bluuebunny/crossref_metadata_2025 huggingface dataset:
Force Constants in Methylamine-A Determination by the Use of 15N Isotope Shifts
Authors: Hirakawa Akiko Y. , Tsuboi Masamichi , Shimanouchi Takehiko
Published: February 2004

Infrared absorption spectrum of methylamine—15N has been examined in the gaseous state, and the amounts of 15N isotope shifts have been determined for 12 absorption bands of undeuterated methylamine. Force constants in the methylamine molecule were adjusted on the bases of the vibrational frequencies of CH3NH2, CH3ND2, CD3NH2, and CD3ND2 and of the 15N isotope shifts of CH3NH2 by the method of the least squares. The 15N isotope shifts have been found to be useful data for selecting the best set of force constants among several sets which are equally good as far as only the agreement of the observed and calculated frequencies are taken into account.
Effect of a Ce3+ Codopant on the Gd3+ EPR Spectrum of SrF2 at Room Temperature
Authors: Miner G. K. , Graham T. P. , Johnston G. T.
Published: February 2004

The room temperature Gd3+ EPR spectrum in SrF2 containing Ce3+ as a second dopant exhibits three types of symmetry sites: cubic, trigonal, and tetragonal. Relative intensities of the spectra from these sites have been determined as a function of the Ce3+ codopant level in crystals having nominally 0.1 molar % of Gd3+. At low Ce3+ concentrations (< 0.1 molar %), the tetragonal-to-trigonal intensity ratio is 1.85 ± 0.25, with the cubic site intensity accounting for less than one tenth of the total observed intensity. At higher Ce3+ concentrations (up to 0.8 molar %), the cubic site intensity grows and the intensity of both axial sites decreases. This increase of cubic intensity is at variance with the generally accepted model of nonlocalized cubic compensation of the Gd3+, and a phenomenological explanation based on a local cubic phase in which rare earth ions are essentially surrounded with interstitial compensating fluorines is presented.
Kinetics of the O + O3 Reaction
Authors: McCrumb J. L. , Kaufman F.
Published: February 2004

The gas phase reaction O+O3 → 2O2 was studied directly in a flow system under conditions of excess ozone, with O atoms produced by thermal decomposition of Ar–O3 mixtures on a Nernst glower, and measurement of the spatial O atom decay by O+NO chemiluminescence with small, variable NO additions. The rate constant was found to be (7.5 ± 0.6) × 10−15 cm3 molecule−1 · sec−1 at 298oK. Over the temperature range 269 to 409°K a rate expression (1.05 ± 0.18) × 10−11 exp[(−4.31 ± 0.10 kcal mole−1)/RT] is reported. The effects of interference by O2(1Δg) and product excitation are discussed, and the present results are compared with earlier investigations.
Elastic Scattering of Li+ Ions in Helium
Authors: Inouye H. , Kita S.
Published: February 2004

Repulsive potentials between a Li+ ion and a He atom have been derived from the experimental values of integral elastic scattering cross sections of the ions in the energy range of 500–4000 eV. The potentials are well represented by the following analytical expression: V(r)=428 exp(−5.11r), 0.78≤ r≤ 1.21, where V(r) is in units of eV and r in angstroms.
Evaluation of Matrix Elements of Spin-Dependent Operators for N-Electron Systems. I One-Body Operators
Authors: Cooper Ian L. , Musher Jeremy I.
Published: February 2004

The properties of the symmetric group are utilized to obtain a decomposition of matrix elements of spin-dependent operators into sums of products of space- and spin-dependent matrix elements. The Wigner-Eckart theorem is then applied, and results in an expression for the matrix elements in terms of reduced matrix elements in both space and spin and a set of coupling coefficients. The coupling coefficients and the reduced spin-matrix elements are evaluated for N=2, 3, 4, and the corresponding reduced spatial matrix elements are evaluated in the simplest case of an orbital approximation.
Vibrational and Other Corrections to the Nuclear Quadrupole Moment of 14N in Ammonia
Authors: Grigolini P. , Moccia R.
Published: February 2004

The field gradient at the nitrogen nucleus has been evaluated for the NH3 molecule using two different rather accurate electronic molecular wavefunctions. The vibrational correction has been obtained by averaging the field gradient for the two totally symmetric vibrations of the C3v point group computed at a number of geometrical configurations. In addition, a careful analysis has been carried out to assess the effect of the electronic quadrupole polarization and other higher order effects. The value for the nuclear quadrupole moment of 14N in ammonia so obtained is 2.16× 10−26 cm2.
Effect of Pressure on the Rates of Reaction of Solvated Electrons in Liquid Ethanol
Authors: Jha Kamal N. , Freeman Gordon R.
Published: February 2004

