bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical Spectroscopic Determination of the Zero-Field Splitting in Vibronic Levels of the Triplet State of Nitrite
Authors: Hochstrasser Robin M. , Zewail Ahmed H.
Published: February 2004

We have used conventional high resolution optical spectroscopic methods to determine the principal values of the fine structure tensor for the lowest triplet state (B31 at 18 959 cm−1) of NO2− in Na NO2 single crystals. From the intensities in the Zeeman spectrum we find D − E = 0.86 ± 0.04 cm−1, D + E = 0.40 ± 0.04 cm−1, where the z axis is taken as the twofold axis and E = (Z − X) / 2. From the measurement of line positions in the high-field Zeeman spectrum we find D − E = 0.84 ± 0.05 cm−1, D + E = 0.41 ± 0.05 cm−1. The values of D and E calculated for one-center spin–spin interaction are D − E = 0.42 cm−1 and D + E = 0.24 cm−1. The calculated ordering of the spin states is the same as that observed, but we suggest that there is significant second-order spin–orbit energy associated with the real splittings. Roughly the same splittings are seen for different vibronic levels of B31 associated with ν2′.
New Method for the Detection of Atomic Oxygen Beams
Authors: Nahr H. , Hoinkes H. , Wilsch H.
Published: February 2004

Atomic oxygen adsorbed on ZnO single crystals causes a decrease of surface conductivity. This fact is used to measure the flux density of atomic oxygen. With a detector surface of 0.3 mm2 the lower limit of detection is 1 × 1011 atoms sec−1·cm−2.
Vibrational Energy Transfer in Diatomic Gas Mixtures
Authors: Horn K. P. , Oettinger P. E.
Published: February 2004

Flow-tube experiments on vibrational energy transfer from N2* to CO and NO are described. A primary flow of N2 was vibrationally excited by an S-band microwave discharge and mixed with either cold CO or NO. The first overtone band radiation from the heteronuclear molecules was spectrally resolved at selected downstream stations, and the data were compared with an analytical model computed for different number density distributions. Flow-tube measurements of rotationally cold, but vibrationally excited, N2*–CO and N2*–NO systems indicate that at steady-state conditions, (1) the CO and NO are not in vibrational equilibrium, and (2) the nonequilibrium populations of the molecules cannot be predicted by the model postulated by Treanor et al.
Differential Cross Sections for the Scattering of CCl4 by Isooctane
Authors: Cardillo M. J. , Chou M. S. , Greene E. F. , Sheen D. B.
Published: February 2004

Differential cross sections for the scattering of CCl4 by isooctane (2,2,4-trimethylpentane) are reported for the range of relative kinetic energy Ē between 1.80 and 26.8 kcal mole−1. The faster beams are produced by adding the CCl4 to an excess of He which accelerates the heavier CCl4 molecules as the mixture flows from the source. The velocity selector has disks with narrow slots produced by chemical etching. The scattered CCl4 molecules are detected by their formation of negative ions at a hot Nb surface. The scattering at the higher energies shows rainbow structure which is used to determine parameters for an assumed form of the interaction potential. The disappearance of the rainbow maximum at low energies, attributed to the onset of orbiting, and the values of parameters derived indicate that the potential has a large central core. The decrease in the measured differential cross section at large angles implies the presence of a substantial amount of inelastic scattering.
Theoretical Studies of Solvent Effects on Nuclear Spin–Spin Coupling Constants. I. The Reaction Field Model
Authors: Johnston Milton D. , Barfield Michael
Published: February 2004

A theoretical study of the solvent dependence of nuclear spin–spin coupling constants is presented in terms of Onsager's reaction field model and self-consistent perturbation theory in the semiempirical INDO (intermediate neglect of differential overlap) approximation of self-consistent-field molecular orbital theory. A possible mechanism for reaction field induced changes in coupling constants is discussed in terms of the sum over virtual orbital method, corresponding to the uncoupled Hartree–Fock approximation. Although the latter method does not give satisfactory values for coupling constants, the reaction field induced shifts are reasonable. Finite perturbation theory, which corresponds to the coupled Hartree–Fock approximation, gives much better coupling constant results. Calculated reaction field induced shifts for a variety of H–H and H–F coupling constants are compared with the experimental results in a variety of solvents. Although the calculated results are linear functions for very large values of the reaction field, best agreement with experiment is obtained in solvents of low dielectric constant. The importance of solute dipole orientation in a series of fluoroethylenes is investigated.
Temperature Dependence of Intramolecular Vibration→Vibration Energy Transfer in CO2
Authors: Stephenson John C. , Wood Robert E. , Moore C. Bradley
Published: February 2004

Intramolecular vibration-to-vibration energy transfer cross sections have been measured for gaseous CO2 with one quantum of asymmetric stretching energy. Data were obtained using the laser-excited vibrational fluorescence method. Results are given over the temperature range 298–800°K for the collision partners n-H2, 3He, 4He, Ne, Ar, Kr, and Xe, and for p-H2, HD, and D2 at 298°K. All cross sections increase with temperature; those for the rare gases depend only weakly on reduced mass. The cross sections for hydrogen are much larger than those for helium, and increase sharply as the reduced mass decreases. The simple form of transition probability as a function of velocity and intermolecular potential used in most theories of vibration–translation energy transfer does not adequately account for these results. Since equal cross sections are observed for n-H2 and p-H2, it is unlikely that energy is transferred into rotation of H2.
Excess Electrons in Liquid Hydrocarbons
Authors: Minday R. M. , Schmidt L. D. , Davis H. T.
Published: February 2004

