bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of pressure on deuteron spin-lattice relaxation in several concentrated deuterium oxide diamagnetic electrolyte solutions
Authors: Lee Yun Ko , Campbell J. H. , Jonas J.
Published: February 2004

The pressure dependence of the deuteron spin-lattice relaxation times of the deuterium oxide molecules in concentrated 4.5m aqueous solutions of CsBr, RbBr, KBr, LiCl, CaCl2, and LaCl3 have been measured at 30°C up to 4.5 kbar. Viscosities of the above solutions, over the same pressure range, at 30°C, have also been determined. From the viscosity data and the deuteron relaxation times at 1 bar, the structure breaking ability of the electrolytes CsBr, RbBr, and KBr is found to increase in the order K+ < Cs+ ∼ Rb+, while the structure making ability of the electrolytes LiCl, CaCl2, and LaCl3 increases in the order Li+ < Ca+2 < La+3. Values for the rotational correlation time τθ+ of the D2O molecules at 1 bar in the hydration spheres of the cations Li+, Ca+2, and La+3 are calculated to be 4.5, 10.0, and 23.0 psec, respectively. The differences between τθNMR and τθDebye observed as a function of electrolyte and pressure are interpreted in terms of changes in the product of the quadrupole coupling constant and the square root of the effective hydrodynamic volume [(QCC)(Vmeff)1/2]. A decrease in this quantity at 1 bar, due to addition of electrolytes, is explained in terms of a change in the effective hydrodynamic volume of the D2O molecules, this being related to the degree of coupling between rotational and translational motion. Over the pressure range of 4.5 kbar the quantity [(QCC)(Vmeff)1/2] decreased approximately 10% to 20% for all solutions and approximately 11% for pure D2O. The data for structure-breaking electrolytes favor the tentative interpretation that an increase in pressure produces a decrease in the average O–O distance in the O–D⋯O hydrogen bonds resulting in a decrease in the magnitude of the deuteron quadrupole coupling constant. The data for structure making electrolytes can be interpreted as either a change in QCC or Vmeff or both.
High-energy approximation for exchange scattering and application to 1 1S → 2 3S excitation of He by electron impact
Authors: Huo Winifred M.
Published: February 2004

A high-energy approximation is derived for the second order term in the T matrix for exchange scattering of electrons by atoms or molecules. A limiting selection rule for exchange scattering at high incident energies is obtained, which states that second-order contributions are important in forward scattering if the initial and final states of the target system have the same orbital term symbol. Calculations on the zero angle differential cross section, approximated by the cross section at zero momentum change, of the 1 1S→2 3S excitation in He by electron impact are carried out over an energy range 100–500 eV using the present approximation. Reasonable agreement with the experimental data of Skerbele, Harshbarger, and Lassettre [J. Chem. Phys. 58, 4285 (1973)] is obtained, indicating that second-order contributions are sufficient to account for the differences between Born-Oppenheimer calculations and the experimental data. The present calculation also shows that, for this transition in He, a minimum exists in the zero angle differential cross section vs incident energy curve. The existence of the minimum has been verified experimentally by Klump and Lassettre.
Vibronic calculations in benzene by CNDO/S
Authors: Ziegler Lawrence , Albrecht A. C.
Published: February 2004

CNDO/S calculations of transition moments at displaced nuclear coordinates (Q) are performed for benzene. At every Q, the sum of the separately calculated Herzberg-Teller (H-T) components from the ground and the excited states is found to be equal to the computed total transition moment for each vibronically active normal mode in the 1B2u and 1B1u electronic transitions. The usually neglected ground state term is seen to be significantly weaker than the excited state component. The Q dependence of these transition moments is determined to be nearly linear, even to twice the root-mean-square displacement, although in some cases, higher order effects are found. The vibronic (H-T) CNDO/S oscillator strengths are presented.
Electron transfer in collisions of doubly charged rare gas ions and rare gas atoms for primary ion energies below 100 eV
Authors: Maier William B.
Published: February 2004

Cross sections for the production of Kr+, Ne+, and Kr++ in collisions of Kr++ with Ne and of Ne++ with Kr have measured for primary ion energies E between 0.5 and 100 eV. For E≳ 10 eV, the cross sections all vary rather slowly and are between 1 and 8 Å2. As E is decreased below 5–10 eV, the cross sections all increase. The cross section σa measured for Kr++ +Ne→Kr+ + ⋯ is expected to be a reasonably accurate representation of the cross section for Kr++ +Ne→Kr+ +Ne+; σa has been compared with three theoretical results for this reaction, but the theoretical and experimental results do not agree very well. The implications of the discrepancies between theory and experiment are discussed. σa is in good agreement with an earlier measurement of Kr++ +Ne → Kr+ + ⋯ at higher E. The efficiency with which product ions are collected by the present apparatus is discussed.
Phonon dispersion and phonon densities of states for ZnS and ZnTe
Authors: Vagelatos N. , Wehe D. , King J. S.
Published: February 2004