At a γ radiolysis dose of 1× 1018 eV/g in ethanol at 296°K the hydrogen yields in neutral ethanol were G(H2)=5.0 at 1 bar and 5.5 at 5.3 kbar; in 1 mM and 1 M sulfuric acid G(H2)=5.7, independent of pressure. The electron scavengers nitrobenzene, acetone, and naphthalene reduce the hydrogen yields in neutral and acidic ethanol at 1 bar and 5.3 kbar; increasing the pressure greatly reduces the ease of scavenging the free ions but has only a small effect on scavenging efficiency in the spurs. Using as a standard the reaction esolv−→ C2H5Osolv−+H with k=1.2× 105 sec−1 at 1 bar and Δ V‡ =−14.4 cm2/mole averaged between 0 and 5.3 kbar, one obtains the following values for k(M−1· sec−1) and Δ V‡ (cm3/mole): esolv−+Hsolv+, 2.8× 1010 at zero ionic strength, +4.5; esolv−+C6H5NO2, 1.5× 1010, +7.5; esolv−+naphthalene, 5.0× 109, +5.6; esolv−+CH3COCH3, 4.2× 109, +5.1. The diffusion coefficient of solvated electrons in ethanol appears to correlate with the liquid viscosity; this is different from the behavior of electrons in alkanes. In ethanol Δ V‡diffusion≈ +7 cm3/mole for esolv− and +4 cm3/mole for Hsolv+. The free ion yield in ethanol is G(esolv−)fi=1.7, independent of pressure from 1 bar to 5.3 kbar; the model of Freeman and Fayadh [J. Chem. Phys. 43, 86 (1965)] is consistent with this behavior and it predicts that Gfi in methanol and water are also independent of pressure.
Laser Raman Spectra of Solid and Molten NaNH2: Evidence for Hindered Rotation of the NH2−1 Ion
Authors: Cunningham Paul T. , Maroni Victor A.
Published: February 2004

Results of a Raman study of solid and molten NaNH2 (mp≃ 211°C) from 25–220°C are reported. Three bands are observed in both the solid (3267, 3218, and 1531 cm−1) and the liquid (3267 dp, 3218 p, and 1550 p cm−1), which are assigned to the three expected fundamental modes of NH2−1 with C2v point symmetry. Additional bands were observed in the 300–700 cm−1 region for both the solid and the liquid. In the case of the liquid, the band envelope in this region was resolved into three Gaussian components, which are attributed to the hindered rotational modes of NH2−. There was no evidence of intermolecular hydrogen bonding between NH2− ions.
Pressure Dependence of Energy Transfer from Pyrene to Perylene
Authors: Johnson P. C. , Offen H. W.
Published: February 2004

The efficiency of singlet-singlet energy transfer between pyrene and perylene in polymethylmethacrylate decreases with increasing pressure, i.e., at 77°K the critical transfer distance R0 is 44 Å at 1 atm and 35 Å at 30 kbar. The factors responsible for the reduced efficiency at high pressure are in order of decreasing importance: the decrease in the fluorescence lifetime of the donor, the increase in the refractive index of the medium, and the decrease in spectral overlap of pyrene fluorescence and perylene absorption.
Translational Diffusion Coefficients of Rodlike Polymers: Application of the Modified Oseen Tensor
Authors: Yamakawa Hiromi , Tanaka Genzo
Published: February 2004

The translational diffusion coefficient of a rodlike polymer is investigated in the Kirkwood-Riseman scheme with the use of the modified Oseen tensor derived previously by Yamakawa for the finite bead model. If it is assumed that the friction coefficient of the beads may be described by Stokes' law, this tensor can remove the Zwanzig singularities from the possible range of the strength of the hydrodynamic interaction. It is pointed out that the preaveraging of the Oseen tensor may remove the singularities apparently in some cases. The correct asymptotic solution is also obtained without transforming a set of simultaneous equations determining the frictional forces to an integral equation. The results show that the finite bead model of a rodlike polymer is intermediate between the ellipsoid and cylinder models in transport behavior.
Second Born Zero Angle Differential Cross Sections in the High Energy Limit for the Electron Impact Excitation of He: The 23S ← 11S and 23P ← 11S Transitions
Authors: Bonham R. A.
Published: February 2004

The high energy limit of the inelastic differential cross section for the excitation of the 23S and 23P states of He from the ground state in the forward direction is investigated by expanding the T matrix in powers of V about zero scattering angle and considering all terms proportional to V and V2 where V is the interaction potential. It is shown that the leading terms in a power series in the reciprocal of the incident energy in this second Born infinite channel close coupling theory can qualitatively account for the observed enhancement of the exchange cross section in the forward direction over the predictions of the first Born theory. The ratio of the square of the leading second Born term to the square of the leading first Born term is shown to be proportional to the incident energy for the 23S ← 11S transitions and of the same order in the incident energy as the first Born form in the case of the 23P ← 11S transition. The value of the ratio at 500 eV for the 23S ← 11P transition is estimated to be close to 100 and is relatively independent of the choice of an effective energy loss parameter introduced to carry out the sum over intermediate states.
Automatic Evaluation of Cartesian Symmetry Coordinates in Molecular Dynamics
Authors: Dellepiane Giovanna , Tubino Riccardo , Ferri Liliana Degli Antoni
Published: February 2004

Cartesian symmetry coordinates for molecules can be automatically derived by diagonalizing the matrix B†B and collecting the eigenvectors of B†B into symmetry species by grouping interacting coordinates in the dynamical matrix. Labeling of each symmetry species according to the irreducible representations of the point group to which the molecule belongs, can be carried out by considering the components of first, second, and higher order tensors which are changed from the particular coordinate under consideration.
Pair Correlation Energies as Derived from the Analysis of Semiempirical Values of Correlation Energies of Atoms
Authors: Anno Tosinobu , Sakai Yoshiko
Published: February 2004

