bluuebunny/crossref_metadata_2025 huggingface dataset:
Lyman-Alpha Emission Cross Sections for Collisions of 1–25 keV H+ and H with CO, CO2, CH4, and NH3
Authors: Birely J. H. , McNeal R. J.
Published: February 2004

Cross sections are reported for emission of Lyman-α radiation in collisions of H+ and H with CO and CO2 in the 1–25-keV energy range and with CH4 and NH3 in the range 5–25 keV. In the experiments with CH4 and NH3 the Doppler-shifted Lyman α, emitted by H(2p) formed in electron capture by fast incident protons or collisional excitation of fast incoming hydrogen atoms, and the virtually unshifted Lyman α, emitted by the far slower H(2p) produced in dissociative excitation, were separated. An electric field was applied within the collision chamber, and the increase in Lyman-α intensity was used to derive cross sections for formation of H(2s). For CO and CO2 targets, H projectiles are more efficient than H+ in formation of H(2p), while at energies above 10 keV, H+ is more efficient than H in formation of H(2s). For both projectiles, the probability of formation of H(2p) is greater than or equal to the probability of forming H(2s). For CH4 and NH3 targets the projectile excitation cross sections are generally similar to those for CO and CO2, and the total projectile excitation cross section for formation of H(n=2) exceeds that for dissociative excitation in either H+ or H impact. For both projectiles formation of H(2p) in dissociative excitation is at least an order of magnitude more probable than formation of H(2s). Protons are found to be more efficient than hydrogen atoms in production of Lyman α via dissociative excitation. Relationships are presented between the projectile excitation cross section and the cross section for electron capture in H+ impact or stripping in H impact which are relatively independent of the identity of the target molecule.
Optically Detected Adiabatic Inversion in Phosphorescent Triplet States and the Measurement of Intramolecular Energy Transfer Processes
Authors: Harris C. B. , Hoover Robert J.
Published: February 2004

The theory and observation of microwave induced population inversion within triplet magnetic sublevels in zero field are presented. It is shown that inversion via adiabatic fast passage can be measured quantitatively by changes in triplet phosphorescence and that population inversion can be accomplished easily and with microwave field strengths even lower than are required for cw saturation. Parameters affecting the ability to invert the sublevel populations, such as dipolar interactions, microwave power, and sweep rates, are studied. General equations relating the intensity of phosphorescence and the fraction of inversion to parameters associated with energy transfer processes into and from the triplet state such as intersystem crossing and radiative and radiationless relaxation are derived and measured for the π π*3 state of 2,3-dichloroquinoxaline.
Enthalpy of Formation of NH
Authors: Kaskan W. E. , Nadler Melvin P.
Published: February 2004

Measurements have been made of [NH], [NH3], and [OH] as a function of distance from the reaction zone of a flat NH3/O2/N2 flame at atmospheric pressure. The function [NH] [H2O]2/[NH3] [OH]2 is shown to behave like the equilibrium constant for the reaction NH3+2OH→ NH+2H2O, but to be about a factor of 10 smaller than the value calculated from the JANAF tables. In order to account for this discrepancy, various uncertainties in experiment and in input data are analyzed. Of these, special attention is given to the extinction coefficient of NH3 near 2300 Å and to the possibility that [NH] is depressed below its equilibrated value by kinetic effects. These uncertainties are found to be not large enough to account for the observations. It is concluded that the discrepancy can best be resolved by adopting an enthalpy of formation of NH of 90 ± 4 kcal/mole, rather than 81 kcal/mole as in the JANAF tables.
Application of the Fisher—Sykes Attrition Relation to the Diamond Lattice
Authors: Gans Paul J.
Published: February 2004

The Fisher—Sykes attrition relations are applied to the diamond lattice using Monte Carlo estimates of the attrition at various walk lengths. It is found that these relations provide accurate estimates of the attrition for walks as small as 10 steps, in distinction to the exponential attrition law which is asymptotically valid only for much larger values of walk length.
Study of Electron Correlation in the Hydride Ion
Authors: Winter Nicholas Wilhelm
Published: February 2004

The influence of angular correlation on the wavefunction and energy of the hydride ion has been investigated by solving various angular limit equations through the I limit. Several one-electron properties are presented along with three-dimensional plots of the wavefunction. The extrapolated energy is −0.527743 a.u. compared to the exact value of −0.527751 a.u.
Vacuum-Ultraviolet Excitation Cross Sections by Electron Impact on NO
Authors: Mentall J. E. , Morgan H. D.
Published: February 2004

Absolute excitation functions were measured for the NO+ A 1Π −X 1Σ+ molecular band system, the nitrogen 1200–, 1243–, and 1493–Å multiplets, and oxygen 1304–Å multiplet. Excitation was by electron impact on NO from threshold to ·250 eV. At 100 eV the excitation cross section for the NO+ A—X system is 9.7 × 10–18  cm2 while the cross sections for the nitrogen and oxygen multiplets are: N, 1200 Å − 4.8 × 10–18 cm2; N, 1243 Å–0.89 × 10–18 cm2; N, 1493 Å–1.5× 10–18 cm2; and O, 1304 Å–1.1× 10–18 cm2. From the vibrational intensity distribution of the A—X system, the variation of electronic transition moment with r centroid was determined and this result used to calculate an array of vibrational transition probabilities. In addition, cross sections were measured at 100 eV only for the N 1135–, N 1745–, O 1152–, and O 1218–Å multiplets. Cross sections for these multiplets are: N, 1135 Å – 1.6× 10–18 cm2; N, 1745 Å–0.87× 10–18 cm2; O, 1152 Å–0.85× 10–18 cm2; and O, 1218 Å–0.39× 10–18 cm2.
Electric Field Induced Perturbations in the B21←A11 Transition of Aniline
Authors: Lombardi John R.
Published: February 2004

