bluuebunny/crossref_metadata_2025 huggingface dataset:
General rotational relaxation matrix: Linewidths for oxygen, their interrelation and relation to theory
Authors: Pickett Herbert M.
Published: February 2003

The interrelation of linewidth measurements for molecular oxygen EPR, millimeter wavelength, and infrared and Raman rotational transitions is described. These kinds of linewidth measurements are interrelated through a limited set of parameters which are sensitive to the nature of collision dynamics and intermolecular potentials. The limitations on these parameters set by theory are discussed, and expected magnitudes of the parameters in the weak-collision and statistical limits are described. The relative magnitudes of the parameters also provide a direct experimental test of approximate theories in which time ordering is neglected. Analysis of the N=1 EPR transitions for oxygen self-broadening indicate that pure reorientation cross sections are small compared with the cross section for rotational energy transfer from the N=1 states. The magnitudes of the experimental parameters for N=1 are best represented by a statistical model.
Translational and internal energy dependences of some ion–neutral reactions
Authors: Lindinger W. , McFarland M. , Fehsenfeld F. C. , Albritton D. L. , Schmeltekopf A. L. , Ferguson E. E.
Published: February 2003

The forward and reverse rate constants for the proton-transfer reaction, N2OH++CO?COH++N2O, have been measured as a function of temperature in a variable-temperature flowing afterglow and as a function of relative kinetic energy in a flow-drift tube using both helium and argon buffer gases. The temperature variation of the rate constant was used to obtain ΔH0 =−4.4±0.4 kcal/mole and ΔS0=−4.0±1.0 entropy units. Furthermore, the comparison of the data taken as a function of temperature with those taken as a function of relative kinetic energy in different buffer gases shows that there are marked effects of ion vibrational energy on these rate constants. Similar data on the charge–transfer reaction, CO2++O2→O2++CO2, show the same effects. In addition, relative kinetic energy data on the proton transfer, ArH++O2→O2H++Ar, also imply strong effects of vibrational excitation on the rate constant.
Theory of inhomogeneous polymers: Lattice model for polymer–polymer interfaces
Authors: Helfand Eugene
Published: February 2003

An inhomogeneous polymer system is analyzed on the basis of a lattice model, in the spirit of the Flory–Huggins approach. Although the theory is developed in some detail, so as to point the way to future applications, only equations for the problem of polymer–polymer interfaces are derived. In the limit of broad interfaces the results of Helfand and Tagami are recovered. For the more general cases numerical results are presented.
Degenerate many-body perturbation theory: Excited states of H2
Authors: Kaldor Uzi
Published: February 2003

The degenerate many-body perturbation theory in Brandow’s diagrammatic expansion is applied to 16 excited states of H2 at two internuclear separations. A single set of molecular orbitals at each separation is used for all states. Energy corrections up to third order (inclusive) are calculated, and higher-order effects are estimated by geometric extrapolation. Results agree with best available values to 1–2 kcal/mole. Differences between Goldstone and Brandow diagrams are discussed.
Test of the Li+–He interaction potential
Authors: Morrison W. F. , Akridge G. R. , Ellis H. W. , Pai R. Y. , McDaniel E. W. , Viehland L. A. , Mason E. A.
Published: February 2003

The mobility of Li+ ions in He has been measured at a gas temperature of 300 °K over a wide range of E/N, where E is the electric field intensity and N is the gas number density. A new theory of ion mobility is used to calculate from these data the standard Ω integral ?(1,1) of kinetic theory for Li+ in He over a range of effective gas temperature extending from 300 to 28 700 °K. The ab initio quantum mechanical interaction potential for the Li+–He system computed by Catlow et al. is also used to calculate ?(1,1) as a function of Teff. A comparison of the two sets of data serves as a test of the Catlow potential. The test is extended to still higher effective temperatures (up to 60 000 °K) by comparison with values of ?(1,1) computed from the short-range repulsive potential derived from Li+ beam scattering experiments in helium. The Catlow potential reproduces the general features of the dependence of the ’’experimental’’ Ω integral on Teff over the entire range of the test. However, significant discrepancies exist; they could be resolved by making substantial alterations in the Catlow potential in the region of short ion–atom separation distance and smaller adjustments in the region of the potential minimum.
On the existence of bound helium trimers by the equivalent two-body method
Authors: Lim T. K. , Zuniga Michael A.
Published: February 2003

The binding energies of the 3,4He trimers are computed for a range of realistic interatomic potentials using the equivalent two-body method of Bodmer and Ali. We find a 4He trimer bound with a binding energy of about 0.25°K and a 3He trimer which is but loosely bound. We also confirm that the Hall–Post–Stenschke method gives poor lower bounds to the energy and that (4He)3 is large, having a root mean square interparticle spacing of 23 Å.
Vibrational relaxation of DF by He and Ar
Authors: Bott J. F.
Published: February 2003

Relaxation times of DF in Ar near 1000 °K and of DF in He between 1000 and 2600 °K have been obtained in a shock tube experiment and the results have been compared with other results and calculations. It is concluded that both rotation and translation must be included in a proper description of the relaxation process. (AIP)
Distortion of the (CN−)4 plane of Ni(CN)43− complex in NaCl: Evidence from EPR
Authors: Reddy K. V. , Reddy T. Rs. , Jain S. C.
Published: February 2003