Stable electronic charge carriers have been observed in n-hexane, n-pentane, benzene, and methylbutene with room temperature mobilities of 0.07, 0.07, 0.6, and 3.6 cm2 V−1·sec−1, respectively. The charge carriers were injected into the highly purified hydrocarbon liquids by photoemission of electrons from a low work function surface. Mobilities increase rapidly with temperature and obey an Arhennius expression with activation energies of 4.3 kcal mole−1 in hexane and 2.6 kcal mole−1 in methylbutene. The carriers in hexane could be drawn out of the liquid into the vapor and had a higher mobility in the solid than in the liquid at temperatures near the melting point. Current versus voltage measurements indicate that the injection process is controlled by transmission over the image barrier at the cathode. The mobilities of the injected charges in these fluids are more than 100 times ionic mobilities in the same fluids but considerably less than the mobilities of electrons in the rare-gas liquids. The free electron theory of Cohen and Lekner, somewhat successful in explaining electron mobilities in the rare-gas liquids, does not give a satisfactory explanation of the hydrocarbon mobilities. A proposed generalization of the Cohen–Lekner theory to account for the effect of internal configurations of the hydrocarbon molecules on electron scattering also seems unable to explain the magnitudes and temperature dependence of the observed mobilities. A trapping model, in which the electron is frequently trapped for short times and otherwise moves as a free electron, appears to explain the mobility properties observed.
Alternative Explanation for Anomalous Molecular Parameters from Electron Resonance Experiments
Authors: Miller Terry A.
Published: February 2004

Values for the rotational g factor in Δ 1SeO and the fine-structure interval in Δ 1IO have been recently reported. These values are, respectively, anomalously large and small in magnitude. In each case, they were obtained from the center of gravity of the electron resonance spectra. We show that there is a heretofore neglected correction to the molecular electronic orbital and spin g values whose estimated magnitude is not negligible for molecules with heavy atoms. It is shown that inclusion of this effect allows alternative analyses of the Δ 1SeO and Δ 2IO spectra which yield more reasonable values for the rotational g factor and fine-structure intervals, respectively. This effect may also be important in the analyses of the Δ 2 spectra of SeF, BrO, SeH, and TeH. This effect is related to the transformation of these molecules from Hund's case (a) to Hund's case (c) coupling.
Interaction Potential between Li+ and H2. II. Region Appropriate for Vibrational Excitation
Authors: Lester William A.
Published: February 2004

A self-consistent-field (SCF) calculation of the interaction energy between Li+(1S) and H2(X 1Σg+) has been computed using wavefunctions near the Hartree–Fock limit. An analytical expression for the intermolecular surface has been determined in the form V(X, ξ, θ) = υ0(X, ξ) + υ2(X, ξ)P2(cosθ) + υ4(X, ξ)P4(cosθ), where X is the distance between the Li+ and H2 centers of mass, ξ = R − Re, Re = 1.4 a.u., R is the H2 bond distance, θ is the angle formed by X and R, and is valid for − 0.4 ≤ ξ ≤ 0.6 and 2.0 ≤ X ≤ 12.0 a.u. Unlike He–H2, the Li+–H2 interaction is found to be consistent with the dumbbell model. SCF calculations appear adequate for the calculation of interaction energies for closed-shell-ion–closed-shell-neutral-diatomic-molecule systems even at large X.
Localized Orbitals. II. Expanded Basis Sets
Authors: Letcher John H.
Published: February 2004

Two methods are presented to delineate localized orbitals defined on large basis sets. These methods calculate equivalent oribitals for polyatomic molecules which are accurate enough for precise quantum mechanical calculations. The localized orbitals are defined in terms of parameters that can be readily visualized by the chemist, yet allow changes in electronic structure during molecular bond formation and substituent exchange reactions to be determined. It is shown that these equivalent orbitals constitute a foolproof starting point for self-consistent field (LCAO–MO–SCF) calculations. The results of calculations on the water molecule using Gaussian basis functions are presented along with a discussion of numerical and computational techniques.
Far-Infrared Spectra and Zeeman Effect of Rare-Earth Double Nitrates
Authors: Bloor D. , Campbell J. A.
Published: February 2004

The far-infrared spectra of several rare-earth double nitrates have been observed over the range 30–170 cm−1. The frequencies of the low lying phonon modes have been determined by comparison of the spectra of the diamagnetic and paramagnetic salts. The absorptions due to the crystal field split ground states of the rare-earth ions have been positively identified by observations of the Zeeman effect. The experimental energies and g values have been compared with the predictions of earlier crystal field calculations based on approximate symmetries. Some of these are in reasonable agreement with the experimental results, but none of them provides a consistent description of the ground state levels for all the ions studied.
Herzberg–Teller Vibronic Coupling and the Duschinsky Effect
Authors: Small Gerald J.
Published: February 2004