For the purpose of obtaining the semiempirical formulas for the pair correlation energy of various types of atoms and ions having the electron configurations 1s22sm2pn(m=0, 1, 2; n=0, 1, ..., 6), semiempirical values of the correlation energies of such atoms are analyzed. It is pointed out that the correlation energy in the average of a configuration is more convenient than the correlation energy in each of the stationary states belonging to the configuration, for the purpose of this analysis. The correlation energy in the average of the configuration is shown to be equal to EAvcorr, the average of the correlation energy in various states belonging to the configuration. The EAvcorr values are obtained for a wide variety of the 1s22sm2pn atoms and regularities are found among these EAvcorr values. From the analysis of these regularities, it is found that the EAvcorr values of the 1s22sm2pn atoms can be reproduced very well with an equation EAvcorr = C1 + C2m + C3n + C4m2 + C5mn + C6n2 + C7m2n + C8mn2 + C9m2n2 + C10 m (m − 1)Z + C11m(m − 1) nZ + C12m (m − 1)Z2, where Z is the atomic number, along with the numerical values of the coefficients Ci's (i=1, 2,..., 12) determined from a least-squares fitting of this equation to various empirical EAvcorr values. The concept of the average pair correlation energy of the configuration εkl is also proposed. Expressions for εkl's are given in terms of the pair correlation energies of various type in each of the states belonging to the configuration. It is shown that EAvcorr can be expressed in a simple form in terms of εkl's. From this expression and the semiempirical expression of EAvcorr mentioned above, a semiempirical formula for the average pair correlation energy is obtained for each type of electron pairs. It is found that these semiempirical formulas are in accord with the results of the Sinanoğlu theory for the ground and the excited states and of nonempirical calculations of pair correlation energies, rather than with those of a previous purely empirical analysis of the correlation energies by Allen, Clementi, and Gladney.
ESR Study of the Vinyl-Type Radical Trapped in a Single Crystal of Maleic Acid Irradiated at 77°K
Authors: Eda Bunzo , Iwasaki Machio
Published: February 2004

The substituted vinyl radical, DOOC–CH=ĊH, trapped in an irradiated single crystal of maleic acid-d2 has been studied by ESR to elucidate the geometrical and electronic structure of the vinyl-type radical. The hyperfine tensors for the 13C and β proton couplings have been determined to be (+133.8, +75.3, +62.2)G and (+59.5, +57.5, +56.8)G, respectively, in addition to the α proton coupling and g tensors preliminarily reported. All the magnetic tensors determined are consistent with the planar structure of the vinyl-type radical in which the unpaired electron occupies the in-plane sp hybrid orbital. The 13C hyperfine tensor indicates the relatively large spin density in the C2pσ orbital which is consistent with the small s character of the vinyl-type radical. The relative orientation of the hyperfine tensor of the α proton to that of 13C gives the clear evidence for the bent structure of the radical carbon atom. The dipolar tensor of the α proton coupling has been calculated using the spin distribution and the geometry obtained in our experiments, and the results are in good agreement with the observation in its magnitude as well as its directions. The apparent difference in the α proton coupling between C–H π and σ radicals has been discussed in relation to the sign of the isotropic coupling.
Paramagnetic Resonance of Interstitial V4+ in TiO2
Authors: Kubec F. , Šroubek Z.
Published: February 2004

The effects of various technological processes on the electronic structure of vanadium-doped TiO2 crystals have been studied. The EPR spectra give clear evidence that by suitable thermal treatment in a reducing atmosphere the tetravalent vanadium ions can be transferred from the substitutional to the interstitial positions. The four inequivalent spectra corresponding to the four interstitial octahedra have been analyzed and interpreted in terms of a microscopical model. The measured values of the components of the g-tensor and hyperfine interaction tensor are: gx = 1.9865 ± 0.0005, | Ax | = 45.4 ± 0.5 × 10−4 cm−1; gy = 1.9930 ± 0.0005, | Ay | = 60.5 ± 0.5 × 10−4 cm−1; gz = 1.9407 ± 0.0005, | Az | = 111.4 ± 0.5 × 10−4 cm−1. The linewidth was found to be approximately 2.8 G. The intensity of the absorption lines is one-tenth of the intensity of the original resonance of the substitutional V4+. The deviation of the axes of the magnetic coordinate systems of the four nonequivalent ions with respect to the substitutional sites was found to be φ = ± 10° (± 0.5°).
Valence Structure from X-Ray Diffraction Data: Physical Properties
Authors: Stewart Robert F.
Published: February 2004

It is assumed that the one-electron density function for a molecular crystal can be determined from x-ray diffraction data with the use of generalized x-ray scattering factors. The relationship between several physical properties and electron population parameters are given. These include molecular dipole moments and atomic electric field gradients, which can be compared to results from other experiments. The physical properties that follow from electron population analysis can serve as criteria in judging the reliability of x-ray diffraction data for charge density information.
Competitive Photolysis of CO2 and N2O at 1633 Å
Authors: Loucks Leon F. , Cvetanović R. J.
Published: February 2004

Mixtures of CO2 and N2O have been photolyzed with 1633 Å radiation. The primary photolytic products are nitrogen and carbon monoxide and their ratio, N2/CO, has been examined as a function of the ratio of reactants, N2O/CO2. The form of this function is entirely explained by a reaction mechanism that involves deactivation of O(1D2) by CO2 and reaction of O(1D2) with N2O. Kinetic analysis of the data gives for the ratio of the rate constant for deactivation of O(1D2) by CO2 to the rate constant for the total reaction of O(1D2) with N2O a value of 0.80, in good agreement with previous determinations of this ratio.
Multiple-Scattering Effects in High-Energy Electron-Molecule Collisions. II Polyatomic Molecules
Authors: Yates Albert C.
Published: February 2004

The Glauber theory of multiple scattering is applied to the elastic collisions of fast electrons with polyatomic molecules in an effort to explain deviations between theory and experiment in recent molecular structure determination by electron diffraction. The full scattering amplitude is developed inclusive of all double-scattering contributions, with the differential cross section for the process given up to terms representative of the interference between single and double scattering. For sufficiently energetic incident electrons, the multiple-scattering contributions to the differential cross section are shown to reduce to simple analytic forms. In particular, the three-atom single-double interference term is shown to be an oscillatory function of momentum transfer. Application of the approximate formulas to the rhenium hexafluoride molecule gives excellent agreement with the experimental results of Jacob and Bartell.
Upper and Lower Bounds to Excited States of Two-Electron Atoms
Authors: Wang P. S. C. , Weinhold F.
Published: February 2004