The complex Ni(CN)43−, which would be expected to be unstable, was produced by x and γ irradiation of NaCl crystals doped with the stable complex Ni(CN)42−. The EPR spectrum of Ni(CN)42− was observed and its temperature dependence explained in terms of distortion of the complex from its square planar structure. (AIP)
Dense liquids. II. The effect of density and temperature on viscosity of tetramethylsilane and benzene
Authors: Parkhurst H. J. , Jonas J.
Published: February 2003

The effect of temperature and pressure on the shear viscosities of liquid tetramethylsilane and benzene are reported in the dense liquid region. In agreement with molecular dynamics results, the Stokes–Einstein relation is found to be valid at the molecular level for the liquids studied. As expected on the basis of self-diffusion data, the shear viscosities can be explained by using the rough hard sphere model based on the modified Enskog theory of liquids by assuming a temperature dependence of the effective hard core diameter. For high packing fractions at which ρσ3≳0.93, the experimental fluidity is much larger than the theoretically predicted fluidity. This observation suggests a possible density effect on the effective hard core diameter at very high densities. In addition, the experimental hard core diameters are compared with the diameters obtained by other techniques.
Semiclassical transition state theory for nonseparable systems: Application to the collinear H+H2 reaction
Authors: Chapman Sally , Garrett Bruce C. , Miller William H.
Published: February 2003

Two different kinds of semiclassical approximations are used to evaluate a previously obtained quantum mechanical transition state theory rate expression. No assumptions, however, such as separability of the Hamiltonian, vibrationally adiabatic motion along a reaction coordinate, etc., are incorporated. Application is made to the collinear H+H2 reaction, and agreement with accurate quantum scattering calculations is found to be reasonably good. The results indicate that transition state theory—provided no assumptions of separability are included—is probably as accurate quantum mechanically as it has been found to be classically for describing the threshold of chemical reactions with an activation barrier.
Energy transfer from argon resonance states to nitrogen, hydrogen, and nitric oxide
Authors: McNeely J. R. , Hurst G. S. , Wagner E. B. , Payne M. G.
Published: February 2003

Transfer of electronic energy from the resonance states Ar(1P1) and Ar(3P1) to diatomic nitrogen, hydrogen, and nitric oxide has been studied with a time-resolved quenching technique. Rate constants for energy transfer were deduced from the changes of the rate of decay of excited states corresponding to known changes of the density of the diatomic molecules. For Ar*–N2 the rate constants were 5.4×10−11 and 0.8×10−11 molecule−1⋅cm3 sec−1 for Ar(1P1) and Ar(3P1), respectively. For Ar*–H2, the measured rate constants were 22×10−11 and 21×10−11 molecule−1 cm3 sec−1 for Ar(1P1) and Ar(3P1), repectively. The results for nitric oxide were 54×210−11 and 32×10−11 molecule−1 cm3 sec−1 for Ar(1P1) and Ar(3P1), respectively.
Millimeter-wave spectrum and molecular constants of cuprous bromide
Authors: Manson E. Lowry , De Lucia Frank C. , Gordy Walter
Published: February 2003

The rotational spectrum of cuprous bromide (CuBr) has been measured in the millimeter-wave range from J=13→14 to J=54→55 in the ground and the excited vibrational states to v=7. Analysis of the results with Dunham’s theory yields the following rotational and vibrational constants for the four stable isotopic species. For 63Cu81Br: Y01=3022.19991(36) MHz, Y11=−13.33271(38) MHz, Y21=0.01987(14) MHz, Y31=−0.028(12) kHz, Y02=−1.25331(10) kHz, Y12=0.00055(4) kHz, Y03=−0.00014717(10) Hz, Be=3022.234(16) MHz, ωe=313.087(12) cm−1, ωexe=0.945(1) cm−1; for 63Cu79Br: Y01=3055.67223(40) MHz, Y11=−13.55482(38) MHz, Y21=0.02031(14) MHz, Y31=−0.029(12) kHz, Y02=−1.28122(10) kHz, Y12=0.00056(4) kHz, Y03=−0.00015211(10) Hz, Be=3055.707(16) MHz, ωe=314.816(12) cm−1, ωexe=0.955(1) cm−1; for 65Cu81Br: Y01=2969.88036(40) MHz, Y11=−12.98799(38) MHz, Y21=0.01918(14) MHz, Y31=−0.027(12) kHz, Y02=−1.21029(10) kHz, Y12=0.00052(4) kHz, Y03=−0.00013966(10) Hz, Be=2969.913(16) MHz, ωe=310.365(12) cm−1, ωexe=0.928(1) cm−1; for 65Cu79Br: Y01=3003.35282(40) MHz, Y11=−13.20818(38) MHz, Y21=0.01962(14) MHz, Y31=−0.028(12) kHz, Y02=−1.23772(10) kHz, Y12=0.00054(4) kHz, Y03=−0.00014443(10) Hz, Be=3003.386(16) MHz, ωe=312.110(12) cm−1, ωexe=0.939(1) cm−1. The Dunham potential constants for cuprous bromide are a0=243 091.(20) cm−1, a1=−3.28353(14), a2=7.229(8), a3=−12.77(9). The value re=2.173435(6) Å was obtained from a combined analysis of the four species. From measurements of incompletely resolved Br nuclear quadrupole hyperfine structure, the coupling constant eQq (81Br) =221(8) MHz was obtained.
Infrared reflection and the vibrational dipole derivatives of azide ion in β-NaN3
Authors: Fredrickson L. R. , Decius J. C.
Published: February 2003