The assumption that the difference in composition, in terms of symmetry coordinates, between the normal vibrational motions of the ground and first excited state (Duschinsky effect) can be neglected in the Herzberg–Teller theory of absorption and fluorescence vibronic intensities is critically examined. A theory of the Duschinsky effect is described which involves expansion of the potential energy of the fluorescent state in terms of the ground state normal coordinate displacements. Off-diagonal quadratic contributions arise in the expansion whenever there is a coupling between the crude Born–Oppenheimer electronic wavefunctions of the fluorescent and other excited states through two or more ground state normal motions of the same symmetry. The importance of the Duschinsky effect depends on the magnitudes of the Herzberg–Teller vibronic matrix elements and the frequency differences between the fundamentals which effect vibronic perturbations. Inclusion of the Duschinsky effect in the Herzberg–Teller theory for two or more nontotally symmetric perturbing vibrations introduces a constructive–destructive interference problem, involving the “forbidden” transition moments similar to the one that arises in the theory of Craig and Small on totally symmetric vibrational perturbations. The interferences can lead to a breakdown in mirror symmetry between the absorption and fluorescence spectra. The theory presented for a two vibrational model enables the relative signs of the two forbidden moments to be determined by comparison of the relative intensities of the two vibronic bands in absorption and fluorescence. In the case of naphthalene the forbidden moments associated with the 509 and 938 cm−1 b3g modes are shown to be antiparallel. Calculations for phenanthrene suggest that, although the Duschinsky effect should be included in any attempt at accurate vibronic intensity calculations, the constructive–destructive interference effects described by Craig and Small are primarily responsible for the gross deviations from mirror symmetry experimentally observed. Illustrative calculations show that the Duschinsky effect should not be neglected in the Herzberg–Teller theory of both fluorescence and absorption vibronic intensities.
Reverse Electrodialysis in Charged Capillary Membranes
Authors: Fair J. C. , Osterle J. F.
Published: February 2004

A detailed study of the transport properties of charged capillary membranes in the reverse electro-dialysis mode of operation is presented. The compromising assumptions of linearized Poisson–Boltzmann equation, large radius to Debye length ratio, and small concentration difference made by some investigators are relaxed. For various tube sizes, wall charge densities, and solutes, results are presented for the operating characteristics of the membrane as functions of transmembrane concentration ratio.
Temperature Dependence of the ESR Spectrum of CO2−CF2CFCO2− in Irradiated Sodium Perfluorosuccinate
Authors: Kispert Lowell D. , Rogers Max T.
Published: February 2004

Irradiated single crystals of sodium perfluorosuccinate show ESR spectra at 300°K characteristic of a single CO2−CF2CFCO2− radical, but on cooling below 130°K the spectra show that motion has been frozen out and that the radicals occupy two crystallographically nonequivalent positions. The hyperfine interaction tensors for one α- and two β-fluorine atoms of each radical have been determined at 77°K and compared with those of the 300°K radical. The average of the hyperfine tensors for the two radicals at 77°K is shown to be close to the observed tensor for the single radical at 300°K. Motional averaging by oscillation about the central C–C bond is indicated. Crystals of sodium perfluorosuccinate irradiated and observed at 77°K without warming up show the presence of a single radical with a somewhat different orientation in the crystal lattice than the room temperature radical or either of the radicals obtained on cooling the room temperature radical to 77°K.
Primary Processes in the Photolysis of Nitrous Oxide
Authors: Preston K. F. , Barr R. F.
Published: February 2004

From measurements of the isotopic composition of the product nitrogen arising from the photolysis at 2288, 2139, and 1849 Å of gaseous N2O containing ∼ 1% 15NO, it is shown that at all three wavelengths the primary production of N atoms is unimportant, representing less than 1% of the primary production of molecular N2. Taken in conjunction with other observations made in this laboratory these results indicate that at 2139 Å, and perhaps at all wavelengths in the region 1800–2300 Å, the decomposition to N2+O(1D2) is the sole primary photolytic step of importance in the photolysis of N2O.
Electron Spin Resonance of Pd(I). II. γ-Irradiated Single Crystals of K2PdCl4 and (NH4)2PdCl4
Authors: Fujiwara Shizuo , Nakamura Michihiro
Published: February 2004

With the use of the electron spin resonance technique, it is confirmed that the Pd(I) complex ion (PdCl4)3− is formed in γ-irradiated K2PDCl4 and (NH4)2PdCl4. The chlorine superhyperfine coupling constants and the g values for the Pd(I) complex ion are used to obtain the fractional unpaired spin density in the chlorine 3s and 3p orbitals and the crystal field splittings, respectively.
Mass Spectrometric Studies of Ion–Neutral Reactions in Perfluoroethane
Authors: Marcotte R. E. , Tiernan T. O.
Published: February 2004

Ion–molecule reactions in perfluoroethane have been investigated using mass spectrometric techniques. Reaction trends observed in the high-pressure mass spectrum of C2F6 are not consistent with kinetic data for the elementary fragment ion reactions determined in a tandem mass spectrometer. At very low kinetic energies (∼ 0.3 eV), C2F5+ undergoes collision-induced dissociation while CF3+ reacts principally by a F− transfer process, both reactions being endothermic for ground state reactants. Charge transfer experiments with CF3+ and C2F5+ indicate that these ions have excess internal energies up to 2.9 and 2.4 eV, respectively, which can account for their endothermic reactions. Apparently, at higher pressures, some of the internal energy is degraded by nonreactive collisions, leading to unexpected differences in the reactivity of the fragments. Other reactions observed in the perfluoroethane system are F-atom transfer and F2 transfer. The generally small rate constants (∼ 10−11 cm3/molecule·sec) determined for ion-molecule reactions in C2F6 suggest that these reactions involve sizable activation energies. The breakdown patterns from dissociative charge transfer reactions of rare gas ions with C2F6 have been re-examined. The results strongly indicate that some fragment ion formation occurs by direct elimination from repulsive electronic states of C2F6+.
Ion-Pair Theory of Concentrated Electrolytes. IV. Ion Atmosphere Charge Distribution
Authors: Stillinger Frank H. , White Ronald J.
Published: February 2004

Arguments are presented indicating that the large-size limiting behavior of the ion-pair size distribution is qualitatively the same both with, and without, Coulomb interactions between ions. This in turn implies that the static dielectric response function ε0 / ε(k) derived in the preceding paper is nonanalytic at k = 0. The specific singular behavior of this response requires a branch cut along the imaginary k axis. It furthermore induces an r−8 tail in the ion atmosphere charge distribution at finite electrolyte concentration.
Modes and Rates of Reaction of Cyclopentene and Methylcyclopentene Ions with Their Parent Molecules
Authors: Lesclaux R. , Searles S. , Sieck L. Wayne , Ausloos P.
Published: February 2004

