bluuebunny/crossref_metadata_2025 huggingface dataset:
Interaction of H2 with (100)W. II. Condensation
Authors: Tamm P. W. , Schmidt L. D.
Published: February 2004

The sticking coefficient of hydrogen on (100)W has been studied as a function of substrate temperature, hydrogen mass, and coverage. A detailed knowledge of the structure and kinetics of this system permits a quantitative determination of the sticking coefficients in the individual states. It is shown that for the more tightly bound atomic or β2 state, the sticking coefficient s is initially independent of coverage, indicating a precurser intermediate; in the molecular β1 state s follows a site occupation model, s = s0(1 − θ1). In both states s is almost independent of substrate temperature in the interval 78 < Ts < 300°K. Considerations of the mass and coverage dependence of s appear to indicate that condensation is limited by chemical bond formation of a precurser state rather than thermal accommodation. The precurser is postulated to be a molecular state singly bonded to a protruding tungsten atom. It is also observed that desorption of one isotope from the surface can be stimulated by the presence of the other isotope in the gas phase at temperatures where ordinary thermal evaporation of these states is negligible. This is shown to occur via a weakly bound intermediate state rather than a direct gas-phase replacement.
Photochemical Reduction of Thionine by Cobalt (II) EDTA Complex in Water–Ether Emulsion
Authors: Srinivasan V. , Rabinowitch E.
Published: February 2004

Thionine undergoes reversible photoreduction by cobalt (II)–EDTA complexes under anaerobic conditions. The back reaction between cobalt (III) EDTA and leucothionine can be largely prevented by extracting the leucodye into ether during irradiation. Fifty-four percent separation of the products of the light reaction can be achieved in this manner at pH 7.2. When the delayed back reaction is allowed to proceed in a galvanic cell, a potential difference of 0.3 V is observed. On complete separation of the products of the light reaction, this potential rises to 0.52 V. This system represents another step towards efficient chemical storage of the energy of visible light.
Separated Wavefunctions for the Ground State of Two-Electron Atoms
Authors: Carlton Terry S. , Hull William E.
Published: February 2004

Partially separated wavefunctions of the form U(r1, r2)W(r12) yield helium ground-state energies in error by as little as 4 × 10−4 a.u. Completely separated functions F(r1)F(r2)W(r12) give distinctly poorer results. The correlation function W(r12) = (1 + Br12)1 / 2 yields energy errors of less than 1 × 10−3 a.u. for H−, He, and Li+.
Electron Correlation and Separated Pair Approximation in Diatomic Molecules. I. Theory
Authors: Silver David M. , Mehler Ernest L. , Ruedenberg Klaus
Published: February 2004

The theory of antisymmetrized products of separated geminals for many-electron systems is developed for arbitrary spin states. The geminals are expanded in terms of their natural spin orbitals, and methods are developed for their optimal determination. New variational equations are derived and cast in the form of one pseudoeigenvalue equation for all natural spin orbitals. An alternative scheme is given for finding optimal symmetry-adapted natural orbitals in terms of an orthonormalized basis set by direct energy minimization. A strategy for optimization is discussed which was found useful in calculations of the ground states of the molecules LiH, BH, NH, and their separated atoms.
Heat Capacity, Entropy, and Intensity of Magnetization of MN(NH4)2(SO4)2·6H2O from 1 to 4°K in Fields up to 24 000 Oe Parallel to the b Axis
Authors: Clark J. T. , Fritz J. J.
Published: February 2004

The magnetothermodynamic behavior of a spherical single crystal has been investigated from 1 to 4°K in fields up to 24 000 Oe parallel to the b crystallographic axis (K3 magnetic axis). The heat capacity of the specimen has been measured over this temperature range at five magnetic fields; these observations have been used in conjunction with the dependence of temperature with field along 16 isentropes to establish the entropy as a function of magnetic field and temperature. The intensity of magnetization has been measured as a function of field and temperature over the entire range. Deviations from ideal behavior are apparent in all measured properties, although smaller than in a specimen oriented perpendicular to the b axis.
Relaxation in a Dilute Binary Gas Mixture
Authors: Kapral Raymond , Ross John
Published: February 2004

The relaxation of a dilute hard-sphere binary gas mixture is studied in the limit of vanishingly small concentration of one of the species. The velocity autocorrelation function and diffusion coefficient are evaluated by the integral approximation and Chapman–Enskog methods. Solutions are obtained as a function of the ratio of the masses of the two species and the limiting cases of the Rayleigh and Lorentz gases are considered in some detail. While the convergence of the Chapman–Enskog method becomes poor as the Lorentz limit is approached, the integral approximation yields solutions which are exact in this limit. In the Rayleigh limit both methods yield the exact result.
Dispersion of the Electrically Induced Refractive-Index Anisotropy in Nonpolar Liquids as a Probe of Reaction Kinetics
Authors: Berne B. J. , Pecora R.
Published: February 2004

