bluuebunny/crossref_metadata_2025 huggingface dataset:
Electron spin resonance of vanadium pentoxide molybdenum trioxide catalysts
Authors: Khulbe K. C. , Mann R. S. , Manoogian A.
Published: February 2004

X-ray, infrared, and electron spin resonance (ESR) studies were made on molybdenum trioxide catalysts doped with 0.25, 0.5, 2.0, 5.0, 10.0, and 20% by weight vanadium pentoxide. X-ray diagrams indicate the existence of two kinds of patterns for catalysts containing more than 2% V2O5. All the samples produced ESR signals, including pure V2O5. For low dopant concentrations the signals were well resolved, and the paramagnetic center was identified as the VO2+ ion in the unit structure VO2+5O2−. The resonance lines increased in width as the dopant concentration was increased to 10%, and only a single broad line existed for 20% V2O5 or pure V2O5.
Convergence of the Rayleigh-Schrödinger perturbation expansions for the energy levels of the Pariser-Parr-Pople model of the benzene molecule
Authors: Pellégatti A. , Čížek J. , Paldus J.
Published: February 2004

Estimates of the radii of convergence of the Rayleigh-Schrödinger perturbation expansions for various energy levels of the π-electronic model of the benzene molecule, described by the PPP (Pariser-Parr-Pople) Hamiltonian, in both weakly and strongly correlated limits, were determined using a ``generalized'' Cauchy criterion and the numerically determined coefficients of the pertinent expansions. The difficulties associated with the numerical approach to the problem, in which one is always limited to a finite number of terms in the expansion, are discussed and the appropriate procedures enabling us to overcome, at least partially, these problems are outlined.
Comparative study of the vacuum ultraviolet absorption and photoelectron spectra of some simple ethers and thioethers
Authors: Planckaert A. A. , Doucet J. , Sandorfy C.
Published: February 2004

The vacuum ultraviolet absorption (from 220 to 120 nm) and photoelectron (from 6 to 21 eV) spectra of the following molecules are compared: tetrahydropyran, tetrahydrothiopyran, methylvinylether, methylvinylthioether, dihydropyran, and 4,4-dimethyl-2,3-dihydrothiopyran. The great similarity between the photoelectron spectra of related ethers and thioethers is stressed. In the case of saturated thioethers the corresponding ultraviolet spectra are, however, very different, showing that the involvement of 3d orbitals is important in the low excited states of saturated sulfur compounds. The uv spectrum of tetrahydrothiopyran is interpreted in terms of at least five closely spaced Rydberg series that are of the s, p, or d type. They all converge to the first (S 3p) ionization potential. Both unsaturated ethers and thioethers have one π* ← π band on which s-, p-, and d-type Rydberg series converging to the first (π-type) IP are superimposed. There is no evidence for the participation of S 3d AO's in the low lying excited states of unsaturated thioethers.
Inequalities for penetrable sphere model systems
Authors: Monroe James , Lebowitz Joel L.
Published: February 2004

We make use of certain inequalities derived for mixtures with a nonnegative interaction between particles of different species and no interaction between particles of the same species to derive bounds on the thermodynamic functions of these systems and of their one component, ``penetrable sphere model,'' analogs.
Ion-polar molecule collisions: Nonreactive collisions of Cl− with dichloroethylene and difluorobenzene
Authors: Su Timothy , Bowers Michael T.
Published: February 2004

Momentum transfer rate constants for Cl− with dichloroethylene and difluorobenzene isomers have been studied by an ion cyclotron resonance line-broadening technique. Rate constants for nonpolar isomers are compared to those predicted by the Langevin theory and the rate constants for polar molecules are compared to the average-dipole-orientation (ADO) theory. All experimental rate constants are consistently higher than theoretical predictions. The incremental effect of a permanent dipole on momentum transfer collision frequencies predicted by ADO theory is in satisfactory agreement with experimental results.
Theory of current characteristics of a thin dielectric film under slow electron impact
Authors: Harrigan M. E. , Lee Hyung Joon
Published: February 2004

A relation between the current transmitted by a thin dielectric film as a function of incident electron energy and the electronic energy structure of the film is derived. These current characteristics have been measured by W. H. Hamill et al. For low energies, 1–4 eV, it is found that the current characteristics are insensitive to the detailed energy structure of the solid. In the moderately high energy range, 4–10 eV, the transmitted current is more sensitive to the energy levels of the solid, but the relation is not straightforward, involving a convolution of a joint density of states and a conduction band density of states. Analysis of the low energy region is shown to give values of parameters, such as energy resolution and energy zero, relevant to a detailed quantitative study of the data.
Electron-diffraction study of the structure of 1,2,7,8-diepoxyoctane
Authors: Smith Zuzana , Kohl D. A.
Published: February 2004

