bluuebunny/crossref_metadata_2025 huggingface dataset:
Absolute Cross Section for Hg(3P1) + H2 and the Imprisonment Lifetimes for Hg(3P1) at Low Opacity
Authors: Michael J. V. , Yeh C.
Published: February 2004

Steady-state hydrogen-atom concentrations produced by the mercury-photosensitized decomposition of molecular hydrogen are detected by Lyman-α photometry. On the basis of the natural lifetime of Hg(3P1) and the mechanism for the reaction, quenching plots are constructed, and the over-all bimolecular rate constant for Hg(3P1) + H2 is calculated. The absolute cross section for Hg(3P1) + H2 is determined to be 10.8 ± 0.4 Å2 in the limit of low mercury opacity. This result agrees with other recent experimental determinations. In addition, experimental values of imprisonment lifetimes for Hg(3P1) as a function of mercury concentration are estimated and are compared with other low-opacity and high-opacity results. The results are also compared to various theoretical predictions of imprisonment lifetimes.
Theory of the Isotropic NMR Shifts in Trigonal Co(II) Complexes
Authors: McGarvey Bruce R.
Published: February 2004

The theory of both the contact and pseudocontact shift in Co(II) trigonal complexes is considered. The theory predicts a pseudocontact shift in Co(II)poly(1-pyrazolyl)borate complexes, in good agreement with experimental results. The predicted contact shifts are found to be much different from that predicted by previously proposed theories. In the region of 200–400°K, the temperature dependence is found to deviate strongly from a 1 / T dependence for the pseudocontact shift but not for the contact portion of the shift. The assumption made in earlier theories, that the contact interaction is the same for all six Kramer's doublets, is examined in detail.
Viscosity, Thermal Conductivity, and Diffusion Coefficient of Ar–Ne and Ar–Kr Gaseous Mixtures in the Temperature Range 25–700°C
Authors: Kestin J. , Wakeham W. , Watanabe K.
Published: February 2004

The paper presents new relative measurements of the viscosity of argon, neon, and krypton and of the binary mixtures Ar–Ne and Ar–Kr, all at atmospheric pressure, in the nominal temperature range 25–700°C, and with a precision of ± 0.1%. The oscillating-disk method was employed. The experimental data were used to calculate the binary diffusion coefficient for the mixtures, and the thermal conductivity of the pure gases as well as the mixtures. The data for the pure gases can be correlated separately with the aid of a suitable potential of the 6-n family, and optimum values of the parameters σ, ε, and n are given for each of them. The same data can be correlated equally well with the aid of a universal, empirical expression for the collision integral with two individual parameters, s and p, being adequate to describe each gas separately. The conventional combination rules as well as those proposed by Kalelkar and Kestin [J. Chem. Phys. 52, 4268 (1970)] have been tested, and it was found that the latter represent the results as well as the expression for mixture viscosity in terms of the viscosity of the pure components and the coefficient of binary diffusion. Wassiljewa coefficients have been evaluated for the representation of the viscosity and the thermal conductivity of the mixtures.
Normal Coordinate Analysis and Force Constants of Nitrogen Trichloride
Authors: Carter James C. , Jackovitz John F. , Devia Jorge E. , Bratton Raymond F.
Published: February 2004

A vibrational analysis has been performed for nitrogen trichloride based on a frequency fit of the 14N and 15N species. Force constants for several modifications of the Urey–Bradley force field (UBFF) are compared to the six constants of the general valence force field. Modification of the UBFF to include angle–angle and bond–bond cross terms results in an excellent agreement with the GVFF constants. The chlorine–chlorine repulsion force constant obtained agrees satisfactorily with the calculated Lennard-Jones nonbonded interaction between two argon atoms.
Anisotropy of the Carbon-13 and Proton Hyperfine Coupling Constants in Organic Radicals
Authors: Barfield Michael
Published: February 2004

A theoretical study of the anisotropy of the carbon-13 and proton hyperfine coupling constants in organic radicals is presented in terms of a spin density formulation which uses the generalized product approximation specialized to valence-bond wavefunctions. Both isotropic and anisotropic components of the 13C and 1H hyperfine coupling tensors are obtained for the methyl and ethyl radicals with inclusion of all valence electrons. Theoretical results for the methyl radical are also based on spin densities from self-consistent-field (SCF) molecular-orbital theory in the approximation of intermediate neglect of differential overlap and from nonempirical spin-restricted SCF calculations with configuration interaction. The calculated results are compared with the available experimental data, and they indicate that inclusion of contributions from the σ-electron framework is essential. But in contrast to isotropic hyperfine coupling constants, components of the anisotropic hyperfine tensor are relatively insensitive to the spin density distribution. Factors which are also discussed are the importance of variation of the effective nuclear charge, radical geometry, contributions from inner shells, and off-diagonal elements of the spin density matrix.
Pulse Radiolysis Studies. XIX. Solvent Effects in Electron Transfer and Proton Transfer Reactions of Aromatic Molecule Ions
Authors: Brandon J. R. , Dorfman Leon M.
Published: February 2004