Electric field induced perturbations have been observed in the 0–0 band of the B21←A11 (π*← π ) transition in aniline. From analysis of this effect, we infer the existence of a second state 0.10 cm−1 away with vibronic symmetry B2. Combined with a reinterpretation of a previously observed Stark effect in aniline, we determine the dipole moment of the π*← π state to be 2.45± 0.10 D, and that of the perturbing state to be 6.0± 0.4 D. The transition moment between the two mutually perturbing states is 0.5± 0.4 D, and lies along the long in-plane molecular axis. Since the perturbing state has such a different dipole moment from either the ground or π*← π state, it is most likely a π*← n or σ ↔ π transition. Possible implications of this effect for intersystem crossing rates are discussed.
Lifetimes and Quantum Yields of Individual Vibronic States of C6D6 and C6H5F
Authors: Abramson Allan S. , Spears Kenneth G. , Rice Stuart A.
Published: February 2004

The lifetimes and quantum yields of fluorescence from 22 vibronic states of C6D6 and 59 vibronic states of C6H5F have been determined under ``free molecule'' conditions. It is found that the dependence of non-radiative lifetime on number of quanta of excess vibrational energy follows a pattern similar to that observed for C6H6. Calculations of the energy dependence of τnr by Heller, Freed, and Gelbart are in good agreement with the observations. An ancillary consequence of the study of the lifetimes of vibronic states of C6H5F is the suggested reassignment of five transitions.
ESR Spectra of the Fluorinated Silyl Radicals
Authors: Merritt Margaret V. , Fessenden Richard W.
Published: February 2004

Isotropic ESR spectra of · SiH2F, · SiHF2, and · SiF3 are reported. The radicals were produced by radiolysis of H3SiF, H2SiF2, and HSiF3 in an SF6 matrix. The hyperfine parameters in gauss are: for · SiH2F, aH=34.6, aF=55.2; for · SiHF2, aH=89.9, aF=77.8; and for · SiF3, aF=136.6, aSi=(−) 498.0. The large 29Si hyperfine constant for · SiF3 shows that the radical is strongly pyramidal, probably as a result of the high ionic character of the Si–F bonds. The proton hyperfine constants are believed to be positive and the parallel of · SiHF2 with · HPO2− (aH=82.5 G) is noted. The radical (CH3)2SiF · was also produced in liquid phase photolysis experiments and has the parameters aH=4.53 and aF=65.21 G.
Configurational Statistics of Polyethylene Chains
Authors: Allegra Giuseppe , Avitabile Gustavo
Published: February 2004

A mathematical procedure is described to handle the configurational statistics of a chain placed on a rigid lattice, allowing for first-neighbor interaction between consecutive rotational states. Many statistics connected with chain bonds orientation with respect to a fixed reference frame are calculated easily. Assuming a diamond lattice, results are reported for polyethylene chains with different lengths: They include the W (r) end-to-end vector distribution, the principal mean-square radii of gyration of the polymer coils both under a fixed force applied to the chain ends and under a fixed end-to-end distance, the plots of 〈cos2Φ〉 and of fG vs r Φ=angle between a chain bond and the direction of the force, fG=fraction of gauche rotational states). The last two results allow derivation of the average optical polarizability and of the internal energy for different chain elongations. Both the calculated characteristic ratio C∞ and its derivative with temperature agree with the experimental data.
k=0 Librational Spectrum for Solid α-N2
Authors: Raich J. C.
Published: February 2004

An alternative description of the k=0 librational spectrum of solid α-N2 is given. A variational method where the wavefunctions of the hindered rotator are expanded in terms of spherical harmonics is used. The present calculations are limited to electrostatic quadrupole—quadrupole interactions. The k=0 librational frequencies are compared with the results obtained by classical lattice dynamics and another variational method as well as experiment.
Image Potentials for Multipoles Embedded in a Cavity and Their Applications to the Surface Tension of Aqueous Solutions of Amino Acids
Authors: Buff Frank P. , Goel Narendra S.
Published: February 2004

The electrostatic theory for a dielectric spherical or spheroidal cavity, with arbitrary charge distribution within it, is presented. The cavity is located in a dielectric medium which is separated from another uniform dielectric medium by a planar interface. The use of a cavity avoids the singularities in the image potential for point charges as they approach the interface. It is shown that the adsorption potential is directly related to the resolvent of a matrix whose elements depend on the position and the dimensions of the cavity. The results are used to calculate the adsorption potential for a species with specified dipole and quadrupole moments. The adsorption potential thus calculated is used to analyze the difference between the surface tension of zwitterionic solutions and the pure solvent. We discuss how the diffuseness of the interface diminishes the calculated increase in the surface tension. The calculated changes, arising from electrostatic forces, in the surface tension of aqueous solutions of small amino acids belonging to an homologous series, compare favorably with those derived from the experimental measurements.
Gravitational Effects in X-Ray Studies of Critical Opalescence
Authors: Dobbs Bill C. , Schmidt Paul W.
Published: February 2004