The molecular structure of gas-phase 1,2,7,8-diepoxyoctane was investigated by electron diffraction to extend a study of straight-chain diepoxides. The synthesis of diepoxyoctane results in a mixture of two diastereomers, which considerably complicates the conformational problem. The distribution of trans and gauche conformers arising from the rotation around the three central C–C bonds was calculated by assuming a free-energy difference of 610 cal/mole between the trans and gauche positions. The positions of major nonbonded peaks in the radial distribution then ruled out all but two orientations (A and B) of the epoxy groups. The end-carbon atoms in conformation A are displaced from the trans position (by about 40°) and the oxygen atom is in a roughly gauche position. In conformation B the positions of the end-carbon atom and the oxygen atom are approximately interchanged with respect to their positions in conformation A. With the assumption that only one orientation was allowed, the angles defining orientations A and B were optimized and a significantly lower standard deviation was obtained with the former. However, without reoptimizing any of the angles, it was found that models involving combinations of orientations A and B gave as good agreement as the model with A alone. The best of the mixed models coupled the orientation of the end group with the conformation of the central carbon atoms. Since consideration of mixed models essentially doubles the number of parameters to be determined, the present experiment was not able to establish completely the distribution of conformers.
Effect of photodecomposition on the infrared spectra of lead azide. I. Far infrared
Authors: Varma S. P. , Williams Ferd , Möller K. D.
Published: February 2004

The far infrared absorption of pure and doped lead azide films has been measured as a function of degree of photodecomposition with ultraviolet radiation. Changes in intensities of absorption by the lattice modes during decomposition are observed. The decomposition is inhomogeneously distributed through the film and the structure changes. The decomposition is limited by depletion of azide in the region of ultraviolet absorption where the photodecomposed product also absorbs. We conclude that regions where approximately 12% or more of the nitrogen has been removed no longer contribute to the far infrared lattice mode absorption. The long-time hyperbolic decay of the photodecomposition is explained.
Shock-tube study of carbon monoxide dissociation kinetics
Authors: Hanson Ronald K.
Published: February 2004

The dissociation kinetics of undiluted carbon monoxide have been investigated over the temperature range 5600–12 000°K. Data were obtained as time-resolved pressure measurements on the end wall of a shock tube and radiation emission histories of the C2 Swan system (0–0 band) behind incident shock waves. The dissociation rate for the over-all process CO+M→ lim k̃d ,MC+O+M was found to be k̃d,M=8.0×1038 T−5.5 exp(−1.29×105/T) cm3/mole·sec, independent of the proportions of the collision partners M=CO, C, and O. The above rate constant is about 10 times that previously measured with argon as a collision partner and is in close agreement with the measurements of k̃d,M(M=CO, C, O) by Chackerian and of k̃d,O by Appleton, Steinberg, and Liquornik.
Vacuum ultraviolet spectroscopy of cyanogen and cyanoacetylenes
Authors: Connors Robert E. , Roebber John L. , Weiss Karl
Published: February 2004

The vapor phase absorption spectra of cyanogen, cyanoacetylene, dicyanoacetylene, and dicyanodiacetylene have been recorded between 2000 and 1050 Å. Substantial perturbations in the intensity and positions of particular bands upon the addition of helium at 1500 psi pressure served to identify several Rydberg series. These series are assigned on the basis of their quantum defects and symmetry considerations. CNDO/2-CI calculations were used to interpret the valence shell transitions. A very intense intravalence shell band, assigned as a Σu+1 ← 1Σg+ system arising from the lowest π→π* configuration, dominates the spectra of all the molecules. A moderately intense intravalence shell band, assigned as a Πu1 ← 1Σg+ transition arising from the lowest n→π* configuration further characterizes the spectra.
Depolarized Rayleigh scattering and hydrogen bonding in liquid water
Authors: Montrose C. J. , Bucaro J. A. , Marshall-Coakley J. , Litovitz T. A.
Published: February 2004

Depolarized Rayleigh scattering spectra have been obtained for water over essentially its entire liquid range at atmospheric pressure. Three principal components of the Rayleigh line were identified and these were described in terms of molecular reorientation of the molecules, the formation and breaking of hydrogen bonds between molecules, and polarizability anisotropies resulting from the collisions or interactions among several molecules. For the region of the spectrum 0 to 50 cm−1, the most intense component of the spectrum is that which we have ascribed to hydrogen bond kinetics; from it we have determined the mean lifetime of a hydrogen bond in water as a function of temperature.
Electronic structure and spectra of small rings. V Photoelectron and electron impact spectra of cyclopropenone
Authors: Harshbarger W. R. , Kuebler N. A. , Robin M. B.
Published: February 2004

The photoelectron and electron impact spectra of cyclopropenone are presented and are interpreted with the aid of Gaussian orbital calculations of double-zeta quality. The spectra and the calculations all lead to the conclusion that there is an unusually large interaction between both the pi and lone pair orbitals in the carbonyl portion of the molecule with the pi and sigma orbitals of the olefin portion. The first ionization potential (9.57 eV) involves ionization of an electron from the oxygen lone pair, whereas the second (11.19 eV) involves ionization of an electron from the olefin pi bond. The most vertical ionization is from the 7a1 MO (16.11 eV), the second lone pair orbital on oxygen. Rydberg series are observed in the electron impact energy loss spectrum converging upon each of these three ionization potentials.
Magnetic susceptibilities of trivalent lanthanide ions in an octahedral environment
Authors: Hoehn M. V. , Karraker D. G.
Published: February 2004