The excited 1,3S and 1,3P states of the helium isoelectronic sequence are treated by the Ritz and Bazley variational methods, which together provide rigorous upper and lower bounds to the true nonrelativistic energy levels. With compact variational functions constructed from about 25 hydrogenic basis terms, up to 20 or more states of each symmetry can be treated for each ion. The error limits finally approach a few parts in 105 or better for many of the more highly excited states (including many not yet observed), an accuracy sufficient to determine the ionization potentials to about 1%.
Photophysical Processes in Polymers. VI. Spectroscopic Properties of 1-Vinylpyrene and Poly(1-Vinylpyrene)
Authors: McDonald J. R. , Echols W. E. , Price T. R. , Fox R. B.
Published: February 2004

The absorption spectra, corrected fluorescence spectra, and fluorescence quantum yields of 1-vinylpyrene and poly(1-vinylpyrene) are reported. The triplet-triplet absorption spectrum of poly(1-vinylpyrene) is compared to that of pyrene, and the excimer fluorescence of the polymer is studied as a function of temperature. Based upon the temperature dependence of the excimer emission, it is concluded that efficient formation and inefficient emission of nonequilibrium-geometry pyrene excimers takes place in poly(1-vinylpyrene). Radiative and radiationless transition mechanisms are discussed. Values reported for poly(1-vinylpyrene) in fluid solution at room temperature are qFM ≅ 0, qFD = 0.44, qPM ≅ 0, φT = 0.005, kFD = 0.83 × 107sec−1, kGD = 1.0 × 107sec−1, kDM >∼ 1 × 107sec−1, and kTM <∼ 5 × 105sec−1.
On Acoustic Measurements of Rotational Energy Transfer
Authors: Bauer H.-J. , Bass H. E.
Published: February 2004

The problem of using acoustic measurements to determine rotational energy transfer rates has been examined. A method to link the rate of energy transfer to the acoustic behavior of the gas was developed and applied to the collision model of Raff and Winter. The results in the case of H2 demonstrate the importance of using an accurate acoustical treatment when testing a reaction model.
Adequacy of the Molecular Orbital Approximation for Predicting Rotation and Inversion Barriers
Authors: Allen Leland C. , Arents John
Published: February 2004

We demonstrate by numerical analysis that quantitatively useful barrier magnitudes may be obtained within the framework of the molecular orbital method. Use is made of a theorem by K. F. Freed that the first derivative at a midpoint between adjacent extrema in a sinusoidal potential energy curve can be determined to second order for Hartree-Fock wavefunctions and the fact that potential energy functions of the form E(x) = ax2 + bx4 + c exp(−gx2),E(x) = ax2 + bx4 + fx3,E(x) = (1/2 ) ∑ j Vj (1−cosjx),are known to represent all existing rotation and inversion barriers within experimental error. We then show by illustrative computations that the stated potential functions usually have first derivatives (at midpoints between adjacent extrema) equal, within ± 5 %, to first derivatives of the sine curve arcs required by Freed's theorem. Thus, barriers may be predicted adequately by ab initio and, in principle, by semiempirical molecular orbital methods. This suggests that quantitative prediction of conformations of large organic molecules may be possible.
Temperature Dependence of Hard-Sphere Interference Functions
Authors: Halder N. C. , Jena P.
Published: February 2004

It is shown in this paper that the Debye-Waller correction is important in the study of hard-sphere interference function IDW(q) for liquid metals. The calculated IDW(q) agree remarkably well with the experimental Iexptl(q) indicating the right trend for the temperature dependence. An evaluation has been also made of the electron transport and nuclear magnetic resonance properties for a number of liquid metals with the calculated IDW(q). The results show much better agreement with the corresponding experimental values than hitherto has been published.
Crystal Coulomb Energies. II. The Electrostatic Binding Energy of Four Organic Donor-Acceptor Crystals by Ewald's Method and Charge Transfer in Organic Lattices
Authors: Metzger Robert Melville
Published: February 2004

In an effort to confirm the classification of four organic donor-acceptor crystals into the almost fully ionic (``holoionic'') class, and the nearly neutral (``nonionic'') class, their electrostatic binding energies EC, based on the point-charge model, have been calculated rigorously. The EC were found to be model independent, and were compared with 2ε0, the cost of ionizing the lattices. EC+ 2ε0>0 was expected for the two crystals which are experimentally known to be nonionic: for (1:1)-(hexamethylbenzene: para-chloranil) the result was EC=−4.4 eV against 2ε0=6.6 eV, and for (1:1)-(naphthalene:tetracyanoethylene) EC=−4.3 eV vs 2 ε0=6.5 eV. For the two crystals which are holoionic by experiment EC+ 2ε0<0 was expected, but for (1:1)-(N, N, N′, N′, -tetramethyl-para-phenylenediamine+ 7, 7, 8, 8-tetracyanoquinodimethan−) the result was EC=−3.9 eV vs 2ε0=4.6 eV, and for (1:1)-(N, N, N′, N′-tetramethyl-para-phenylenediamine+ -para-chloranil−) EC=−4.4 and 2ε0=4.9 eV. Clearly in these crystals the total binding energy must include a nonnegligible exchange Coulomb energy.
Linear Momentum Transfer Effects in Molecular Dissociation Produced by Electron Impact
Authors: Misakian Martin , Pearl John C. , Mumma Michael J.
Published: February 2004