Absolute rate constants were determined, by the pulse radiolysis technique, for the electron transfer reaction from an aromatic radical anion to a different neutral aromatic molecule: A1·−+A2=A1+A2·− for a number of aromatic molecule pairs in ethanol, in ethylenediamine, and in diethylamine. The dependence of these rate constants upon the standard free energy for reaction of the pair and upon the dielectric properties of the solvent, as predicted by the theory of Marcus for electron transfer reactions, is found to support this theory, at least semiquantitatively, over a limited range. The effect of solvent on the rate of protonation of the biphenyl radical anion by an alcohol: C12H10·−+ROH=C12H11·+RO− was studied for a number of mixed solvent systems, namely, ethanol–ethylenediamine, ethanol–cyclohexane, ethanol–triethylamine, ethanol–diethylamine, ethylene glycol–ethylenediamine, and ethylene glycol–triethylamine. In the alcohol–amine systems the first order rate constant for the protonation reaction was drastically reduced in amine-rich solution and increased in alcohol-rich solution. The rate constant was increased at all concentrations of cyclohexane in the ethanol–cyclohexane system. These effects of the presence of a second solvent were attributed to the formation of a hydrogen-bonded complex between the amine and the alcohol, which reduces the rate in these systems, and to the solvent structure breaking effect of the cyclohexane, which increases the rate.
Intra- and Intermolecular Vibrational De-excitation in Impulsive Atom–Diatomic Molecule Collisions
Authors: Kelley J. Daniel
Published: February 2004

The de-excitation of vibrationally energetic Morse oscillators via impulsive collision with an atom is discussed. In certain types of atom–oscillator systems intramolecular vibration-to-rotation energy transfer is more important than intermolecular vibration-to-translation transfer. Since the efficiency of this intramolecular de-excitation has a different dependence on particle mass and collision energy than does the intermolecular de-excitation, restricting consideration to the latter, e.g., using a collinear collision model, does not always lead to an adequate description of the de-excitation process.
Perturbation Energies for the Hooke's Law Model of the Two-Electron Atom
Authors: Benson John M. , Brown W. Byers
Published: February 2004

The Rayleigh–Schrödlinger perturbation energies E(n) for the ground state of the Hooke's law model atom are calculated through tenth order. The E(n) are expressed as singly infinite sums whose terms are obtained from recurrence relations. Very slow convergence limited the method to E(10) and below. The results are compared with those of Midtdal (1965) for heliumlike atoms, and it appears that the convergence of the Hooke series is more rapid. However, no recognizable patterns are observable in the Hooke E(n) through E(10). The nature and position of the singularity determining the radius of convergence is discussed.
Collisional Destruction of the 63P1 State of Mercury
Authors: Waddell B. V. , Hurst G. S.
Published: February 2004

Inclusion of collisional destruction mechanisms as sink terms in the theory of imprisonment of resonance radiation appears to have been neglected in the case of the 2537-Å mercury line. In this paper, the Holstein photon transport equation is employed to determine the effect of destructive or self-quenching collisions between resonance state and ground state atoms, processes in which the resonance state is converted to another excited state with the release of kinetic energy. These mechanisms seem to explain experimental work in which the decay constant of the 2537-Å mercury line reaches a minimum and then increases with density. Comparison of theory with experimental data yields a cross section between 3.0 and 10.0 × 10−18 for the conversion of Hg(3P1) to metastable Hg(3P0) by two-body collisions with Hg(1S0). The sharp increase at high density of the decay constant of the 2537-Å mercury line has not been predicted by previous theories but is a general consequence of the inclusion of collisional destruction mechanisms.
Oscillator Strength of the Resonance Transitions of Ground-State N and O
Authors: Lin Chorng-Lieh , Parkes David A. , Kaufman Frederick
Published: February 2004

Multiplet oscillator strengths, ΣgLfLU, for the resonance triplets of N and O were determined using the line absorption method and measuring atom concentrations by chemical “titration.” For the NI triplet at 1200 Å, ΣgLfLU = 0.87 ± 0.20, and excellent internal agreement was obtained among the separately measured fLU of the three lines. A value of (3 ± 1) × 10−11 cm3 sec−1 is required for the rate constant of the N+NO→N2+O reaction in the analysis of the data. For the OI triplet near 1300 Å, the apparent ΣgLfLU increased sharply and reproducibly from 0.19 to 0.42 when the diluent gas in the discharge light source was changed from Ar to He, which indicates that excitation transfer is a major source of excitation in such Ar–O2 resonance lamps. The larger oscillator strength obtained with He–O2 light sources is in excellent agreement with results of lifetime measurements by other workers.
Glory Scattering in Molecular Collisions: Formal Expressions for the Total Cross Section
Authors: Biolsi Louis
Published: February 2004

An extended distorted-wave treatment is used to obtain formal expressions for the total cross section when two rigid diatomic molecules with orbital and nuclear-spin angular momenta collide. Explicit expressions are obtained through second order, including the lowest-order inelastic effects.
EPR of Free Radicals in an Adamantane Matrix. I. Aliphatic Aminoalkyl Radicals
Authors: Wood David E. , Lloyd Roger V.
Published: February 2004

Aliphatic aminoalkyl radicals RR′Ċ–NR″R″ are found to be produced by x irradiation of aliphatic amines in adamantane. The EPR spectra are isotropic with ∼ 2-G linewidths for radicals with less than eight heavy atoms. Spectral parameters are obtained for 24 of these radicals by computer simulation of the EPR spectra. A nontwisted anti conformation is found for the geometry of the aminoalkyl radicals by comparison of observed hyperfine splitting constants with those calculated by INDO. The radicals have a substantial stabilization from a three-electron π bond between the trigonal carbon and the nitrogen. The spin density on carbon is about 34. The stability of the radicals with respect to carbon substitution is found to be H2ĊNH2>RHĊNH2>R2ĊNH2. This ordering, which is the reverse of that found for alkyl radicals, is discussed with respect to the electron withdrawing ability of the substituents. The effects of the substituents on the geometry of the radicals is also discussed.
Molecular Quadrupole Moments of SF4
Authors: Stone R. G. , Tigelaar H. L. , Flygare W. H.
Published: February 2004