Cyclopentene and methylcyclopentene ions were generated by irradiating the respective parent compounds with 10.0-eV photons; cyclopentene was also irradiated with 11.6–11.8-eV photons. The ionic products of ion–molecule reactions were observed in the NBS high-pressure photoionization mass spectrometer, while the neutral products of these reactions were determined by chemical analysis of products formed in photolytic experiments in a closed system. The cyclopentene ion, which at 10.0 eV retains its cyclic structure, undergoes an H2 transfer reaction (c-C5H8++c-C6H8→c-C5H10+c-C5H6+, k = 3.3 × 10−10cm3/molecule·sec) and a condensation reaction (c-C5H8++c-C5H8→C10H16, k = 2.7 × 10−10cm3/molecule·sec) with the parent molecule. The same reactions are observed for ions formed at 11.6–11.8 eV, but at the higher energy, approximately 20% of the ions are observed to undergo ring opening to form 1,3-C5H8+ ions; the latter ions undergo an H2 transfer reaction with the cyclopentene molecule (1,3-C5H8++c-C5H8→2-C5H10+C5H6+, k = 1 × 10−10cm3/molecule·sec). The three methylcyclopentene ions also undergo H2 transfer reactions with the corresponding parent molecules [C6H10++C6H10→(CH3)C5H9+C6H8+, k = 4.6, 1.8, and 2.9 × 10−10cm3/molecule·sec for 1-, 3-, and 4-methylcyclopentene, respectively]. Condensation reactions between these ions and their parent molecules are observed to only a minor extent, but a second major mode of reaction, namely H transfer, is observed (C6H10++C6H10→C6H11+C6H9+, k = 0.6, 2.8, and 1.2 × 10−10cm3/molecule·sec for 1-, 3-, and 4-methylcyclopentene, respectively). Structural reasons for these rate variations are discussed.
Pulse Radiolysis Studies. XX. Kinetics of Some Addition Reactions of Gaseous Hydrogen Atoms by Fast Lyman-α Absorption Spectrophotometry
Authors: Hikida T. , Eyre J. A. , Dorfman Leon M.
Published: February 2004

The pulse radiolysis technique combined with fast Lyman-α absorption spectrophotometry, has been used to study the kinetics of several addition reactions of gaseous hydrogen atoms. The following absolute rate constants, at 298°K, have been obtained: H+O2+Ar=HO2+Ar, (5.9 ± 0.7) × 109M−2·sec−1, H+CO+H2=HCO+H2, (4.0 ± 0.6) × 107M−2·sec−1, H+CO+Ar=HCO+Ar, (2.6 ± 0.4) × 107M−2·sec−1, H+NO+H2=HNO+H2, (1.4 ± 0.2) × 1010M−2·sec−1. These results, and our earlier value for k1 with H2 as third body, give values of k1H2 / k1Ar = 2.9 and k2H2 / k2Ar = 1.5 for the relative third-body efficiencies of hydrogen and argon. The high-pressure limiting rate constant for H-atom addition to ethylene, obtained directly in the high-pressure region, was found to be H+C2H4=C2H5*, (5.5 ± 0.5) × 108M−1·sec−1, with both H2 and Ar as third body.
Nuclear Magnetic Resonance in Antiferromagnetic KMnCl3·2H2O
Authors: Spence R. D. , de Jonge W. J. M. , Rao K. V. S. Rama
Published: February 2004

The Cl and H nuclear magnetic resonance is used to examine the magnetic structure of antiferromagnetic KMnCl3·2H2O. The chemical unit cell contains two Mn ions surrounded by coordination octahedra which are edge linked to form a dimer. Within the dimer the two Mn spins are parallel. The over-all antiferro-magnetism is obtained by repeatedly translating the pair of parallel spins through a distance s and reversing their direction. The magnetic space group is Ps1̄. The most probable direction of the antitranslation s is along the a axis of the chemical unit cell. The magnetization direction lies 18° from the pseudofourfold symmetry axis of the coordination octahedra. Geometrically similar octahedra occur in MnCl2·2H2O but the nearest neighbor spins are antiparallel. From this fact we infer that the magnitude of the nearest neighbor exchange in such structures is quite small.
Molecular g Values, Magnetic Susceptibility Anisotropies, Molecular Quadrupole Moments, Diamagnetic and Paramagnetic Susceptibilities, and the Second Moment of the Electronic Charge Distribution in CHFO, CH2CHF, CF2CHF, CH3CH2F, and CH3CHF2
Authors: Rock S. L. , Hancock J. K. , Flygare W. H.
Published: February 2004

The high-field rotational Zeeman effect has been observed in formyl fluoride (CHFO), vinyl fluoride (CH2CHF), trifluoroethylene (CF2CHF), ethyl fluoride (CH3CH2F), and 1, 1-difluoroethane (CH3CHF2). The signs and magnitudes of the magnetic susceptibility anisotropies [(2χaa − χbb − χcc) and (2χbb − χaa − χcc)] and the magnitudes of the molecular g values (gaa, gbb, and gcc) were obtained and are listed. Although only the relative signs of the g values could be obtained by experiment, the signs were determined through analysis of molecular quadrupole moments and the second moments of the electronic charge distribution. The molecular quadrupole moments (Qaa, Qbb, and Qcc) are also given. Using the magnetic susceptibility anisotropies, g values, the known structures, and the bulk susceptibilities, the diagonal elements of the paramagnetic, diamagnetic, and total susceptibility tensors were calculated along with the second moments of the electronic charge distribution.
Viscoelastic Relaxation of the Bulk Modulus in Two Supercooled Benzene Derivatives
Authors: Dexter A. R. , Matheson A. J.
Published: February 2004