Dissociative processes in molecules excited by electron impact can be studied by examining the angular distributions of dissociation fragments. Previous theoretical calculations of angular distributions have not included the effects of linear momentum transfer in the collision process. Such effects can be significant. A procedure, valid near threshold, is developed which permits the calculation of laboratory angular and velocity distributions. The results are applied with some success to dissociative ionization in molecular hydrogen.
On a Gas-Phase Electron Diffraction Study of Vinyl Chloride
Authors: Ivey R. C. , Davis M. I.
Published: February 2004

The molecular structure of vinyl chloride has been determined by the technique of gas-phase electron diffraction. The structural parameters, with estimated uncertainties, were found to be r (C=C) = 1.355 (0.008) Å, r (C–Cl)=1.728 (0.007) Å, r (C–H)=1.078 (0.011) Å, and ≮CCCl=121.1° (0.9°).
Single Crystal ESR Study of Mn2+ in Natural Tremolite
Authors: Golding R. M. , Newman R. H. , Rae A. D. , Tennant W. C.
Published: February 2004

The room temperature 9.5 GHz ESR spectrum of a natural tremolite single crystal containing 0.15% Mn2+ is analysed using both perturbation and numerical solutions to the experimental Hamiltonian. The analysis is in three parts: (i) allowed, Δ MS=± 1, Δ MI=0 transitions, (ii) forbidden, Δ MS=± 1, Δ MI>0 transitions, and (iii) forbidden, | Δ MS | > 1 transitions. Mn2+ occupies only a single site in the tremolite structure.
Optimized Cluster Expansions for Classical Fluids. II. Theory of Molecular Liquids
Authors: Chandler David , Andersen Hans C.
Published: February 2004

The optimized cluster expansion methods developed in the first article of this series (I) are generalized to apply to molecular fluids. These methods make use of summations of ring and chain cluster diagrams. The summations are performed explicitly for certain classes of molecular models. The molecules in these classes contain several ``interaction sites,'' and the total interaction between two molecules is a sum of site-site potentials that depend on the scalar distances between sites on the two molecules. The principal results of this work are computationally simple techniques for calculating the thermo-dynamic properties and pair correlation functions of molecular fluids in which the intermolecular interactions are highly angular dependent. The techniques should be reliable since they arise from the same approximations that have been shown to be very accurate when applied to simple fluids.
Effect of VV Transfer on the Rate of Diatomic Dissociation
Authors: Kiefer John H.
Published: February 2004

The effect of VV transfer processes on the rate of thermal dissociation of diatomic molecules is considered within the steady-state approximation for a single-quantum step master equation. An accurate rate law is obtained for the truncated harmonic oscillator through replacement of the agents for VV transfer by the vibrational energy. Approximate numerical solutions for a Morse oscillator model of the representative species O2, H2, and HCl are in quite satisfactory agreement with the measured rates and provide at least qualitative explanations for nearly all the unusual features of the measurements. The rate enhancement effect of VV transfer is found to be slight; the primary, and quite general consequence of VV transfer is rather a depression of the rate, especially at high temperatures, which then appears as a considerable reduction in activation energy. This effect is shown to arise from a violation of detailed balance for the VV processes whenever the vibrational energy is depleted by rapid dissociation.
Autoionizing 2s22p43s3l States of Ne and Related Ne− Resonances
Authors: Bolduc E. , Quéméner J. J. , Marmet P.
Published: February 2004

Many autoionizing levels of Ne are seen in the ionization efficiency (I.E.) curve between 42 and 51 eV and reported for the first time. A method to estimate energies of 2s22p43s3l states leading to the interpretation of our data is presented. Four negative-ion states are also identified, and their shape factors q and widths Γ are given. New techniques had to be developed and are described.
Number Dependence of Small-Crystal Thermodynamic Properties. II
Authors: Abraham Farid F. , Kortzeborn Robert N.
Published: February 2004

Using computer calculated entropies for various two and three dimensional crystallites, a least-squares analysis is performed to determine the coefficients of a function which is assumed to represent the functional dependence of the entropy on crystal size and shape. With a complete determination of the coefficients, this entropy function may be applied to any shape crystallite. The features of the entropy function are discussed. In particular, the replacement entropy is found to a good approximation to be independent of crystal shape and may be described by a very simple dependence on the dimensionality of the crystal.
Radiative Recombination of Atoms as a Resonance Scattering Process
Authors: Carrington Tucker
Published: February 2004

The rate coefficient for two-body radiative recombination of atoms via the ``crossing'' of two potential curves is derived from the Breit-Wigner cross section for resonance scattering. The level widths, the natural parameters in terms of which to describe the scattering, are the starting point. The development allows one to investigate the dependence of the recombination rate on level widths and on the position of the dissociation limit of the outer potential curve relative to the rotational structure in the inner curve. It also provides a unique definition of the probability of radiative recombination per collision.
Ballistic Mechanism for Vibrational and Rotational Energy Transfer in Ar + CsI Collisions
Authors: Loesch H. J. , Herschbach D. R.
Published: February 2004

