bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical Spectrum of Triply Ionized Erbium in Calcium Tungstate
Authors: Wortman D. E.
Published: February 2004

The energy levels of the I4 ground term of Er3+ in single crystals of CaWO4 were established by absorption and fluorescence spectra measurements. The measurements were made using crystals at temperatures of 2, 20, and 85°K. The energy level scheme allows an interpretation of the 1.612-μ four-level CaWO4:Er3+ laser transition and shows the terminal energy level of this transition to be 318 cm−1 above the ground state rather than 375 cm−1 as reported by Kiss and Duncan. An effective Hamiltonian of the form suggested by Karayianis was diagonalized in a basis of Russell–Saunders wavefunctions to obtain the calculated energy levels and wavefunctions for the entire ground term of Er3+. The calculation takes into account the complete J mixing of the states within the ground term and is equivalent to determining the effects of the spin–orbit interaction to better than second order. An rms deviation of 18 cm−1 was found as the best agreement between the calculated and experimental energy levels using the Hamiltonian: H = λ1(L·S) + λ2(L·S)2 + λ3(L·S)3 + ΣlmBlm†Clm. The empirically determined parameters are (in cm−1) λ1 = − 613, λ2 = − 19.3, λ3 = − 0.499, B20 = 404, B40 = − 685, B60 = 12.4, B44 = 728, ReB64 = 452, and ImB64 = 164. Using wavefunctions determined with these parameters, the g factors were calculated for the states of the ground term. The calculated and measured g factors for the two lower energy states are in good agreement where the calculated values are g‖ (ground state) = 1.265, g⊥ (ground state) = 8.487, g‖* (first excited state) = 3.22, and g⊥* (first excited state) = 7.06, and the measured values in the same order are g‖ = 1.247, g⊥ = 8.400, g‖* = 3.42, and g⊥* = 6.98. A Γ5,6 ground state wavefunction is compatible with the results obtained here, whereas a Γ7,8 ground state wavefunction is not. Previous studies had not established the ground state wavefunction uniquely.
Rotational Moment, Rotational g Factor, Electronic Orbital g Factor, and Anisotropy of the Magnetic Susceptibility of Δ1 O2
Authors: Miller Terry A.
Published: February 2004

The electron paramagnetic resonance spectrum of the Δ1 state of O2 has been investigated in both the J = 2 and J = 3 rotational levels. The line positions in the J = 2 state have been determined to a higher accuracy than previously reported and the J = 3 line positions have been measured for the first time. The combined spectra are analyzed to obtain the rotational constant, rotational g value, electronic orbital g value, and the anisotropy of the magnetic susceptibility of Δ1 O2. From the anisotropy of the susceptibility the electronic second and quadrupole moments are derived. The experimentally determined parameters are B0′ = 1.41808 ± 0.00020 cm−1, gr = − 1.234 ± 0.025 × 10−4, gL = 0.999866 ± 0.000010, χAd = − 4.68 ± 0.94 × 10−29erg/molecule, where the symbols are defined in the text. The quoted uncertainties (except for gL) represent two standard errors and correspond to about a 95% confidence limit inclusive of parameter correlation effects.
On the Elastic Theory of Uniaxial Liquid Crystals
Authors: Nehring Jürgen , Saupe Alfred
Published: February 2004

Simple derivations of the elastic theory of liquid crystals with uniaxial molecular order are given using a molecular Cauchy-like approach and a more general phenomenological approach. In a second-order approximation, both methods lead to the same expression for the elastic energy density, except for the existence of one “Cauchy relation” between the elastic constants in the molecular case. Our phenomenological equation contains nine elastic constants which is two more than in Frank's earlier derivation. Our molecular equation is in agreement with Oseen's original expression. Differences between the molecular and the phenomenological approach and the justification of neglecting terms which do not contribute to the Euler–Lagrange differential equation are discussed. Higher than second-order terms are given for cholesteric liquids. In addition, the consequence of curvature-induced electric polarization for the equilibrium structure of liquid crystals is discussed.
Higher-Order Finite Difference Solutions of the Schrödinger Equation for the Helium Atom
Authors: Barraclough C. G. , Mooney J. R.
Published: February 2004

Higher-order finite difference solutions of the Schrödinger equation for the helium atom have been obtained. For the S-limit equation the ground- and first-excited-state energy values were found. There was a substantial reduction in the difference error in comparison with the treatment of Winter, Diestler, and McKoy (1968). For the complete (nonrelativistic) Schrödinger equation for He finite difference expressions of error O(h6) gave the ground-state energy to five significant figures (− 2.9038 hartree). This problem seems to be near the limit of practical solution by the finite difference method.
Computer Simulation of the ESR Spectra of the Naphthalene, Anthracene, and Perylene Radical Cations in a Polycrystalline Medium
Authors: Owen G. S. , Vincow G.
Published: February 2004

Computer simulation of ESR spectra in polycrystalline environments is extended to the case of free radicals in which the unpaired spin is extensively delocalized. An approximate model is proposed for the anisotropic effects (g tensor, dipolar hyperfine tensor, component shape and width). This model is tested on the spectra of anthracene and perylene radical cations in boric-acid glass [G. Vincow and P. M. Johnson, J. Chem. Phys. 39, 1143 (1963)]. The spectral structure is reproduced by the calculations. A principal application of this simulation procedure is the extraction of values of the Fermi contact hyperfine splittings in cases for which these have not been measured. As an illustration, the powder spectrum of the naphthalene cation radical is considered, yielding | a1H | = 5.4 ± 0.3 G and | a2H | = 1.62 ± 0.3 G. In addition calculations are performed which indicate the sensitivity of the simulated spectra to variations in values of the parameters of the model.
Equilibrium Cosine Law and Scattering Symmetry at the Gas–Surface Interface
Authors: Wenaas E. P.
Published: February 2004