The theory of the dispersion of the refractive-index anisotropy induced in nonpolar fluids by external electric fields is extended to the case of chemically reacting fluids. Explicit expressions for the induced anisotropy are derived for a model nonpolar fluid with (1) no pair correlations, (2) rotational diffusion dynamics, and (3) a simple two-state (or species) chemical equilibrium. Limiting cases of the results are discussed.
Oxidation of 4a,4b-Dihydrophenanthrenes. III. A Theoretical Study of the Large Kinetic Isotope Effect of Deuterium in the Initiation Step of the Thermal Reaction with Oxygen
Authors: Warshel A. , Bromberg A.
Published: February 2004

The large kinetic isotope effect of deuterium that occurs in the reaction of perdeuterio-4a,4b-dihydrophenanthrene with O2 is studied by a semiempirical calculation. The large effect is a consequence of two significant effects, the existence of quantum mechanical tunneling and the loss of zero-point energy. The theoretical study is mainly based on the construction of the potential surface by the method of bond eigen-functions, and the treatment of the reaction as the solution of a 10-electron problem. The calculated tunneling effect, which is found by integration of all possible transmission probabilities through the potential barrier, results in factors of 11.8 at 242°K and 8.1 at 263°K. A conformational and normal mode analysis shows that the contribution of the zero-point energy effect amounts to a factor of 7.6 at 242°K and 6.4 at 263°K.
Electron Trapping and Hydrogen-Atom Reactions in Irradiated Polyethylene
Authors: Partridge Roger H.
Published: February 2004

The absorption spectrum of electrons trapped in polyethylene during irradiation at low temperature is studied here, and an approximate G value for this of ∼0.8 at low doses is deduced. The spectrum stretches from the vacuum ultraviolet to the infrared (thus differing entirely from that in short-chain branched alkanes) and changes somewhat with increasing irradiation dose. Another absorption spectrum is found, which bleaches thermally but not optically, that is probably due to alkyl radicals. Thermal H atoms were studied at low temperature by adding benzene to the polyethylene and observing the ultraviolet absorption spectrum of the resulting cyclohexadienyl radicals. The G value for thermal H-atom production was found to be ∼1.8, similar to the value in short-chain alkanes at room temperature, and the atoms apparently migrated considerable distances even at −170°C. Addition also of olefin with the benzene showed that olefin double bonds react ∼600 times more efficiently with thermal H atoms than do methylene groups, but despite this H-atom capture is not an important mechanism for the destruction of these double bonds by radiation.
Classical Inelastic Collision Cross Sections for Loaded Spheres
Authors: Miles John R. N. , Dahler John S.
Published: February 2004

Formal expressions are given for the transition rates and related cross sections appropriate to collisions between molecules with internal degrees of freedom whose initial and final states are specified in varying degrees of detail. The formalism is specialized to the case of rigid-body collisions between spherical and loaded spherical molecules. The simplicity of the collision dynamics for this system enables an exact expression to be found for the basic cross section σ(L′, c′ → L, c) for scattering from a beam of specified velocity c′ and angular momentum L′ to a state of velocity c and angular momentum L. Experimentally observable cross sections such as σ(c′,| L′ | → c,| L |) and σtotal(| L | → | L′ |) can be obtained by numerical integration of the basic cross section. Numerical values for these cross sections are calculated for the case of excitations from the “ground state” (L′ = 0) for HD–He and HT–HE collisions. The total cross sections for these collisional pairs are found to be 0.92πR2 and 0.86πR2, respectively, where πR2 is the rigid-sphere cross section.
Electronic Spectra of the Azide Ion, Hydrazoic Acid, and Azido Molecules
Authors: McDonald J. R. , Rabalais J. W. , McGlynn S. P.
Published: February 2004