The molecular Zeeman effect in SF4 has been observed in magnetic fields around 21 000 G. The linear and quadratic Zeeman effects lead to the molecular g values of gaa = − 0.0555 ± 0.0008, gbb = − 0.0510 ± 0.0021, and gcc = − 0.0492 ± 0.0023. The two independent values of the magnetic-susceptibility anisotropies are 2χaa − χbb − χcc = − 4.9 ± 1.8 and 2χbb − χaa − χcc = 2.0 ± 1.6 in units of 10−6 erg/G2·mol. The a axis contains the near-linear F–S–F group in SF4, and the c axis bisects the SF2 angle for the other two fluorine atoms. The c axis is the electric dipole axis. The molecular quadrupole moments are Qaa = − 10.7 ± 2.8, Qbb = 0.6 ± 3.1, and Qcc = 10.1 ± 4.4 in units of 10−26 esu·cm2. The charge distribution in the SF4 molecule is discussed in some detail.
Unified Treatment of Two-Center Overlap, Coulomb, and Kinetic-Energy Integrals
Authors: Todd H. David , Kay Kenneth G. , Silverstone Harris J.
Published: February 2004

A single analytical formula is derived which gives the two-center overlap, Coulomb, nuclear-attraction, and kinetic-energy integrals as special cases. There are no difficulties when orbital exponents are nearly equal. Simplification of the derivative operators, which are characteristic of the approach, is discussed in detail. A computational scheme is outlined, and computing times are given.
Vibrational Relaxation of Carbon Dioxide in Argon
Authors: Kamimoto Goro , Matsui Hiroyuki
Published: February 2004

Vibrational relaxation of CO2(ν3) diluted in Ar was studied over the temperature range 700–2000°K by using a shock-tube technique. Measurements were made by monitoring the infrared emission of the asymmetric stretching mode of CO2 at 4.3 μ. The relaxation profile of CO2(ν3) was found to be nonexponential by intramolecular V–V couplings with other modes and all the modes in CO2 had approximately the same final relaxation time τf on CO2–Ar collisions. The relaxation time for the V–V process between ν1,2 and ν3 modes was estimated by using a simplified two-modes model.
Hyperfine Structure and Dipole Moment of CH3D
Authors: Wofsy S. C. , Muenter J. S. , Klemperer W.
Published: February 2004

The electric resonance spectrum of deuteromethane (CH3D) was measured in the two rotational states, J = 1, K = 1 and J = 2, K = 2. From these data the dipole moment and hyperfine constants of the molecule were obtained. The results for the methane-related spin rotation constants are cα = 16.54 ± 0.35, and cβ = − 1.58 ± 1.0 kHz. The quadrupole coupling constant eqQ at the deuterium nucleus is found to be eqQ = 191.48 ± 0.77 kHz. The electric dipole moments μ(J, K) are μ(1, 1) = 5.6409 × 10−3 and μ(2, 2) = 5.6794 × 10−3D.
Analytical Mechanics of Chemical Reactions. V. Application to the Linear Reactive H +H2 Systems
Authors: Wu Shiou-fu , Marcus R. A.
Published: February 2004

Natural collision coordinates and a zeroth-order vibrational–adiabatic approximation are used to treat linear reactive collisions. Nonadiabatic effects on barrier transmission and on vibrational state of products are calculated. The present results are classical and are compared with exact classical numerical results for the H+H2 reaction in the range 7–20 kcal/mol of initial relative translational energy. The agreement is encouraging and the results support the concepts introduced earlier of statistical adiabaticity and of nonadiabatic leak. At low energies the reaction is adiabatic on the average (initial vibrational phase average), thus justifying activated complex theory for this system. The relative importance of reaction path curvature and of vibrational frequency variation along the reaction path in inducing nonadiabatic effects is described. Implications for a quantum treatment, activated complex theory, and highly nonadiabatic systems are noted.
Structure, Pseudorotation, and Vibrational Mode Coupling in IF7: An Electron Diffraction Study
Authors: Adams W. J. , Thompson H. Bradford , Bartell L. S.
Published: February 2004

Free vapor-phase molecules of iodine heptafluoride are pentagonal bipyramids with axial bonds (1.786 ± 0.007 Å esd) shorter than equatorial bonds (1.858 ± 0.004 Å). They are deformed from D5h symmetry on the average by 7.5° ring puckering displacements (e2″ symmetry) and 4.5° axial bend displacements (e1″ symmetry). The distortion from D5h, interpreted in terms of the points-on-a-sphere variant of the valence-shell electron-pair theory, is compatible with an effective force law between electron pairs of Vij ∼ rij−n with n in the broad vicinity of 3.5. Expressing forces harder than simple Coulomb repulsions and much softer than conventional atom–atom nonbonded repulsions, the potential-energy law is in a range consistent with Gillespie's bond–bond repulsion theory. The simplest interpretation of the diffraction intensities is that the molecules undergo essentially free pseudorotation along a pathway (predominantly e2″ displacement coordinates) connecting 10 equivalent C2 structures via Cs intermediates. The observed pseudoradial displacement suggests a value of about 5 cm−1 for the pseudoangular rotation constant h / 8π2cIeff. The appreciable axial bend induced by the ring pucker is correlated in phase with the pucker displacement. This correlation is responsible for introducing a pronounced skewing of the Fax···Feq radial distribution peak (i.e., an “anharmonic shrinkage”) and also presumably imparts significant infrared activity to the e2″ modes in overtones and combination bands. Furthermore, the axial bend gives the molecule a dipole moment which may explain recent molecular-beam experiments by Klemperer et al.
Interaction Phenomena in Ionization Processes
Authors: Morrison J. D. , Traeger J. C.
Published: February 2004