Because of the high value of the isothermal compressibility of a one-component fluid when the fluid is near its liquid—vapor critical point, the fluid density can vary appreciably at different heights in a sample cell. A calculation is made of the magnitude of these gravitational effects in small angle x-ray scattering experiments. First, the scaling-law equation of state is used to develop a method for computing the density profile in a sample cell. The calculated density profile is then employed to find the scattered intensity expected in a small angle x-ray scattering apparatus employing slit collimation. The slit arrangement is chosen to be simple enough to permit relatively easy calculation while still providing collimation similar to the collimation used in present-day equipment. The scattered intensity is assumed to be given by the Ornstein—Zernike scattering relation. After collimation corrections are applied to the computed ``observed'' intensity, the corrected intensity is compared with the intensity expected in the absence of gravitational effects. This comparison indicates that while gravitational effects almost certainly have not appreciably affected the recently published x-ray studies of critical opalescence, gravitational effects will be significant if experimental techniques are refined to permit measurements at smaller scattering angles and at temperatures closer to the critical point.
Deconvolution of Molecular Beam Inelastic Scattering Data
Authors: Gillen Keith T. , Mahan Bruce H.
Published: February 2004

Two deconvolution techniques and their application to large angle scattering of molecular beams are considered. The first method, an iterative unfolding (IU) technique due to Ioup and Thomas, is shown to contain an error; this error is corrected, but still further limitations are shown to exist. The second deconvolution method, which involves a folding together of apparatus and assumed scattering functions, is used to analyze some data previously analyzed by the IU method. The new results in every case show that average (vibrational) inelasticities were overestimated both by analysis of the scattering results without deconvolution and by application of the IU method. The reason for the original overestimate is quite general and is easily understood. A simple classical theory agrees reasonably well with the new energy transfer values over a wide range of collision energy.
Dielectric Relaxation of Some Aliphatic Ketones in Cyclohexane Solution
Authors: Crossley John
Published: February 2004

Dielectric constant and loss data are presented for cyclohexane solutions of 2-hexanone, 2-, 3-, 4-, and 5-nonanone, 2- and 4-decanone, 2-, 4-, and 8-pentadecanone, and 2- and 10-nonadecanone in cyclohexane at up to nine frequencies between 1.5 and 145 GHz at 25°C. The absorption for each system may be represented by a Cole—Cole distribution. For the 2-alkanones, all the nonanones, and 4-decanone, dipole orientation occurs predominantly by intramolecular motion. Rotational orientation of the molecule as a whole appears to make an appreciable contribution also when the dipole is located away from the chain end in the longer molecules.
Dynamics of Dissociation. I. Computational Investigation of Unimolecular Breakdown Processes
Authors: Shapiro Moshe
Published: February 2004

An explicit method for the exact calculation of unimolecular linewidths and line shapes, using an adaptation of known numerical techniques, is presented. The method renders feasible the calculation of decay from one composite ``bound'' subspace, into another composite ``continuum'' subspace. The eigenvalues of the Hamiltonian for the whole ``bound'' subspace are also obtained to a high degree of accuracy. Two specific examples are studied: (a) A single closed channel (containing four bound states) coupled to a single open channel, and (b) three closed channels corresponding to eight bound states, interacting with a single open channel. The exact line shapes for the first of these cases are computed. Interference effects, due to overlapping resonances, are clearly demonstrated and discussed in terms of Fano's theory. Line-widths and resonance energies are calculated for the second case. The results are contrasted to those of the related scattering problem and discussed in terms of the different boundary conditions.
Structure and Phase Transitions of Solid Heavy Methane (CD4)
Authors: Press W.
Published: February 2004

The orientational structures and the phase transitions (27.0 and 22.1°K) of solid CD4 are investigated by coherent neutron scattering from powder samples as well as from single crystals. In its high temperature phase, CD4 is found to crystallize within the space group Fm3m with four molecules per unit cell and a lattice constant a0=5.96 Å at 77°K. The molecular orientations are completely disordered at 35°K, while an indication of partial order was detected at 77°K. The transition to phase II is accompanied by critical fluctuations with a correlation length of about 24 Å (at 27.7°K) and appears to be of second order (critical exponent β =0.4± 0.1. In phase II six of eight molecules order with a local symmetry 42m, while the remaining two are orientationally disordered. The space group is cubic Fm3c with 32 molecules per unit cell and a0=11.64 Å at 24.5°K. The transition to phase III is predominantly of first order. With the present data the structure of phase III cannot be determined unambiguously. Superlattice reflections can be indexed cubic primitive. The number of molecules per unit cell remains 32, with a0=11.61 Å at 17.5°K. The data suggest, that the low temperature structure is to be understood by an ordering within the sublattices of molecules disordered in phase II together with slight distortions of the other sublattices. The structures of phases I and II agree with the ones predicted by James and Keenan under the assumption of octupole—octupole interaction between nearest neighbour molecules. For phase III the model of James and Keenan, as well as other predictions, hitherto published, must be ruled out.
Collision-Induced Light Scattering in Liquids
Authors: Shin Hyung Kyu
Published: February 2004

The isolated binary collision model of light scattering in liquids has been developed to obtain an analytical expression for the spectral intensity in the wings of the Rayleigh spectrum. The expression shows the dependence of the spectral intensity on the nature of the interaction potential energies between the collision pair, on the frequency shift, and on the temperature. The exponential part of the intensity appears in the form exp( − constω12/19T−7/19 + constω6/19T−13/19 − constT−1),where ω is the frequency shift and T is the temperature. The pre-exponential part is shown to be weakly dependent on ω and T. Numerical studies for Xe, Ar, and CCl4 show that the calculation agrees quantitatively with experiment. Both the ω and T dependence of the spectra have been investigated.
Ice IV
Authors: Engelhardt H. , Whalley E.
Published: February 2004