The electronic absorption spectra of aqueous hydrazoic acid solutions have been studied as a function of concentration. The spectra are analyzed on the basis of complementary absorption by the azide ion and the associated acid species, and the acid dissociation constant has been determined. The absorption of azide ion in hydrazoic acid solutions is found to be identical to that of solutions of the azide salts. The aqueous solution spectrum of associated hydrazoic acid is shown to be the same in the near-ultraviolet region as that of hydrazoic acid gas and very similar to that of n-amylazide. Vibrational analyses have been carried out on the structured regions of the absorption spectra of NH3 gas. The absorption spectra of HN3 and n-amylazide have been determined in the vacuum ultraviolet and four series of Rybderg transitions have been identified in the spectrum of HN3. Ionization potentials of 11.5 and 12.6 eV have been determined for HN3. MWH-type computations have been performed on the azide ion and on hydrazoic acid. These computations, coupled with experimental data and with the knowledge of the spectra of other isoelectronic molecules and ions, are used to assign all molecular transitions observed in the spectra of the azide ion and of the azido molecules. The electronic states, in order of increasing energy, of N3−, D∞h (R–N3, Cs) are: Σg+1(A′) < 1Σu1−(A″) < 1Δu1(A″ < 1A′) < 1Π(g,u)1(A″ < 1A′) < 1Σu+1(A′)1.
Crystal Field in Rare-Earth Trichlorides. V. Estimation of Ligand–Ligand Overlap Effects
Authors: Curtis M. M. , Newman D. J.
Published: February 2004

Ab initio calculations of certain ligand–ligand overlap contributions to the crystal field in the complex (PrCl9)6− are described. Estimates are made of those terms which have not been calculated directly. Contributions of third order in the overlap integrals are shown to be about 15% of the total n = 6 crystal field parameters for this complex and thus provide an effective limitation to the use of the superposition approximation in analyzing experimental data.
Theory of Singlet–Triplet Transitions in Cyclic Tetramers: Applications to Tetraphenyl Group IV Compounds
Authors: Hochstrasser Robin M. , Marchetti A. P.
Published: February 2004

A description of singlet–triplet transitions in cyclic molecules is presented such that the selection rules take full advantage of the cyclic symmetry. It is found that unlike singlet–singlet transitions, all component triplet states of a cyclic tetramer have allowed transitions to the ground state in electric dipole radiation. The relative intensities of transitions to the various excitonlike states is determined by the geometrical transformation involved in switching the axis of spin quantization from the monometer to the cyclic tetramer basis. The theoretical predictions are convincingly exemplified by the T1 ← S0 low-temperature absorption spectra of crystals of the tetraphenyl Group IV (C, Si, Ge, Sn, and Pb) compounds, all of which have S4 symmetry. The absorption spectra of the singlet states of neat crystals of these materials is also presented and these also demonstrate the cyclic exciton selection rules but in this case only two of the four states are seen as predicted. The tetraphenyl-X triplets all show four excitonlike states—A, 3B, 3andE3: The total splittings are: X = Si, E3−B3 = 1.1 cm−1; X = Ge, E3 − B3 = 2.8 cm−1; X = Sn, E3−A3 = 7.4 cm−1; X = Pb, A3− = 6.6 cm−1. The E3 state is always at highest energy. In the singlet states only the E and B states are seen and the splittings are: X = Ge, B − 3E3 = 11 cm−1; X = Sn, B3−E3 = 10 cm−1; and X = Si, B3−B3cm−1. The spectra in high magnetic fields (Zeeman effect) confirm the detailed assignments and the theoretical model. In addition we have seen the spin–orbit interaction between different monomer based triplet states.
Geometry Optimization in the Computation of Barriers to Internal Rotation
Authors: Stevens Richard M.
Published: February 2004

A minimum basis set of STO's has been used to compute wavefunctions for eclipsed and staggered C2H6 and for several forms of H2O2. For each form all the exponents and free geometric parameters have been varied to obtain the minimum energy. It has been found that the geometry variation has little effect on the computed barrier in C2H6, and the results agree well with experiment. For H2O2, it has been found that the minimum geometry changes substantially between the cis and trans forms, and the results agree poorly with experiment. However, the geometry variation does produce better agreement for the barrier than similar calculations with fixed geometry.
Phase Equilibria in Fluid Mixtures at High Pressures: The Helium–Nitrogen System
Authors: Streett W. B. , Hill J. L. E.
Published: February 2004

Experimental phase equilibrium data are reported for the He–N2 system at pressures up to 4000 atm, over the temperature range 78–137°K. The mixture critical line and the three-phase region solid–liquid–gas have been determined over the entire pressure range, and the system is shown to exhibit fluid–fluid phase separations which extend to temperatures above the critical temperature of N2. Some characteristics of phase diagrams for binary fluid mixtures at high pressures are described, and the relevance of these diagrams to problems of deep atmosphere structures of the major planets is briefly considered.
Periodic Kinetics in Diffusion-Controlled Electrochemical Reactions
Authors: Wojtowicz J. , Conway B. E.
Published: February 2004