It is suggested that in several instances, ionization of atoms and molecules by photon and electron impact may exhibit an interaction phenomenon, whereby the lower charged or parent ion cross-section decreases at the appearance energy of the multiply charged or fragment ion. This competition between cross sections is first interpreted in terms of configuration interaction and then in relation to a collision complex model, similar to the compound nucleus model used to describe nuclear excitation processes.
Theory of Charge Transfer in Aromatic Donor–Acceptor Crystals
Authors: Strebel Paul J. , Soos Zoltán G.
Published: February 2004

A narrow-band, localized model is developed for charge transfer (CT) interactions in 1:1 stacks of planar, π-electron donors (D) and acceptors (A). The inequivalence of D and A sites and the Madelung constant for the ionic lattice are treated phenomenologically. The electronic states, for arbitrary CT in the aromatic D–A stacks, are found self-consistently by an equation-of-motion method. The ground-state charge density and the band structures correspond to primarily neutral, ···DADA···, diamagnetic or to primarily ionic, ···D+A−D+A−···, paramagnetic one-dimensional semiconductors. The activation energies for CT and for semiconduction, together with the CT stabilization, are found self-consistently. In ionic lattices, CT is shown to provide an activation energy for paramagnetism of the proper magnitude. When the sites are equivalent, the theory reduces to a half-filled Hubbard model, and the self-consistent solutions are in good agreement with exact results.
Frictional Force Exerted by a Flowing Fluid on a Permeable Particle, with Particular Reference to Polymer Coils
Authors: Ooms G. , Mijnlieff P. F. , Beckers H. L.
Published: February 2004

A procedure has been developed to calculate the frictional coefficient of a porous sphere with radially varying permeability. Application to polymer coils, where permeability values can be derived from sedimentation data at finite concentration, shows agreement with experimental frictional coefficients of polymer coils at infinite dilution.
Shock Tube Study of the Effect of Vibrational Energy of N2 on the Kinetics of the O+N2→NO+N Reaction
Authors: Wray Kurt L. , Feldman Eugene V. , Lewis Paul F.
Published: February 2004

The kinetics of the reaction O+N2+3.3 eV→NO+N were investigated under conditions where the vibrational temperature of the nitrogen was less than the translational temperature. The formation of NO behind incident shock waves in dilute O3–N2 mixtures was studied over the temperature range 3100–6400°K with initial pressures of 2–25 torr. In the shock front O3→O+O2 and the reaction of the O with N2 is then rate-limiting, followed by the fast reaction N+O2→NO+O. The NO was monitored in emission at 5.3 μ and the initial slopes were compared to theoretical calculations which included vibrational relaxation processes. The radiation rose linearly from the shock front with no incubation in accord with the theoretical calculations employing only translational energy to determine the fraction of collisions whose energy was above the endothermicity of reaction.
Polarizations of Electronic Transitions from Azimuthal Variation in Fluorescence Intensity—with Application to Biphenyl
Authors: Edwards L. O. , Simpson W. T.
Published: February 2004

It is shown that the angle between absorbing and emitting transition moment vectors may be obtained from a ratio of intensities measured in fluorescence; the intensities to be taken from an azimuthal circle with the propagation vector of the incident beam as polar axis. The incident light must be polarized and the intensities are measured at azimuthal stations selected according to the direction of polarization. Results are compared with those obtained using conventional polarized fluorescence—for aniline and for indole. The azimuthal ratio method is then used to obtain polarizations for biphenyl and substituted biphenyls. Use of the method may facilitate penetration into the region below 200 nm; in fact a determination using excitation at 197 nm has already been made. Finally, the results for biphenyl are interpreted so as to constitute several new assignments of electronic transitions.
Collisional Deactivation of H(22P) Fluorescence
Authors: Braun Walter , Carlone Cosmo , Carrington Tucker , Van Volkenburgh Gregg , Young Robert A.
Published: February 2004

Collision cross sections for deactivation of H*(n = 2) at 300°K have been measured by observations of the quenching of Lyman-α fluorescence in a discharge flow system. The quenchers (with cross section in Å2) are H2(84 ± 8), D2(84 ± 8), N2(62 ± 6), He(< 3). For H*+H2, less than 1% of the total quenching produces ions. Care has been taken to work with systems optically thin in Lyman α so that the rate of escape of radiation, which is the reference to which the quenching rate is compared, is not reduced by resonance trapping.
Mössbauer Spectroscopy of Gold Compounds
Authors: Faltens Marjorie O. , Shirley D. A.
Published: February 2004

Mössbauer spectra at 4.2°K were taken with 197Au in several aurous and auric compounds. For each oxidation state a linear correlation was observed between the isomer shift (IS) and the quadrupole splitting (QS). Both the IS and QS varied over wide ranges in both auric and aurous compounds. Neither IS nor QS alone could be used to determine the oxidation state, but together they appear to determine it uniquely. The results for linear aurous and square-planar auric complexes are interpreted in terms of 6s6p and 5d6s6p2 hybridization, respectively, with varying degrees of ionic character. Attempts to interpret the results quantitatively in terms of the atomic parameters ψ2(O) and 〈r−3〉 were only partially successful: It was not possible to reproduce the large experimental values for 〈r−3〉6p using free atom theory. The nuclear factor was determined as δR / R = + (2.5 ± 0.6) using the simple hybridization model.
Linewidths of HCl Broadened by H2, D2, and HCN
Authors: Toth Robert A. , Hunt Robert H. , Plyler Earle K.
Published: February 2004

