M. L. , Weiss V. , Flygare W. H.
Published: January 2005

The microwave spectra of CH3C35Cl:CH2 and CH3C37Cl:CH2 have been observed in the ground and first excited torsional states. The ground-state rotational constants of CH3C35Cl:CH2 are A=9272.79±0.10 Mc/sec, B=4983.84±0.10 Mc/sec, and C=3304.39±0.10 Mc/sec. The ground-state rotational constants for CH3C37Cl:CH2 are A=9272.31±0.10 Mc/sec, B=4850.48±0.10 Mc/sec, and C=3245.11±0.10 Mc/sec. The quadrupole coupling constants along the appropriate principal inertial axes in the ground torsional state of CH3C35Cl:CH2 are χaa=−68.15±0.10 Mc/sec, χbb=37.11±0.10 Mc/sec, and χcc=31.04±0.10 Mc/sec. The quadrupole coupling constants for CH3C35Cl:CH2 in the excited torsional state were within the experimental error of the corresponding ground-state values. The quadrupole coupling constants in CH3C37Cl:CH2 are χaa=−53.80±0.10 Mc/sec, χbb=29.30±0.10 Mc/sec, and χcc=24.50±0.10 Mc/sec. Analysis of the first excited-torsional-state rotational spectrum yielded a barrier to the internal rotation of the methyl group of 2671±20 cal/mole.

Microwave double-resonance experiments were used to provide a positive confirmation for the assignments of the 000→101 and 101→202 transitions in CH3C35Cl:CH2 as well as exhibiting some interesting features in the energy levels involved in the transitions. Two types of experiments were performed. The first experiments involved irradiating the quadrupole components in the 000→101 transition while observing the 101→202 transition. The second set of experiments involved irradiating one of the quadrupole components in the 000→101 transition and using a second klystron to observe the entire 000→101 triplet.
Effect of Electric Fields on the Radiation-Induced Reaction between Carbon Dioxide and Graphite
Authors: Watanabe Tsutomu , Matsumura Hisao , Washino Masamitsu , Natori Makoto
Published: January 2005

The effect of an electric field on the γ-ray-induced reaction of CO formation from CO2 and graphite was investigated. The experiment was carried out at room temperature under an exposure dose rate of 1.5×105 R/h using diodelike tubes with graphite and metal (tungsten or molybdenum) electrodes filled with CO2 gas at 300 mm Hg. When a negative voltage was applied to the graphite to obtain a saturation current, the yield of CO was about 2.5 times as much as that in the absence of any field. However, on application of a positive field, the yield was not significantly different than the zero field case. The G value for CO formation was found to be 0.62∼1.01 in the absence of the field.

The ionic reaction mechanisms CO2++C−(graphite electrode)→2COand/or CO2++C−(graphite electrode)→C(graphite)O+COare proposed for the increased yield of CO in the case of negative voltage application to the graphite.
Light Scattering by Linear Macromolecules Oriented in Laminar Flow. V. Intensity and Depolarization by a Perfectly Flexible Coil with High Solvent Immobilization
Authors: Reinhold Chr. , Peterlin A.
Published: January 2005

In the last of a series of papers that deal with light-scattering intensity and depolarization, the Zimm model for linear macromolecules in laminar flow is applied. The interference factor P and the orientation functions hh, hv, and vh are calculated for Z=10 in the flow plane and in the plane perpendicular to the flow vector. The interference factor averages the intersegmental phase relations. The orientation functions depend on the average orientation of all segment pairs. The products of the orientation functions and P are approximately the scattering intensities Hh, Hv, and Vh. The results are compared with previous analogous computations in which the hydrodynamic interactions were neglected (Rouse model). The amplitude fluctuation as a function of the observation angle decreases with hydrodynamic interaction for the interference factor and orientation functions. The positions of the extreme values of P, hh, hv, and vh for a constant flow gradient are shifted to larger angles. But all these changes are small so that one may say that the intensity and polarization of scattered light by macromolecules in laminar flow plotted as functions of β, where β=M[η]η0G/NkT, do not strongly depend on hydrodynamic interaction.
Method for Calculating Internal Rotation Barriers
Authors: Scott Roy A. , Scheraga Harold A.
Published: January 2005