Magnetic susceptibilities for eight lanthanide ions in Cs2NaLnCl6 were measured from 2.5 to [inverted lazy s] 80°K with a vibrating sample magnetometer. Computer fitting of the data for Cs2NaCeCl6 gave g = 1.43 for the Γ7 ground level, and f2 = 3.85 for the Γ8 excited level. These values are in good agreement with values calculated from first-order wavefunctions. The ground crystal field level for Nd3+ in Cs2NaNdCl6 was found to be a Γ8 level. Because of singlet ground levels and small crystal field splitting, no positive information on the ground crystal field levels was obtained for Pr3+, Tb3+, Dy3+, Ho3+, Er3+, or Tm3+ compounds. Based on Nd3+ and Ce3+ results, the ratio A40/A60 was estimated to be about 20; A40, of the order of 10 cm−1; and A60, of the order of 1 cm−1.
Temperature dependence of the isotopic liquid-vapor fractionation factor for nitric oxide
Authors: Eshelman Donald M. , Torre Frank J. , Bigeleisen Jacob
Published: February 2004

The 15N/14N isotope fractionation factor between NO liquid and vapor has been determined in the temperature range 110–173°K. The results are in good agreement with the isotopic vapor pressure data of Clusius et al., which cover the range 110–121°K. The isotope fractionation data follow the T−2 law up to 135°K. A refinement of the T−2 law analysis of the isotopic vapor pressure data given by Bigeleisen in 1960 has been carried out by the harmonic oscillator cell model to include T−1 and T0 terms. It is shown that the T−2 terms from the dimerization of the monomer in the liquid and the hindered translation and rotations of the dimer dominate the isotope fractionation factor. The falloff from the T−2 law for the liquid-vapor fractionation factor in NO is steeper than in argon. This is reconciled with the dissociation of the dimer in the liquid and the association of the monomer in the vapor at high temperatures.
Temperature dependence of vibrational energy transfer from DF (v = 1) to several diatomics
Authors: Bott J. F.
Published: February 2004

The V-V energy transfer rates from DF (v=1) to HCl, HBr, DBr, D2, N2, O2, CO, and NO have been measured at temperatures from 295 to ∼ 800°K. The measurements were made behind reflected shock waves with the laser-induced fluorescence technique. The rates for V-V transfer to the infrared-active molecules show an inverse temperature dependence near room temperature, characteristic of collisions dominated by attractive potentials. The rates for V-V transfer to the homonuclear diatomics have positive temperature dependences, typical of short-range repulsive potential interactions. Several rates of V-R, T deactivation by DF were also obtained. The available data for the hydrogen halides show that PHY-HX > PHX-HY when PHX-HX > PHY-HY. HF and DF are equally efficient in deactivating HCl (v=1) and HBr (v=1).
Quantum mechanical perturbation expansion of the second virial coefficient and the Ursell-Mayer function. II. The Heitler-London linear polarizability model
Authors: Baer S. , Bergmann E.
Published: February 2004

By a modification of a previous method of quantum mechanical perturbation expansion, the Ursell-Mayer function f(R) is obtained in the form 1 + f(R) = exp(−ΔE)(1 + βU1 + β2U2 + ⋯) where ΔE is the Heitler-London energy and Un is at least of order 2n in the Coulomb interaction energy of the pair of molecules. The Un's depend on electron overlap integrals and distorted charge distributions. When electron overlap and charge distribution distortion are neglected the Un's become products of long range dispersion interaction potentials. Furthermore when the effect of nonlinear polarizabilities is neglected one obtains Un = U1n /n!. The results are restricted to temperatures sufficiently low compared to the excitation energies of the two molecules.
Spontaneous decay of the ``3Σu+'' state of Xe2
Authors: Weihofen William H.
Published: February 2004

The upper lasing level (first excited ``3Σu+'' state) of molecular xenon is examined in the context of a particle-hole model, with a view toward gaining insight into the electronic configuration and the electric dipole transition to the ground state. It is found that the spontaneous decay time of this lasing transition, reasonably independent of the form of the molecular binding, is in this model 23 ± 8 nsec.
Radiative lifetime of O2+
Authors: Fairbairn A. R.
Published: February 2004

The radiative lifetimes of ν′=1, 2, and 3 levels of the b4Σ state of O2+ have been measured by a delayed coincidence method using an electron beam as excitation source. The data showed no clear variation from band to band and an average lifetime was found to be 1.05 ± 0.15 × 10−6 sec.
Results of Percus-Yevick approximation for a binary mixture of hard spheres with nonadditive diameters; R11=R22=0, R12 > 0
Authors: Ahn Saeyoung , Lebowitz Joel L.
Published: February 2004

We investigate the properties of binary mixtures of hard sphere fluids with nonadditive diameters: Calling Rij the distance of closest approach between particles of species i and j we assume R12=½ (R11 + R22)+α with α≠0. We find the exact solution of the Percus-Yevick integral equation for this system in both one and three dimensions when R11 = R22 = 0, α > 0 (Widom-Rowlinson model). The solution of the PY equation for the Widom-Rowlinson model exhibits a phase transition (corresponding to a separation of the components) in three but not in one dimension. This is in agreement with the true behavior of this system. The critical indices in three dimensions are classical.
Molecular orbital calculations of the electronic structure of borazane
Authors: Fujimoto Hiroshi , Kato Shigeki , Yamabe Shinichi , Fukui Kenichi
Published: February 2004

An ab initio molecular orbital calculation of the addition compound of boron hydride and ammonia has been carried out. By expanding the molecular orbitals of the addition compound in terms of the molecular orbitals of boron hydride and of ammonia in a separated state, the origin of charge transfer and bond formation between these two species in the interaction has been studied. A configuration analysis of the wavefunction of the addition compound has been performed.
Orientation dependent spin density matrix of tumbling molecules in thermal equilibrium
Authors: Vega Alexander J. , Fiat Daniel
Published: February 2004