The linewidths in the 1–0 band of HCl broadened by H2, D2, and HCN have been measured at 297°K with a resolution of 0.02 cm−1. The experimental results are compared with linewidths calculated from Anderson's impact theory as extended by Tsao and Curnutte. The agreement between experiment and theory is good for HCl+D2 and qualitatively correct for HCl+H2 provided the small impact-parameter approximation of Fiutak and Van Kranendonk is used. For HCl+HCN, the agreement between experiment and theory is fair. Best-fit values for the quadrupole moments and hard-sphere diameters of HCl, H2, D2, and HCN are listed and compared with previous values.
Separation of Light Isotopic Gas Mixtures in the Thermal Diffusion Column
Authors: Rutherford W. M.
Published: February 2004

The theory of the thermal diffusion column, originally developed by Jones and Furry for mixtures of heavy isotopes, is extended to include mixtures of light isotopes, the properties of which depend on composition. The transport equation which results is similar to previous equations for mixtures of heavy isotopes, but atom fractions are replaced by mass fractions. Experimental separation measurements of the 3He–4He system were used to test the theory. The predicted effect of 3He concentration on the reduced initial transport coefficient is closely followed experimentally. The general agreement between theory and experiment is within the mutual uncertainties of the experiments and of the calculations. The uncertainty in the experimental column transport coefficients is estimated to be ± 9%, and the uncertainty in the coefficients calculated from theory is estimated to be ± 5%. The theory is also expected to apply to the separation of mixtures of unlike gases, although this aspect was not tested experimentally.
δ-Function Scattering. Molecular Collisions
Authors: Locker David J.
Published: February 2004

Molecular interactions are examined in which the intermolecular potential energy surface is approximated by a series of δ functions of appropriate integrated areas. The method is verified by comparisons with the results of other procedures. The δ-function technique is found to require little computation time even for potentials approximated by 60 δ functions. The dependence of flux conservation upon atomic masses is explored. The procedure is extended to include four-body collinear interactions.
Fluorescence Quenching and Solvent Excitation Migration in Liquid Alkylnaphthalenes
Authors: Eastman J. W. , Smutny E. J. , Coppinger G. M.
Published: February 2004

The fluorescence of neat alkylnaphthalene liquids is quenched to varying degrees by the addition of 16 organic compounds. Rate constants for the quenching (kq) have been calculated using the intrinsic fluorescence lifetime reported previously by Birks and King. For the series of quenchers, the rate constant appears to increase as increasing amounts of charge are transferred to or from the alkylnaphthalene. A limiting maximum of kq = 45 × 109 (M·sec)−1 is obtained. This may be interpreted to mean that the migration of energy through liquid alkylnaphthalenes occurs in jumps of 4.5 Å every 4 × 10−12 sec.
Some Effects of Vibration and Molecular Structure on Internal Rotation in CH2DSH and CHD2SH
Authors: Knopp John V. , Daniel Donald D. , Quade C. R.
Published: February 2004

The J = 1 ← 0, ΔK = 0 lines have been assigned in the microwave rotational spectra for the partially deuterated methyl mercaptans. The fine structure of the transitions for the torsional ground state has been analyzed on the basis of internal rotation and molecular structure. It is necessary to introduce a V1 cosα term into the effective potential energy for internal rotation to account for the relative splittings. Although it is not possible to determine a unique value for V1, the limits 1.5 cm−1 ≤ | V1 | ≤ 10 cm−1 are obtained. From the splittings it is possible to determine an improved value of 3°5′ for the so-called C–S tilt with respect to the methyl axis. The staggered configuration for the thiol–methyl orientation is found to be the minimum in the threefold potential energy.
Comments on the Theory of Self-Diffusion in Liquids
Authors: Jordan Peter C. , Greenberg Allan D.
Published: February 2004

The assumptions which have been used to effect a closure of the heirarchy of distribution functions for fluids in which self-diffusion is the only nonequilibrium process are outlined. We investigate the fundamental equation which has been derived under these assumptions and show that, in general, it has no solutions of physical interest. We suggest possible ways in which existing theories may be modified to yield physically significant results.
Three-Particle Correlation Functions. I. Fourier Transform Methods
Authors: Wertheim M. S.
Published: February 2004

When a function of r, the absolute value of the distance between two points, falls off so slowly that not all its moments exist, then the decay of the function at large r can be related to the behavior of its three-dimensional Fourier transform at small k. These results are extended to functions F(r1, r2, r3) of the three relative distances between three points. The behavior of F for large r1, r2, r3 is related to the behavior of the six-dimensional Fourier transform for small k1, k2, k3. We treat a class of functions which asymptotically become homogeneous in r1, r2, and r3. The dependence on the degree of homogeneity is considered in detail. The results can be applied to the convolution-type integral equations which arise in statistical mechanics.
Concentration Study Determination of the 6P, 6I, and 6D Energy Levels of Gd3+ in SrF2 at a C4υ Site
Authors: Detrio J. A. , Ferralli M. W. , Yaney P. P. , Ware D. M. , Donlan V. L.
Published: February 2004