A method is proposed for calculating internal rotation barriers in ethanelike molecules based on two effects, exchange interactions of the electrons in bonds adjacent to the bond about which internal rotation occurs and nonbonded or van der Waals interactions. A modified Buckingham or ``6-exp'' potential is used for the nonbonded interactions and a semiempirical method is used to obtain the constants in the 6-exp potential for the various kinds of nonbonded interactions. The equation for U(ω) contains one adjustable parameter, U0, which theoretically should be constant for all molecules within certain classes. An average value for U0 is obtained for each class from selected microwave values of ΔU by letting ΔU have the microwave experimental value and solving for U0. It was found that U0 was essentially constant within each class, thus allowing these average values to be used to calculate ΔU for all molecules in each class. Satisfactory agreement between the calculated values and experimental values of ΔU was obtained in all cases tested except two. A discussion is included of the extension of this method to more complex molecules with more than one internal rotational degree of freedom, allowing for other energy contributions such as distortion of bond angles. Brief mention is also made of the possible extension of the method to the conformational analysis of macromolecules such as polypeptides and synthetic polymers.
On the Nature of the Crystal-Field Approximation Results. III. Generalization of the Expanded Hamiltonian—Separated-Atom—Molecular Orbital Method
Authors: Goldberg Henry
Published: January 2005

A modified molecular orbital technique was used to study the effect of neglect of wavefunction overlap and electron exchange on the results of crystal-field theory. Formal results were given by Herzfeld and Goldberg for the interaction of a hydrogen atom in a 2p state and a hydrogen molecule in the ground state for two different but simple nuclear configurations. In this paper the method is generalized and applied to give formal results for the interaction of an atom in a pn configuration (n = 1, 2, 3, 4, 5) with a hydrogen molecule in its ground state for the simple nuclear configuration, where all three nuclei lie on a line. The comparison of these formal results with conventional crystal-field theory shows the appearance of new effects where one does not neglect wavefunction overlap and electron exchange. These new effects readily suggest an explanation for the experimental observation of the appearance of extraneous lines in the α group of lines emitted by nitrogen atoms trapped in solid nitrogen at low temperatures.
Study of Separated Electron Pairs in the LiH Molecule
Authors: Ebbing Darrell D. , Henderson Richard C.
Published: January 2005

The separated-pair model is applied to the ground state of the LiH molecule in an effort to estimate the inherent accuracy of this model, and to investigate a method for computing accurate pair functions. The procedure employs direct calculation with natural orbitals and is found to be rapidly convergent if molecular orbitals are used as first guess in the iteration. The energy for seven σ orbitals is only slightly higher than the corresponding 41-term MO—CI function. A detailed comparison of the two functions is given.
Vibrational Spectra and Valence Force Constants of the Square-Pyramidal Molecules—XeOF4, IF5, BrF5, and ClF5
Authors: Begun G. M. , Fletcher W. H. , Smith D. F.
Published: January 2005

The infrared and Raman spectra of XeOF4, IF5, BrF5, and ClF5 have been recorded. The data have been tabulated and assignments of the fundamental vibration and combination frequencies made on the basis of a square-pyramidal structure for these molecules. Valence force constants, based on estimated molecular parameters, have been calculated for these molecules. Comparisons between the different members of the series show that the bonding in XeOF4 is remarkably similar to that in the interhalogen compounds.
Melting Properties of the Alkali Nitrates to 10 000 Atmospheres
Authors: Owens B. B.
Published: January 2005

The melting points and the volumes of fusion of the alkali nitrates were determined at pressures up to 10 000 atm. LiNO3, NaNO3, and CsNO3 have normal melting curves. However, the RbNO3 melting curve exhibits an initial negative slope followed by normal behavior at higher pressures, whereas the KNO3 melting curve is initially normal, but goes through a maximum at elevated pressures. The results of this investigation indicate that the RbNO3 liquidus curve has two triple points, one at 310° and 200 atm and the other at 315° and 1900 atm.
Infrared Spectroscopic Investigation of Ultraviolet-Irradiated Sodium Azide Crystals
Authors: Bryant James I.
Published: January 2005