Neutron scattering data are reported for II–VI zincblende crystals, which are believed to be of sufficient precision to refine earlier ZnS ambiguities and to provide a basis for model fitting comparable to existing III-V results. Valence shell models, including 9–12 parameters (VSM) and a variable shell charge extension (VCM), were fit to the data and used to generate phonon density of states and Debye temperatures. Very good fits to the neutron data were obtained, but no model was found that also predicts an accurate set of electric and mechanical constants. It is concluded that an unambiguous ionic charge Z cannot be assigned from the neutron results in either case.
Calculation of heavy-atom kinetic isotope effects: Barrier curvature and internal coordinate effects with three-element reaction coordinates
Authors: Wei G.-J. , Yankwich Peter E.
Published: February 2004

Effects of barrier curvature and of a restricted method for selection of values for off-diagonal force constants in the transition state were studied by computation for several three-element reaction coordinates assumed for decomposition of formic acid; the temperature independent (TIF) and temperature dependent factors (TDF) of the rate constant ratio k/k′ = k12c/k13c were calculated. As barrier curvature increases, the area in eigenvector space corresponding to valid transition states decreases in extent and alters in shape; these changes depend on the method of selection of certain secondary off-diagonal force constants. TIF is not affected. TDF is affected, particularly in the part of eigenvector space where the extent of the allowed region is being reduced by barrier curvature. While shapes and values associated with the TIF and TDF surfaces in eigenvector space can be related at least approximately to the input F- and G-matrix properties in some cases, such accounting is generally not accurate in the first order high temperature approximation.
Photoionization study of the ionization potentials and fragmentation paths of the chlorinated methanes and carbon tetrabromide
Authors: Werner Arthur S. , Tsai Bilin P. , Baer Tomas
Published: February 2004

The photoionization yields of CH3Cl, CH2Cl2, CHCl3, CCl4, and CBr4 have been measured in the 10–13.5 eV energy range. Ionization potentials and fragment appearance potentials derived from a detailed study of the hot band contribution at 300°K have been obtained. Although CCl4+ is apparently unstable, we have found that CBr4+ is stable. Fragmentation of the chlorinated and brominated methanes in the energy range studied appears to be limited to halogen loss, even though hydrogen loss is in certain cases energetically favored. An argument based on the symmetry of the fragments and the transition state producing these fragments is proposed to account for this observation.
Classical mechanics of recombination via the resonance complex mechanism: H + H + M → H2 + M for M = H, H2, He, and Ar
Authors: Whitlock P. A. , Muckerman J. T. , Roberts R. E.
Published: February 2004

Rate constants for the recombination reaction H + H + M→H2 + M are calculated within the framework of the resonance complex theory for a variety of third bodies (M=H, He, Ar, and H2). The stabilization cross sections for bimolecular collisions of M with the highly excited orbiting resonance states of H2 were computed from exact three-dimensional classical trajectories. Calculations were carried out for several different reasonable potential surfaces in order to determine the effects of variations in the interaction potential upon the macroscopic rate constant. For example, the inclusion of long range attractive forces between the inert third body and each H atom in H2 leads to a systematic increase in the low temperature rate constant. Using a best estimate for the potential parameters, good agreement with experiment is found for all the third bodies investigated over the temperature range ∼77–300°K. For inert third bodies it is shown that the so-called ``energy transfer'' mechanism is much more important than the ``chaperon'' mechanism. However, for the case M=H, both mechanisms play a significant role with the ``chaperon'' mechanism being the more important. Furthermore, H atoms are found to be more efficient than inert M in causing recombination to occur. Data for the nonequilibrium ortho/para product distribution are also presented.
On the surface tension theory of van der Waals and of Cahn and Hilliard
Authors: Woodbury George W.
Published: February 2004

The following features of the theory of van der Waals and of Cahn and Hilliard are proven to be true: It is possible to find a local free energy, ψi, depending upon T and the density profile, that sums (over i) to give the total free energy of the system; when the total free energy is minimized with respect to the density profile, the exact equilibrium profile results. The local free energy has the form ψi = δi + μiρi, where ρi is the local density and δi and μi both depend upon T and the entire density profile. For the equilibrium profile, the surface tension σ is given by σ = hΣi(δi + P) (h is the interaction range and P is the pressure); the grand canonical partition function Ξ for the system is κT InΞ = − AhΣiδi (A is surface area), and μi is equal to the chemical potential μ. The van der Waals and Cahn-Hilliard theory is recovered by making ``reasonable'' approximations for μi and δi.
Experimental thermal diffusion factors for 20Ne–22Ne and their application as a test of the neon interatomic potential
Authors: Taylor W. L. , Weissman Stanley
Published: February 2004

The thermal diffusion factor of 20Ne–22Ne was measured from approximately 200 to 900°K in a 20-tube trennschaukel. The results of previous workers were examined in detail, and those considered the most reliable were combined with the present data and fitted to a polynomial in powers of T1/2. The resulting expression represents existing thermal diffusion data from 75 to 1200°K with an average standard deviation of ±3.1%. Eighteen intermolecular potentials for neon of various functional forms were investigated, but none were found that produced a satisfactory theoretical value for αT over the entire temperature range.
Circular dichroism: A general theory based on quantum electrodynamics
Authors: Power E. A. , Thirunamachandran T.
Published: February 2004