Earlier derivations of the equilibrium cosine scattering law at the gas–surface interface based on the second law of thermodynamics and on the principle of detailed balance are shown to be inconclusive. Presented is a derivation involving time reversal invariance, along with an assumption of a canonical distribution of states in the solid, which results in a reciprocity relationship for the surface scattering cross section that yields the cosine law at equilibrium. A symmetry property for the scattered particle flux results from the reciprocity relationship, and molecular beam data are shown to exhibit the indicated symmetry. An application of this previously unrecognized symmetry permits the prediction of the scattered particle flux distribution for an arbitrary angle of incidence from experimental data reported for a limited number of incident angles.
Direct Observation of the Thermal Dissociation of Molecular Nitrogen
Authors: Moore George E. , Hansen Howard H.
Published: February 2004

Published experiments on the thermal dissociation of N2 generally report a failure to detect it. These negative results were helpful in deciding between the two possible values 9.765 and 7.385 eV for the dissociation energy, proposed by band spectroscopists, because the experiments should have detected dissociation if the lower energy were correct. Our experiments performed with a mass spectrometer employed a tungsten ribbon as a catalyst. This was mounted adjacent to the ionization chamber. The observed rate of dissociation, in the range 2450–2800°K, was only consistent with the larger dissociation energy. As in reactions previously studied by this technique, the rate-limiting step appears to occur inside the catalyst, rather than on its surface. However, the high temperatures required for measurable dissociation prevented a detailed examination, so that one cannot be as confident of a volume process as for past tests. Our measurements have relevance for processes proposed by others which had not previously been re-examined.
Applications of the Quantum Mechanical Green's Function Technique to Unimolecular Dissociation Reactions. V
Authors: Paul R. , Coombe D. A.
Published: February 2004

A theory for unimolecular dissociation reactions using the quantum mechanical Green's function technique is presented. An unusual pressure dependence is shown by the introduction of a rigorously derived spectral function.
Test of Combination Rules for Prediction of Interaction Second Virial Coefficients
Authors: Lin H.-M. , Robinson R. L.
Published: February 2004

The recently proposed argon pair potential of Dymond and Alder is shown to provide a satisfactory two-parameter corresponding states description of the second virial coefficients of the rare gases. The potential is used as a basis for testing various combination rules for predicting interaction second virial coefficients for rare-gas pairs. For helium binary systems, none of the rules tested produces uniformly acceptable results. Only the expression εij = 2εiiεjj / (εii + εjj) appears satisfactory for all pairs not containing helium.
Rydberg Terms of Acetylene
Authors: Greene Elwood W. , Barnard Jonathan , Duncan A. B. F.
Published: February 2004

It is assumed that two observed Rydberg series in acetylene correspond to (ns) and (nd) orbital excitation. Calculations in a one-electron approximation support the assumption in both cases. The core is assumed to be frozen and linear and interatomic distances unchanged from normal state values in the Rydberg states and in the lowest state of the ion. The terms agree well with experimental values. The Rydberg functions are obtained as linear combinations of Slater functions and energies are stable to variation of both linear and nonlinear parameters.
Far-Infrared Spectra of Ethane, Ethylene, and Acetylene
Authors: Schwartz Y. A. , Ron A. , Kimel S.
Published: February 2004

The far-infrared spectra of crystalline C2H6, C2D6, C2H4, C2D4, C2H2, and C2D2 have been recorded at various temperatures between 25 and 140°K. Each compound showed two absorption bands which were shown to be due to translational lattice modes. Upon heating, these bands broadened and decreased in intensity; they were also displaced toward lower frequencies by about 0.1 cm−1/°K. For ethylene an analysis was carried out based on the “diatomic potential.” Here each molecule was assumed to consist of a pair of centers separated by an effective distance d, each center interacting, through a Lennard-Jones-type potential, with the centers in all neighboring molecules. Frequencies and thermal frequency shifts were calculated as a function of d, and good agreement was attained with the observed values for ethylene, with d = 1.04 Å.
17O NMR Studies of Uranium Oxides
Authors: Eastman Michael P. , Hecht Harry G. , Lewis W. Burton
Published: February 2004

The 17O NMR of 17O-enriched UO2, BiUO4, and KUO3 has been observed. A paramagnetic NMR shift was observed for UO2 at 192.5, 299.5, and 405.2°K. The average isotropic coupling constant, As, calculated from these shifts is 2.84 × 10−5 cm−1. In this calculation of As the magnitude of 〈sz〉 on the uranium atom in UO2 is determined assuming a 3H4 ground state for the U4+. Paramagnetic shifts were also observed for BiUO4 and KUO3 at 299.5°K. The value of As for BiUO4 was determined to be 3.79 × 10−4 cm−1. This value was calculated after assuming a 2F5/2 ground state for U5+. The same assumption in the case of KUO3 yielded a value of 1.08 × 10−3 cm−1 for As. The validity of the assumption of pure Russell–Saunders ground states for these compounds is discussed. For KUO3 the previously published spin–orbit coupling constant and crystal field terms are used to calculate a more reliable value of 〈Sz〉 on the central uranium atom. These calculations lead to a value of 7.01 × 10−4 cm−1 for As. The important conclusions of this study are that the fractional s character in these compounds is small and that there is a negative spin density on the 17O nuclei. Apparently the major contribution to the hyperfine interaction arises from the involvement of excited metal orbitals and/or from exchange polarization of core electrons. The NMR spectra of KUO3 and BiUO4 show the effect of anisotropic hyperfine interactions. The anisotropic interactions in BiUO4 are shown to be predominantly π in character. An analysis of the KUO3 spectrum indicates that anisotropic interactions are predominantly π in character and that Aπ ∼ − 6 × 10−5cm−1. The linewidth of the isotropic UO2 resonance is interpreted in terms of the Moriya spin-exchange mechanism and the value of ωe is found to be 1.2 × 10+13 sec−1.
Inelastic Electron Scattering from Formaldehyde
Authors: Weiss M. J. , Kuyatt C. E. , Mielczarek S.
Published: February 2004