Samples of ice IV have been made and recovered in a metastable state at liquid-nitrogen temperature by using the nucleators discovered by Evans and a modification of his technique. No appreciable thermal effect that can be associated with a phase transition was observed on cooling. During the course of the preparation, measurements were made of the melting lines of ice III, IV, V, and VI. The intersections of these lines allows the coordinates of the hitherto unreported triple points III-IV-L and III-VI-L for both H2O and D2O and IV-VI-L for H2O to be obtained as well as new values of the coordinates of known triple points. The equilibrium pressure pe of a first-order phase transformation is given by pe=− Δ A / Δ V where ΔA and ΔV are the changes of the Helmholtz energy and the volume at the transition. By using this equation, the effect of isotopic substitution on solid—solid transitions is shown to be caused by the change of vibration frequencies at a transition and for the phases of ice is largely caused by the change of the zero-point energy of the vibrations.
On a Thermal and Magnetic Study of the Crystal Field Energy Levels in Dilute Rare-Earth Alloys. I. Lu0.9035Er0.0965
Authors: Taylor W. A. , Gerstein B. C. , Shickell W. D. , Spedding F. H.
Published: February 2004

The heat capacity from 6 to 300°K and initial susceptibility from 1.3 to 145°K of an Lu1—xErx alloy with x=0.0965 were measured. The susceptibility indicated magnetic transitions at 2.3 and 10.3°K. The magnetic contribution to the heat capacity exhibited an anomaly at approximately 10.3°K along with a Schottky anomaly which is attributed to the crystal field levels of the Er in the alloy. In order to fit the high-temperature tail of the Schottky anomaly, the crystal field levels must have a total splitting of approximately 70 cm−1 with the levels bunched toward higher energies.
Fluorescence Spectrum and Relaxation Time Measurement of Cs2UO2Br4
Authors: Wong Dorothy Pan , Wong Andrew Y. C. , Wong Eugene Y.
Published: February 2004

Fluorescence spectra of Cs2UO2Br4 were studied at 14, 4.2, and 1.4°K. Raman spectrum and relaxation times were also measured. At low temperatures, the fluorescence spectra showed additional lines which had highly temperature-dependent relative intensities. These lines are thought of as originating from dislocations of the uranyl complex. The problem of parity of the first excited electronic state of the uranyl ion is also discussed.
Onset of Brownian Motion in a One-Dimensional Fluid
Authors: Bishop Marvin , Berne Bruce J.
Published: February 2004

In this article we describe a computer study of the onset of Brownian motion in a model, one-dimensional system. It is shown that clusters of particles behave like Brownian particles in the limit of large mass. The normalized velocity autocorrelation functions and the corresponding memory functions of these clusters have been determined and compared to theoretical predictions. An interesting result of this study is the mass independence of the self-diffusion coefficient.
Electron-Impact Excitation of Nitric Oxide
Authors: Stone E. J. , Zipf E. C.
Published: February 2004

The absolute cross sections for the excitation of the NO+ Baer-Miescher bands (A 1Πu → X 1Σg+), two nitric oxide β′ bands (B′ 2Δi → X 2Πr), and several atomic nitrogen multiplets in the vacuum ultraviolet by electron impact on NO have been measured over an energy range extending from threshold to 300 eV. The variation of the dipole transition moment for the NO+ (A 1 Πu → X 1Σg−) band system was also determined.
Atomic and Molecular Diffraction and Scattering from a Tungsten Carbide Surface Characterized by LEED
Authors: Weinberg W. H. , Merrill R. P.
Published: February 2004

The scattering of collimated beams of helium, deuterium, neon, and argon are reported from two tungsten carbide surfaces which form on the (110) face of tungsten. On a (3× 5) surface both helium and deuterium give sharp, well-defined diffraction peaks corresponding to the (2̄, 0), (1, 0), (0, 0), (1, 0), (2, 0) directions along the 5 spacing. No diffraction is observed on the (1× 1) carbide surface or the clean metal surface which is also (1× 1). Fractions scattered in the specular ray, (0, 0), as high as 55% have been observed from the carbide surfaces. The scattering of neon is in the inelastic regime and argon is trapping dominated. Analysis of the scattering in combination with the LEED suggests a dense carbide, perhaps WC, with a Debye temperature of 1200°K or higher. This diffractive scattering is the first reported on a surface other than alkali halides and some comments on the sort of periodic potential which is likely to give rise to diffractive scattering of atoms are given.
Millimeter Wave Rotational Spectrum of HSSH and DSSD. II. Anomalous K Doubling Caused by Centrifugal Distortion in DSSD
Authors: Winnewisser Gisbert
Published: February 2004

The microwave spectrum of DSSD in the ground vibrational state has been measured and assigned. Although the DSSD molecule in the ground state is extremely close to a symmetric top (bp=−1.69× 10−7; κ=−0.99999934) the observed spectrum could not be explained by the symmetric-rotor centrifugal-distortion formula, even if higher distortion terms such as P6 or P8 are included. The most remarkable anomaly in the observed spectra is the splitting of the K=2 energy levels, which is several orders of magnitude larger than that expected from the small asymmetry splitting. For J>10 the splitting of the K=2 levels is larger than that of the K=1 levels. These anomalies are shown to be due to the additional K-type doubling caused by the centrifugal-distortion operator (Ĵ+4+Ĵ−4) in the rotational Hamiltonian. This effect, which is predicted to exist in both symmetric-top as well as asymmetric-top molecules, is normally masked in the latter ones by the much larger asymmetry splitting.
Absorbing-Sphere Model for Calculating Ion—Ion Recombination Total Cross Sections
Authors: Olson Ronald E.
Published: February 2004