A theory of circular dichroism is developed through a direct calculation of the absorption rates for circularly polarized light on molecules. From this a differential rate as between left and right circularly polarized light is calculated. This is immediately related to the experimental data on circular dichroism. When the calculations are restricted to the dipole approximation we reproduce the rotatory strength in the form of a differential Einstein B coefficient. Higher moments are considered in detail and their effects analyzed for both the locked-in situation and the case of randomly oriented molecular absorbers. A general expression is obtained for the differential absorption rate.
Unified theory for the intermolecular forces between closed shell atoms and ions
Authors: Kim Yung Sik , Gordon R. G.
Published: February 2004

A simple theoretical model for intermolecular forces is developed in such a way that it includes simultaneously the effects of short-range and long-range interactions. At long distances the calculated intermolecular forces reduce to the usual dispersion and induction effects. At short distances, the results approach those of the short-range interaction, which in the present calculation followed our previous work [J. Chem. Phys. 56, 3122 (1972)]. The results of the method are in good agreement with available experimental results for closed shell atom-atom and ion-atom interactions, over the whole range of internuclear distances.
ELDOR enhancement arising from admixture of nuclear spin states
Authors: Iwasaki Machio , Toriyama Kazumi , Nunome Keichi
Published: February 2004

ELDOR enhancement effects arising from the admixture of nuclear spin states have been studied with the irradiated single crystals of potassium hydrogen maleate, which give strong forbidden ESR lines. When the magnetic field was applied along the c axis, all of the ELDOR transitions involving no level in common showed enhancement while those involving a level in common showed reduction. In the different orientations of the crystal, some of the enhanced lines changed into reduced ones with decreasing forbidden ESR transition probabilities. The temperature changes of the ELDOR spectra were also studied. With decreasing temperature, all of the enhanced lines at room temperature changed into reduced lines giving maximum R factors at around − 100°C. These results were interpreted in terms of large intramolecular cross relaxation probabilities that are due to the admixture of the nuclear spin states in our system. To calculate the R factors for our system, the generalized expression has been derived for the R factor in multiobserving and multipumping ELDOR experiments. The variation of the observed R factors with pumping transitions is qualitatively understood from the R factors calculated with appropriate assumptions on the relaxation probabilities. The calculated R factors also show that increasing nuclear spin relaxation probabilities with decreasing temperature are responsible for the temperature change of the observed R factors.
Partial structure factors in the long wavelength limit for binary liquid mixtures of argon-krypton and krypton-xenon
Authors: Crozier E. D. , McAlister S. P. , Turner R.
Published: February 2004

Available thermodynamic data have been used to calculate the partial structure factors in the long wavelength limit for binary mixtures of Ar–Kr and of Kr–Xe. Comparison with statistical models for binary mixtures shows that the composition dependence of the partial structure factors is determined primarily by the nonzero interaction between components. The partial structure factors are used to show that spatial correlations of like atoms are preferred over correlations of unlike atoms in both Ar–Kr and Kr–Xe mixtures.
Vibrational spectra of H5O2+ ion in crystalline YH5O2(C2O4)2 · H2 O
Authors: Bates J. B. , Toth L. M.
Published: February 2004

Polarized Raman and infrared spectra of crystalline YH5O2(C2O4)2 · H2O and its deuterated analogs were measured over the frequency interval from 20 to 4000 cm−1. Primary consideration was given to recording the vibrational spectrum of the diaquated hydrogen ion, H5O2+, and to correlating the spectral properties of this species with the results from recent neutron diffraction studies of yttrium oxalate trihydrate. Calculations based on models of H5O2+ produced root-mean-square displacements of the central proton which were compared with the thermal parameters derived from neutron diffraction data. A comparison of calculated and observed properties suggested that H5O2+ may be represented by a model based on a proton trapped between two water molecules.
On a general relationship between solutions of alternative sets of equations for rearrangement channel T operators
Authors: Kouri D. J. , Levin F. S. , Craigie Michael , Secrest Don
Published: February 2004

A general relationship between the solutions for two alternative sets of coupled equations for channel T operators describing rearrangement scattering is derived. The relation involves analogously defined channel K operators for rearrangement scattering. A symmetrized form of the relationship is also derived that can account for differing numerical results obtained in recent coupled T equation studies of e-H scattering.
Dynamics of electron transfer collisions of fast Li atoms with several molecules
Authors: Young C. E. , Beuhler R. J. , Wexler S.
Published: February 2004