Infrared reflection from single crystals of β-NaN3 has been observed at room temperature in the ν2 and ν3 regions. The samples are plates with the large surface perpendicular to the threefold and hence the azide ion axis. In TE polarization only ν2 is observed, whereas in TM polarization with the use of incidence angles in the vicinity of 45° both fundamental modes appear. The reflection bands are analyzed with the aid of a dielectric function model apropriate for a damped harmonic oscillator. The transverse frequencies are found to be ν2=638, ν3=2090 cm−1, and the molecular dipole derivatives are ∂μ/∂q2=±29.2 and ∂μ/∂q3=±423, with perhaps 10% uncertainties. These values are transformed into ∂μ/∂S values (where S is an internal symmetry coordinate) and compared with the corresponding values for isoelectronic CO2.
Semiclassical theory of rotational excitation in collisions of diatomic molecules
Authors: Curtiss C. F.
Published: February 2003

In previous developments of the theory of rotational excitation in collisions of diatomic molecules, the cross sections have been expressed in terms of a generalized phase shift. In the present paper, the equations which determine the successive terms in a semiclassical expansion of the generalized phase shift are discussed and the first two equations are developed explicitly.
Average and directional Compton profiles for the O2 and CH2O molecules. II. Anisotropy in the momentum charge distribution
Authors: Langhoff Stephen R. , Tawil R. A.
Published: February 2003

The average Compton profiles and the profiles along various directions are obtained for the occupied canonical orbitals of the ground state of the oxygen and formaldehyde molecules. It is demonstrated that the oscillatory nature of the profiles calculated along the bond direction in a homonuclear diatomic molecule is strictly a consequence of molecular symmetry. The information extracted from these profiles give insight into the nature of the molecular orbitals comparable to that obtained from the electron density plots in coordinate space for formaldehyde. The profiles for individual orbitals are then used to explain the anisotropy in the total momentum distribution of the molecules which occurs upon chemical bonding.
Negative ion properties of p-benzoquinone: Electron affinity and compound states
Authors: Cooper C. D. , Naff W. T. , Compton R. N.
Published: February 2003

Bound and excited negative ion states of para-benzoquinone (PBQ) are studied from experiments involving collisions of electrons and cesium beams with PBQ. The electron affinity of PBQ was measured to be 1.89+0.2−0.3 eV using the cesium collisional ionization technique. PBQ−(C6H4O−2) was the dominant negative ion observed following collisions of cesium beams with PBQ. Direct electron attachment to PBQ produced the fragment ions C5H4O−, C5H3O−, C4O2H−2, C2HO−, and C2H− as well as the parent C6H4O−2 ion. Our observations showed that the cross section for producing the metastable parent negative ion, C6H4O−2, peaks at 1.40±0.1 eV which is in disagreement with a previous value of 2.1 eV. Attachment of thermal electrons to PBQ at low pressure (<10−4 mm Hg) was not observed. Compound negative ion states were observed to peak at 0.70, 1.35, and 1.90 eV using the SF6 scavenger technique. The energies of these compound states agree qualitatively with the energies if the manifold of unfilled π* orbitals. The long-lived state at 1.4 eV is attributed to either (a) direct attachment of the incident electron into the 2b1u orbital followed by internal conversion to the ground 2B3g of PBQ− or (b) simultaneous excitation of a core electron and attachment of the incident electron into an excited orbital (i.e., core excited Feshbach resonance) as previously suggested. Evidence is presented for the former explanation.
On electron mobility models for liquid hydrocarbons
Authors: Dodelet J.-P. , Shinsaka K. , Freeman G. R.
Published: February 2003

The electron mobility and actication energy of some liquid hydrocarbons have been measured and compared to theoretical values. The results indicate that an intermediate theoretical model is necessary. (AIP)
Radioluminescence of H2O and D2O ice
Authors: Steen H. B. , Holteng J. Aa.
Published: February 2003

The luminescence emitted during x-ray irradiation of H2O and D2O ice at 77 K exhibits an identical emission band peaked at 373 nm. D2O also exhibits a band peaked at 534 nm which is not seen for H2O. The 373 nm band appears to have a decay time in the range 10−4–10−3 sec, whereas the 534 nm band decays completely in less than 10−4 sec. The emission yield is G∼2×10−2 and G∼2×10−3 for D2O and H2O, respectively. The yield of the peak at 373 nm is significantly increased by NaCl, NaBr, NaI, and HCl in concentrations above 10−3M, whereas the 534 nm band in D2O is not affected by any of these additives. AgNO3, H2O2, and NaNO3 reduce the emission yield whereas other efficient electron and OH scavengers like CCl3COONa and acrylamide do not affect the luminescence even in concentrations of 1M. The identity of the luminescent species is obscure. The scavenger effects indicate that it has a mobile precursor which is not electrons or OH and probably not H atoms. The emission yields, as well as the decay time of the 373 nm band, decrease with increasing temperature. The 373 nm band is more sensitive to heating than the 534 nm band. In mixtures of D2O and H2O the emission yields fall off more rapidly with increasing H2O concentration than expected if the emissions from D2O and H2O were additive. This effect is consistent with the assumption that the differences between H2O and D2O are largely due to quenching processes that are more efficient in H2O.
Metric geometry of equilibrium thermodynamics. IV. Vector-algebraic evaluation of thermodynamic derivatives
Authors: Weinhold F.
Published: February 2003