The spin state of randomly moving paramagnetic molecules is described by a density matrix ρ(Ω), which is a function of the random molecular coordinate Ω. As a typical example, Ω denotes the orientation of molecules in a liquid. It is shown that in thermal equilibrium ρ(Ω) is equal to a statistical Boltzmann distribution, which is determined by the full Ω-dependent spin Hamiltonian ℋ(Ω). Thus the effect of the anisotropic part of ℋ(Ω) is not canceled in the case of rapid tumbling. This result is proved using a quantum mechanical description of the lattice, in a way similar to Van Vleck's derivation of the Langevin-Debye formula for susceptibilities. Based on the same formalism, an extension of the equation of motion of ρ(Ω) (the stochastic Liouville equation) is proposed. The modified equation guarantees the approach of ρ(Ω) to its thermal equilibrium value. The new term in the equation is also discussed in terms of Brownian motion.
Computer studies of the onset of Brownian motion in a hard sphere fluid
Authors: Subramanian G. , Levitt D. , Davis H. T.
Published: February 2004

Molecular dynamics calculations on a system of identical hard spheres containing a single test particle of larger size yield a velocity autocorrelation function that has an initial exponential decay agreeing with Enskog exponential decay, followed by a much slower decay. The slow decay does not agree with Stokes exponential decay but fits well the hydrodynamical model which takes into account the dependence of the frictional resistance of the particle on its time history as well as the effect of the inertia of the fluid surrounding the test particle. Binary collision rates computed from the molecular dynamics agree very well with Enskog's theory.
Effects of variations in reaction coordinate eigenvalue on heavy-atom kinetic isotope effects: Comparison of two methods for curving the potential barrier
Authors: Kidd Richard W. , Yankwich Peter E.
Published: February 2004

The formic acid molecule is used as a model for a computational comparison of the Willi-Wolfsberg curvature parameter (K) method (Type K calculations) and the Johnston-Bonner-Wilson method (Type II calculations), both including bond order (N) and barrier curvature (ν1‡ ≠ 0) effects, for calculation of 13C kinetic isotope effects involving reaction coordinate eigenvectors consisting nominally of two nonzero elements. Results obtained by the two methods cover similar ranges of value of calculated k12C/k13C. Reaction coordinate eigenvectors (uncontaminated for Type II results) may involve as much as 20% extraneous displacement in Type K results when ν1‡ ≅ 800 i cm−1; however, the effect on (ν1‡/ν′1‡), the temperature independent factor (TIF) in k12C/k13C, is so small as to be of limited practical significance. The remainder (TDF) of the isotopic rate constant ratio for various combinations of K and N (Type K) or of ν1‡ and N (Type II) can be arranged well into magnitude sequence by invocation of details of the input F and G matrices in the first order high temperature approximation. But, Type K and Type II results similar only with respect to barrier curvature (as indicated by value of ν1‡) may be very different. The Type K approach (at least for two-element reaction coordinates) seems the more serviceable for data matching and may be conceptually the simpler. The Type II approach, however, seems the more instructive concerning the influence of specific internal coordinate displacements on values of the kinetic isotope effect.
New procedure for generating valence and Rydberg orbitals. I. Atomic oscillator strengths
Authors: Simons Gary
Published: February 2004

A new procedure for generating approximate valence and Rydberg orbitals is proposed. The method involves the analytic determination of the eigenfunctions of a model Hamiltonian and leads to orbitals which are functions of quantum numbers and quantum defects. The new functions are shown to be similar to previously obtained orbitals and are used to derive a general formula for transition integrals. Illustrative results for Li and Be+ are excellent; results for Na, K, and Mg are satisfactory.
Nonadiabatic molecular collisions: Charge exchange and chemical reaction in the Ar+ + H2 system
Authors: Chapman Sally , Preston Richard K.
Published: February 2004

The three adiabatic surfaces needed to describe Ar+ + H2 in the nonrelativistic limit are calculated using the diatomics-in-molecules with zero overlap approach. Approximate nonadiabatic interaction terms which couple these surfaces are computed. Using these terms, a first-order semiclassical calculation of the electronic transition probabilities is carried out. The results imply that all the important nonadiabatic transitions are localized in the reactant channel around an avoided crossing between the surfaces formed from combination of Ar(1S)+H2+(2Σg) and of Ar+(2P)+H2(1Σ). Because the results show that the transitions are induced by vibrational motion of the diatomic, any realistic study of the dynamics must include the full three dimensionality of the problem. We investigated the dynamics using the 3D trajectory surface hopping model proposed by Tully and Preston. Ar+ + H2 (v=0) was studied at a relative energy of 3.36 eV. The predictions of the model for cross sections, average final translational energy, and average scattering angle agree well with experiment for both charge exchange and molecular rearrangement products. A discussion of the conceptual picture which emerges from this model is given.
3
B
1-1A1 transition of SO2 gas. I. Franck-Condon treatment and transition moments
Authors: Vikesland John P. , Strickler S. J.
Published: February 2004