The angular distributions of Li+ ions produced in electron transfer collisions of neutral lithium atoms with the molecules Br2, Cl2, HBr, HCl, O2, and SF6 have been measured. For each system, studied by the crossed molecular beam method, data were obtained at several collision energies, ranging from near threshold [ΔE = 5.390-target electron affinity (eV)] to approximately 14 eV in the center-of-mass (c.m.) system. The fast Li atoms were produced by surface sputtering and then velocity selected. An in-plane experimental geometry was used, with fixed beam sources and a rotatable quadrupole mass filter detection system. The laboratory angular distributions of Li+ ions fall into two groups. For molecules possessing high electron affinities, i.e., Br2 and Cl2, the distributions exhibit undulations, whereas for targets with low electron affinities, the angular distributions decrease monotonically. All show a strong peaking in the forward direction. Differential cross sections obtained by inversion to the c.m. system, with nominal collision velocities and ΔE, were well represented by σ(Eθ), a function of the c.m. collision energy times the scattering angle. By use of an iterative procedure, a single function σ(Eθ) was found to fit the data for each system at all E when averaged over the experimental velocity and angular spreads. Essential features of the scattering are interpreted in terms of classical motion of the heavy particles on potential curves representing the neutral and ionic collidants, using a central-force model of interaction. Electron transfer, which corresponds to a change in adiabatic surface, is considered to occur in a localized region of space where the surfaces are nearly degenerate. The Landau-Zener description of these transitions is followed. The results of the classical theory are discussed for Li–Br2 and Li–HBr, which are representative of the two distinct categories of collision systems studied-those having large electron affinities and thus long-range surface crossings, and those having small electron affinities with corresponding close collisions for electron transfer. A modification of the collision mechanism, which provides for dissociation of the negative molecular ion, leads to good agreement with the long-range crossing data. The influences on the angular distributions of several parameters in the classical scattering model, namely the asymptotic surface separation, the adiabatic well depth, the repulsion parameter, and the polarizability sum, are evaluated. However, for the short-range crossing cases, the classical model gives angular distributions in poorer agreement with the experimental results.
Spectra and structure of small ring compounds. XXXI Microwave, Raman and infrared spectra, conformation, dipole moment, and quadrupole coupling constants of 2-oxazoline
Authors: Durig J. R. , Riethmiller S. , Li Y. S.
Published: February 2004

The microwave spectrum of 2-oxazoline has been recorded from 12.4–40.0 GHz. Both Q-branch and R-branch assignments have been made for the ground and five vibrationally excited states of the ring puckering mode for both A - and B-type transitions. The components of the diple moment were determined by the Stark effect to be μa = 1.14±0.01, μb = 1.35±0.01, μc = 0.00±0.00, and μt = 1.77±0.01 D. The quadrupole coupling constants were found to have the following values: χa a = −3.54, χb b = 2.03, and χc c = 1.51 MHz. From the inertial defect Δc and the dipole moment, it is concluded that the heavy atom skeleton is planar. From the relative intensity measurements, the first excited state of the ring puckering vibration was found to have a frequency of 79±8 cm−1 and from a series of difference bands in the infrared spectrum, the ν = 0→1, 1→2, 2→3, 3→4, and 4→5 transitions were found to have the following frequencies: 74, 95, 103, 110, and 117 cm−1, respectively. The potential function governing the ring puckering motion was found to be of the form V = 22.2 (Z4+1.31Z2), where Z is the reduced ring puckering coordinate. The Raman spectra of gaseous, liquid, and solid 2-oxazoline was investigated from 0–3500 cm−1 and the infrared spectra of the gas and solid were recorded from 33–3500 cm−1. The vibrational assignment of the fundamentals is proposed which is consistent with the Cs conformation. The assignment is based on the gas-phase band contours, the depolarization values, and group frequency correlations. The number of lattice modes indicate that there are at least two molecules per primitive cell. The results are compared with those obtained for other similar five-membered rings.
Quantum mechanical theory of translation-internal mode energy transfer in collisions of atoms with diatomic systems
Authors: Csanak Gy. , Taylor H. S. , Varracchio E. Ficocelli
Published: February 2004

The field theoretical Green's function technique has been used to define an elastic scattering optical and inelastic scattering transition potential for the structureless atom-diatom scattering problem. The functional differentiation technique of Schwinger has been utilized to generate approximations for these potentials. First and second order approximations are given and their physical interpretation discussed.
Magnetic susceptibility study of φ4AsCuCl3: An example of a Cu2Cl62− dimer with a ground state triplet
Authors: Chow Chee , Caputo Ruth , Willett Roger D. , Gerstein Bernard C.
Published: February 2004

The magnetic susceptibility data for φ4AsCuCl3 is presented. The data is consistant with the existance of isolated Cu2Cl62 dimers with a S = 1 ground state. A singlet state lies 46 cm−1 above the ground state.
Assignments of Rydberg and valence transitions in the electronic absorption spectrum of dimethyl sulfide
Authors: McDiarmid Ruth
Published: February 2004

The electronic absorption spectra of (CH3)2S and (CD3)2S have been recorded between 1250 and 2500 Å. Twenty-four of the observed transitions have been arranged into three Rydberg series originating from the b1 nonbonding orbital. These Rydberg series have been identified as one s, one p and one d series. From their isotope zero point energy shifts and observed vibronic structures, the Rydberg states were deduced to be contaminated by other states. Two unmistakenly non-Rydberg transitions were observed. From solution and solvent shift data, they were proposed to arise from promotions out of the a1 bonding orbital.
Magnetothermodynamics of gadolinium gallium garnet. II. Heat capacity, entropy, magnetic moment from 0.5 to 4.2°K, with fields to 90 kG, along the [111] axis
Authors: Hornung E. W. , Fisher R. A. , Brodale G. E. , Giauque W. F.
Published: February 2004