This study is concerned with new absorption bands which appear in the infrared spectrum when sodium azide crystals are irradiated with ultraviolet light at 77°K. The observed frequencies and frequency shifts of the irradiation bands produced by NaN3, NaN15NN, NaNN15N, and Na15N3 indicate that they are caused by some configuration of vibrating nitrogen atoms. Calculated frequency-shift values for various polyatomic nitrogen defects, which have a high probability of being produced by ultraviolet photolysis, were obtained using expressions derived on the assumption of valence forces. By comparing calculated and observed values, considerations are given to the capability of several polyatomic nitrogen structures to produce the new infrared absorptions.
Experimental Study of the Absolute Temperature Scale. XI. Deviation of the International Practical from the Kelvin Temperature Scale in the Range 0° to 444.6°C
Authors: Beattie James A. , Benedict Manson , Blaisdell B. Edwin , Kaye Joseph
Published: January 2005

The deviations of the International Practical Temperature Scale from the thermodynamic Celsius scale were determined at eleven temperatures in the range 0° to 444.6°C by a comparison of the indications of four platinum resistance thermometers with those of two constant-volume nitrogen-gas thermometers in a stirred-liquid thermostat. In each gas thermometer several different ice-point pressures were used to permit corrections to be made for the imperfection of the thermometric fluid. The arithmetic means of the observed differences between temperatures on the thermodynamic Celsius scale as it was defined in 1954 and those on the IPTS at the eleven temperatures, each weighted in accordance with the number of observations, are represented by the equation t(therm.)−t(Int.)=[−0.0060+(0.01t−1)(0.04106–7.363×10−5t)](0.01t),where t in the right-hand member is on the IPTS. The standard deviation of a determination of Δt of unit weight from the equation is 18×10−4 deg.
Critical Opalescence of a Binary Liquid Mixture, n-Decane—β,β′-Dichloroethyl Ether. II. Small-Angle X-Ray Scattering
Authors: Chu B.
Published: January 2005

The small-angle x-ray scattering of n-decane and β,β′-dichloroethyl ether has been investigated at the critical-solution concentration over a range of temperatures near the phase-separation temperature in the one-phase region. Composite light- and x-ray scattering curves were constructed. The angular distribution of the scattering was analysed in terms of the Debye theory of critical opalescence. Deviations from the straight-line behavior in plots of reciprocal scattered intensity versus (s/λ)2(s=2 sin½θ, and λ is the wavelength in the medium) were observed.
On the Effect of the Ground-State Dipole Moment on Optical Transition Probability
Authors: Hameka Hendrik F. , Goodman Lionel
Published: January 2005

The customary procedure in the theory of transition probabilities of transforming the dipole-velocity expression into the dipole-length expression is subjected to a critical investigation. It is concluded that in the case of triplet—singlet transitions this transformation should follow rather than preceed the substitution of the perturbed triplet and singlet wavefunctions. The result is that the ground-state dipole moment does not contribute to the transition probability. In many other cases, where approximate eigenfunctions are substituted, it is not clear whether the transformation should preceed or follow the substitution. Therefore it becomes uncertain as to whether ground-state dipole moments contribute to the transition probability.
Entropy and Related Thermodynamic Properties of n-Valeric Acid
Authors: McDougall Lee A. , Kilpatrick John E.
Published: January 2005

The heat capacity from 15° to 300°K, the heat of fusion (3384.7±1.0 cal/mole), the temperature of fusion (239.49°±0.02°K), and the entropy of the ideal gas at 1 atm, 25°C (105.12±0.15 cal/deg·mole) of valeric acid have been determined experimentally.
Radiolysis of Ethylene. IV. Unimolecular Dissociation of Intermediate Ion—Molecule Complexes
Authors: Meisels G. G.
Published: January 2005

Kinetic analysis of free-radical reactions in the radiolysis of ethylene demonstrates that the relative extent of radical addition to ethylene can be held constant by maintaining the ratio of accelerator beam current to ethylene pressure invariant. The pressure dependence of the methane and methyl radical yields when this ratio is constant reveals that the mechanism of their formation includes competition between unimolecular dissociation of an intermediate ion and its participation in an ion—molecule reaction. Consideration of known ion—molecule reactions suggests that the species involved in the competing steps are [C6H11+] (methane formation) and [C6H12+] or [C4H8+] (methyl radical formation). Rate constants of 4.2×108 and 1.0×109 sec−1, respectively, are calculated for the dissociation processes on the basis of collision efficiency for the competing ion—molecule reactions.