A new set of procedures is given for the systematic evaluation of thermodynamic derivatives by vector-algebraic means. The new procedures are at once simpler and more general than previously available methods, and require no special tables. General thermodynamic derivatives are evaluated for the familiar one-component homogeneous fluid (where the techniques are extensively illustrated) and for multicomponent systems of arbitrary complexity.
An ESR study of [V(CN)5NO]4− in γ-irradiated K3V(CN)5NO⋅2H2O
Authors: Manoharan P. T. , Vijaya S. , Shock J. R. , Rogers Max T.
Published: February 2003

An ESR study of electron damaged K3V(CN)5NO⋅2H2O shows the presence of a d5 species V(CN)5NO4− with the spin Hamiltonian parameters g∥ = 1.974, g⊥ = 2.0007, A (51V) = −116.03×10−4 cm−1, B (51V) = −43.76×10−4 cm−1, A (14N) = −1.8×10−4 cm−1, and B (14N) = −6.42×10−4 cm−1. Results of a simplified semiempirical molecular orbital approach have been used to correlate the experimental spin Hamiltonian parameters of the isoelectronic d5 series from vanadium to iron. In addition, the ligand hyperfine splittings due to 14N have been explained on the basis of a configuration interaction mechanism.
Nuclear relaxation in coupled spin systems. A heteronuclear two pulse experiment and a general numerical method for analyzing spin dynamics
Authors: Mayne Charles L. , Alderman Donald W. , Grant David M.
Published: February 2003

A convenient new heteronuclear two pulse nuclear spin relaxation experiment is described. When combined with relaxation experiments already in the literature, each of the interlevel transition probabilities for a system of weakly coupled nuclear spins may be determined. Previous work in coupled spin relaxation has yielded only certain linear combinations of these transition probabilities. The well understood AX spin system was selected to illustrate the method, and sodium formate in D2O solution is used as the specific case. Values for all four interlevel transition probabilities characterizing the spin lattice relaxation of the 1H–13C spin system of the formate ion are obtained. These data yield the first experimental verification of the extreme narrowing condition commonly assumed for small molecules in nonviscous liquids. A general numerical method is described for estimating the relaxation parameters from measurements of the time evolution of nonequilibrium magnetization. The method involves numerical solution of coupled linear homogeneous differential equations with constant coefficients. These coefficients are linear combinations of relaxation parameters. The approach is sufficiently general to allow for a variety of initial conditions which characterize the manner in which the spin system is prepared in its nonequilibrium configuration. Several types of spin perturbations are described in detail.
Intrinsic viscosity of stiff dumbbells from time correlation functions
Authors: Wilemski Gerald
Published: February 2003

The intrinsic viscosity of a suspension of stiff dumbbells is evaluated by a time correlation function method. The required moments of the internal coordinates are calculated directly from the diffusion equation, without explicit evaluation of the Green’s function. For the rigid dumbbell, the correct high frequency limit is obtained, disposing of recent doubts over this possibility. The interplay of dumbbell stiffness and shearing frequency is also illustrated.
Anisotropy of the proton spin–lattice relaxation time in the superconducting intercalation complex TaS2(NH3): Structural and bonding implications
Authors: Gamble F. R. , Silbernagel B. G.
Published: February 2003

The nature of the interaction responsible for the formation of molecular intercalation complexes between Lewis bases and layered transition metal dichalcogenides is not well understood. To some extent this is due to a lack of structural information. A prototype of these complexes is TaS2(NH3), in which monolayers of ammonia are inserted between the metallic, superconducting layers of TaS2. The compound is crystalline and stoichiometric. Measurement of the anisotropy of the proton spin–lattice relaxation time at 300 °K indicates that the molecular threefold symmetry axis is not perpendicular to the disulfide layers as suggested by other workers, but is parallel to the layers. This orientation precludes direct interaction between the molecular lone pair orbital and the transition metal atoms. The interactions governing the structure of this complex may be similar to those obtaining in the intercalation complexes between TaS2 and a number of substituted pyridines, in which complexes the axis of the lone pair orbital is also parallel to the layers.
Effect of superexchange interactions on conformations and barriers to rotation in molecules containing a double bond
Authors: Lombardi E. , Tarantini G. , Pirola L. , Ritter R.
Published: February 2003

Exchange perturbation theory of the Rayleigh–Schrödinger type is applied, in first and second order, to a calculation of the conformations of simple molecules containing a double bond and of barriers to internal rotation around a single or a double bond. Indirect exchange (’’superexchange’’) interactions between nonbonded atoms via the double bond are considered explicitly. In the model, the electrons of the nonbonded atoms are replaced by one effective electron per atom, those of the double bond by two spin-paired effective electrons. The charge distribution of the effective electrons are of Gaussian form. The method is applied to acetaldehyde, the acyl halides and related compounds, and to the ethylene molecule; calculated results are in good agreement with experiment. A decomposotion of the interaction energy is given, for different conformers, in terms of two- and many-atom interactions.
Multiple potential energy surfaces in a semiclassical study of molecular collisions
Authors: McLafferty Francis J. , George Thomas F.
Published: February 2003