An ``absorbing-sphere'' model based on the Landau—Zener method is set up for calculating the upper limit thermal energy (300°K) reaction rate and the energy dependence of the total cross sections for the ion—ion recombination reaction, A++B−→ A*+B+Δ E, in which A or B may be atomic or molecular species. The crucial parameter needed for the calculation is the electron detachment energy for the outer electron on B−. For a given system and energy, we find that, as the electron detachment energy is decreased because of the existence of metastable electronic states or excited vibrational states, the cross sections increase. The calculated cross sections and rates are compared with afterglow results and with those obtained from ``merged-beam'' experimental data. We find good agreement with the existing results for atomic negative ions. There are differences for molecular negative ions, and the possible cause of these differences is discussed.
Phosphorescence Spectrum of Acetophenone; An Example of Pseudo-Jahn-Teller Distortion
Authors: Koyanagi Motohiko , Zwarich Ronald J. , Goodman Lionel
Published: February 2004

The phosphorescence spectra and lifetimes of acetophenone, aceto-d3-phenone and acetophenone-d5 were recorded in a variety of close packed and relaxed matrices. The variable vibronic lifetime changes, temperature dependence, and deuteration effects on the acetophenone phosphorescence from solvent to solvent are manifestations of perturbation between close lying 3ππ* and 3nπ* states. The acetophenone phosphorescence problem is marked by environmental perturbations superimposed on pseudo-Jahn-Teller interactions. The result is an environmental sensitive potential surface for the lowest triplet state marked by failure of the Condon approximation. Five cases are distinguished. (i) Only the dynamical pseudo-Jahn-Teller effect is operative as in acetophenone vapor. The emission here is interpreted to be from a distorted, i.e., largely torsionally twisted acetophenone about the COCH3 group. (ii) and (iii) There are environmental (static) interactions larger than dynamical interactions leading to strong characteristic out-of-plane vibrations and medium lifetime, e.g., COCH3 group modes in methylbenzoate matrix, where 3nπ* is lowest, and ring out-of-plane modes in acetophenone-d5 matrix, where 3ππ* is lowest. (iv) There is a dynamical Jahn-Teller interaction stronger than the environmental interaction. In some instances the resulting triple minimum potential curve results in dual phosphorescence emissions even at low temperatures (1.68°K) from the lowest 3nπ* state—one with a very short lifetime from a highly distorted region of the potential surface (the zero point region) and the other with a medium lifetime from an excited vibronic region, e.g., in pentane and other relaxed hydrocarbon matrices. The upper vibronic region is kept from rapidly cascading to the lower region of the triplet state by a potential barrier leading to temperature dependent phosphorescence. Breakdown of the Condon approximation for the lowest triplet state is observed, probably due to rapid change of the singlet—triplet transition moment with the distortion coordinate in the vicinity of near degeneracy of the zeroth order states. (v) Again the dynamical Jahn-Teller interaction is stronger than the environmental interaction except that the zeroth order 3ππ* state is now lowest, e.g., at 77°K in a benzene matrix the emission with its vibrational structure and lifetime characteristic of 3nπ is from the zeroth order region—whose electronic wavefunction is described largely by 3nπ. At 4.2°K, the vibrational structure and lifetime represent phosphorescence from an excited vibronic region of the lowest triplet state whose electronic wavefunction is largely 3ππ*. The rapid change in transition moment with vibrational coordinate also renders the Condon approximation inappropriate in this case.
Thermal Energy Reaction Rate Constants for H+ and CO+ with O and NO
Authors: Fehsenfeld F. C. , Ferguson E. E.
Published: February 2004

Thermal energy rate constants for the charge transfer of CO+ with O and NO have been measured to be 1.4 and 3.3 × 10−10 cm3/sec at 300°K. The rate constants for H+ with O and NO are 3.8 and 19 × 10−10 cm3/sec. The H+ + O charge-transfer data agree remarkably well with the value extrapolated from crossed-beam studies at much higher energies.
Computations for Higher Valence Electrolytes in the Restricted Primitive Model
Authors: Rasaiah Jayendran C.
Published: February 2004

A detailed account of the hypernetted chain (HNC) equation for 1–1, 2–1, 3–1, and 2–2 electrolytes in the restricted primitive model (charged hard spheres of equal size) is given, and comparisons are made with some other approximations for the excess thermodynamic functions. On the basis of self-consistency tests, it is concluded that at a given concentration, the osmotic coefficients from the HNC approximation decrease in accuracy as the charges on the ions are increased. By comparison with the Monte Carlo results of Card and Valleau, it is concluded that the excess energy functions for all of these electrolytes are accurate to within a few percent. It is found that the HNC and DHLL + B2 approximations show certain anomalies in the thermodynamic functions of 2–2 electrolytes which also occur in real electrolytes but are not predicted to occur in some of the other theories developed recently. The charge densities around ions, derived from the HNC theory, are compared with the well-known predictions of Debye and Hückel. Oscillations in these charge densities are found to occur at sufficiently high concentrations for all of the model electrolytes considered in this study.
Mean Spherical Model Integral Equation for Charged Hard Spheres I. Method of Solution
Authors: Waisman Eduardo , Lebowitz Joel L.
Published: February 2004