The velocity and absorption coefficient of ultrasonic longitudinal waves have been measured in sec-butyl benzene and 3-phenylpropyl chloride at temperatures between the glass transition temperature and room temperature and at frequencies between 5 and 55 MHz. A relaxation process caused by rotational isomerisation has been observed in sec-butylbenzene with ΔHb‡ = (3.6 ± 0.7) kcal mol−1. The total “structural” relaxation region of the liquids bears no resemblance to the shear relaxation region because the former contains contributions from two different processes. The first of these is the true structural relaxation process which is similar to the shear relaxation process. The other, lower temperature process gives rise to considerable excess absorption and velocity dispersion at temperatures below the structural relaxation region. It is caused not by a hysteresis loss mechanism but by a combination of non-Hookean behavior and internal molecular motion.
Dynamics of the Collinear H+H2 Reaction. I. Probability Density and Flux
Authors: McCullough Edward A. , Wyatt Robert E.
Published: February 2004

The time evolution of the collinear H+H2 reaction as given by classical mechanics and by time-dependent quantum mechanics has been studied. The calculations employed the Porter–Karplus potential surface. The relevant equations of motion were solved to high accuracy by direct numerical integration. The evolution of the quantal probability density in the interaction region of the potential surface is shown in a series of perspective plots. Classical mechanics gives an amazingly good description of the probability density and flux patterns during most of the reaction; however, the classical and quantal descriptions begin to diverge near the end of the reaction. Essentially, the classical reaction terminates before the quantal reaction. The dynamic behavior of the reaction is hydrodynamically turbulent, as shown by transient whirlpool formation on the inside of the reaction path. All results reported in this paper are for one average system energy, namely, 0.65 eV (initial average translational energy = 0.38 eV).
General Quartic Force Field of CS2
Authors: Smith D. Foss , Overend John
Published: February 2004

New experimental measurements at high resolution on the ν2 band of CS2 at about 390 cm−1 are reported and analyzed, together with previous data on this molecule, to obtain sufficient vibrational and rotational constants for the calculation of the force constants in the general quartic force field. The well-known Fermi resonance between the vibrational states | υ1, υ2, l2, υ3 〉 and | υ1 − 1, υ2 + 2, l2, υ3 〉 is analyzed taking into account the dependence of the matrix element of the Fermi resonance operator on the rotational quantum number J and on the three vibrational quantum numbers. The anharmonic force constants were determined by least-squares adjustment to the observed spectroscopic data.
Effect of Pressure on the 19F Spin–Rotation Interactions in Benzotrifluoride in the Liquid State
Authors: Bull T. E. , Barthel J. S. , Jonas J.
Published: February 2004

The 19F spin–lattice relaxation times in liquid benzotrifluoride and its mixtures with toluene-d8 have been measured to 3.5 kbar at 50°C, 4.5 kbar at 70°C, and to 5 kbar at 90°C using the NMR pulse method. The separation of the intramolecular and intermolecular contributions to relaxation was carried out by extrapolation of the measured T1 values to infinite dilution in toluene-d8. The pressure dependence of the 19F T1 due to spin–rotation interactions was explained in terms of the Burke and Chan's model based on the independence of the fluctuating rotational magnetic fields generated by over-all and internal rotation and the existence of two distinct correlation times describing these fields. Our previous tentative interpretation neglecting the spin–over-all-rotation interactions in benzotrifluoride failed to describe the observed pressure behavior. The experimental data show that the dynamically coherent internal rotation of the CF3 group is not affected by increased pressure in the pressure range studied.
Corresponding States: A Universal Reduced Potential Energy Function for Spherical Molecules
Authors: Dymond J. H.
Published: February 2004

Second virial coefficients and dilute-gas transport coefficient data for the inert gases neon to xenon are satisfactorily interpreted on the basis of a universal reduced pair potential energy function. However, molecular beam data and high-temperature viscosity data, considered together, provide evidence that the repulsive region of this curve is much harder for neon than for the other rare gas molecules.
Theory of Brownian Motion. IV. A Hydrodynamic Model for the Friction Factor
Authors: Mazo Robert M.
Published: February 2004

The hydrodynamical theory of the velocity correlation function of a Brownian particle, due to Widom, is combined with the non-Markovian generalized Fokker–Planck equation given by the molecular theory of Brownian motion. An expression for the friction kernel (force autocorrelation) is derived. On the basis of the model here considered, the friction kernel decays as t−3/2 for long times.
Mass Spectrometric Determination of the Heats of Formation and Atomization of Gaseous AuBO
Authors: Gingerich K. A. , Pupp C.
Published: February 2004

During evaporation of Ce and Au from a boron nitride Knudsen cell the molecule AuBO(g) was detected by mass spectrometric analysis. The heat of formation of this molecule was determined from the following reaction equilibria by a third law method: (1) AuBO(g)→Au(g)+BO(g), ΔH0° = 81.2 ± 1.7 kcal mol−1, (2) Au(g)+BO(g)→AuBO(g)+Au(g), ΔH0° = − 28.1 ± 1.3 kcal mol−1, (3) CeAu(g)+BO(g)→AuBO(g)+Ce(g), ΔH0° = 6.4 ± 0.8 kcal mol−1. The heats of formation and atomization calculated from these reaction enthalpies for the AuBO molecule are ΔH298f° = 2.2 ± 5.5 kcal mol−1 and ΔH0 atom° = 273.1 ± 5.5 kcal mol−1.
Internal Viscosity and Quasielastic Scattering
Authors: Bidaux R. , Cotton J. P. , Farnoux B. , Jannink G.
Published: February 2004