The electron scattering spectrum of H2CO has been determined in the energy loss range between 0 and 16.0 eV. Three Rydberg series in the region 7–11 eV can be identified with the s, p, and d series reported in the literature by ultraviolet absorption studies. Oscillator strengths are determined for some of the Rydberg states and comparison is made with recent ultraviolet absorption work employing photoelectric methods of detection. A serious disagreement exists between the f values obtained by the two methods for the 3sa1 Rydberg. Another Rydberg series, probably converging to the third ionization potential of H2CO, is observed in the electron scattering spectrum in the region 12.4–14.0-eV energy loss. Erratic behavior of the quantum defects of the first Rydberg series as well as failure to detect the π → π* transition in H2CO is discussed in the light of recent theories involving valence states which can seriously perturb members of a Rydberg series.
Internal Conversion in Benzene, Benzene-d6, and Sulfur Dioxide
Authors: Smith Wm. Hayden
Published: February 2004

Lifetime studies of benzene and benzene-d6 at pressures below 1 μHg, using an electron beam phase shift method, yield a lifetime of 73.5 ± 8.0 nsec for the measured levels of the 1B̃2u state of benzene and lifetimes varying from 89 ± 9 to 113 ± 11 nsec for essentially the same levels in benzene-d6. From the measured absorption oscillator strength, the nonradiative processes depopulating the 1B̃2u state must proceed at a rate of 1.2 ± 0.14 × 107 sec−1. These results are compared with previous theory and experimental data. Radiative lifetime measurements for SO2 have been extended from those given previously and have been reanalyzed with a model assuming spectral overlap of two different SO2 upper states. This analysis is shown to be consistent with certain previous discussions of the emission spectrum and, in particular, with those of Douglas3 concerning the anomalous lengthening of the 1B̃1-state radiative lifetime.
Measurement of the Polarizabilities and Field Evaporation Rates of Individual Tungsten Atoms
Authors: Tsong Tien Tzou
Published: February 2004

The relative field evaporation rates of tungsten kink site atoms at (110) plane edges and the absolute field evaporation rates of individual tungsten adatoms on tungsten (110) planes have been measured covering nine orders of magnitude. From the experimental data, the effective polarizabilities of the tungsten kink site atoms and the adatoms are found to be 4.6 ± 0.6 and 6.8 ± 1.0 Å3, respectively. A theoretical consideration is given to explain why the effective polarizability of metal surface atoms depends on the atom-to-surface mirror plane distance, and therefore the atomic sites. The calculation also reveals a first power field dependent energy level shift, which is dependent upon the atom-to-surface plane distance. It is further shown that the classical image potential no longer holds at a distance smaller than 1 Å from the metal surface.
Exciton Theory of the Electronic States of Dye–Polymer Complexes. II. Stationary States of Helical Complexes
Authors: Philpott Michael R.
Published: February 2004

The stationary states are found for a system composed of one or two dye molecules attached to an infinite single stranded helical polymer. It is assumed that each dye and monomer has a stack of separable excited vibronic levels belonging to a fixed electronic state.
Collision-Induced Vibrational Excitation and Dissociation of Hydrogen with Alkali Atoms and Ions from 2 to 50 eV
Authors: Dittner Peter F. , Datz Sheldon
Published: February 2004

Inelastic energy losses for Na0, Na+, K0, and K+ backscattered from H2 and D2 have been measured. At center-of-mass energies below15 ∼ eV for Na and ∼ 20 eV for K, the collisions yield vibrational excitations which are compared with the one-dimensional exact classical calculations of Secrest. The vibrational excitation in the Na+–H2 and Na0–H2 system is in excellent agreement with three-dimensional classical calculations of Cheng and Wolfsberg. Above these energies the molecules are dissociated but the energy loss distribution of the alkali projectile remains sharp and in the case of Na–H approaches the maximum loss possible at 50 eV.
Single-Center Calculations on the Electronically Excited States of Equilateral H3+ Ion
Authors: Kawaoka Kenji , Borkman Raymond F.
Published: February 2004