Absorption and emission spectra for the 3B1-1A1 transition in SO2 gas are reported and subjected to a Franck-Condon type of analysis. It is shown that the transition moment varies rapidly with bond angle, and a modification of the usual Franck-Condon factors is necessary to deal with this case. The bond length and angle of the excited state are calculated to be 1.491 ± 0.002 Å and 126.1 ± 0.1°, respectively, in good agreement with values from rotational analysis. The oscillator strength of the absorption band is estimated to be (3.34 ± 0.12) × 10−7.
Theoretical studies of hydrogen-rare gas complexes: HenH and HenH+ clusters
Authors: Milleur Mac B. , Matcha Robert L. , Hayes Edward F.
Published: February 2004

Results of LCAO-SCF-MO calculations of the ground states of HenH and HenH+ clusters (n = 1–4) are presented and discussed. A potential energy surface is reported for the collinear He2H+ system and for selected nonlinear arrangements. The relative stability of the various complexes is explored, and some preliminary excited state calculations are reported. Based on these calculations a speculation is made regarding the possible identity of the matrix isolated species responsible for the infrared bands observed by Bondybey and Pimentel in certain hydrogen-rare gas mixtures.
Einstein coefficients for diatomic molecules
Authors: Herbelin J. M. , Emanuel G.
Published: February 2004

Re-examination of current semiempirical methods for computing Einstein coefficients for diatomic molecules has resulted in the development of a new technique for predicting infrared transition probabilities. The method uses a nonlinear transformation of existing polynomial dipole expressions with the subsequent application of appropriate boundary conditions to arrive at improved dipole curves. The transition probabilities predicted for HF are found to yield the most consistent agreement with the available experimental data when compared with existing results. Reanalysis of experimental data by the use of the new transition probabilities yields an HF(v) distribution for the reaction, H + F2 → HF(v) + F, 0 ≤ v ≤ 9, that is in better agreement with independent theoretical predictions than the uncorrected distribution. The method has also been used to compute the Einstein A coefficients of DF, HCl, and DCl.
Mössbauer effect experiments in a series of t2gn iron complexes
Authors: Oosterhuis W. T. , Weaver D. L. , Paez E. A.
Published: February 2004

Mössbauer effect experiments have been done on trans- [Fe(diars)2Cl2](BF4) and trans-[Fe(diars)2Cl2] under variable conditions of temperature and magnetic fields. Paramagnetic hyperfine interactions have been observed in fields up to 60 kOe at temperatures down to 4.2°K. The spectra are characterized by spin Hamiltonians for S=0, (1/2) which in turn have been interpreted in terms of a ligand field of orthorhombic symmetry acting on the t2g5 and t2g6 electronic configurations. A comparison is made with the results for a t2g4 configuration in trans-[Fe(diars)2Cl2](BF4)2, which is a third member of this series of t2gn complexes.
Vibration-to-vibration energy transfer in near-resonant collisions
Authors: Shin Hyung Kyu
Published: February 2004

An analytic approach is presented for the calculation of vibration-to-vibration (VV) energy transfer in near-resonant systems and is applied to several collision systems over the temperature range of 300–4000°K with particular emphasis on N2+CO collisions. Calculated values of VV probabilities for CO+N2 and CO+NO are in good agreement with experimental data. For CO+O2 and CO+D2, calculated probabilities are larger than high temperature experimental data by factors of 3 to 5. For all systems, including NO+N2, the calculated result at low temperatures (≃300°K) is in reasonable agreement with experiment. It is also shown that the VV probability for CO+N2 is very large compared with the VT probability for N2(v=1)+CO → N2(v=0)+CO at lower temperatures.
Brownian motion model of surface chemical reactions. Derivation in the large mass limit
Authors: Schaich William L.
Published: February 2004

We present arguments for the utility of a Brownian motion model of the interaction between reacting chemicals on surfaces and the substrate electrons. The basic equation of such a model, the Fokker-Planck equation for the description of the chemicals' kinetics, is derived in the limit of their mass becoming infinite. Since we envisage the practical application of this equation, a discussion is given of the physical significance of the corrections due to the finite mass of the chemicals. Several general assumptions of the derivation, valid in the infinite mass limit, lead to apparent temperature restrictions for finite mass. The necessity of these restrictions is examined and argued to be not of critical importance.
Binary homogeneous nucleation as a mechanism for the formation of aerosols
Authors: Mirabel Philippe , Katz Joseph L.
Published: February 2004

The rates of nucleation of liquid aerosols from the gaseous maxtures H2SO4+H2O and HNO3+H2O at 25°C for various relative humidities (10% to 100%) and various activities of acid vapor are calculated using the Flood-Neumann-Döring-Reiss-Doyle theory of binary homogeneous necleation. The activities of acid vapor needed for nucleation are 25 to 300 times smaller for H2SO4+H2O than for HNO3+H2O. This is due to the much larger free energy of mixing in the liquid phase for H2SO4+H2O. Conversion from activities to actual pressures leads to condentrations of nitric acid which are much too high to be found under normal atmospheric conditions. On the other hand, the concentrations of sulfuric acid vapor needed to nucleate droplets in the H2SO4+H2O system are in the range 4(10−5) to 1.3(10−2) ppm, a concentration which can result from photo-oxidation of SO2 in the atmosphere. Calculations are made of the growth curves for H2SO4+H2O droplets (radius versus composition) at various relative humidities from the critical size radius up to a 1000 Å radius, corresponding to nuclei large enough to serve as condensation centers for heterogeneous nucleation. A generalized version of the Kelvin equation which includes the composition dependence of the surface tension for a binary mixture is derived and applied in calculating these growth curves. Sign errors in the second derivatives of the free energy in Doyle's paper are corrected. The limitations of the binary homogeneous nucleation theory at extremely low concentrations of one of the components are discussed and it is shown that this theory becomes inapplicable if the actual vapor pressure of one component is below 10−6 torr.
High resolution observation of microwave-optical double resonance in NO2
Authors: Solarz Richard , Levy Donald H. , Abe Koichi , Curl R. F.
Published: February 2004