The hypotheses leading to internal viscosity of polymers are formulated in terms of the neutron incoherent quasielastic scattering law. The mean squared displacement, calculated in the free draining limit, is obtained as an analytical function of the internal viscosity parameter and is shown to decrease uniformly as this parameter increases. As a consequence, the half-width at half-maximum of the quasielastic scattering law deviates from the q4 behavior predicted for the free chain, and increases less rapidly. The observation of the half-width will be more difficult for this reason. However, the time scale associated with motions reflecting internal viscosity is smaller and therefore more suitable for a neutron scattering experiment.
Gaseous Metal Nitrides. IV. The Dissociation Energy of Cerium Mononitride
Authors: Gingerich Karl A.
Published: February 2004

The CeN molecule has been identified in the vapor phase over a Au–Ce–CeS–BN–C mixture, using a combination of Knudsen effusion and mass spectrometric techniques. The third law enthalpies for the reactions 2CeN(g)=N2(g)+Ce2(g), 2CeN(g)+Au2(g)=2CeAu(g)+N2(g), 2CeN(g)=2Ce(g)+N2(g), and 2CeN(g)+2Au(g)=2CeAu(g)+N2(g) were determined. Combined with published ancillary data, these reaction enthalpies yielded the following thermodynamic properties for gaseous CeN: CeN(g)=Ce(g)+N(g); D0° = 123.0 ± 5.0 kcal mol−1 or 514.6 ± 21 kJ mol−1 Ce(s)+0.5 N2(g)=CeN(g); ΔHf,298° = 90.1 ± 4.0 kcal mol−1 or 377.0 ± 17 kJ mol−1.
Mixture Rules for the Mie (n, 6) Intermolecular Pair Potential and the Dymond–Alder Pair Potential
Authors: Calvin D. W. , Reed T. M.
Published: February 2004

Formulas for the unlike-pair parameters in terms of the like-pair parameters for the Mie (n, 6) potential energy model are examined for their abilities to predict cross-term second virial coefficients. Formulas based on the London dispersion formula and an assumption of geometric mean repulsion energies are tested and shown to apply only for special cases. A geometric mean rule for each one of the parameters including the repulsion exponent, n, is shown to have far more general applicability and to give high accuracy in predicting the cross-term second virial coefficient. Potential energy parameters for several molecules are obtained using corresponding states relationships and the Dymond and Alder numerical potential energy function for argon. The geometric mean rule for the energy and distance parameter is shown to perform well for predicting the cross-term second virial coefficient for mixtures of molecules which obey the Dymond and Alder potential energy function.
Molecular Motion in the Ferroelectric Phase of Hydrogen Chloride
Authors: Yi Pon-Nyong , Gavrielides Athanasios T.
Published: February 2004

The mean-square angular displacements of the hydrogen halide molecules in the ferroelectric phase are calculated in the harmonic approximation in terms of the normal mode frequencies assuming four molecules per unit cell. When the infrared (ir) absorption frequencies are used in the calculation of the mean-square angular displacements, the results do not agree with those obtained from the neutron diffraction. The comparison of the NQR frequency data with the spontaneous polarization measurements suggests chain-polarization-reversing excitations. The two-dimensional Ising model is applied to calculate the temperature dependence of the polarization, and results in reasonable agreement with the experimental data are obtained.
Generalized Oscillator Strength of the Ã ← X̃ Transition of Ammonia
Authors: Harshbarger William R. , Skerbele Ausma , Lassettre Edwin N.
Published: February 2004

The generalized oscillator strength for the Ã ← X̃ transition in NH3 has been determined by electron impact spectroscopy. A high-resolution spectrometer was used to measure the intensity of the strongest vibrational peak, 6.390 eV, relative to the elastic scattering. These intensity ratios were used to determine inelastic cross sections at electron kinetic energies of 300, 400, and 500 eV and scattering angles between 2°–7°. These inelastic cross sections were put on an absolute basis by comparison with absolute elastic cross sections for NH3, measured by Bromberg (unpublished work). The generalized oscillator strength, integrated over all vibrational terms of the transition, was extrapolated to zero momentum change for comparison with optical values. The extrapolated oscillator strength is 0.0696 ± 0.006.
Theoretical Interpretation of the Optical and Electron Scattering Spectra of H2O
Authors: Claydon C. R. , Segal G. A. , Taylor H. S.
Published: February 2004

Energies and potential surface characteristics are assigned to the first eight excited states of the water molecule. This assignment is shown to be consistent with all data from optical spectra, electron scattering, rotational distributions of the OH fragment in photodissociation and associated data, and with semi-empirical INDO calculations. Energies and potential surfaces are given for the lowest resonant states of H2O−. These are consistent within the explainable error of the INDO calculations, as well as with the data on dissociative attachment and associative detachment in which H2O− is an intemediate for species. Assignment-confirming experiments are suggested.
Rayleigh Scattering: Collisional Motions in Liquids
Authors: Bucaro J. A. , Litovitz T. A.
Published: February 2004