A theoretical investigation of the excited electronic states of the equilateral triangular H3+ ion is reported. Ab initio calculations were performed for the lowest energy states of symmetries A1′3,A2″1,A2″3,E′1, and E′3, using the single-center expansion configuration-interaction method. For each state we have obtained the potential-energy curve in D3h symmetry. The calculated state energies are expected to be in error by at most 0.01 hartree (6 kcal/mole). Two of the excited states E′1 and E′3 were found to be purely repulsive with respect to the totally symmetric nuclear coordinate, while three excited states A2″1,A2″3, and A1′3 showed minima with respect to the totally symmetric nuclear coordinate. However, arguments based on group-theoretical correlation between our calculated D3h state energies and the energies of possible dissociation products suggest that none of the excited states considered achieves an absolute energy minimum in D3h symmetry. For the allowed electric dipole transitions A2″1 ← A1'1 and E'1 ← A1'1 we have calculated the vertical (Franck–Condon) transition energies, oscillator strengths, and polarizations. The nature of the excited-state energy curves, at the ground-state equilibrium geometry, indicates that in every case only continuum absorption from the A1'1 ground state would be observed experimentally.
Photoionization of Methane: Ionization Potential and Proton Affinity of CH4
Authors: Chupka W. A. , Berkowitz J.
Published: February 2004

The relative photoionization cross section of methane has been measured at room temperature and at liquid-nitrogen temperature. The data show that the ionization potential of methane is 12.615 ± 0.010 eV or lower. This result is discussed and compared with those obtained by photoelectron spectroscopy. The photoionization-efficiency curve of CH5+ was also measured and found to have the same threshold as that of CH4+. This observation sets a lower limit on the proton affinity of methane, namely PA(CH4) ≥ 5.46 eV. Consideration of other data supports the value PA(CH4) = 5.50−0.05+0.20 eV.
Qualitative Aspects of the Quantum Mechanical Second Virial Coefficient
Authors: Bruch Ludwig W.
Published: February 2004

Upper and lower bounds on the quantum mechanical direct second virial coefficient are derived from theorems of Golden, of Thompson, and of Feynman and Hibbs. These bounds severely limit the magnitude of quantum effects for some proposed helium potential models. The Frisch and Helfand theorem on maxima in the second virial coefficient is discussed.
Spin-Free Computation of Matrix Elements. I. Group-Theoretical Computation of Pauling Numbers
Authors: Klein D. J. , Junker B. R.
Published: February 2004

Spin-free wavefunctions may be symmetry adapted to a given irreducible representation of the symmetric group SN by a number of different operators. When matrix elements over these symmetry-adapted wavefunctions are computed, one obtains terms which are group theoretical in nature and terms which are dynamical. In this paper we present formulas for computing the group-theoretical coefficients for four types of projectors–spin-free equivalent of the Löwdin projection operator, ξY; structure projector (spin-free equivalent of valence-bond-type functions), κY; sequence-adapted spin-free equivalent of the Löwdin projection operator, ξYG; and sequence-adapted structure projector, κYG. We also give a formula relating the Pauling numbers for the different symmetry projectors to a reference projector.
Effects of Surface Crossing in Chemical Reactions: The H3+ System
Authors: Preston Richard K. , Tully John C.
Published: February 2004

Approximate potential-energy surfaces for the two lowest singlet states of H3+ are calculated using the diatomics-in-molecules approach. The nonadiabatic terms which couple these surfaces can be directly computed in this approximation. From the magnitudes of these coupling terms it is apparent that, for excitation energies below about 10 eV, nonadiabatic transitions must be confined almost entirely to a region localized at the avoided crossing of the two surfaces. This fact suggests the following simplified picture of the dynamics of the H++H2 reaction: As the H+ and H2 approach, they remain on the lower potential surface (there is no initial electron jump). They continue to follow adiabatically the lower surface in the close-collision region, so the probability of a nonadiabatic transition does not appear to be related to the lifetime of the collision complex. It is while the products are receding that electronic transitions become important. Consequences of this model on the threshold for formation of H2+ and on the partition of vibrational energy in the products are discussed, and a comparison with recent experiments of Krenos and Wolfgang is included.
Vibrational Spectra of IOF5, OsOF5, and ReOF5
Authors: Holloway J. H. , Selig H. , Claassen Howard H.
Published: February 2004

Raman spectra of IOF5, OsOF5, and ReOF5, and the infrared spectra of OsOF5 and ReOF5 are presented, all for the gaseous state. Complete assignments of fundamental frequencies are made, and these confirm the expected C4ν symmetry. Fundamental frequencies in cm−1 in the order, 4a1, 2b1, b2, and 4e, are: for IOF5, 927.0, 680.4, 640.2, 362.9, 647, 307, ∼  330, 710.3, 372.2, 343, and 204.8; for OsOF5, 962.6, 716.4, 644, 280.5, 644, 210, 332, 700.6, 263, 367, and 164; and for ReOF5, 989.8, 738.6, 643, 309, 652, 234, 334, 713.0, 260, 365, and 125 cm−1.
Geminal Product Wavefunctions: A General Formalism
Authors: Nicely Vincent A. , Harrison James F.
Published: February 2004

We consider the construction of a wavefunction composed of Nβ singlet coupled geminals and Nα − Nβ α spin orbitals where Nα + Nβ is the total number of electrons. An orthonormal basis {χ} is introduced and each geminal and orbital is expanded in this basis. The wavefunction is expressed as a linear combination of determinants over the {χ} basis and the energy expression is obtained. It is suggested that the geminal and orbital expansion coefficients be obtained using a numerical minimization technique. As an example we construct an APG function for LiH and BH (using only σ orbitals) and compare the energies obtained with this model to the corresponding MO–SCF, APSG, and CI results over the same (σ) basis. We find that the APG function recovers 99.9% and 98.0% of the energy difference between the CI and MO–SCF, while our APSG function recovers 96.6% and 80% for these two molecules. Since most pair function models of electronic structure may be viewed as special cases of the parent APG model, this approach includes these models and in addition allows one to construct wavefunctions within a unified formalism in which different pairs in a given molecule may be treated at different levels of accuracy.
Application of Third-Order Constitutive Relations to Poiseuille Flow of a Rarefied Gas
Authors: Cha C. Y. , McCoy B. J.
Published: February 2004