A semiclassical treatment of multiple (electronic) potential energy surfaces in molecular collisions is presented. Focusing on three surfaces, this treatment can be regarded as a generalization of a previous semiclassical treatment restricted to two surfaces [J. Chem. Phys. 56, 5637 (1972); 60, 2340 (1974)]. Suitable approximations lead to the formal simplicity of the elimination of nonadiabatic coupling terms by the analytic continuation of potential surfaces to their complex intersection points. The analysis first considers the semiclassical evaluation of the electronic propagator, which is a function of the nuclear path and appears inside a nuclear path integral. Then the nuclear path integral is evaluated by the method of steepest descent to yield S-matrix elements connecting initial and final states of a collision. The nuclear normalization for the S matrix is presented in its usual form, and possible corrections to this form are discussed. Finally, certain modifications of the treatment that might be necessary when dealing with different collision systems are mentioned.
A refinement of the structure of deuterium peroxide
Authors: Prince E. , Trevino S. F. , Choi C. S. , Farr M. K.
Published: February 2003

The structure of deuterated hydrogen peroxide, D2O2, at −15 °C was refined by least-squares methods from three dimensional neutron diffraction data. The data were fitted to two models, one with conventional anisotropic temperature factors and the other with the molecule treated as a rigid body except for torsional oscillations of the O–D groups about the O–O bond. The weighted agreement indices were 0.030 over 106 observed reflections for the conventional model and 0.032 over 102 reflections for the rigid body model. The structure is tetragonal, space group P41212 or P43212, with a=4.035 Å, c=7.97 Å, Z=4. Position parameters for the two models are essentially the same. The O–O distance in the molecule, 1.455(2) Å, is identical to that found in H2O2, but the O–D bond is about 0.015 Å shorter than the O–H bond, 0.993 Å as compared with 1.008 Å when corrected for thermal motion by the riding model. The O–O distance corrected for thermal motion in the rigid body model is 1.49 Å, in fair agreement with the value 1.48 Å found in the vapor phase.
The sublimation of basal surfaces of zinc oxide
Authors: McVicker J. E. , Rapp R. A. , Hirth J. P.
Published: February 2003

Basal surfaces of both undoped and lithium-doped single crystals of zinc oxide were sublimated under Langmuir free vaporization conditions and under various partial pressures of oxygen. The vaporization coefficient was lower for the (0001̄) surface than for the (0001) surface. Oxygen suppressed the sublimation rates except for the (0001) surface at high temperatures. Lithium doping produced a large increase in sublimation rates. An earlier theory of surface-charge influenced sublimation was modified to include specific effects of surface kinks, surface roughening, and doping. The experimental results could be interpreted in terms of this modified theory.
PNO–CI and CEPA studies of electron correlation effects. III. Spectroscopic constants and dipole moment functions for the ground states of the first-row and second-row diatomic hydrides
Authors: Meyer W. , Rosmus P.
Published: February 2003

A systematic investigation of the ground state potential curves and dipole moment functions has been performed for the diatomic hydrides LiH to HCl on the basis of variational configuration interaction wavefunctions PNO–CI and the coupled electron pair approximation CEPA. The basis sets of Gaussian-type orbitals are derived by simple rules from optimized atomic sets available in the literature. Between 95% (LiH) and 85% (HCl) of the valence shell correlation energies are accounted for in the CEPA calculations. Core–valence intershell correlation has been included for several members of each row, and its effect on the potential curves is analyzed. Comparison of the spectroscopic constants derived from the CEPA potential curves with experiment shows a high reliability of the theoretical values. The standard deviations over both rows are as follows: re:0.003 Å, ωe:14 cm−1, αe:0.005 cm−1, and ωexe:1.5 cm−1. The errors of the calculated dissociation energies go up to 0.3 eV but behave very regularly. They are believed to allow for predictions which are correct to about ±0.05 eV. The following new D0 values are recommended (empirical values in parenthesis): NH:3.40 (3.2±0.16); NaH:1.88 (2.05±0.2); MgH:1.23 (2.0±0.5); PH:3.02 (3.5±0.3). Various vibrational matrix elements have been calculated from the dipole moment curves. The μ0 values show errors of 0.02–0.04 D. The differences between diagonal elements as well as the transition elements for the first few levels deviate by only about 10% from the available experimental data.
Molecular dynamics of the rough sphere fluid. I. Rotational relaxation
Authors: O’Dell J. , Berne Bruce J.
Published: February 2003

A systematic study is made of rotational relaxation in rough sphere fluids for densities ranging from 0.1 to 0.666 of the closest packed density. Many of the current models of rotational relaxation are tested against the results of molecular dynamics. It is found that for densities higher than 0.40 of the closest packed density only the Fokker–Planck model is consistent with experiment. The various extended diffusion models, the jump diffusion model, and the rotational diffusion model are not only internally inconsistent, but also do not agree with experiment. No theory is consistent with experiment at intermediate densities where the collisional and the inertial time scales are comparable. In addition to the foregoing, it appears that the rough spheres tumble more freely in the solid state than they do in the fluid state at the melting density.
Raman and depolarized Rayleigh scattering in the liquid state: Reorientational motions and correlations in orientation for symmetric top molecules
Authors: Patterson G. D. , Griffiths J. E.
Published: February 2003