A correlation of changes in the absorption coefficients of the spectra of SrF2:Gd3+ containing from 0.1 to 0.5 mole% doping is used to determine some of the 51 lowest energy levels of Gd3+ at a site of C4υ symmetry. The concentration study was necessary to separate the spectral lines of the tetragonal site from transitions due to ions in other sites. The various sites are the result of the charge compensation that occurs when Gd3+ substitutes for Sr2+. Previously unreported 6I and 6D levels are tabulated and prior work on the 6P multiplets is supported. The details of a “concentration study” in which the concentrations are unknown are given.
Photoionization Study of Chlorine Monofluoride and the Dissociation Energy of Fluorine
Authors: Dibeler Vernon H. , Walker James A. , McCulloh K. E.
Published: February 2004

Mass spectra and photoionization yield curves are obtained for the molecular and atomic ions of chlorine monofluoride. The atomic ions are formed both by ion-pair and by dissociative ionization processes, although the F+ ion formed by the latter process is too weak for quantitative measurements. The ClF+ curve exhibits a weak onset at 12.55 eV, ascribed to a hot band. An intense onset at 12.65 eV is ascribed to the (0, 0) transition. The observed thresholds for the Cl+ ion support the spectroscopic determination of D(ClF) = 2.558 eV and, combined with a recent determination of the heat of formation of ClF, support the previously reported photoionization value of D0°(F2) = 1.34 eV.
Molecular Momentum Distributions and Compton Profiles. II. Localized Orbital Transferability and Hydrocarbons
Authors: Epstein Irving R.
Published: February 2004

Momentum distributions, expectation values, and Compton profiles are calculated for methane, ethane, ethylene, acetylene, methyl acetylene, trans-butadiene, cyclopropane, and benzene by transforming SCF wavefunctions from position space to momentum space. Agreement with available experimental profiles is found to be somewhat better than for earlier calculations. Distributions and profiles for localized molecular orbitals (LMO's) in hydrocarbons are computed and are found to show a high degree of transferability. With the addition of LMO distributions and profiles representing various functional groups, formulas are given for predicting the distributions and profiles of several homologous series of organic molecules. The problem of quantitatively comparing similar profiles is discussed briefly.
Longitudinal Modes in Hydrogen and Deuterium Halide Crystals
Authors: Friedrich H. B. , Carlson R. E.
Published: February 2004

The observation of four bands in the Raman spectra of the internal modes of crystalline HCl, DCl, HBr, and DBr has previously been explained either by assuming a four-molecule primitive cell, which is different than the structure suggested by diffraction studies, or by assuming that two of the bands were due to longitudinal modes. We have used the experimental infrared intensities with a dipolar coupling model appropriate to the cell symmetry to compute the LO frequencies. The calculated frequencies are in excellent agreement with those observed in the hydrogen and deuterium halide crystals.
Infrared Dispersion in Liquid Benzene and Benzene-d6
Authors: Zelano A. J. , King W. T.
Published: February 2004

The intensities of the major infrared absorption bands in liquid C6H6 and C6D6 were measured by an interferometric method. The intensities of the very intense a2u modes were found to be 14 450 ± 110 and 8600 ± 110 cm−1 cm2/mM for C6H6 and C6D6, respectively. Small, but significant deviations from the predictions of the “oriented gas model,” used to interpret these measurements, were observed.
Nonadiabatic Effects in the Internal Rotation of ·CH2COO− in Irradiated Zinc Acetate Dihydrate
Authors: Hayes Robert G. , Steible Daniel J. , Tolles William M. , Hunt John W.
Published: February 2004

The EPR spectrum of the ·CH2COO− radical in a single crystal host displays nonadiabatic motional effects. A phenomenological theory is suggested, based on the density matrix of the spin system, and a technique is described for rapid calculation of simulated spectra.
Molecular Zeeman Effect and the Determination of the Molecular Magnetic Moments (g Values), Magnetic Susceptibilities, and Molecular Quadrupole Moments in Methyl Formate and Glycolaldehyde
Authors: Wang J. H. S. , Flygare W. H.
Published: February 2004

The high-field first- and second-order Zeeman effect has been observed in methyl formate and glycolaldehyde. The molecular parameters in the inertial axis system for both molecules are listed below. Only the relative signs of the molecular g values are obtained experimentally. However, the absolute signs are conclusively assigned in both molecules by an analysis of the second moment of the charge distribution or molecular quadrupole moments. For methyl formate, the measured g values and magnetic susceptibility anisotropies are gaa = − 0.1267 ± 0.0013, gbb = − 0.0391 ± 0.0010, gcc = − 0.0168 ± 0.0017, 2χaa − χbb − χcc = (11.0 ± 1.0) × 10−6erg/G2·mol, and 2χbb − χcc − χaa = (3.1 ± 1.0) × 10−6erg/G2·mol. The molecular quadrupole moments are Qaa = (2.3 ± 0.8), Qbb = (4.2 ± 1.0), and Qcc = − (6.5 ± 1.3) all in units of 10−26 esu·cm2. For glycolaldehyde, the measured g values and magnetic susceptibility anisotropies are gaa = − 0.1239 ± 0.0013, gbb = − 0.0726 ± 0.0010, gcc = − 0.0178 ± 0.0010, 2χaa − χbb − χcc = (7.1 ± 2.5) × 10−6erg/G2·mol, and 2χbb − χcc − χaa = (18.8 ± 2.0) × 10−6erg/G2·mol. The molecular quadrupole moments are Qaa = − (5.6 ± 2.0), Qbb = (3.8 ± 1.8) and Qcc = (1.8 ± 3.3) in units of 10−26 esu·cm2. Using the molecular structures allows a determination of the diagonal elements in the paramagnetic susceptibility tensor and the anisotropies in the second moment of the charge distribution. Using the bulk susceptibilities, gives the diagonal elements in the total magnetic susceptibility tensor and the individual elements of the second moment of the charge distribution. The results in these two molecules are compared to similar systems.
Matrix-Isolation Spectra of H2S and D2S: An Example of the Application of the Uncoupled Oscillator Approximation
Authors: Pacansky Jacob , Calder V.
Published: February 2004