The magnetic moment of a 2.44 cm diam spherical single crystal of gadolinium gallium garnet has been measured with stabilized fields of 500, 1000, 2500, 5000, 10 000, 15 000, 25 000, 40 000, 65 000, and 90 000 G along the [111] axis, over the range 0.35–4.2°K. The heat capacity was measured at the same fields and over the range 0.5–4.2°K, except that 500 G was omitted and zero field included. The magnetic moment reached saturation at 0.35°K and 90 000 G. Within the limit of error, a zero of entropy for the electronic and lattice systems was located at 90 000 G. By means of temperatures measured on 39 adiabatics, corrected with respect to entropy, which intersected the various isoerstedic heat capacity series, the entropies were evaluated as a function of field and temperature. The sample had an excess of electronic entropy of 0.5% over the maximum R ln8 for Gd3+ ion. Thus the sample must have contained 0.5% excess gadolinium over the stoichiometric amount for Gd3Ga5O12. Using the related correction factor 0.9950, the saturation value for Gd3Ga5O12 is found to be Msat[111] = 38 979 G · cm3/mole Gd3+, corresponding to a g[111] = 1.994±0.002. A correction of Msat[100], taken from J. Chem Phys. 59, 4652 (1973), using the correction factor 0.9950, gives Msat[100] = 39 056 G · cm3/mole Gd3+, corresponding to g[100] = 1.998±0.002. Smoothed correlated values of the heat capacity, entropy, enthalpy, internal energy, magnetic moment and its differential isoerstedic temperature coefficient, differential isothermal magnetic susceptibility, and the isothermal work of magnetization have been tabulated over the ranges 0–90 kG and 0.5–4.2°K. The problem of location of the zero of entropy in a system where nuclear spin contributes to the heat capacity has been discussed.
Kinetic theory of dense fluids
Authors: Schrodt I. B. , Davis H. T.
Published: February 2004

The kinetic theoretical model recently presented by Davis is used to predict the thermal conductivity, shear viscosity, and self-diffusivity of liquid argon. The pair correlation functions used in the computations are determined from the Percus-Yevick theory using the Weeks-Chandler-Andersen effective hard sphere technique. The agreement between the experimental and theoretical transport coefficients is quite good (disagreement never worse than 40%). Although the theory uses the Rice-Allnatt breakup of the collisions into ``hard'' and ``soft'' collisions, the requirement that the interaction potential have a hard core cutoff is relaxed by introducing an effective hard sphere collision-the procedure, though not as rigorous, is in the spirit of the WCA perturbation theory of equilibrium properties. Computations are done for both the Lennard-Jones and the truncated Lennard-Jones potential models with very similar results.
Pressure and temperature-dependent Raman scattering study of the phase transitions in ammonium bromide
Authors: Wang C. H. , Wright R. B.
Published: February 2004

The pressure and temperature dependences of the lattice phonons and internal ν4 modes in NH4Br have been measured, with special emphasis on the Raman bands connected with the recently discovered high pressure phase (OII). It has been shown from this work that the ammonium ions in phase OII are ordered and the crystal structure of the OII phase is cubic. The pretransition effect associated with the OII–OT transition has also been found. The frequencies of the 68 cm−1 phonon mode and the LO component of the ν4 mode in phase OII have been found to decrease with increasing pressure, indicating that the pressure decreases the curvature of the potential function of the Br− ion at equilibrium. This work has shown that the phonon and internal vibrational spectra of NH4Br in phase OII closely resembles the ordered phase of NH4Cl. This contrasts with the suggestion made previously that the structure of the OII NH4Br is similar to the disordered phase of NH4Cl.
Expansion variables for general quartic force fields of triatomic molecules
Authors: Simons Gary
Published: February 2004

A framework for general quartic force fields of polyatomic molecules, employing expansion coordinates of the form ρ=(r − re)/r, is developed. The new approach is shown to be superior in terms of both rate and region of convergence to traditional expansions, and a procedure for obtaining the necessary coefficients is outlined. Results are presented for CO2, CS2, HCN, and N2O, and the chemical utility of the new force fields is assessed.
Nuclear magnetic resonance of 27Al in epidote, Ca2Al2(Fe,Al)Si3O12(OH)
Authors: Tsang Tung , Ghose Subrata
Published: February 2004

Two types of nuclear electric quadrupole tensors have been observed for 27Al in epidote. The quadrupole coupling constant C and asymmetry parameter η are AlI |C|=11.9 MHz, η=0.3; AlII, |C|=4.6 MHz, η=0.34. They correspond to the Al1 and Al2 sites, respectively, of the epidote crystal structure. The electric field gradient tensors, with principal contributions from its nearest neighbors in the highly distorted AlO6 tetrahedra, are consistent with the epidote structure and with other aluminosilicate minerals.
Calculation of the pressure-broadening of HCl and DCl infrared and Raman lines
Authors: Gray C. G.
Published: February 2004