Velocity and angular distributions have been measured for scattering from crossed beams of Ar and CsI. The Ar beam was generated by the seeded-nozzle technique, using dilution with H2 and varying the source temperature to obtain collision energies from 0.35 to 1.1 eV. The CsI beam was generated by thermal effusion at ∼ 1000 ° K. Mass spectrometric analysis of the scattered CsI was carried out for both the parent CsI+ ion and the fragment Cs+ ion. The velocity spectra for Cs+ show very pronounced peaks located near the ArCsI centroid. These peaks correspond to an extremely inelastic, ``ballistic'' process in which most of the initial relative translational energy goes into vibrational or rotational excitation. The velocity spectra for CsI+ agree with Cs+ in the elastic region but show almost no inelastic peak. This is consistent with the ballistic process, since highly vibrationally excited molecules are likely to be readily fragmented by electron bombardment. Kinematic analysis of the data indicates the fractional energy transfer Δ E/E> 90 % for the wide-angle inelastic scattering. The energy transfer decreases appreciably at smaller angles. The intensity of inelastic scattering into the forward hemisphere is roughly a factor of 2 larger than that into the backward hemisphere. The angular distribution of elastic scattering also has an unusual shape, with a pronounced minimum apparently due to attenuation by the inelastic scattering. The total cross section for ballistic energy transfer is about 20 Å2. An optical model treatment shows the angular distributions are consistent with an inelastic transition probability which is low for small impact parameters and high for large impact parameters. Vibrational and rotational energy transfer are shown to be comparable for impact parameters that give the maximum transition probability, near b ∼ 2.7 ± 0.7 Å. At smaller b the excitation is primarily vibrational, at larger b primarily rotational. The Δ E/E predicted for a completely impulsive hard-sphere collision (determined solely by mass ratios) is only 40%. This suggests the ballistic mechanism differs qualitatively from Landau-Teller; it may involve a resonant or quasibound ArCsI complex.
Physical Interpretation of Glory Undulations in Scattering Cross Sections
Authors: Greene E. F. , Mason E. A.
Published: February 2004

The physical interpretation of the spacing of glory undulations as a function of energy is approached through the interpretation of the coefficients in a semiclassical expansion in the relative kinetic energy of the form (a1 − A1 K−1+ A2K−2+ ··· ). The coefficient a1 measures the area of the intermolecular potential well along the glory trajectory, whereas A1 and A2 give measures of the square and cube of the well, respectively. Examples are given for square-well and Lennard-Jones (n, 6) potentials. Measured values of the spacings of the glory oscillations for a system do not give as specific information on the potential as has sometimes been conjectured, but the information obtainable is quite definite and can be used to put constraints on the form of the potential for that system.
Gas Phase Pulse Radiolysis of Hydrocarbon Mixtures; Determination of the Charge Recombination Rate Coefficient and Absolute Rate Constants of Ion-Molecule Reactions of the t-Butyl Ion through a Competitive Kinetic Method
Authors: Lias S. G. , Rebbert R. E. , Ausloos P.
Published: February 2004

The gas phase pulse radiolysis of several neopentane-d12-alkane mixtures has been studied with the purpose of examining the competition between the reaction of the fragment t-butyl ion with the alkane to form isobutane, t-C4D9+ +RH2→ i-C4D9H+RH+, and the neutralization of the t-butyl ion by an electron or SF6− ion, t-C4D9++X−→products. Using a computer calculation which takes into account the pulse characteristics as a function of time, the yield of isobutane observed in the reaction with 2,3-dimethylbutane (for which krn was accurately determined to be 5.7 ± 0.5 × 10−11 cm3/molecule·sec) and the dose per pulse, rate coefficients of the competing neutralization reactions were determined. These are α=1.92 ± 0.2 × 10−6 cm3/molecule· sec for neutralization by an electron, and 0.40± 0.04 × 10−6 cm3/molecule· sec for neutralization by the SF6− ion. The latter value is independent of SF6 concentration and both are independent of pressure between 40 and 200 torr. Finally, these values of the neutralization rate coefficients and yields of isobutane measured in the pulse radiolysis of neopentane in the presence of other added alkanes (2-methylpentane, 3-methylpentane, methylcyclopentane) are used to calculate absolute rate coefficients of the hydride transfer reactions between the t-C4D9+ ion and these compounds; the values determined are in good agreement with those measured by other techniques. The unique feature of the competitive method described here consists of the fact that the positive ion which is neutralized can be identified by the conventional analysis of a known reaction product.
Single Crystal Broad-Line 55Mn NMR in Adducts of Manganese Pentacarbonyl, X3M–Mn(CO)
Authors: Slater J. L. , Pupp M. , Sheline R. K.
Published: February 2004

Single crystals of four members of the series X3M–Mn(CO)5 [X3M is (C6H5)3Pb, (C6H5)3Sn, (C6H5)3Ge, and Cl3Sn] were grown and the 55Mn broad-line NMR was studied at room temperature. The 55Mn quadrupole coupling constants (e2qQ/h) are 7.3 MHz [Cl3Sn–Mn(CO)5], 12.04 MHz [(C6H5)3Pb–Mn(CO)4], 18.33 MHz [(C6H5)3Sn–Mn(CO)5], and 24.636 MHz [(C6H5)3Ge–Mn(CO)5]. The quadrupole coupling constants are related to the electronegativities and are discussed by comparison to empirical predictions derived from NQR data on the similar X3M–Co(CO)4 series. The asymmetry parameters are in the range 0.11–0.37. For (C6H5)3Ge–Mn(CO)5, the anisotropic chemical shift tensor was determined and the charge distribution around the manganese was found to be isotropic.
Resolution of the Absorption Spectrum of Solvated Electrons
Authors: Lugo Roberto , Delahay Paul
Published: February 2004