Reorientational motions perpendicular to the major axis of symmetric top molecules in the liquid state have been examined as a function of temperature by investigating isotropic and anisotropic Raman scattering vibrational band contours. These studies yield information about single molecule reorientation for the systems C6H6, C6D6, CH3CN, CD3CN, CH3I, DCCl3, and HCBr3. Depolarized Rayleigh scattering measurements on the same systems, also as a function of temperature, are combined with data on single particle reorientations to yield information about correlations in orientations between pairs of molecules. These correlations between molecules are found to be important for most symmetric top molecules in the liquid state and the temperature dependence of the Raman and Rayleigh band shapes and bandwidths suggest that hard core forces dominate the cooperative motions in the systems studied.
Raman spectroscopic investigation of the structure of silicate glasses. I. The binary alkali silicates
Authors: Brawer Steven A. , White William B.
Published: February 2003

The Raman spectra of some binary alkali silicate glasses and crystals have been measured and the results interpreted. The glasses are of composition M2O⋅xSiO2, 1⩽x⩽4 and M = Li, Na, K. There is a strong resemblance between glassy and crystalline spectra which is consistent with a considerable amount of structural disorder of the glass. The reason is that the disorder acts as a perturbation on the spectrum of an elementary vibrating unit from which the glass is largely constructed. As a result, the general nature of the glass structure may be determined. Furthermore, glasses of the same x but with different alkali have different amounts of short-range order. This is demonstrated by showing that the widths of certain Raman peaks increase with increasing disorder of the Si–O network of the glass. A strong argument is made against the microcrystallite theory of glass structure. For any composition x, glasses increase in disorder in the direction K → Na → Li. The crystallization rates increase in the same direction, just the opposite of what would be expected on the basis of a microcrystallite theory. Finally, evidence is given for the existence of microscopic concentration fluctuations in presumably single-phase disilicate glasses.
Model for multiple-collision trajectories in nonreactive atom–diatom collisions
Authors: Gottdiener Luis
Published: February 2003

The extent of the complex (multiple-collision) region (CR) is investigated for a classical nonreactive collinear atom–diatom system. A simple model to estimate the extent of the CR is given, based on the different roles the repulsive and attractive parts of the interaction potential V have in the collision. The model is extended to obtain more detailed information on the CR, such as the extent of m-collision regions within the CR. In the extended model, a multiple-collision trajectory is treated as a sequence of single-collision trajectories on a purely repulsive interaction potential Vr. The vibrational excitation produced by V and Vr is compared, and it is pointed out that if the motion of the system with V is to be described adequately by Vr, it is necessary that multiple-collision trajectories do not occur.
Molecular orbital theory for heavy-metal luminescent centers: Application to the La2O3:Bi phosphor
Authors: Jacquier Bernard , Richardson J. W.
Published: February 2003

A detailed semiempirical self-consistent charge and configuration molecular orbital theory is constructed for the problem of optical electronic states in phosphors doped by heavy metal ions. A cluster model is assumed for the luminescent center and all Madelung potential effects are included within the LCAO–MO framework. Expressions for energies of lower singly and doubly excited configurations are fomulated. Total energies for the cluster are obtained including spin–orbit and limited configuration interaction effects. The procedures are applied to the case of La2O3:Bi and reasonable agreement is found with presently available excitation spectra, thermoluminescence, and decay time data. The results confirm the presence of metastable levels and suggest a new interpretation of the luminescent processes in which the aspherical electronic delocalization about the Bi center plays a significant role.
Flow-tube studies of vibrational energy transfer in HF(v)+HF, DF(v)+HF, and DF(v)+D2 systems
Authors: Kwok Munson A. , Wilkins Roger L.
Published: February 2003

A medium-pressure (1 Torr), large-diameter (10 cm) flow tube has been used to measure rate coefficients at 298 °K for (a) total relaxation (sum of vibrational–vibrational and vibrational–rotational, translational processes) of HF(v=1, 2, 3, 4, and 5) by HF, (b) relaxation of DF(1, 2, 3, and 4) by HF, and (c) over-all relaxation of DF(v=1, 2, 3, and 4) by D2. The chemically produced vibrationally excited HF or DF species have been studied by monitoring their vibrational–rotational emission in a fast-flow system. The rate coefficient for the relaxation of HF(1) by HF is 5.3×104 sec−1⋅Torr−1. The measured rate coefficients for the deexcitation of HF(v=2, 3, 4, and 5) by HF are 5.3×105, 8.5×105, 8.8×105, and 2.8×105 sec−1⋅Torr−1, respectively. The rate coefficients for the vibrational–rotational, translational deexcitation from the upper vibrational levels of DF(v) by HF are found to have a nonlinear vibrational dependence. The rate coefficient for the relaxation of DF(v=1) by D2 is 1.35×104 sec−1⋅Torr−1.
Collective electron effects of O2− in potassium superoxide
Authors: Khan Ahsan U. , Mahanti S. D.
Published: February 2003

A temperature variation study of dc conductivity, magnetic susceptibility, and ESR on powdered potassium superoxide has been carried out. Also reported is a room temperature measurement of the electronic absorption spectrum. We find that at temperatures above the structural phase transition temperature Tc (193.5°K) reported by Carter and Templeton, the susceptibility is given by χ = c/(T + ϑ) with ϑ ∼ 250°K. Below Tc, χ = c′/(T + ϑ) with ϑ′ ∼ 18°K. There is no magnetic ordering down to liquid nitrogen temperature. ESR spectra shows two distinct lines above Tc. The broad line is Lorenzian in shape with a width at half-maximum of about 700 G. The narrow line has a width of 25 G and the area under this resonance is 10−4 times that under the broad one. The broad line splits into two below Tc. The number of spins contributing to the broad resonance has a temperature dependence which is qualitatively similar to that of the susceptibility. The narrow ESR line persists through the phase transition. At temperatures greater than 250°K, KO2 is semiconducting with an activation energy of 1.3 eV. The yellow color of KO2 at room temperature is due to an absorption band peaked at 350 nm degrading to 600 nm. A simple theoretical model based on correlation and disorder is proposed which can explain most of these experimental data.
Relaxation of CO2(101), CO2(021), and N2O(101) vibrational levels by near-resonant V→V energy transfer
Authors: Finzi Jack , Moore C. Bradley
Published: February 2003