The thermodynamic properties and radial distribution function of a ``primitive model electrolyte'' are calculated in the Mean Spherical Model (MSM) approximation. The system considered is formally described as a classical fluid of charged hard spheres (hard sheets in one dimension). The interaction potential between an ion of species i and an ion of species j, vij(r) is the sum of a Coulomb part and a hard core part qij(r)=∞ for r < Rij or 0 otherwise. The MSM approximation consists of supplementing the fact that the radial distribution function gij(r) is zero for r < Rij by equating the Ornstein—Zernike direct correlation function Cij(r) to -βvij(r) for r > Rij, β being the inverse temperature. In this paper, which is the first of two in this topic, we give the method of solution for this approximation and obtain Cij(r) for r < Rij as polynomials in r, which have a structure similar to that found in the PY approximation for a mixture of uncharged hard spheres. We give the solution up to a set of algebraic equations in the polynomial coefficients. In the second paper we discuss the explicit solution and derived thermodynamic quantities.
Proton Motions in Methanol by Cold Neutron Scattering
Authors: Rodriguez C. , do Amaral L. Q. , Vinhas L. A. , Herdade S. B.
Published: February 2004

Cold neutron scattering data are reported for methyl alcohol in the liquid phase at room temperature. The quasielastic scattering was interpreted using the Larsson and Bergstedt model, that takes into account intramolecular motions and molecular diffusion. On the basis of this model, one finds for the relaxation time of the hindered rotation of the CH3 group within the molecule a value of 2.4 × 10−12 sec. The analysis of the quasielastic scattering according to the L-B model explains in a consistent way our experimental results in a range of momentum transfers of about 0.80–1.55 Å−1. In the inelastic region some structure is observed at energy transfers of 22, 17, and 5 meV. The 17-meV energy transfer is associated with the 1 → 0 transition of the torsional oscillations of the methyl group. The activation energy for the above motion was calculated to be E=1.3 kcal/mol, in good agreement with the value of the barrier height for internal rotation of the CH3 in methanol, obtained by microwave methods.
Slow Electronic Relaxation in T52−A11 Spin Equilibria of Tris(2-methyl-1,10-phenanthroline)Iron(II) Complexes: A Mössbauer Effect Study
Authors: König E. , Ritter G. , Spiering H. , Kremer S. , Madeja K. , Rosenkranz A.
Published: February 2004

The 57Fe Mössbauer effect in [FeL3](ClO4)2 (I) and [FeL3](BF4)2 (II) has been studied between 295 and 4.2°K (L=2-methyl-1,10-phenanthroline). At 295°K, compound I exhibits a quadrupole split pair of lines characteristic of a 5T2 ground state, ΔEQ(5T2)=1.03 mm sec−1 and δIS(5T2)=+ 0.95 mm sec−1. At 244°K, line broadening is observed. At even lower temperatures, e.g., at 196°K, the relative intensity of the doublet has decreased and a second doublet typical of a 1A1 ground state has appeared. At 4.2°K, 72.7% of the intensity is due to 1A1, ΔEQ(1A1)=0.57 mm sec−1, and δIS(1A1)=0.38 mm sec−1. Similar behavior is encountered in II. The observations are accounted for by slow electronic relaxation between 5T2 and 1A1 in the temperature range between 230 and 120°K and the assumption of permanently paramagnetic molecules which become apparent below 77°K. A change of the relaxation at about 244°K is likely. From the temperature dependence of ΔEQ(5T2), the axial field splitting is δ=− 640 cm−1 in I and δ=− 580 cm−1 in II. In conjunction with magnetic data it is demonstrated that the T52−A11 energy separation ε varies with temperature: ε=300 cm−1 at 294°K and ε=990 cm−1 at 98°K in I and similarly in II. In an applied field of 50 kG, the sign of Vzz is positive for the 1A1 component in both I and II.
Effect of Inertia on the Brownian Motion of Rigid Particles in a Viscous Fluid
Authors: Chow T. S. , Hermans J. J.
Published: February 2004

From Boussinesq's work it is known that the frictional resistance of a particle in a viscous, inert fluid, depends on its history. This plays an important part in Brownian motion. The general theory of fluctuations in fluid dynamics leads to explicit expressions for the autocorrelation function G(t) for the random force acting on a Brownian particle and the autocorrelation function φ(t) for its velocity. It is demonstrated that G(t) contains an inertial term which depends on the velocity distribution in the liquid surrounding the particle. The results obtained lead to the correct value of the diffusivity.
Recombination of Iodine Atoms by Flash Photolysis over a Wide Temperature Range. II I2 in He, Ar, Xe, N2, CO
Authors: Ip J. K. K. , Burns George
Published: February 2004

The recombination of iodine atoms in the presence of I2 and He, Ar, Xe, N2, and CO has been studied by flash photolysis between 300–1173°K. The rate constants (in liters2 mole−2 · sec−1) and their temperature dependences may be represented by logkrHe=9.136 − 1.716 log (T/300) + 0.994 log2(T/300),logkrAr=9.439 − 2.418 log (T/300) + 1.911 log2(T/300),logkrXe=9.652 − 2.787 log (T/300) + 1.678 log2(T/300),logkrN2=9.641 − 2.645 log (T/300) + 1.880 log2(T/300),logkrCO=9.729 − 2.606 log (T/300) + 1.457 log2(T/300).The present recombination rate data for He, Ar, and N2 overlap the available shock wave dissociation rate data by 70 to 300°K. Above 1000°K, the recombination rate constants calculated from shock wave data are generally higher and show a steeper negative temperature dependence than the flash photolysis rate constants obtained at the same temperatures. The rate constant krI2 has also been determined from rate experiments on iodine—helium mixtures, from room temperature to 723°K. The present k2I2 data agree well with the flash photolysis data obtained over the same temperature range from iodine—argon experiments [J. A. Blake and G. Burns, J. Chem. Phys. 54, 1480 (1971)]. The two sets of krI2 measurements, when combined, may be represented by logkrI2=12.122 − 5.844 log (T/300) + 2.163 log2(T/300).
Shock Tube Rotational Relaxation Measurements in Low-Temperature Hydrogen
Authors: Yoder M. John
Published: February 2004