The abosprtion spectrum of solvated electrons is resolved by superposition of one or several Gaussian-shaped bound-bound (bb) bands and one bound-continuum (bc) band. A previously derived equation is applied for the bc band. Energy levels, band amplitudes, widths, and contributions are given for tetrahydrofuran, ethylenediamine, hexamethylphosphoric triamide, water (all at room temperature), ammonia (−65°C), and 3-methylpentane (77°K). Resolution is tentative for ethylenediamine because of insufficient experimental data and for ammonia and water because of inadequancy of the equation for the bc band. Experimental evidence supports this equation for all solvents except ammonia and water. A theoretical limitation is indicated. Energy levels are correlated with the nature of the solvent as characterized by the difference β between the reciprocals of the optical and static dielectric constants. Spectra of solvated electrons in solvents with low β's show a major contribution from the bc transition and only one bb transition. Conversely, a high β results in a more complex spectrum with a relatively minor bc contribution.
Photoelectron Emission Spectroscopy of Cyanometalate Complexes in Aqueous Solutions
Authors: Nemec Ladislav , Delahay Paul
Published: February 2004

Improved experimental methods for photoelectron emission (PEE) spectroscopy of solutions were developed and applied to aqueous solutions of K4Fe(CN)6 and similar emitters. Aspects covered for K4Fe(CN)6: back scattering of electrons in water vapor; lack of detectable Schottky effect; determination of a red shift of the PEE spectrum at constant current upon temperature increase (≈ − 5 × 10−4 eV per degree); variation of quantum yield (≈ 2 × 10−9 to ≈ 2 × 10−5 collected electron per incident photon) with photon energy for concentrations from 0.005 to 0.1 mole liter−1; dependence of molar quantum yield on emitter concentration. PEE spectra are also given for 0.1M aqueous solutions of Na3[Fe(CN)5H2O], Na3[Fe(CN)5NH3], K4Mn(CN)6, K4Ru(CN)6, K4Mo(CN)8, K4W(CN)8.
Single Crystal Study of the 19F Shielding Tensors of a Trifluoromethyl Group
Authors: Griffin R. G. , Ellett J. D. , Mehring M. , Bullitt J. G. , Waugh J. S.
Published: February 2004

Coherent averaging techniques are used to examine the 19F shielding tensors of the trifluoromethyl group in single crystals of silver trifluoroacetate. At room temperature, where the CF3 groups are rotating rapidly, the spectrum consists of a single line whose orientation dependence allows a determination of the orientation of the CF3 groups in the unit cell. The rigid lattice (40°K) spectra exhibit the six lines expected on the basis of the x-ray crystal structure, also determined in this work, and allow a determination of all six independent elements of each of the three incongruent chemical shift tensors.
Vacuum Ultraviolet Photochemistry of Cyclobutanone
Authors: Scala Alfred A. , Ballan Daniel G.
Published: February 2004

The photodecomposition of cyclobutanone in the vacuum ultraviolet is characterized by → C2H4 + CH2 + CO,→ CO+C3H6.At 147.0 nm and high pressure the quantum yields of Reactions (1) and (2) are approximately 0.7 and 0.25 respectively. At 123.6 and 106.7–4.8 nm the ratio of the quantum yield of Reaction (2) relative to Reaction (1) is 0.28. The quantum yield of carbon monoxide is unity at 147.0 and 123.6 nm and 0.81 at 106.7–4.8. Although Reaction (2) is best interpreted in terms of a trimethylene diradical intermediate, at 147.0 nm Reaction (2) produces propylene in a primary process with a quantum yield of 0.09. There is no evidence for the production of primary propylene at 123.6 or 106.7–4.8 nm. Pressure studies at 106.7–4.8 nm indicate that the cyclopropane produced in Reaction (2) contains only about 90 kcal.mole of excess vibrational energy. This result requires that carbon monoxide is produced either with 175 kcal/mole of excess vibrational energy or more likely in an electronically excited state.
Reactions of NO+ with H2O in a Photoionization Mass Spectrometer
Authors: McAdams M. J. , Bone L. I.
Published: February 2004

The reactions of NO+ with H2O have been studied in a photoionization mass spectrometer. Nitrosonium ions produced by Kr resonance radiation at 10.03 eV react with water in a field free region. Products observed are NO(H2O)n+ (n=1, 2, 3) and H(H2O)n+ (n=1–5). Rate constants are calculated, heats of formation of hydrated NO+ are estimated and some evidence is presented which is consistent with a structure of NO(H2O)n+ where the waters are hydrogen bonded in a linear fashion rather than forming a solvation sphere.
Collision Broadening of Rotational Spectrum
Authors: Gross Eugene P. , Otieno-Malo J.
Published: February 2004

The problem studied is the rotational absorption spectrum of linear molecules of moment inertia I in a simple nonpolar buffer gas. The focus is on the behavior of the spectrum as the buffer gas pressure and the associated collision frequency ν is increased. Four regions are distinguished. (1) ν≪ℏ/I, there are sharp lines with a van Vleck-Weisskopf line shape; (2) ν≃ℏ/I, the contributions from overlapping lines are summed analytically. The ratio of minimum to maximum absorption in the weakly oscillatory spectrum is computed. (3) ℏ/I<ν<(2kT/I)1/2, This is the classical inertial region where there is a single maximum in the absorption per cycle. We compute its position as it moves from an angular frequency (2kT/I)1/2 to lower frequencies with increasing collision frequency. (4) ν>(2kT/I)1/2, this is the region where the Debye frequency profile is valid, with the peak of absorption at an angular frequency (1/ν) (2kT/I). The calculations are based on a kinetic equation for the density matrix with a single relaxation time, no position change, collision model. We also compute the time dependent correlation functions needed in the theory of the rotational Raman effect of linear molecules.
Polarization Dependence of Three-Photon Phenomena for Randomly Oriented Molecules
Authors: McClain W. M.
Published: February 2004