The third-order constitutive relation for the shear stress tensor is applied to Poiseuille flow of rarefied monatomic gases in three geometries: parallel plates, cylindrical tube, and cylindrical annulus. The expressions for subsonic flow rates and velocity profiles in the transition regime are derived on the basis of reasonable boundary conditions for the three geometries. The flow rate shows a minimum as a function of the Kundsen number. One numerical constant which fixes this curve could not be determined theoretically, but experimental data and other independent theories indicate that this constant has the same value for the three geometries.
Far-Infrared Magnetic Resonance in Fe(III) and Mn(III) Porphyrins, Myoglobin, Hemoglobin, Ferrichrome A, and Fe(III) Dithiocarbamates
Authors: Brackett G. C. , Richards P. L. , Caughey W. S.
Published: February 2004

Far-infrared spectroscopic techniques are used to study the magnetic resonance of Fe(III) and Mn(III) ions in molecular sites with large axial and rhombic ligand fields. Measurements of transmission spectra over the range 3–100 cm−1 are discussed for a group of polycrystalline compounds, including several biological complexes, at temperatures between 1.3 and 50°K and in applied magnetic fields up to 50 kOe. The spectra show magnetic resonance absorptions which are consistent with a number of cases of the spin-Hamiltonian formulation, and the spin-Hamiltonian parameters (D, E ≳ 1 cm−1) are directly obtained from the spectra. The observation of resonances due to high-spin Mn(III) and to the ferromagnetic resonance of ((C2H5)2NCS2)2 Fe(III)Cl is reported. These measurements show that present far-infrared techniques offer a direct method for the investigation of the effects of large ligand fields on paramagnetic ions in molecules.
Isotope Rules for the Harmonic Vibrational Frequencies of Isotopic Molecules: A Generalization of Mayants' Method
Authors: Strey G. , Cederbaum L. , Engelke K.
Published: February 2004

New isotope rules are derived by a generalization of Mayants' method. To obtain them one has to solve a set of linear homogeneous equations, the coefficients of which depend on the atomic masses.
Effect of Concentration and Intermolecular Forces on the Sedimentation of Polystyrene Spheres
Authors: Goldstein Byron , Zimm Bruno H.
Published: February 2004

At low concentration, the sedimentation coefficient s can be related to the sedimentation coefficient at zero concentration s0 through a power series expansion in the volume fraction Φ, i.e., s = s0(1 + KΦ···). We discuss the calculation of the constant K for sedimenting charged spheres. The spheres interact hydrodynamically as well as through a potential consisting of a hard-core repulsion, a screened Coulomb repulsion, and a London–van der Waals attraction. To calculate K one must know the value of the electrostatic potential in the vicinity of the surface of the sedimenting sphere ψδ, and the Hamaker constant, the constant which measures the strength of the London–van der Waals attraction. It is shown that knowledge of any two of the three quantities K, ψδ, and the Hamaker constant allows one to find the third. It is also shown that if both ψδ and the Hamaker constant are unknown the experimental determination of K can be used to obtain upper and lower bounds on the Hamaker constant. Using Cheng and Schachman's experimental value of K for polystyrene latex spheres, the following bounds for the Hamaker constant for polystyrene in aqueous solution are found: 3–8 × 10−14 erg. These bounds are in good agreement with previous experimental determinations.
Microwave Spectrum of Acetic Acid, CH3COOH and CD3COOH
Authors: Krisher Lawrence C. , Saegebarth Ellen
Published: February 2004

The microwave spectra of two isotopic species of acetic acid, CH3COOH and CD3COOH, have been re-examined. Using the principal axis method and a computer program extended to include terms through n = 6 in the perturbation series and denominator corrections, 30 new E-type transitions have been identified. For CH3COOH, an excellent fit of the observed A–E splittings is obtained using the parameters Iα = 3.216 ± 0.002 amu·Å2, θ = 4°30′ ± 15′ for the angle between the methyl group axis and the a principal axis, and s = 13.232 ± 0.002. Assigned splittings are very large (up to 3600 MHz), and the calculated spectrum is sensitive to all three parameters. The value for the barrier to internal rotation of the methyl group is V3 = 480.8 ± 0.5 cal/mole for CH3COOH, and 468 ± 2 for CD3COOH. Stark effect measurements using four A-type transitions give the dipole moment components: μa = 0.86 ± 0.01 D, μb = 1.47 ± 0.02 D, and μ = 1.70 ± 0.02 D.
Low-Temperature Paramagnetism in Calcium Copper(II) Acetate Hexahydrate
Authors: McElearney J. N. , Losee D. B. , Merchant S. , Carlin R. L.
Published: February 2004

Single-crystal magnetic-susceptibility measurements have been made on CaCu(OAc)4·6H2O between 1.5 and 20°K. The present data cannot be fitted to Fisher's linear chain model with J / k = − 1.4°K as had been previously reported for data taken at higher temperatures. However, the Curie–Weiss law with a value of θ = − 0.18°K describes both the present data and the previous results. In addition, the low-temperature results are equally well fitted by the linear chain model with J / k = − 0.095°K.
Remarks Concerning the Scaling Relations for Critical Exponents
Authors: Snider Neil S.
Published: February 2004