The impact theory of pressure broadening is used to calculate the pure rotational linewidths at room temperature for the ir and Raman spectra of HCl and DCl. The broadening due to the four multipole interactions of lowest order is discussed for the self-broadening in HCl and DCl, and the foreign broadening of HCl by DCl and DCl by HCl. There are no adjustable parameters in the calculations; the molecular dipole and quadrupole moments are obtained from other sources. Three features distinguish the linewidths predicted for these polar molecules as compared with previous results for nonpolar molecules: (i) The linewidths are considerably larger; (ii) there is a maximum in the J dependence at small J; and (iii) there is an oscillation in the J dependence at large J for the Raman lines in HCl–DCl and DCl–HCl. The calculations are compared with the data that are available.
Ultrasonic absorption in liquid Na–K and Na–Rb alloys
Authors: Amaral J. E. , Letcher S. V.
Published: February 2004

Ultrasonic absorption and velocity have been measured in liquid Na–K and Na–Rb alloys. A slight peak in the absorption vs concentration curve for Na–K is consistent with the earlier results of Jarzynski and Litovitz. The substantial peak found for Na–Rb is reminiscent of a similar peak found earlier in Na–Cs. Estimation of the location of the submerged miscibility curves suggests that the peak absorptions are due to the critical phase separations of the binary mixtures.
Diffusion measurements in dense gases. The systems He–Ar and He–Ne
Authors: De Paz M. , Tantalo F. , Varni G.
Published: February 2004

Diffusion experiments have been carried out in He–Ar and He–Ne mixtures at pressures from 40 to 150 atm and temperatures 80–300°K. Both systems, up to 150 amagat units of density, are in substantial agreement with the predictions of the Chapman-Enskog theory and the Enskog-Thorne extension to high density. In the He–Ar mixture, however, deviations are observed around 150°K in the neighborhood of the characteristic potential hole depth of pure Ar.
Photoabsorption of solid carbon dioxide from 7 to 12 eV
Authors: Monahan K. M. , Walker W. C.
Published: February 2004

The photoabsorption spectra of solid and gas phase carbon dioxide were measured in the region from 7 to 12 eV. Transition energies were found to be shifted in the solid, and one forbidden transition was anomalously enhanced relative to its gas phase counterpart.
Model of pre-existing traps for electrons in polar condensed media. II. Effect of dipole-dipole correlation
Authors: Tachiya M. , Mozumder A.
Published: February 2004

A model of pre-existing traps for electrons in polar condensed media is further developed. We calculate the distribution of the depth of pre-existing traps taking into account the interaction between the dipoles. In this manner we consider the effect of temperature on the depth distribution. Inclusion of the dipole-dipole interaction changes the results significantly.
Microwave spectrum and internal rotation potential of propanal
Authors: Pickett Herbert M. , Scroggin Don G.
Published: February 2004

The gas-phase microwave spectrum of the gauche rotational isomer of propanal (propionaldehyde, CH3CH2CHO) has been studied in detail. Vibration-rotation interaction between torsional energy levels which are split by quantum tunneling results in the splitting of several ground-state absorption lines. Treatment of this interaction by methods described in an earlier paper successfully accounts for the anomalous spectrum. Observation of several predicted transitions (including transitions nominally forbidden) confirms the theoretical treatment and allows an accurate determination of the energy level splitting (471.80±0.07 MHz) of the two lowest levels of gauche propanal. This new information is used in the determination of an internal rotation potential, which is compared with recent theoretical calculations for propanal.
End-chain flexibility and the nematic-isotropic transition in liquid crystals: A lattice model of hard particles with rigid, rodlike, central cores and semiflexible pendant segments
Authors: Ågren Göran I. , Martire Daniel E.
Published: February 2004

A simple cubic lattice model is utilized to develop the statistics of a system of hard particles with a rigid, rodlike, central core to each end of which is attached a semiflexible chain (tail). The core occupies L collinear sites on the lattice, whereas each of the tails occupies λ adjoining sites. An energy u (of order k T) is required for a tail segment to make a bend, i.e., to change direction. The partition function for the system is obtained by utilizing DiMarzio's counting method for the configurational partition function and an exact matrix method to determine the partition function for a tail. With L =5 (1≤λ≤6) and L =10 (1≤λ≤9), first order anisotropic (larger fraction of cores pointing in the preferred direction than in either of the two perpendicular directions) to isotropic phase transitions are found. The results of the model are compared with those for completely rigid rods, revealing that our transitions occur at higher densities and with smaller relative density changes. Our model is found to exhibit the same qualitative behavior, with increasing λ, in the transition temperature and transition entropy as has been observed for the nematic-isotropic transition in various homologous series.
Semiclassical S-matrix theory of vibrationally inelastic collisions between two diatomic molecules
Authors: Cohen Steven C. , Alexander Millard H.
Published: February 2004

We derive a semiclassical S matrix for vibrationally inelastic collisions between two diatomic molecules, assuming a collinear geometry. Our theory incorporates a quantum mechanical superposition principle with classical dynamics and, as such, is an extension of the atom-diatomic molecule theory of Miller. The several approximations to the S matrix differ in the complexity with which the interference between various classical trajectories is treated. We report numerical calculations for H2–D2 and D2–D2 collisions based on two different interaction potentials. The cruder approximations yield transition probabilities which agree with exact quantum mechanical results to within a factor of 2. More sophisticated approximations to the S matrix yield excellent quantitative agreement with the quantum calculations. We also examine in detail the classical dynamics of the collision process and show that the molecules pass through a number of intermediate states during the encounter.
Simplified impedance/frequency-response results for intrinsically conducting solids and liquids
Authors: Macdonald J. Ross
Published: February 2004