Laser-excited vibrational fluorescence experiments on CO2 and N2O combination levels were performed using a tunable optical parametric oscillator. Rate constants near gas kinetic were obtained and assigned to the near-resonant V→V transfer of an asymmetric stretching quantum. Stimulated emission occurring at 4.3 μ was observed during 2.7 μ excitation of CO2 to the (1001) combination level.
Limit cycle oscillations in the reversible Oregonator
Authors: Field Richard J.
Published: February 2003

The five-step Oregonator model of the oscillatory Belousov–Zhabotinskii reaction has been expanded by taking into account the reversibility of the various steps. Forward and reverse rate constants have been assigned to four of the five steps by direct analogy to the detailed Field, Körös, and Noyes model of the Belousov–Zhabotinskii reaction. The rate constants and stoichiometry of the fifth step were parametrized and the stability of the steady state was investigated as a function of both of these parameters and the over-all distance of the system from equilibrium. It was found that there is a critical distance from equilibrium which must be exceeded before the steady state becomes unstable. Numerical integration of the differential equations resulting from the model indicated that the system executes apparent limit cycle oscillations when the steady state is unstable. Introduction of reversibility into the Oregonator leads to a striking change in the range of values of the fifth step stoichiometric parameter over which oscillations will occur. This change is discussed in terms of the chemistry of the Belousov–Zhabotinskii reaction. Under some conditions the reversible Oregonator shows excitability such that a small finite perturbation of an infinitesimally stable steady state may be greatly amplified before the system returns to rest. An apparently analogous phenomenon appears in the Belousov–Zhabotinskii reaction itself.
On the glass transition in organic halide–alcohol mixtures
Authors: Lesikar Arnold V.
Published: February 2003

The glass transition temperatures of binary mixtures of various aliphatic organic halides with the lower normal alcohols have been determined. For each halide a correlation is found between the alcohol glass temperature and the initial slope at the pure alcohol end of the curve of glass temperature against the mole fraction of halide. This correlation is related to the hydrogen bonding properties of the halide. For several proton donor halides a wide composition range for the glass transition is found. The excess glass temperature above that expected for an ideal mixture of these halides with the alcohols shows a maximum value of 5° or more. For some of these halides the excess glass temperature becomes negative in halide rich mixtures. These results are taken to indicate the formation of alcohol–halide clusters in alcohol rich mixtures and dissolution of hydrogen bonded alcohol aggregates in halide rich mixtures.
Spectra and structure of organophosphorus compounds. XIV. Infrared and Raman spectra, vibrational assignment and the asymmetric potential function for ethylphosphine and ethylphosphine-d2
Authors: Durig J. R. , Cox A. W.
Published: February 2003

The infrared spectra of gaseous and solid CH3CH2PH2 and CH3CH2PD2 have been recorded from 200 to 3500 cm−1. The Raman spectra of gaseous, liquid, and solid CH3CH2PH2 and CH3CH2PD2 have been recorded from 100 to 3500 cm−1. The gauche and trans isomers have been observed in the fluid phases and only the trans exists in the solid state. A vibrational assignment of the 24 normal modes has been made. Fundamental and hot band transitions have been observed for both the methyl and phosphino torsions. The methyl barrier in the trans d0 molecule was determined to be 3.74±0.05 kcal/mole and 3.14±0.05 for the gauche d0 molecule. The potential function for internal rotation around the C–P bond in CH3CH2PD2 was determined and the following potential constants found: V2=207±6 cm−1, V3=785±5 cm−1, and V6=−25±3 cm−1. The energy difference between the potential energy minima of the gauche and trans conformations is 150 cm−1, the trans being the more stable form. The calculated gauche–gauche barrier is 635 cm−1 (1.82 kcal/mole) and the trans–gauche barrier is 944 cm−1 (2.70 kcal/mole). A similar potential function was determined for the CH3CH2PH2 isomer but the fit to this one-dimensional model was not as good as that for the deuterium compound probably because of greater coupling in the light molecule.
Pretransitional behavior of conductivity and dielectric properties above a smectic C–nematic transition in 4-4′-di(n-alkyloxy)azoxybenzenes
Authors: Mircea-Roussel A. , Rondelez F.
Published: February 2003

Electrical conductivity and dielectric relaxation measurements have been made in the nematic phases of the 4-4′-di(n-alkoxy)azoxybenzenes. The higher members of this series have a smectic C phase at lower temperatures. In that case, we have observed that (1) the ratio of the conductivities parallel and perpendicular to the local optical axis is abnormally low (<1) above the smectic–nematic phase transition and increases with temperature, and (2) the activation energy corresponding to the molecular rotational diffusion in the frequency range 0.1–10 MHz is significantly larger than for the lower homologs. We tentatively suggest that our results are due to fluctuations of the smectic order in the nematic phase as first pointed out by Chystiakov and Chaikowsky [Mol. Cryst. Liq. Cryst. 7, 269 (1969)] through observation of x-ray diagrams.
Narrow-line fluorescence spectra of perylene as a function of excitation wavelength
Authors: Abram I. I. , Auerbach R. A. , Birge R. R. , Kohler B. E. , Stevenson J. M.
Published: February 2003