Here proposed is a revised version of the scaling theory of equilibrium critical phenomena. This revised theory is based on hypotheses which differ only slightly from those set forth in original formulations. The conclusions reached are essentially equivalent to those of Stell's weak scaling theory. One obtains relations which require prior knowledge of three exponents for the derivation of the rest. An additional exponent, denoted w, enters certain relations containing exponents which pertain to the correlation function. This exponent must be greater than or equal to one in order to satisfy certain generally accepted inequalities. An argument for why w should be greater than or equal to one is formulable within the framework of the original hypotheses of scaling theory. While the revised theory has the drawback of containing an extra unknown, it is nevertheless capable of reconciling scaling theory with other theories of critical exponents.
Microwave Investigation of Methyl Sulfone and Methane Sulfonyl Fluoride
Authors: Jacob E. Jean , Lide David R.
Published: February 2004

Rotational constants for the ground state of methyl sulfone and for the ground and first excited torsional state of methane sulfonyl fluoride have been derived from microwave spectra observed in the 18 000–37 000-MHz region. Molecular dipole moments of 4.50 ± 0.10 D for (CH3)2SO2 and 3.88 ± 0.04 D for CH3SO2F were measured. Relative intensity measurements place the barrier to methyl rotation in CH3SO2F at 880 ± 120 cm−1 (2.52 ± 0.35 kcal/mole). Alternative structures for (CH3)2SO2, based on assumption of either the SO or the SC bond length from a recent electron diffraction study, are presented. Both reveal a significant discrepancy between the microwave and diffraction values for the OSO angle.
NMR Studies of 7Li, 23Na, and 27Al in Y-Faujasite
Authors: Genser E. E.
Published: February 2004

NMR methods were used to study specific atom environment and distribution in Y-faujasite. The widths of the 27Al and 23Na signal in the hydrate were dominated by second-order quadrupolar effects; they were not observable in the dehydrated material. The exchange of lithium for sodium and the subsequent observation of the 7Li NMR in the dehydrated Y-faujasite provided a convenient structural probe and permitted a comparison of the experimental and theoretical second moments, the latter being based upon the cation distribution known for the sodium form from x-ray diffraction data. Magnetic dipolar broadening dominates the linebreadth of the 7Li resonance.
Temperature and Pressure Effects in the Addition of H Atoms to Propylene
Authors: Kurylo Michael J. , Peterson Norman C. , Braun Walter
Published: February 2004

The effect of He pressure on the rate of addition of hydrogen atoms to propylene was measured at 298°K. H-atom concentration was measured by the method of resonance fluorescence of Lyman α radiation at 121.6 nm. The results are consistent with the 1 / p1/2 dependence of kbi recently observed in the H-atom–ethylene system. The limiting high-pressure rate constant obtained in this work is H+C3H6→C3H7, k1 = 1.61 ± 0.04 × 10−12cm3molecule−1·sec−1. The temperature dependence of the H-atom addition was investigated at 50 torr total pressure over the temperature range 177–473°K. Analysis of the data below room temperature gives the following Arrhenius parameters for addition to the terminal olefinic position: kbi50 = (10.18 ± 0.26) × 10−12exp[− (1211 ± 11) / 1.987T] cm3molecule−1·sec−1. Deviations from this dependence above 298°K can be assigned to nonterminal addition, H-atom abstraction, and increased decomposition of the excited propyl radicals.
Liquid Crystal Properties of Some Steryl Chlorides
Authors: Leder Lewis B.
Published: February 2004

The liquid crystalline properties of cholestanyl, cholesteryl, campesteryl, sitosteryl, and stigmasteryl chlorides were studied by measuring their behavior in mixtures with cholesteryl nonanoate. Of the five chlorides only cholesteryl chloride shows an obvious mesophase temperature range and microscopic texture, but all of the chloride–nonanoate mixtures are cholesteric over a wide range of compositions. The decrease in effective pitch observed as the 17β side chain is modified appears to correspond directly to the complexity of the modification. We conclude that all of the chlorides studied are liquid crystalline despite the fact that the ordinary tests for mesomorphism do not give this indication.
Electron Attachment to Brominated Aliphatic Hydrocarbons of the Form n-CNH2N+1Br (N = 1–6, 8, and 10). I. An Electron Swarm Study
Authors: Christodoulides A. A. , Christophorou L. G.
Published: February 2004

An electron swarm study has been made of brominated aliphatic hydrocarbons of the form n-CNH2N+1Br(N = 1–6, 8, and 10). Attachment rates, αw, as a function of mean electron energy 〈ε〉, are reported. The attachment rates reach a maximum value at ≤ 0.038, 0.76, 0.76, 0.75, 0.74, 0.73, 0.20, and ≤ 0.038 eV for N = 1 to 6, 8, and 10, respectively. The observed variation in both the magnitude of αw and in the widths of the αw vs 〈ε〉 functions within this series of molecules are discussed within the resonance scattering theory. In addition to a dissociative electron attachment process yielding Br− via a short-lived (< 10−13 sec) compound negative ion state, another electron attachment process involving a longer-lived (∼ 10−10–10−6 sec) state is suggested by the data. For the fast process leading to Br− production, these molecules can be considered as diatomiclike R(=CNH2N+1)–Br systems. The cross sections for the CH3Br and n-C10H21Br molecules reach a maximum value at energies < 3 / 2kT. Over the energy range from 3 / 2kT to ∼ 0.8 eV the cross section for n-C10H21Br can be represented by Aγε−γ, where ε is the electron energy in electron volts, Aγ is equal to 3.5 × 10−18 (eV)γ·cm2, and γ is equal to 1.398. Attachment rates as a function of 〈ε〉 are reported also for some chlorinated aliphatic compounds including CCl4 for which the attachment cross section over the energy range from 3 / 2kT to 0.6 eV can be approximated also by Aγε−γ with Aγ = 3 × 10−16 (eV)γ·cm2 and γ = 1.226. The data presented in this paper distinctly demonstrate the potential of the electron swarm method in electron attachment studies.
Electron Attachment to Aliphatic Hydrocarbons of the Form n-CNH2N+1Br(N = 2–6 and 8) II. A Swarm-Beam Study
Authors: Christophorou L. G. , Carter J. G. , Collins P. M. , Christodoulides A. A.
Published: February 2004