The small-signal ac response is considered of a system containing a single species of positive charge and a single species of negative charge. The charge carriers may be of many different types (ions, electrons, vacancies, etc.) and are assumed to have arbitrary mobilities and valences. Quite general boundary conditions are considered which encompass the range from complete blocking to zero blocking (infinite reaction rate at the electrodes) for positive and negative charges separately. The present paper deals primarily with approximations to an earlier exact solution of the problem which, in general, lead to an equivalent circuit made up of three parallel R C combinations in series. The elements of one of these parallel circuits, associated only with bulk effects, are frequency independent, and those of another, which are associated with nonzero blocking, may often be well approximated as independent. The third R C section arises from diffusion effects, involves frequency dependent elements, and exhibits approximate Warburg frequency response over a considerable frequency range. In general, Cole-Cole or Nyquist impedance plane plots show three connected arcs, two of which are frequently good semicircles. These arcs are directly associated with the three R C sections. Under many conditions, only two of the three arcs may appear and melding of arcs into each other can also occur. Very simple, as well as less simple, approximations are developed for the impedances of the individual R C sections as well as the over-all impedance of the system. The accuracy of these approximations is evaluated, and it is shown how they may be used in unambiguous cases to analyze frequency response data to yield estimates of mobilities, valences, electrode reaction rate parameters, and bulk charge concentrations. Surprisingly, it is found that for a certain mobility ratio range, the center arc, associated with electrode reactions, well approximates a depressed semicircle of the Cole-Cole relaxation time distribution type, yet no distribution of relaxation times is present. Further, in the completely blocking case, where the center approximate semicircle is not depressed but has an infinite radius, the lower frequency portion does not necessarily begin with a vertical segment as frequency decreases but may be curved away from vertical over a considerable frequency range. General impedance results for the present unsupported conduction situation are found to be quite different in some ways from those following from supported electrolyte treatments. Such treatments should thus not be used to analyze unsupported situations. Finally, it is found that the parallel capacitance of the system, which may be far greater than ordinary double layer values, can exhibit appreciable regions of ω−m frequency response with 0≤m ≤2, and with m =0.5, 1, 1.5, and 2 values especially prominent.
Molecular model for ice clusters in a supersaturated vapor
Authors: Hale B. N. , Plummer P. L. M.
Published: February 2004

A molecular model previously applied to prenucleation water clusters is used to examine ice Ih embryos. The canonical partition function is evaluated for clusters having from 6 to 64 water molecules. The intermolecular vibrational free energies are extrapolated to clusters containing up to 120 molecules and free energies of formation, nucleation rates, and critical supersaturation ratios are calculated and compared with experiment. For the clusters studied, the ice Ih structure appears to be much less stable at all temperatures than the more spherical clathratelike cluster.
Reflection of clusters of helium, hydrogen, and nitrogen as function of the reflector temperature
Authors: Gspann J. , Krieg G.
Published: February 2004

Clusters of helium, hydrogen, and nitrogen are reflected at a polished stainless steel plate at temperatures ranging from 80 to 550 K. The incident clusters contain on the average about 1.5×105 atoms of helium or molecules of hydrogen or 104 molecules of nitrogen, as measured by time-of-flight mass spectrometry. The angular distributions of the average sizes, the velocities, and the molecular intensities of the reflected cluster beams show that in the investigated range of reflector temperatures the reflection of the helium clusters corresponds to the hydrogen cluster reflection at higher reflector temperatures while the nitrogen cluster reflection corresponds to the hydrogen cluster reflection at lower reflector temperatures. The transition between the two regimes of reflection as observed with hydrogen clusters is marked by an optimum reflector temperature leading to a maximum intensity of the reflected beam, a minimum loss of clustered material, and a distinct angular separation of incident cluster sizes. At a grazing incidence angle of 84.3° the measured optimum reflector temperature for the hydrogen cluster reflection is 215 K and increases with decreasing angle of incidence. The two regimes of high-temperature and low-temperature reflection of clusters exhibit close phenomenological relationship to the regimes of thermal and structure dominated scattering of atoms from single crystal planes. In both cases the transition region is characterized by a maximum angle of reflection and a minimum divergence of the reflected beam. The features of high-temperature cluster reflection are explained by a semiempirical model based on the evaporation recoil of the cluster molecules ablating after contact with the comparatively hot reflector surface.
High-temperature thermodynamics of the solid solutions of hydrogen in bcc vanadium, niobium, and tantalum
Authors: Kleppa O. J. , Dantzer P. , Melnichak M. E.
Published: February 2004