Rotational relaxation times are measured for normal hydrogen and parahydrogen in a cryogenic shock tube with initial temperatures of 80–100°K. A sensitive schlieren optical system, employing a laser light source and a photomultiplier, is used to measure laboratory relaxation times of the order of 0.1 μsec, with a spatial resolution of 0.1 mm. Measurements are made over a temperature range of 140–450°K. Relaxation times are in general agreement with results obtained by other methods.
Shock Tube Vibrational Relaxation Measurements: N2 Relaxation by H2O and the CO–N2 V–V Rate
Authors: von Rosenberg C. W. , Bray K. N. C. , Pratt N. H.
Published: February 2004

Shock tube measurements of the rates of vibrational relaxation of N2 by H2O and the vibrational exchange between N2 and CO are described. Simultaneous measurements of H2O v2 ν2 band and CO fundamental band ir emission were performed in mixtures of 1%–10% CO+∼1% H2O+N2. Measurement of H2O emission by a calibrated optical system allowed an accurate determination of the concentration of H2O for each run. The CO emission had two, almost decoupled, regions of behavior which allowed determination of two relaxation times: Pτ NCe≈ 1.6 atm· μsec (V–V exchange relaxation time between N2 and CO) and Pτ NH≈ 1.5 atm· μsec (T–V relaxation of N2 by H2O), both for 960 〈T〈2200°K.
Use of the Nonsymmetrical Wavefunction. III. Magnetic Susceptibility of Molecular Hydrogen
Authors: Saika A. , Musher Jeremy I. , Miyabe Nobuaki
Published: February 2004

The nonsymmetrical (NS) wavefunction is used to calculate the magnetic susceptibility of the hydrogen molecule. Triple perturbation theory with the aid of the interchange theorem allows one to calculate the susceptibility through first order in electron correlation and it is found that the NS function yields reasonable results.
Vibration-to-Rotation Energy Transfer in HBr and DBr Mixtures
Authors: Chen Mark Y.-D. , Chen Hao-Lin
Published: February 2004

Vibrational energy transfer rates in HBr–DBr mixtures have been measured by laser-excited vibrational fluorescence. The cross section for vibration→vibration energy exchange is σHBr → DBrV → V=(1.5 ± 0.15) × 10−18 cm2. For vibration→rotation and translation energy transfer the cross sections are σDBr–DBr=(1.3 ± 0.2) × 10−19 cm2 and σDBr–HBr=(2.7 ± 0.5) × 10−19 cm2.
Nuclear Magnetic Resonance of 1H and 27Al and Al–Si Order in Low Cordierite, Mg2Al4Si5O18 · nH2O
Authors: Tsang Tung , Ghose Subrata
Published: February 2004

Proton resonance data in the low-temperature form of cordierite indicate the presence of isolated water molecules in the channel formed of the AlSi5O18 rings, with H–H directions along the crystallographic c axis and with large vibration amplitudes. Two crystallographically nonequivalent aluminum sites have been observed. The quadrupole coupling constant e2qQ/h, the asymmetry parameter η, and the principal axes directions are: AlI: | e2qQ/h |=10.6 MHz; η=0.38; X ‖ c; Z and Y, 30° away from a and b.AlII: | e2qQ/h |=5.6 MHz; η=0.34; Y ‖ c; Z and X, 20° away from a and b.The AlI and AlII sites correspond to the distorted tetrahedral T1 site outside the six-membered ring and T5 site within the ring in the cordierite structure. The AlI NMR data also agree with Fe3+ paramagnetic resonance data, indicating that the Fe3+ ions preferentially occupy the larger T1 sites. The 27Al NMR results indicate a high degree of Al–Si order in low cordierite.
Use of Ab Initio G1 Effective Potentials for Calculations of Molecular Excited States
Authors: Melius Carl F. , Goddard William A. , Kahn Luis R.
Published: February 2004

The validity of using ab initio G1 effective potentials for excited states of molecules is tested for a number of excited states of LiH. We find that the effective potentials lead to wavefunctions and properties which are in excellent agreement with those obtained from full-electron ab initio calculations.
Orbital Description of the Excited States of LiH
Authors: Melius Carl F. , Goddard William A.
Published: February 2004

The wavefunctions for the first five 1Σ+ states, the first four 3Σ+ states, and the first three 1II and 3II states of LiH have been obtained from ab initio G1 and SOGI calculations. The orbital description of the excited states of Li and LiH and the resulting correlation diagram are discussed.
Relative and Absolute Raman Scattering Cross Sections in Liquids
Authors: Colles M. J. , Griffiths J. E.
Published: February 2004

Peak and total differential Raman scattering cross sections for several liquids, CH3OH, C2H5OH, i-C3H7OH, (CH3)2CO, CH3CCl3, CH3I, c-C6H12, and C6H5Br, were determined relative to the v2 (a1g)=944 cm−1 line of C6D6 as an internal standard. Using an absolute value for the peak differential cross section of this line and measured values of the radiant intensities and depolarization ratios of selected Raman lines in the above liquids, we have obtained absolute values for ∂σ and ∂σ/∂Ω. Results are expected to be accurate to ± 10 % unless specified otherwise. Measurements were made using a medium power cw argon ion laser operating at 4880 Å, a double monochromator and a photomultiplier (S-20 and S-11) detector.
Raman and Infrared Spectra of LiO2 in Oxygen Matrices
Authors: Hatzenbuhler Douglas A. , Andrews Lester
Published: February 2004