A swarm-beam study has been made of brominated hydrocarbons of the form n-CNH2N+1Br(N = 2–6 and 8). At energies below ∼ 3 eV the abundant ion found in the beam study was Br−. The dissociative attachment cross section σda(ε) peaked at 0.76, 0.74, 0.73, 0.70, 0.71, and 0.13 eV, and had peak values equal to 3.95, 4.14, 5.50, 6.13, 7.41, and 32.2 × 10−18 cm2 for N = 2–6 and 8, respectively. A small decrease has been observed in the cross-section width with increasing reduced mass Mr of the R(= n − CNH2N+1)–Br molecules. This and the increase in σda with Mr are discussed within the resonance-scattering-theory treatment of dissociative electron attachment to diatomic molecules. For some of the molecules studied, potential energy diagrams for RBr and RBr−* and separation and autoionization lifetimes for RBr−* are given.
Nanosecond Time-Resolved Emission Spectroscopy: Spectral Shifts due to Solvent-Excited Solute Relaxation
Authors: Ware William R. , Lee Sai K. , Brant Gary J. , Chow Peter P.
Published: February 2004

Nanosecond time-resolved emission spectral techniques have been applied to the problem of the origin and nature of the well-known temperature-dependent spectral shifts characteristic of the aminophthalimides in alcohol solvents. It is demonstrated that the temperature-dependent spectral shifts are in fact due to time-dependent spectral shifts. At least two relaxation times characterize this phenomenon. One relaxation time is observed to be subnanosecond in character and may be associated with the exciplex that presumably is present in the system. The other relaxation time is presumably associated with the nonspecific dipolar reorientation although it has distinctly different characteristics from the solvent dielectric relaxation time. Wavelength-dependent fluorescence decay that can be explained by the time dependence of the emission spectrum is also observed.
Binding States of Hydrogen on Tungsten
Authors: Tamm P. W. , Schmidt L. D.
Published: February 2004

The binding states, adsorbate densities, and desorption kinetics of hydrogen on the (110), (111), and (100) crystal planes of tungsten are examined. There are two atomic states on the (110) plane and four atomic states on the (111) plane. Saturation hydrogen densities are approximately equal in the major states on both planes and correspond to one hydrogen atom for each surface tungsten atom on the (110) plane and approximately four hydrogen atoms for each surface tungsten atom on the (111) plane. While the desorption activation energies of the most tightly bound states on all three planes are nearly identical, there are weakly bound (Ed = 14 and 22 kcal mole−1) atomic states on the (111) plane which are entirely lacking on the other planes. These results show that there are considerable variations in hydrogen adsorption on these planes. Arguments are advanced that the surface atom configurations are nearly those of the bulk crystal, and hydrogen surface structures are proposed to account for the observed binding states. Some qualitative aspects of the adsorption bonds are also considered.
EPR of O2 Impurity in Solid N2, CO, Ar, and CD4 Prepared from the Vapor
Authors: Simoneau R. , Harvey J. S. M. , Graham G. M.
Published: February 2004

The EPR spectra of O2 impurity in specimens of N2, CO, Ar, and CD4 condensed from the gas at 4.2°K have been studied at X- and K-band frequencies. For the N2 host, studies have been made of the effect of varying concentration and temperature. The polycrystalline absorption profiles for N2 and CO show structure and are analyzed. Those for Ar and CD4 show only broad structureless absorption. The results show that in N2 and CO the O2 molecules occupy isolated and essentially axial symmetry sites at low concentrations but that new features, attributed to different sites arising from clustering or defects, appear at higher concentrations. The extraction of useful information is limited by the polycrystalline nature of the samples.
Effect of Pressure on the Spin State of Iron in Ferrous Phenanthroline Compounds
Authors: Fisher D. C. , Drickamer H. G.
Published: February 2004

The effect of pressure to 175 kbar has been measured on the spin state of Fe(II) in bis- and trisphenanthroline complexes, using Mössbauer resonance and optical absorption. The bis complexes can be classified according to the degree of back bonding to the nonphenanthroline ligands. Compounds with halide ligands are high spin at low pressure. They convert to low spin with increasing pressure, but the rate of conversion with pressure decreases above 80 kbar. Compounds with intermediate back bonding (e.g., cyanates, thiocyanates, selenocyanates, or azides) are high spin at low pressure. With increasing pressure they tend to convert to low spin, but above ∼ 30–40 kbar there is a net low-to-high spin conversion. The biscyanide is low spin at low pressure. At high pressure significant conversion to high spin is observed. All tris complexes are low spin at low pressure and exhibit measurable conversion to high spin at high pressure. The optical absorption data indicate large red shifts for the ligand π–π* transitions and smaller red shifts for the metal-to-ligand charge transfer peaks. These results are explained in terms of reduced back donation due to thermal occupation of the ligand n* orbitals by ligand π electrons. The behavior is compared to that of the ferrocyanides. Similar experimental results are presented and briefly discussed for an intermediate-spin phenanthroline complex and for several bipyridyl compounds.
Initial Pressure Dependence of the Viscosity of Polar Gases
Authors: Danon F. , Amdur I.
Published: February 2004