The first direct observation of the ν3 vibration of H2S and D2S is reported. The location of this fundamental in the matrix spectra is consonant with the band center calculated from the overtone-combination frequencies in the gas phase. General, quadratic, valence force constants are calculated from the isotopic shifts using simple equations based on the uncoupled oscillator approximation.
Photoelectron Spectra of Bicyclic and Exocyclic Olefins
Authors: Demeo Daniel A. , Yencha Andrew J.
Published: February 2004

The construction and operational characteristics of a newly built photoelectron spectrometer are described. The photoelectron spectra of some bicyclic and exocyclic olefins and related saturated hydrocarbons have been recorded and their ionization potentials reported. The lowest ionization potentials are examined and discussed in terms of substitutional and ring strain effects. Ionization potential changes accompanying substitution in these molecules are explained by using empirically generalized substitution rules for saturated and unsaturated hydrocarbons. There appear to be no significant ring strain effects upon the lowest ionization potentials of four-, five-, or six-membered ring exocyclic olefins or for the bicyclic molecules norbornane, norbornene, and norbornadiene. From a comparison of the ionization potential changes between 1, 3- and 1,4-dienes, it is estimated that the two double bonds in norbornadiene are directionally coupled across the ring by an interaction energy of about 0.3 eV. From analyses of the spectral characteristics of the photoelectron spectra, the lowest ionization potentials of all the alkenes studied and the two lowest ionization potentials of norbornadiene are assigned to π ionization.
ESR of SO2−
Authors: Reuveni A. , Luz Z. , Silver Brian L.
Published: February 2004

The ESR spectrum of normal and 17O labeled SO2− in aqueous solutions of Na2S2O4 and in γ-irradiated K2S2O5 has been studied. The 33S and 17O hyperfine tensors are very nearly axially symmetric with parallel and perpendicular principal values of 58.0 ± 0.5 and 4 ± 4 G for 33S and 30.0 ± 0.5 and 3 ± 3 G for 17O. The principal values of the g tensor are 2.0057 ± 0.0005, 2.012 ± 0.003, and 2.0019 ± 0.0020 where the smallest component is parallel to the major 33S and 17O hyperfine components. The results are consistent with the unpaired electron occupying a 2b1 π molecular orbital for which semiempirical coefficients are derived.
Lattice Dynamics of Potassium Azide. A Group-Theoretical Analysis
Authors: Rao K. R. , Trevino S. F.
Published: February 2004

The symmetry properties of normal modes of lattice vibrations of the lattice of potassium azide are investigated using the formalism of Maradudin and Vosko. Using a computer code, the symmetry vectors at several points of the Brillouin zone are determined. The interrelations between elements of the dynamical matrix corresponding to these points have also been obtained from the same code. This information has helped in developing a force model to analyze experimental results of neutron scattering studies made recently at this laboratory.
Ion Mobilities with Charge Exchange
Authors: Heiche Gerhard , Mason E. A.
Published: February 2004

Quantum-mechanical calculations are presented for various elastic cross sections that describe the motion of atomic ions through their parent gases; the effects of nuclear spin are included. The cross sections are linear in the gerade–ungerade pairs of molecular states. An exact relation between the diffusion and charge-exchange cross sections is derived. Detailed calculations are given for the total, charge-exchange, and first three transport cross sections over the energy range of about 10—6–10 eV, for potentials and masses corresponding to He+ in He, and Cs+ in Cs. The cross sections exhibit structure due to orbiting resonances and glory interferences, but the ion mobility depends smoothly on temperature. The semiclassical, impact-parameter, random-phase, and polarization approximations are tested and found to be surprisingly accurate, apart from the quantum-mechanical structure.
Variational Formulation of the Harris Expansion Technique
Authors: Kolker H. J.
Published: February 2004

The Harris expansion technique for calculating elastic scattering phase shifts is studied within the context of the Kohn variational principle. It is shown that Harris' method is capable of yielding upper and lower bounds for the tangent of the phase shift.
On the Nature of the Crystal-Field Approximation. IV. Generalization and Numerical Results
Authors: Trivedi P. C.
Published: February 2004

A modified molecular orbital theory was developed by Herzfeld and Goldberg to show the effect of the neglect of the wavefunction overlap and the electron exchange on the results of the conventional crystalfield theory. It was applied by them to calculate the interaction of a hydrogen atom in the 2p state and a hydrogen molecule in the ground state in two different simple nuclear configurations. In one case the atom nucleus was taken to lie on the perpendicular bisector of the molecular axis (T case), and in the other all the three nuclei were taken to lie on a line (L case). The method was generalized for the pn-atom–H2-molecule system (L case) by Goldberg (n = 1–5). Numerical results were given for the p1-atom–H2-molecule system (L and T cases) by Berger and Herzfeld. In the present calculation this generalization is further extended to the pn-atom–H2-molecule system (T case) with numerical results given for the L and T cases. It is shown that the generalized crystal-field theory can account for some of the shortcomings of the conventional crystal-field theory. In particular, calculation shows how the “center of gravity” rule and the inversion result are modified. It also shows how the degeneracy is lifted in a system consisting of a diatomic molecule and an atom in the pn configuration. The generalization of the Herzfeld–Goldberg method clearly demonstrates that the conventional crystal-field theory cannot be considered to be a fundamental theory for the description of the wide range of phenomena that as a semiempirical method it has dealt with so well.
Excited-State Variational Calculations with Orthogonality Constraint
Authors: Bustard Thomas M. , Jaffé H. H.
Published: February 2004