The Raman spectrum of the LiO2 molecule has been observed from samples of oxygen codeposited with lithium atoms at 15°K. An intense band at 1093 cm−1 in the Raman spectrum exhibited appropriate oxygen isotopic shifts for assignment to the symmetric oxygen-oxygen vibrational mode. Experiments using a 16O2, 16O18O, 18O2 sample produced a triplet indicating equivalent oxygen atoms in the LiO2 molecule. Lithium oxygen vibrations, which were very intense bands in the infrared spectrum, were not detected in the Raman spectrum. The observed Raman intensities strongly support the ionic model for LiO2 proposed earlier. The experimental apparatus and techniques for laser-Raman matrix-isolation spectroscopy are described.
Photodissociation of CO2 to Produce CO(a 3Π)
Authors: Lawrence George M.
Published: February 2004

Carbon dioxide in a helium buffer at room temperature was irradiated with a photon beam of wavelengths 1090 to 850 Å. ``Phosphorescence'' from the CO(a 3Π - X 1Σ) Cameron bands was observed. The phosphorescent yield is zero at threshold and increases smoothly to a maximum of ∼ 60% near 900 Å. The smoothness of the percentage yield was an unexpected observation and is explained by postulating that the relevant potential surface crossings are outside the Franck-Condon region of CO2 absorption. Approximate vibrational distributions have been determined and are also smooth functions of photon energy.
Derivation from the Liouville Equation of the Fuoss-Onsager Theory of Ionic Conductivity
Authors: Murphy T. J.
Published: February 2004

Recent advances in the theory of Brownian motion are used to derive the Fuoss-Onsager theory of the conductivity of ionic solutions from the Liouville equation for N solvent particles and two heavy Brownian particles. The Fuoss-Onsager theory is shown to be sufficiently accurate to give the correct value of the conductivity through order c lnc in the concentration c; however, it is seen that the Fuoss-Onsager theory does not take into account some terms which affect the conductivity to first order in the concentration.
Lateral Surface Energy of Polyethylene Crystals
Authors: Kim Hyo-gun , Markovitz Hershel
Published: February 2004

Based on the theory originally devised by Born and Stern for crystals of the rare gases and alkali halides, lateral specific surface energies have been calculated for polyethylene from interatomic potentials. The specific surface energy of the {110} face was found to be about 100 to 140 ergs/cm2; of the {100} face, about 6% greater and of the {010} face, about 14% greater. The broad range of values is due to the wide variety of interatomic potentials found in the literature. For infinitely long crystals of rhomboidal cross section the average edge energy is about 3 × 10−6 erg/cm. In a crystal of this type containing nine chains, the edge energy constitutes about 30% of the surface energy.
Ion Dipole Capture Cross Sections at Low Ion and Rotational Energies; Comparison of Integrated Capture Cross Sections with Reaction Cross Sections for NH3 and H2O Parent-Ion Collisions
Authors: Dugan John V. , Canright Richard B.
Published: February 2004

Numerical capture cross sections calculated for CH3CN++CH3CN collisions for a rotational temperature TR of 77°K are in the range 1000–3500 Å2. Comparisons of capture cross sections (integrated over experimental ion energies) for H2O and NH3 at TR ≈ 300°K are in mixed agreement with experimental data from (1) a conventional mass spectrometer and (2) an ion cyclotron resonance device.
Triatomic Photofragment Spectra. II. Angular Distributions from NO2 Photodissociation
Authors: Busch George E. , Wilson Kent R.
Published: February 2004

The angular distribution of recoil of O atoms from the photodissociation of NO2 at 28 810 cm−1 is presented and analyzed to obtain information about the lifetime and symmetry of the excited dissociative state. The theoretical effects on photofragment angular distributions of excited state symmetry, lifetime, angular momentum, and angular recoil distribution with respect to internal coordinates are considered. The actual angular distribution measured by photofragment spectroscopy, peaks in the direction of the electric vector of the light, indicating that the predominant upper state is of 2B2 symmetry. Some absorption leading to states of different symmetry cannot be excluded. An upper limit for the lifetime of the excited NO2 molecule before dissociation is ∼ 2 × 10−13 sec, indicating that break-up is too rapid to be affected by collisions in the atmosphere where NO2 photodissociation is an important step in photochemical air pollution.
Time-Dependent Flows of Dilute Solutions of Rodlike Macromolecules
Authors: Bird R. Byron , Armstrong Robert C.
Published: February 2004

For a suspension of rigid macromolecules with Brownian motion, expressions are obtained for the components of the stress tensor for any time-dependent shearing flow. The results are expressed up to terms of the fourth order as a series of memory integrals. The first two terms in the series enable one to calculate the explicit expressions for the kernel functions for second-order viscoelasticity. It is established that the Oldroyd six-constant model does not give kernel functions which are of the same form as those given by the molecular theory of rigid macromolecules. The general time-dependent elongational flow results are also given through terms of the third order.
Evidence for Rb-Rare-Gas Molecules from the Relaxation of Polarized Rb Atoms in a Rare Gas. Experimental Results
Authors: Bouchiat M. A. , Brossel J. , Pottier L. C.
Published: February 2004

Relaxation experiments have been performed between 0–200 G on optically polarized Rb atoms in argon, krypton or xenon, at pressures ranging from 0.1 to 20 torr. They clearly show the existence of Rb–Ar, Rb–Kr and Rb–Xe molecules of low binding energy (smaller than kT). Molecular parameters such as lifetime, spin-orbit coupling constant, formation rate, constant of mass action, etc., are measured, or evaluated when they cannot be directly measured. Experimental values of the diffusion coefficient of Rb in the gas (except xenon) and of the disorientation cross sections by usual binary collisions are also obtained.