The initial pressure dependence of the viscosity of polar gases is studied within the approximate treatment of Stogryn and Herschfelder. An important simplification is that the contribution of the bound molecules can be handled by a free-energy preaveraged potential, which is simpler than the assumption of fixed relative orientation during binary collisions. Values for the initial pressure dependence of the viscosity of ammonia and stream are calculated starting from the angular-dependent Stockmayer potential and show satisfactory agreement with experiment.
Ion–Molecule Reactions in NO–NH3 Gas Mixtures
Authors: Puckett L. J. , Teague M. W.
Published: February 2004

Stationary afterglow techniques have been employed to produce and observe ions reacting in NO–NH3 gas mixtures. The precursor ion, NO+, is found to cluster with NH3 and then reacts further to yield NH4+. Arguments are presented for the formation of ONNH2 as a byproduct of the latter reaction. The NH4+ ion undergoes successive clustering with NH3 to produce NH4+·nNH3, n = 1, 2, 3. The NH3 clustering reactions are similar to those observed for H2O in NO–H2O and O2–H2O gas mixtures. Rate constants for all forward and all observed reverse reactions have been measured at 296°K.
Tunneling in Isotopic Collinear H+H2 Reactions
Authors: Russell J. D. , Light J. C.
Published: February 2004

Quantum calculations of the collinear isotopic H+H2 systems are presented. The use of reaction coordinates allows the specific two-dimensional effects of reaction path curvature and vibrational force constant to be studied. It is shown that both of these effects must be included in order to obtain accurate transmission coefficients at low energies.
Pyrene Dimer Cation as Studied by Pulse Radiolysis
Authors: Kira Akira , Arai Shigeyoshi , Imamura Masashi
Published: February 2004

Radical cations of pyrene were investigated by the pulse radiolysis technique in solutions of benzonitrile, acetone, and dichloroethane. A 450-nm absorption band of a pyrene monomer cation was replaced by new bands with maxima at 500, 580, and 750 nm as the pyrene concentration was increased. The latter absorption bands were exclusively assigned to a pyrene dimer cation in equilibrium with the monomer cation at room temperature. Equilibrium constants evaluated were (2.7 ± 0.2) × 102and (5.1 ± 0.5) × 102M−1 at 20°C for benzonitrile and acetone solutions, respectively. The decay processes of both the monomer and dimer cations were discussed. In addition, rate constants of the reactions of both the monomer and dimer cations with triethylamine were found to be 2.7 × 109and 5.4 × 108M−1·sec−1, respectively.
Raman Spectra of Molten NaBF4 to 606°C and 8% NaF-92% to 503°C
Authors: Quist Arvin S. , Bates John B. , Boyd George E.
Published: February 2004

The Raman spectra of molten NaBF4 samples have been measured to 606°C, and spectra of samples of the eutectic mixture of 8 mole % NaF in NaBF4 were recorded to 503° using 4880-Å radiation from an argon-ion laser for excitation. The BF4− ion appeared to retain its tetrahedral symmetry under all the conditions studied in this investigation. The frequency of the ν1(a1) mode of BF4− decreased with increasing melt temperature, and weak, asymmetric features on the bands from the ν2(e) and ν4(f2) modes were observed in molten NaBF4 and in the melts with 8 mole % NaF. The interpretation of the Raman spectra of molten NaBF4 does not require postulating the existence of a quasilattice structure or phonons in the molten state.
Study of Various Properties of Silica Gel by Positron Annihilation
Authors: Chuang S. Y. , Tao S. J.
Published: February 2004

The lifetimes of o-positronium in silica gel adsorbed with various amounts of water, n-hexane, or nitromethane were measured. The fraction of o-positronium escaping the condensed phase can be related to the specific area and the pore volume of the silica gel. The mean life of o-positronium in the pores is found to be very sensitive to the surface properties of silica gel. The formation of free radicals on the surface of silica and the reactions between these free radicals and o-positronium are suggested as the explanations.
Magnetothermodynamics of CuK2(SO4)2·6H2O.III. Fields along the γ Axis. Thermodynamic Temperature without Heat Introduction below 0.4°K
Authors: Giauque W. F. , Fisher R. A. , Brodale G. E. , Hornung E. W.
Published: February 2004

The magnetothermodynamic properties of a 3.912-cm-diam spherical single crystal of CuK2(SO4)2·6H2O have been investigated down to 0.012°K with fields along the γ magnetic axis. Fifty-two adiabatic magnetizations from unknown lower temperatures were performed and 49 were shown to be isentropes within small limits of accuracy. Measurements of magnetic moment as a function of field on these isentropes have been combined with our previous thermodynamic data above 0.4°K [J. Chem. Phys. 54, 273 (1971)] to determine the thermodynamic temperature and heat capacity, both in and out of magnetic fields, without heat introduction below 0.4°K. The effects of entropy transfer between nuclear spin and electron spin systems on the magnetothermodynamic properties are discussed. Although the equations of reversible thermodynamics may be and sometimes are inaccurate for the narrow temperature region in which nuclear spins lose equilibrium contact with an electron system, entropy differentials derived from isentropes are valid in the equation, T = (∂H / ∂S)H, after the nuclear spins are essentially “frozen-in.” The lambda maximum temperature was found to be 0.029°K at zero field.