Open-shell pi-electron calculations have been performed on several singlet excited states of pyridine, pyrazine, pyrimidine, pyridazine, and naphthalene using a recently developed variational technique. Spectral results obtained via the new method are compared with results based on virtual orbitals and experiment. Configuration interaction was found to be necessary for adequate state representation, and the results of the new method are generally better than virtual orbital results, but the CI calculation over separately minimized configurations is very laborious. This new method has some computational advantages in certain applications, but it cannot be recommended for spectral calculations since acceptable spectral results can be obtained more easily using the Pariser–Parr–Pople scheme.
Nuclear Quadrupole Resonance in Hexamethylenetetramine: Modulation and Reorientational Broadening
Authors: Eletr S.
Published: February 2004

The temperature dependences of the frequency and linewidth of the nuclear quadrupole resonance absorption in hexamethylenetetramine have been measured in the range between 297–380°K using a Zeeman modulated spectrometer. The results are reported and interpreted both in terms of the molecular reorientation that is known to take place at these temperatures and the modulation broadening expected from this type of instrument.
Analytical Approach to the Shock Compressibility of 18 Cubic-Lattice Metals
Authors: Huang Y. K.
Published: February 2004

An average value of 11 / 6 is taken to represent the Grüneisen constant of these eighteen metals: Li, Na, K, Rb, Cs, Fe, Mo, Ta, W, Al, Co, Ni, Cu, Pd, Ag, Pt, Au, and Pb. An analytical model is formulated for the interpretation of shock-wave behavior of the_e metals. The model is shown to be as heuristic as the classical model of gas dynamics, and the adiabatic indices and compression ratios of both models at shock infinity may now be arranged as orderly spectra (53, 32, 75, 43) and (4, 5, 6, 7), respectively. The investigation seeks to emphasize the interrelation between shock and isentropic compressibilities, and it also provides favorable evidence for the use of Slater formula to evaluate γ at high pressure.
High-Accuracy Wavefunctions and Matrix Elements for Vibration–Rotation States of Diatomic Molecules Using the Dunham Potential
Authors: Herman R. M. , Tipping R. H. , Short S.
Published: February 2004

An iterative procedure for deriving accurate analytic wavefunctions for the Dunham molecular oscillator is described, and the wavefunctions so obtained are tabulated for the 10 lowest vibrational states. These wavefunctions are more accurate than those which are available for simpler models (e.g., the simple harmonic oscillator with an added cubic term or the Morse oscillator) and, in fact, can be credited with accuracies at least as great as those associated with the Rydberg–Klein–Rees numerical methods. The inclusion of rotational motion is also described. Finally, a method for the rapid derivation of analytic expressions for off-diagonal radial matrix elements between vibration–rotation states is detailed. This method makes use of only certain parts of the analytic wavefunctions, relaying on a recursion relation to complete the development.
Relation between State-Selected or State-Averaged Cross Sections of Endothermic Reactions and Rate Constants of Exothermic Reactions. Application of Bimolecular Microcanonical Activated Complex Theory
Authors: Marcus R. A.
Published: February 2004

An expression is derived relating state-selected or state-averaged molecular beam reaction cross sections of endothermic reactions to observed rate constants for the inverse (exothermic) reactions. An approximation of Anlauf, Maylotte, Polanyi, and Bernstein is used, together with bimolecular microcanonical activated complex theory [R. A. Marcus, J. Chem. Phys. 45, 2138 (1966)].
Perturbation Corrections to the Uncoupled Hartree–Fock Method. Dipole Polarizabilities of the Neon Isoelectronic Sequence
Authors: Tuan Debbie Fu-Tai , Wu Kang Kun
Published: February 2004

The polarizability, α = α0 + α1, for the 10-electron atomic systems Ne, Na+, Mg2+, Al3+, and Si4+ has been calculated by the uncoupled Hartree–Fock method with the perturbation correction of Tuan and co-workers (PUCHF Method). The correction is rather significant, with the percentage ratio α1 / α% being around 20%. The contributions to α from individual orbitals were also investigated. It is shown that the outermost orbitals and the orbitals along the direction of external electric field give the largest contribution to α: The contribution from the two 2p0 orbitals is around 31.1%–42.2%. The α obtained by the PUCHF method differs from the coupled Hartree–Fock (CHF) method by 3.6% to 4.8% except for the neutral atom Ne which differs by 7.8%. The agreement of α between the PUCHF and CHF methods improves with increase of nuclear charge, as has been observed previously for the dipole and quadrupole polarizabilities of He, Li, and Be isoelectronic sequences by Epstein and Johnson. It is concluded that (1) the PUCHF method offers a simple and tractable way to study the contribution of individual orbitals to physical properties, and (2) for polarizabilities of positive ions the PUCHF method gives results with accuracy comparable to those obtained from the CHF method.
Infrared Spectrum, Structure, and Heat of Formation of Gaseous (NO)2
Authors: Dinerman Carl E. , Ewing George E.
Published: February 2004

Gaseous nitric oxide was examined from 4000 to 1600 cm−1 at temperatures between 77 and 150°K with a 3.9-m and a 6-cm cell. Features found at 1860 and 1788 cm−1 exhibited a quadratic pressure dependence and were assigned to (NO)2. The band shape of these features indicated the presence of a cis-(NO)2 isomer. The heat of formation of (NO)2 from monomeric NO is ΔH = − 2450 cal/mol. Other bands due to (NO)2 are reported.