Measurements of light scattered in the Rayleigh wing were made over the range from 5 to 500 cm−1 in CCl4, C6H12, C5H12, CH3OH, C2H5OH, H2O, NH3, and CHCl3. These data when compared with earlier data on Ar, Xe, and SnBr4 indicate that in all of these liquids there is present the essentially exponential frequency dependence typical of collision induced effects. A calculation of the spectrum for large frequency shifts based on a binary interaction picture employing a Lennard-Jones potential and a short range electronic overlap distortion model agrees well with the experimental results in liquid argon. Further, assuming that molecular frame distortion is proportional to the interaction force, a similar calculation yields excellent agreement for the molecular systems. It is concluded that isolated binary interactions are mainly responsible for the spectral density in the wings of the Rayleigh spectrum.
Investigation of Back-Scattering in the D+/H2 Reaction System
Authors: Holliday M. G. , Muckerman J. T. , Friedman L.
Published: February 2004

A collision chamber designed for efficient collection of product ions was used to determine the extent of back scattering in the reactions of D+ and H2 to form H+ and HD+. No significant amount of back scattering in the laboratory system was detected.
Collinear Collisions of an Atom and Harmonic Oscillator
Authors: Heidrich Fred E. , Wilson Kent R. , Rapp Donald
Published: February 2004

A comparison is made between quantum, semiclassical, and classical treatments of collinear collisions, with exponential repulsive potential, between an atom and a harmonic oscillator. The quantum calculations used for comparison are those of Secrest and Johnson. The semiclassical treatment, which we call ITFITS, gives analytic transition probabilities in the form of a quantum forced oscillator whose energy transfer is determined separately for each combination of initial and final states by a “refined impulsive” classical approximation symmetrized over initial and final states. Detailed balance is obeyed. The classical treatment is phase averaged, the energy transfer, calculated by numerical integration of the equations of motion, being averaged over the initial phase of the oscillator. The quantum transition probabilities are very well matched for both single and multiple quantum jumps by the semiclassical ITFITS approximation. The quantum average energy transfer is closely approximated both by the semiclassical and classical treatments. We conclude that, over the range of the quantum data, a semiclassical analysis is quite reasonable for transition probabilities and that both semiclassical and classical treatments give an essentially accurate description of average energy partitioning.
Dipole Moments of Mercuric Halides in Benzene and Dioxane
Authors: Reger A. , Eliezer I.
Published: February 2004

Measurements on benzene and dioxane solutions of mercuric halides show that, notwithstanding recent objections, the solutions of these halides exhibit considerable dipole moments. The values obtained were 1.01 and 1.47 D for the chloride and bromide in benzene, respectively, and 1.27, 1.79, and 1.87 for the chloride, bromide, and iodide in dioxane, respectively. These values are consistent with the formation of donor–acceptor (DA) complexes between the benzene or dioxane and the mercuric halides. Calculated dipole moments agree with the experimental results by assuming either an X–Hg–X angle of 140°–160°, or a δ value of 0.07–0.15 for the complex Dδ+Aδ−. The true situation is probably intermediate with both factors playing a part so that both the partial charges and the deviations from linearity are probably smaller than the values quoted above.
Theory of Anomalous Electron Spin Resonance Spectra of Free Radicals in Solution. Role of Diffusion-Controlled Separation and Reencounter of Radical Pairs
Authors: Adrian Frank J.
Published: February 2004

It is proposed that the anomalous spin state populations observed in electron spin resonance spectra of transient radicals in liquids are produced by the following sequence of encounters between two radicals: The radicals either collide or are produced together by a chemical reaction and, instead of recombining, diffuse apart and subsequently undergo a second nonreactive collision. During the interval between the first and second encounters the radical pair wavefunction changes under the influence of singlet–triplet mixing by the magnetic interactions within the radicals. At the second encounter the singlet–triplet splitting associated with the valence bonding–antibonding interactions between the radicals produces further changes in the radical pair wavefunction. The net effect of these changes in the radical pair wavefunction is to increase somewhat the probability of finding the finally separated radicals in those spin states which correlate separationwise with the initial state of the radical pair. The advantage of this mechanism over a somewhat similar mechanism in which singlet–triplet mixing and singlet–triplet splitting operate simultaneously on a radical pair trapped briefly in a solvent cage is that the relatively long time between separation and return of the diffusing radicals gives the weak separation-independent magnetic interactions ample time to change the radical pair wave function. If the nuclear hyperfine interactions dominate the magnetic interaction mixed emission–absorption spectra result; purely emissive or absorptive spectra result if the electron Zeeman interactions predominate. Collision of independently produced radicals with uncorrelated spins gives the same polarizations as a radical pair produced in an antibonding triplet state. Good agreement between theory and experiment has been obtained for several cases.
Matrix-Isolation Study of the Vacuum-Ultraviolet Photolysis of Chloroform. Infrared Spectra of the CCl3+, HCCl2+, and HCCl2− Molecular Ions
Authors: Jacox Marilyn E. , Milligan Dolphus E.
Published: February 2004

Photolysis of samples of HCCl3 isolated in an argon matrix at 14°K using 1216-Å radiation leads not only to the isolation of a high yield of CCl3, but also to the photoionization of CCl3, resulting in the stabilization of a sufficient concentration of CCl3+ for direct infrared spectroscopic identification. The assignment of still other infrared absorptions which appear in this system to negatively charged species has been confirmed by experiments in which a small concentration of an alkali metal atom is also present in the matrix, providing a photoelectron source. When matrix-isolated HCCl3 is subjected to photolysis by 1067-Å argon resonance radiation, very little CCl3 is produced, but HCCl2, HCCl2+, and the same negatively charged species are stabilized in significant concentration. Studies of chloroform samples enriched in carbon-13 and of DCCl3 samples have provided support for these identifications and have yielded data necessary for obtaining several of the force constants of these species. The infrared spectrum of the negatively charged species can most satisfactorily be explained by postulating that dissociative electron attachment to chloroform occurs, resulting in the stabilization of HCCl2− in the matrix environment.
Proof of Two Conjectures of Widom
Authors: Mermin N. D.
Published: February 2004