A previously reported microwave-optical double resonance observed in the fluorescence of NO2 excited by the 4880 Å argon ion laser has been observed through a high resolution spectrograph. The common level in the double resonance is the 524 rotational level of a vibrational state of B2 symmetry of the 2B2 electronic state of NO2. The optical transition exciting this level originates from the 431 level of the ground vibrational state of the 2A1 ground electronic state of NO2. The most likely explanation of the double resonance is that the microwave transition is to the 523 level of another vibrational state of the 2B2 electronic state with A1 vibrational symmetry. This level structure could be produced by an inversion splitting if the molecule had unequal N–O bond lengths in its equilibrium geometry or by an accidental near coincidence between vibrational levels of a symmetrical molecule.
Model for spin-orbit interactions with inclusion of d electrons: Applications to photoelectron spectroscopy
Authors: Lee Ting Ho , Rabalais J. Wayne
Published: February 2004

A previously developed semiempirical model for estimating spin-orbit interactions in molecular ion states has been extended to include valence nd electrons as well as ns and np electrons. The model follows a perturbation approach with an effective spin-orbit interaction operator Hso and Mulliken-Wolfsberg-Helmholz molecular orbital wavefunctions. The He I photelectron spectra of the AsX3 and SbX3 (X=Cl, Br, I) series have been measured. Splittings observed in some of the ionization bands have been successfully interpreted as spin-orbit splittings using the proposed model. The results indicate that virtual nd orbitals are of minor importance in the spin-orbit interactions of AX3-type molecules.
Rotational relaxation of molecules in isotropic and anisotropic fluids
Authors: Cukier Robert I.
Published: February 2004

A theory of rotational relaxation in isotropic and anisotropic liquids is presented. The Debye rotational diffusion model is generalized so as to include reorientations of arbitrary angle with the use of a nonlocal in orientation master equation for the orientational conditional probability. For isotropic media, we have previously demonstrated that spectral line shapes (Fourier transforms of time correlation functions) appropriate to, for example, Raman and ir line broadening spectroscopy, are always superpositions of Lorentzian lines. We present here an algebraic formulation which gives the linewidths of the Lorentzian lines in terms of the transition probability describing the reorientational motion. Several models and general trends for these linewidths are discussed in order to facilitate the comparison of experimental results and this theory. For anisotropic media, such as liquid crystals or small molecules ordered by liquid crystals, a nonlocal reorientational mechanism leads to a continuous spectrum and singular eigenfunctions in the eigenvalue-eigenvector decomposition of the conditional probability. This leads to formal line shape expressions which, while certainly non-Lorentzian, are difficult to evaluate. For a special model transition probability and for the long times relevant to line shape measurements, explicit asymptotic expressions for the time correlation functions can be obtained which also lead to non-Lorentzian line shapes.
Oxygen diffusion in a vapor deposited solid argon matrix at 33°K
Authors: Meyer B. , Metzger J. L.
Published: February 2004

Diffusion of molecular oxygen in a vapor deposited argon matrix at 33°K was investigated by monitoring, as a function of time, the phosphorescence of a perdeuteronaphthalene-doped argon matrix coated with an oxygen film. In pure argon, C10D8 emits bright phosphorescence with a lifetime of 12.0 sec. In pure oxygen, emission is totally quenched. In our experiments, oxygen from the surface film migrates into the matrix and quenches naphthalene impurity emission, thus decreasing the emission intensity. Diffusion kinetics are well reproducible; thus, matrices seem to have well-defined, reproducible structure. At 33°K, in a 10−3 cm thick matrix containing 1 mole% naphthalene, a 50% drop in triplet intensity is observed after 35 min. The perdeutero naphthalene decay time remains unchanged at 12.0 sec and the triplet decay remains exponential at all stages of the experiment. An analysis assuming simultaneous diffusion of oxygen and argon shows that the diffusion coefficient D is a function of L, the total thickness of the sample, of γ, the oxygen to matrix ratio, and of K, the quenching constant. From the observed parameters, we compute the diffusion constant: D = 10−12×10±2 cm2 sec−1. Diffusion in a matrix is about 1011 times faster than what data for argon single crystals indicates, but it is slow enough to be discriminated against in a normal matrix experiment.
Energetics of charged transfer in collisions of Ar+ ions with H2, D2, and CO2
Authors: Rayborn G. H. , Bailey T. L.
Published: February 2004