About one-fourth of the methane and one-half of the methyl radicals are formed by reactions which are independent of pressure below 1 atm. This may be ascribed to rate constants larger than 1010 sec−1 for dissociation of [C8H15+] and [C8H16+] ion, respectively, or to the existence of at least two discrete energy levels for the dissociating species. Relative dissociation probabilities of intermediate ion—molecule complexes, determined by mass spectrometry, are used to estimate G(C2H4+) ≈ 1.5 and G(C2H3+) ≈ 1.0 ions/100 eV at approximately atmospheric pressure, in good agreement with values of 1.51 and 0.96, respectively, which may be calculated from W and fragmentation patterns for 70-eV electrons.
Least-Squares Adjustment of Anharmonic Potential Constants: Application to 12CO2 and 13CO2
Authors: Pariseau M. A. , Suzuki I. , Overend John
Published: January 2005

An algorithm for the calculation of anharmonic potential constants from the observed vibrational energy levels and rotational constants has been set up. Values have been obtained for the cubic and quartic force constants in the most general valence anharmonic potential for carbon dioxide.
Incoherent X-Ray Scattering Factors
Authors: Pohler R. F. , Hanson H. P.
Published: January 2005

Incoherent scattering factors for C, O, Cl, Al, and I are calculated from Hartree—Fock—Slater wavefunctions. Comparison of the values of C and Al with Hartree—Fock values show good agreement. Results for I, which represent the heaviest element for which calculations of this type have been performed, are compared with statistical Thomas—Fermi values.
Variation-Perturbation Approach to Electron-Cluster Wavefunctions
Authors: Stanton Richard E.
Published: January 2005

Sinanoğlu's cluster expansion formula for the exact wavefunction of a many-electron system is investigated by variation-perturbation techniques. The perturbation operator is the difference between the actual Hamiltonian and a symmetric sum of arbitrary one-electron Hamiltonians. Each perturbation function is then expanded in accordance with the cluster formula.

When the occupied orbitals are chosen to be eigenfunctions of the one-electron Hamiltonian the variational equations determining different nth-order clusters are completely independent. If the orbitals are unitarily transformed to achieve greater localization the variational equations for each cluster are coupled.

The perturbation governing first-order two-electron clusters has the form of a dipole potential. This result does not depend on the nature of the one-electron Hamiltonian. It is primarily useful, however, in studying the question of interorbital vs intraorbital correlation, i.e., when the one-electron Hamiltonian is the Hartree—Fock operator. It is shown that interorbital correlation is small if the Hartree—Fock orbitals are well separated. The advantage of transforming to localized orbitals is shown to be questionable because of the coupling between the clusters.

Differential equations governing first- and second-order orbital correction functions are derived and partially interpreted. In accordance with Brillouin's theorem the first-order corrections vanish as the one-electron Hamiltonian approaches the form of the Hartree—Fock operator. In the Hartree—Fock case the role of the second-order orbital correction functions is to relax the charge density subsequent to correlation. An investigation of the derivative of the correlation energy with respect to nuclear charge, a one-electron property, suggests that the second order correction functions may be important whenever it is necessary to evaluate one-electron properties to an accuracy beyond the Hartree—Fock estimate.

The second order four-electron cluster is shown to be exactly expressible as a sum of products of first-order two-electron clusters.

Explicit variational equations are derived also for the second-order two- and three-electron Hartree—Fock clusters.
Energy-Term Calculations with Hellmann-Type Pseudopotential
Authors: Szasz Levente , McGinn George
Published: January 2005

The Hellmann pseudopotential method is used to calculate the energies of the ground states of the atoms Mg, Ca, Sr, Ba, Ra, Zn, Cd, and Hg. Two different types of wavefunctions were employed for the valence electrons: wavefunctions of Hylleraas type explicitly containing r12, and a superposition of the configurations (1s)2 1S and (2p)2 1S. The agreement between the calculated and empirical energies is very good. The results are better with the superposition of configurations than with the wavefunction containing r12.