The high-temperature thermodynamic properties of V+H2 and Nb+H2 solid solutions have been studied by a combined calorimetric and equilibrium method at 264, 300, and 437° (V), and at 356 and 440° (Nb). The results demonstrate experimentally that the relative partial enthalpies and entropies of hydrogen in these solid solutions are very nearly independent of temperature in this temperature range. The observed enthalpies are compared with data derived from equilibrium work, and with our earlier data at 430° for Ta+H2. From the equilibrium pressures and the partial enthalpies, we have calculated the partial entropies, also the partial excess entropies of hydrogen. The limiting values (at NH=0) of the excess entropies are compared with values derived from the sum of the contributions from the volume expansion and from vibrational and electronic heat capacity terms. These calculated values are systematically about 0.5–1.0 cal/deg · g-atom lower than the experimental ones. This difference is too small to allow for any site degeneracy term in the excess entropies.
Rotational diffusion of spherical top molecules in liquids and gases. IV. Semiclassical theory and applications to the v3 and v4 band shapes of methane in high pressure gas mixtures
Authors: Eagles T. E. , McClung R. E. D.
Published: February 2004

Semiclassical versions of the extended rotational diffusion models for molecular motion in fluids are developed by means of the memory function formalism. These semiclassical models have distinct advantages over the approximate semiclassical models described in a previous paper in this series. Application of the present theory is not severely restricted to the description of band shapes derived from a small number of vibration-rotation transitions as the previous theory was. Application of these new semiclassical models to calculations of the v3 and v4 infrared band contours of CH4 in dense gas mixtures indicates that these models account satisfactorily for the observed bandwidths and asymmetries. The angular momentum correlation times obtained from the analysis of the v3 and v4 bands of CH4 under similar conditions are shown to be in agreement.
Depolarized Rayleigh scattering in liquids: The density and temperature dependence of the orientational pair correlations in liquids composed of anisometric molecules
Authors: Alms G. R. , Gierke T. D. , Flygare W. H.
Published: February 2004

Structural analogs of the nematic liquid crystal p-methoxybenzylidene-n-butylaniline (MBBA) have been synthesized and the static orientational pair correlations (OPC) have been examined by light scattering. From the intensity of the depolarized Rayleigh scattered light, the OPC's have been determined in the neat isotropic liquid and in solution with carbon tetrachloride as a function of concentration and temperature for two of these molecules, p -methylbenzylidene-n -butylaniline (MBA) and p -ethylbenzylidene-n -butylaniline (EBA). The density dependence of the OPC's of these molecules and MBBA are analyzed in terms of the structure and polarity of the scattering molecules. The OPC's of the isotropic liquid trans -cinnamaldehyde have also been determined. We find that the molecular size and shape (repulsive forces) largely determine the extent of orientational order in these liquids. The attractive intermolecular forces affect the orientational order (static OPC) by increasing the density (at a given temperature). Several conclusions relating the static OPC and the onset of the nematic liquid crystalline phase are also discussed.
Crystal-field model study of the xenon hexafluoride molecule. III. Electronic transitions and band shapes
Authors: Wang Sylvester Y. , Lohr Lawrence L.
Published: February 2004

The application of a two-electron crystal-field model to the electronic structure of xenon hexafluoride is extended to include the calculation of oscillator strengths for absorption transitions to the largely spin singlet and the largely spin triplet excited states. Band shapes are calculated in terms of their spectral moments by obtaining vibrational energies and wavefunctions for the mixed quadratic-quartic potential energy functions calculated from the crystal-field model. The key experimental features of the absorption spectrum of the vapor are reproduced, namely the pronounced red shift and the increased bandwidth with rising temperature. The over-all similarity of the vapor spectrum to that of the isovalent hexahalotellurate (IV) complexes in solids in noted. It is concluded that the experimental data of Claassen, Goodman, and Kim are compatible with the pseudo-Jahn-Teller model of Gillespie as developed by Bartell and Gavin and by Wang and Lohr, and that the data do not require the use of the electronic isomers model of Goodman, although the latter model is not excluded.
Numerical study of the statistical thermodynamic properties of a surface-interacting polymer chain
Authors: Lax Melvin
Published: February 2004

Statistical thermodynamic properties of surface interacting self-avoiding walks confined to the diamond lattice have been obtained. The existence of a transition for the infinite chain is inferred from the behavior of the specific heat versus energy curves. It was found that the long-range critical exponent αs in the partition for such a system goes to zero at a particular energy corresponding to the point where the mean-square end-to-end distance and mean-square radius of gyration display minima.
Optical properties of a guest molecule in a discrete lattice
Authors: Fulton Robert L.
Published: February 2004

The optical properties of a simple model system consisting of an anisotropic guest molecule situated on a lattice site of a cubic lattice, the other sites being occupied by isotropic solvent molecules, are found. The results are compared to those found by a continuum (Onsager) approximation. It is found that some quantities, such as the dependence of the energy shift on the solvent dielectric constant εs, are qualitatively little affected by the discrete lattice structure, while others, such as radiative lifetimes and scattering cross sections, have a qualitatively different behavior for large εs. The Rayleigh ratio Ranis describing the anisotropic contribution to light scattering is found to contain a factor [(εs+2)/3]4 (in addition to another correction) in contrast to the usually assumed [(εs+2)/3]2 factor. The experimental ratio of the ratio Ranis (solution)/Ranis (gas) for CS2 and benzene in cyclohexane is satisfactorily reproduced by the present treatment while the continuum approximation gives a result about 20% too high. Some special optical properties arising from the anomalous dispersion of the energy bands of a simple cubic lattice are discussed.