The energetics of charge transfer in collisions of low-energy Ar+ ions with H2, D2, and CO2 molecules have been investigated in ion beam-gas scattering experiments, which utilize a special feature of collision kinematics. The kinetic energy (KE) distributions of product ions which emerge from their collision sites at 90° with respect to the projectile beam direction were determined by electrostatic analysis, using a parallel-plate analyzer. At this angle, exothermic transfer channels dominate the observed distributions, and the coupling between projectile and product ion kinetic energies is minimized. Information concerning the contributing transfer channels, and therefore concerning the internal states of the product H2+, D2+, and CO2+ ions, has been deduced from the measured KE distributions. For the Ar+–H2, D2 systems, measurements were carried out at a number of projectile ion KE's, over the range 20<E1<150 eV. For the Ar+–CO2 system, runs were made at E1≃6 eV and E1 =20.1 eV. In addition, a single distribution for the Ne+–CO2 system was obtained, at E1=50.1 eV. The distributions for Ar+–D2 and Ar+–H2 at the lower collision energies revealed a surprising isotope effect, in that the former showed contributions of fairly energetic ions, whereas the latter consisted solely of ions with near-thermal energies. The Ar+–CO2 data at E1=6 eV gave evidence of CO2+ ions with energies 0≤E3≤∼1 eV, from which it was inferred that transfer proceeds via a number of exothermic transfer channels, having internal energy changes Q over the entire accessible range 0<Q≤2.16 eV. The effect of the thermal motions of the target particles (Doppler broadening) has been discussed in some detail. This effect is particularly important in these studies, since the kinetic energies of the product ions were small (for the most part, less than a few tenths of an electron volt).
A method to estimate the critical probability in bond percolation problems
Authors: Vuorio M.
Published: February 2004

A method based on the symmetry of bonding directions i = 1, 2, …, n is introduced to estimate the critical probability pc in bond percolation problems. The leading terms in the critical equation Q(p1, p2,…, pi,…, pn) = 1 are derived for some two- and three-dimensional lattices and consequently pc can be evaluated by setting all pi's equal. In two dimensions the three exact, known values of pc are regained in addition to an estimate for the kagome lattice pc≃0.535. In three dimensions a one-parameter fitting to diamond and bcc lattices gives for simple cubic lattice the estimate pc ≃ 0.258 in agreement with its lower limit 1/4.
Raman scattering study of the effect of pressure and temperature on the order-disorder phase transition in ammonium chloride
Authors: Wang C. H. , Wright R. B.
Published: February 2004

The temperature and pressure dependence of the lattice and internal modes in NH4Cl have been measured. By keeping the temperature fixed, it has been possible to induce the phase transition by changing the external pressure. From the frequency and intensity measurements of several lattice modes as a function of temperature at various pressures, it was found that the character of the order-disorder phase transition in NH4Cl varies significantly at different points along the phase transition line in the P-T plane. An analysis of the Grüneisen parameter for the various lattice modes was presented. The isobaric temperature dependent frequencies of the lattice modes was discussed in terms of the pure-volume contributions. From the pure-temperature contribution, it was found that anharmonic interaction potential is the main mechanism responsible for the temperature dependence of the anomalous 93 cm−1 mode in NH4Cl.
On the formulation of microscopic rate equations
Authors: Robertson David , Frank F. C.
Published: February 2004

It is advocated that in the formulation of kinetic equations governing any complex process the terms representing opposite unit processes, whose rates must be equal at equilibrium in accordance with the principle of detailed balance should always be grouped in pairs. In approximate treatments such pairs must be struck out together. This makes for avoidance of thermodynamic error and the appreciation of terms which might otherwise be overlooked, and can give assistance in estimating the rates of particular unit processes. Incidentally it makes it easier to perceive the physical meaning of terms in the equations. The microscopic rate equations governing the populations of various sizes of adsorbed aggregates during heterogeneous nucleation and growth are considered as an example.
Even-tempered atomic orbitals. VI. Optimal orbital exponents and optimal contractions of Gaussian primitives for hydrogen, carbon, and oxygen in molecules
Authors: Bardo Richard D. , Ruedenberg Klaus
Published: February 2004

Bases of even-tempered Gaussian primitives are optimized with respect to all parameters in the molecules hydrogen, methane, acetylene, ethylene, ethane, methyl acetylene, water, carbon monoxide, carbon dioxide, formaldehyde, and carbon suboxide. A method is introduced for constructing contracted atomic orbitals from the optimized molecular orbitals of these molecules. Transferability of the optimal even-tempered primitive and contracted bases between molecules is shown. Certain minimization schemes for the even-tempered basis are discussed which greatly reduce the amount of work involved in molecular optimizations.
Even-tempered atomic orbitals. VII. Theoretical equilibrium geometries and reaction energies for carbon suboxide and other molecules containing carbon, oxygen, and hydrogen
Authors: Bardo Richard D. , Ruedenberg Klaus
Published: February 2004

The quality of molecule-optimized even-tempered Gaussian bases is ascertained from calculations of theoretical equilibrium conformations and of reaction energies for the molecules hydrogen, methane, acetylene, ethylene, ethane, methyl acetylene, water, carbon monoxide, carbon dioxide, and formaldehyde. The equilibrium geometry of C3O2 is determined and compared to known results.
Shear viscosity of nitroethane-3-methylpentane in the critical region
Authors: Tsai B. C. , McIntyre D.
Published: February 2004

The viscosities of nitroethane-3-methylpentane mixtures were measured in an Ostwald viscometer over the entire composition range, and over a temperature range of ΔT(= T - Tc) from 11.673 °C to 0.003 °C. The experimental data of this work show quantitatively that the best fit of the viscosity data is to the equation η = (A/φ) (ε−φ − 1) + Bε + C, where A/φ = 0.478 ± 0.04, B = − (1.09 ± 0.05), C = 0.335 ± 0.01, and φ = 0.03 ± 0.01. The value of φ is within experimental error positive and not zero. It clearly indicates that at a temperature very close to the critical temperature the anomalous viscosity shows a very weak power law divergence and is not a cusp nor a logarithmic divergence. The excess shear viscosity is approximately related to the composition by a Gaussian distribution in composition centered about the critical composition, X2c: Δη = f(T) exp {− (1/2)[10(X2 − X2c)]2}.
Hindered rotation of the borohydride ion in potassium and sodium borohydride
Authors: Smith David
Published: February 2004