Experiments on the laser excited fluorescence spectrum of perylene in n-octane and ethanol hosts at low temperatures are reported. Monochromatic excitation leads to a dramatic sharpening of the emission lines. The dependence of the spectrum on both excitation wavelength and temperature are presented and discussed qualitatively in terms of a model which applies the basic concepts of the theory of mixed crystal spectra to systems with inhomogeneous broadening.
Metric geometry of equilibrium thermodynamics
Authors: Weinhold F.
Published: February 2003

It is shown that the principal empirical laws of equilibrium thermodynamics can be brought into correspondence with the mathematical axioms of an abstract metric space. This formal correspondence permits one to associate with the thermodynamic formalism a geometrical aspect, with intrinsic metric structure, which is distinct from that arising from graphical representations of equilibrium surfaces in phase space.
Three-dimensional quantum mechanical studies of D+H2→HD+H reactive scattering. II
Authors: Choi B. H. , Tang K. T.
Published: February 2003

Three-dimensional quantum mechanical calculations are carried out for the reactive scattering of D+H2→DH+H on the Yates–Lester potential surface. The differential and total cross sections as well as the S-matrix elements are obtained and are compared with the corresponding results obtained on the Porter–Karplus potential surface. The differential cross sections and the distributions over final angular momentum states are in much better agreement with the experimental measurements than the previous results obtained on the Porter–Karplus surface. However, the calculated threshold energy for the reaction seems too high whereas the threshold on the Porter–Karplus potential seems too low. These dynamic attributes are discussed in terms of the two-body potentials between the atom and the molecule.
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o force constants for the HCN molecule: SCF and CI results
Authors: Wahlgren U. , Pacansky J. , Bagus P. S.
Published: February 2003

Force constants for HCN have been determined from both the one-electron model, SCF, and correlated, CI, wavefunctions. Using SCF wavefunctions, the stretching force constant for the CH bond, K11, is 9% larger than experimentally determined values and the CN stretch, K22, is 23% larger. When electron correlation is included through the use of configuration interaction wavefunctions the agreement of computed and experimental force constants is greatly improved; K11 is 5% larger than the experimental value and K22 is 9% larger. The force constants are determined by making least square polynomial fits to computed points on the potential surface. Force constants for both stretch and bending modes are reported through quartic terms.
Experimental observations of gas phase–adsorbed phase interactions during counterdiffusion in porous alumina
Authors: Spencer Jean L. , Brown Lee F.
Published: February 2003

The binary gas systems helium–argon, helium–nitrogen, helium–1-butene, and argon–1-butene were counterdiffused through a plug of porous alumina at 135° and 150 °C and 1–3 atm pressure in a Wicke–Kallenbach experiment. The helium, nitrogen, and argon were essentially nonadsorbing; the butene was significantly adsorbed and diffused along the surface. Knudsen flow existed within the pores at most experimental conditions, i.e., the gas–gas molecular collisions were negligible in comparison with gas–surface collisions. The results showed that gas-adsorbed phase collisions can have significant effects at conditions typical of laboratory and industrial practice. Strong evidence of interactions between all gas-phase molecules and adsorbed butene molecules was observed whenever the butene was present. Both helium and argon fluxes were significantly less when counterdiffused with 1-butene than when counterdiffused with nonadsorbing gases. The butene flux was markedly less when diffused against the argon than when diffused against the helium. The collisional effects were so strong in the argon–butene system that at low pressure the adsorbed 1-butene was driven in a direction counter to the concentration-gradient driving force. Apparently the efficiency of momentum transfer during the argon-adsorbed butene collision was much greater than during the gaseous butene-adsorbed butene collision.
Kinetics of concentration fluctuations in a binary alkali–silicate system
Authors: Schroeder J. , Montrose C. J. , Macedo P. B.
Published: February 2003

Laser light scattering was applied to a potassium–silicate system to observe the growth of supercritical concentration fluctuations. The Rayleigh and Brillouin spectra of our glass samples were measured as a function of heat treatment time duration and temperature. From the spectra we obtained the Landau–Placzek ratios and Brillouin shifts for each heat treatment interval and temperature. In glass forming melts, critical points may occur in regions of high shear viscosity; here because of the low mobility, relaxation times for concentration fluctuations are on the order of many hours. Thus, heat treatment followed by rapid quenching ’’freezes in’’ the fluctuations characteristic of the treatment temperature, and consequently the light scattering measurements detect the high temperature structure. The measurements reported here provide the first direct evidence for a phase transition in a potassium–silicate system. From the equilibrium Landau–Placzek ratios, the spinodal temperatures were calculated. We also discuss the relaxation times for the system and the critical exponents.
On the relation between gaseous ion mobility and diffusion coefficients at arbitrary electric field strengths
Authors: Viehland Larry A. , Mason E. A.
Published: February 2003

A generalized Einstein relation for gaseous ions is shown to be accurate even at high electric field strengths, provided care is taken in the evaluation of the ion temperature. Comparison with experiment is made for K+ ions in He, Ne, and Ar. The validity of this relation means that gaseous ion diffusion coefficients can be calculated from the more easily measured mobilities.