We examine the polarization dependence of phenomena involving the interaction of three photons and a molecule, in the regime where the interaction is complete before the molecule has time to rotate. We obtain an explicit general formula for the orientation average of the observed intensity, which will be applicable to a randomly oriented sample of molecules. The results apply to simultaneous three-photon absorption, hyper-Raman or double quantum scattering, or other simultaneous three-photon effects in fluids. In viscous media the results apply to sequential three-photon absorptions or to simultaneous two-photon absorption followed by fluorescence, and to three-step photochemical processes in solid matrices. An experimental procedure is given for determining all the available molecular parameters of such processes. Certain simplifications of the general procedure arise in special cases. In all cases the formulas obtained are of the form I=〈|λAμBνCTABC|2〉=Pi(λμν) MijQj(T), where I is the intensity of the effect, (λ, μ, ν) are the polarization vectors, T is the three-photon tensor, the Pi(λ, μ, ν) are a set of polarization parameters, the Qj (T) are a set of molecular parameters, and Mij is an averaging matrix. The Pi, Mij, and Qj are given explicitly for all cases considered. Thus the polarization dependence problem has been reduced to a linear algebra problem.
Lattice Vibrations in Ammonium Chloride in the Low-Temperature Ordered Phase
Authors: Kim C. H. , Rafizadeh Hamid A. , Yip Sidney
Published: February 2004

A rigid-molecule model is used to analyze the lattice vibrations in ammonium chloride in the ordered phase (III). The ammonium and chlorine are treated as rigid ions with a partial charge, and short-range forces out to the third nearest neighbor are considered. The model is shown to give a good fit of the neutron dispersion curve data on ND4Cl at 85°K. Lattice frequency spectra are computed and decomposed into components associated with chlorine vibrations and ammonium translations and librations. Comparison with a recent shell-model calculation shows that the numerical results are quite similar. The present results are also used to discuss the lattice heat capacity, mean square displacements, and incoherent neutron scattering.
Nonlinear Coupling among Critical Fluctuations: A Possible Source of Weak Divergences at a Critical Point
Authors: Mistura L.
Published: February 2004

It is shown that a nonlinear coupling among critical fluctuations produces weak divergences in certain thermodynamic derivatives in agreement with the scaling law predictions. Moreover, restricting our analysis to quadratic terms in the order parameter fluctuations, an explicit expression is provided for the amplitude of the singularities. Weak divergences in binary mixtures are discussed in detail, including several exceptional cases, such as critical azeotropy. No divergence is predicted in general for the heat capacity at constant volume and concentration.
Sound Propagation near a Critical Point in Multicomponent Fluid Systems
Authors: Mistura L.
Published: February 2004

As formulated by Fixman and by Kawasaki and Tanaka, the theory for sound propagation near a consolute critical point is inconsistent with the Wheeler and Griffiths thermodynamic bounds. A modification of the original version of the theory is proposed to avoid this difficulty. Sound propagation in binary mixtures is discussed in detail including special critical points such as critical azeotropy. Formulas for sound absorption and dispersion are also given for a multicomponent system in the general case. We found that, increasing the number of components, the magnitude of critical sound absorption and dispersion should decrease.
Perturbation Calculation of the Nuclear Spin-Spin Coupling Constant in HD based on the Bare-Nucleus Potential
Authors: Schulman Jerome M. , Kaufman D. Neal
Published: February 2004

Perturbation calculations of the Fermi contact part of the electron-coupled nuclear spin-spin coupling constant (J) in the HD molecule have been performed in the bare-nucleus potential. A very large Gaussian basis has been employed and, in addition, the effect on J of varying the HD internuclear separation has been considered. The term zeroth order in correlation, J0, is in good agreement with an independent basis set study as is the geometric approximate to the coupled Hartree-Fock value. The J0 and J1 values reported here differ significantly from those reported in a recent bare-nucleus perturbation study using numerical H2+ orbitals. We give here a refined value of our previous Hartree perturbative results based on this larger atomic basis set.
Measurement of the Thermal Conductivity of Argon, Krypton, and Nitrogen in the Range 800–2000°K
Authors: Faubert Francis M. , Springer George S.
Published: February 2004

The thermal conductivities of argon, krypton, and nitrogen were measured at 760 mm Hg in the temperature range 800–2000°K. Two thermal conductivity columns of different outside diameters were used in the experiments to provide an assessment of the convective heat transfer. In addition, potential leads were employed to minimize convection and end effects. The thermal conductivity values obtained were compared with existing data, with results of viscosity measurements, and with theoretical predictions.
Theory of the Spontaneous Polarization and the Pyroelectric Coefficient of Linear Chain Polymers
Authors: Aslaksen Erik W.
Published: February 2004

Polyvinylidene fluoride (PVF2) films consist of two crystalline phases; their relative abundance is determined by the draw temperature. One phase has a chain repeat of two monomer units, the other a planar zig-zag conformation. We assume that the latter phase is responsible for the spontaneous polarization, and present a model, which should be applicable to linear chain polymers in general, of the polarization state of such a phase, in which the temperature dependence of the polarization arises from the torsional oscillations of the macromolecules. Three torques are taken into account: a phenomenological one due to nearest neighbor interaction, one due to the torsional stiffness of the macromolecule, and one due to the interaction of the permanent dipole moment with the local electric field. Numerical calculations show that this model can account for all the experimental data known so far, and the calculations also clearly demonstrate the dynamics of the poling process.