The hindered rotational energy levels of the borohydride ion in the high temperature phases of NaBH4 and KBH4 have been computed. The Hamiltonian which describes the motion of the borohydride ion in NaBH4 is invariant under the direct product group Ō × O, while the Hamiltonian for the borohydride ion in KBH4 is invariant under the direct product group T̄ × T. The rotational heat capacity of the borohydride ion computed from the energy levels is compared with the rotational heat capacity derived from the observed heat capacity for both NaBH4 and KBH4. The torsional frequency of the borohydride ion in NaBH4 is found to be 240 cm−1 and in KBH4 244 cm−1.
Corrected Enskog theory and the transport coefficients of liquids
Authors: Dymond J. H.
Published: February 2004

Corrections to the approximate hard sphere dense fluid transport theory of Enskog, determined by the method of molecular dynamics, have been incorporated in analytical expressions for the exact coefficients of self-diffusion, viscosity, and thermal conductivity in hard sphere systems in terms of the molar volume at densities greater than one-half the close packed density. Application of these equations to recent experimental transport coefficient data for liquid carbon tetrachloride shows that these data can be satisfactorily interpreted on the basis of this simple model with temperature- and pressure-dependent molecular diameters. Self-diffusion and viscosity data for liquid methane are also adequately accounted for in terms of the hard sphere theory, but for argon the calculated self-diffusion coefficients are somewhat greater than recent experimental values.
Self-consistent extended Hückel theory. II
Authors: Kalman Barry L.
Published: February 2004

Using self-consistent extended Hückel theory and the exsin approximation, equilibrium bond lengths are calculated for the C–H, N–H, O–H, C–C, C–N, C–O, C=C, C=O, C≡C, and C≡N bonds. The calculated single bond lengths are generally longer than experimental values, but the calculated multiple bond lengths are in good agreement with experimental values. The results for the equilibrium bond lengths show that the exsin approximation is superior to any previously used off diagonal approximation. Calculations on the two butanes and the two propanols indicate that the analysis of the results of an earlier article are correct and that self-consistent extended Hückel theory coupled with the exsin approximation is as good CNDO for comparing stabilities of various isomers.
Effects of intermacromolecular interactions on diffusion. I. Two-component solutions
Authors: Phillies George D. J.
Published: February 2004

The effect on the diffusion coefficient of nondissipative interactions between diffusing macromolecules is evaluated for two-component solvent-macromolecule solutions. For linear concentration gradients, the generalized Stokes-Einstein relation is obtained from purely microscopic arguments. Application of these results to a model solution of hard spheres demonstrates new effects of conformational change on the mutual diffusion coefficient. For spatially sinusoidal concentration gradients, such as those observed by quasielastic light scattering spectroscopy, the mutual diffusion coefficient is shown to have an intrisic dependence on the wavelength of the gradient. Consideration of a dilute solution of charged macromolecules illustrates the wavelength dependence of the mutual diffusion coefficient.
Magnetic interactions in iron(III) bis(dithiocarbamates)
Authors: Chapps G. E. , McCann S. W. , Wickman H. H. , Sherwood R. C.
Published: February 2004

Further magnetic and structural studies have been made of the bis(N,N-diethyldithiocarbamato) iron(III)X complexes (X = Cl−, Br−, I−, SCN−). The I− homolog is antiferromagnetic (TN = 1.9 °K), while the SCN− derivative is a simple paramagnet (to 1.4 °K). The crystal structure of the paramagnetic bromo derivative was found to be nearly identical to that of the ferromagnetic chloro homolog. The different collective magnetic properties of the chloro and bromo homologs arise from combined exchange and uniaxial crystal field interactions. Using known crystal field parameters and a molecular field description of magnetic interactions, an effective intermolecular exchange constant of 0.12 ± 0.03 °K is derived. Exchange broadened paramagnetic resonance spectra are shown to correlate well with the collective magnetic behavior of the complexes. Solution proton NMR data are interpreted in terms of d-electron delocalization to the dithiocarbamate ligand π-type orbital system.
Electron spin resonance studies of irradiated succinamic acid. II. Monoclinic single crystals
Authors: Straw David C. , Moulton Grace C.
Published: February 2004

The radiation products and decay mechanisms have been studied in single crystals of monoclinic succinamic acid using electron spin resonance spectroscopy over the temperature range from 77° through 300°K. At 77°K the primary radical observed is the anion radical COOHCH2CH2(ĊONH2)− where the unpaired electron is delocalized throughout the entire amide group. This radical decays at about 180°K to a nonparamagnetic species. The minor product at 77°K is the cation product and decays at about 157°K by intermolecular hydrogen abstraction to two radicals which are stable at room temperature, COOHĊHCH2CONH2, and COOHCH2ĊHCONH2. The spectra observed at 300°K are identical in crystals irradiated at 77°K and warmed to 300°K. The differences in the radiation products and mechanisms for the monoclinic and triclinic forms are discussed.