Two conjectures are proved that are pertinent to the thermodynamics of the new statistical-mechanical model of Widom and Rowlinson.
Compressive Behavior of Some Globular Hydrocarbons and Their Effective Intermolecular Interaction Potentials
Authors: Breitling Shirl M. , Jones Allan D. , Boyd Richard H.
Published: February 2004

The compressive behavior of neopentane, bicyclo[2.2.2]octane, and adamantane has been measured at room temperature in a piston cylinder apparatus. A phase transition was found in each system. The results for phase I (low pressure) for the average of compression and decompression runs were fit to an equation of the form − ΔV / V0 = a0 + a1P + a2P2. Literature results for methane (at 77°K) were also fit to this equation. The following results were obtained (per kilobar): methane, phase I, a0 = 3.64 × 10−3, a1 = 4.98 × 10−2, a2 = − 3.46 × 10−3, − ΔV / V0 (transition) = 0.022; neopentane, phase I, a0 = 0.000, a1 = 4.08 × 10−2, a2 = − 2.60 × 10−3, − ΔV / V0 (transition)=0.049 at 6.5 ± 0.5 kbar; bicyclo[2.2.2]octane, phase I, a0 = 0.000, a1 = 2.65 × 10−2, a2 = − 1.04 × 10−3, − ΔV / V0 (transition) = 0.022 at 9.1 ± 0.7 kbar. adamantane, phase I, a0 = 0.000, a1 = 2.59 × 10−2, a2 = − 2.04 × 10−3, − ΔV / V0 (transition) = 0.014 at 4.1 ± 0.5 kbar. The well-depth, minimum distance, and repulsive exponents of a “N-6” potential derived from heats of sublimation, crystal lattice parameters, and compressibilities are, respectively: methane, ε / k = 142°K, rm = 4.27 Å, n = 11.2; neopentane, 436°K, 6.32 Å, 16.0; bicyclo[2.2.2]octane, 737°K, 6.58 Å, 14.2; adamantane, 915°K, 6.82 Å, 13.8. The volume thermal expansions of phase I for bicyclo[2.2.2]octane and adamantane are 4.4 ± 0.2 × 10−4 °K−1 and 4.7 ± 0.5 × 10−4 °K−1, respectively.
Theory of Semiclassical Transition Probabilities (S Matrix) for Inelastic and Reactive Collisions
Authors: Marcus R. A.
Published: February 2004

In the present paper the time-independent Schrödinger equation for inelastic collisions is solved directly in the WKB approximation, using action-angle variables and the method of characteristics. A single wavefunction, consisting of an ingoing and an outgoing term, is thereby derived, describing all collision channels and so avoiding the application of WKB methods to an infinite set of coupled differential equations. An integral is obtained for the S matrix, and asymptotic methods (e.g., steepest descents, stationary phase) are used for its evaluation. The expressions can be calculated using numerical data on classical trajectories or using approximations. To facilitate the latter and to show the connection with approximations in the literature, a canonical perturbation theory is described for the wave phase and amplitude, in a form suited to collisions, and used to relate the theory to those approximations. The topic of collisional selection rules is also considered. The extension of the method employed in the present paper to the direct calculation of differential and total inelastic cross sections, rather than via the S matrix, is briefly described, and the extension to reactive cross sections is also noted. The method can also be used to treat time-dependent problems, and so is not restricted to collisions. These topics and other applications will be described in later papers of this series.
A Short, Slightly Asymmetrical, Intramolecular Hydrogen Bond: A Neutron Diffraction Study of Bis(2-amino-2-methyl-3-butanone Oximato)Nickel(II) Chloride Monohydrate {Ni(C5H11N2O)2H}+Cl−·H2O
Authors: Schlemper E. O. , Hamilton Walter C. , Placa Sam J. La
Published: February 2004

A neutron diffraction study of bis(2-amino-2-methyl-3-butanone oximato)nickel(II) chloride monohydrate {Ni(C5H11N2O)2H}+Cl−·H2O has provided a wealth of precise information concerning the short intramolecular hydrogen bond, the dynamics of rotating methyl groups, and the effects of intermolecular environment on potential functions. The intensities of 3500 single-crystal reflections were measured at the Brookhaven High Flux Beam Reactor. These data were used in conjunction with the earlier x-ray determination to locate all atoms including the 25 hydrogen atoms. After least squares refinement with anisotropic temperature factors, the agreement factor R = ΣΔ(F2) / ΣF02 was 0.055. The short intramolecular hydrogen bond O···O [2.420(3) Å] is unique in that no bond symmetry is imposed by the space group, and it is slightly asymmetrical. The O–H bond lengths for the hydrogen bond are 1.242(5) and 1.187(5) Å, and the O–H–O angle is 169.9(3)°. The potential apparently has a broad, flat, single minimum, shifted toward one oxygen, possibly because of intermolecular packing forces. The N–O bonds adjacent to the hydrogen bond are of lengths 1.335(2) and 1.346(2) Å with the shorter N–O distance associated with the longer O–H distance. The water molecule and chloride ion are extensively hydrogen bonded to each other and to the amine hydrogens of the cation. The methyl groups attached to sp2 carbon atoms have large rotational amplitudes (19–30°) resulting in short apparent C–H bond lengths (1.006 Å average) from the harmonic treatment; the bond length shortening is well correlated with the rms rotational amplitude. Other average uncorrected bond distances involving hydrogens are O–H in H2O (0.950 Å); N–H (1.024 Å); and C–H (1.081 Å) for methyl groups attached to the sp3 carbons.