Periodic processes are often encountered in electrode reactions, particularly in the case of anodic oxidations. Analogous effects have been found by other workers in systems of biological interest, e.g., with processes involving membranes and enzymes. The general problem is to account for why no chemical steady-state arises under conditions of controlled potential (potentiostatic) or controlled over-all current or rate (galvanostatic). Here, a diffusion-controlled process with a coupled adsorption–electrochemical oxidation reaction (e.g., oxidation of C2H4) is examined and the special conditions which can lead to unstable steady states, and hence periodicity, are established under simplifying assumptions.
Effects of Vibronic Coupling on the Rate of Spreading of an Exciton Wave Packet: Higher-Order Effects
Authors: Lowy E. , Bierman A.
Published: February 2004

The results presented here are an extension to higher order of the computation of the rate of speading of an exciton wave packet in an infinite one-dimensional crystal. Attention was paid to both the initial conditions and the effects of phonon–exciton coupling. Strong nearest-neighbor coupling was assumed, and agreement with the Franck–Condon principle was explicitly required. Previous calculations by one of the authors carried through second-order perturbation (all odd-number orders being zero) showed a time-dependent decrease of the rate of spreading. For large t (time), this decrease goes at t, lnt, or a constant, depending on whether ℏω < 2W, ℏω = 2W, or ℏω > 2W. Here W is the intermonomer coupling energy and ℏω is the vibrational quantum of energy. In this paper we pursue this calculation to fourth order, showing that the rate of spreading is now increased by a term which goes at t2 or t2lnt depending on whether ℏω ≤ 2W or ℏω < 2W, respectively. We have calculated the limits of z = (2W / ℏ)t for which the results are valid and also computed the successive terms of the rate of spreading for typical values of the parameters σ = ℏω / 2W and λ = KQ02 / 2W. Finally, we discuss the behavior of the rate of spreading, υ, as a function of λ, z, and σ and also suggest some possible experimental verification of the results of this work.
Padé Approximants to the Normal Dispersion Expansion of Dynamic Polarizabilities
Authors: Langhoff P. W. , Karplus M.
Published: February 2004

A procedure for investigating the dispersion of dynamic polarizabilities and associated molecular excitation spectra is presented. The time-dependent Schrödinger equation is replaced through the expedient of an ansatz by a frequency-dependent equivalent and the pertinent first-order perturbation function expanded in a power series in the applied frequency. There results a set of coupled inhomogeneous differential equations which can be solved sequentially by utilizing the methods for static polarizability calculations, providing the coefficients for a power-series expansion in frequency of the polarizability (Cauchy series). The latter is identified as a series of Stieltjes, which can be summed within and continued outside its radius of convergence by Padé approximants, furnishing an approximation to the polarizability throughout the entire (cut-) complex plane. The power-series coefficients from the expansion of the polarizability further provide a test of the convegence of the computation, which is independent of applied frequency. Applications are made in the dipole case to atomic hydrogen, for which exact solution for the expanded perturbation function is calculated, and to the helium atom and hydrogen molecule in the coupled Hartree–Fock approximation (time-dependent Hartree–Fock theory), for which the equations are solved using a convenient variational procedure. Lower-bounded rapid convergence to the correct polarizabilities and associated refractivities in the normal dispersion region is obtained using a small number of Cauchy coefficients and the lowest-order Padé approximants. Further, accurate approximations to the lowest-lying transition frequencies and oscillator strengths are obtained from the poles and residues, respectively, of the Padé approximants. These results indicate that variational computations of optical susceptibilities in the normal dispersion region, combined with subsequent summation and analytical continuation in frequency, can provide a practical procedure for investigating the optical dispersion and excitation spectra in atomic and molecular systems.
Vibrational Deactivation in Methane Mixtures
Authors: Yardley James T. , Fertig Margaret N. , Moore C. Bradley
Published: February 2004

The vibrational relaxation of the bending modes of CH4 in mixtures with rare gases and diatomic molecules has been studied by laser-excited vibrational fluorescence. The measured energy transfer probabilities cannot be understood, even qualitatively, in terms of simple theories of either vibration-to-translation energy transfer or vibration-to-rotation energy transfer. The data indicate that vibrational energy is transferred into translation, methane rotation, and collision partner rotation. The relative distribution among these degrees of freedom appears to vary greatly among the collision partners studied. Ethane was found to be an efficient catalyst for the vibrational relaxation of CH4. Since it is one of the major impurities in methane samples, this observation explains why some authors have observed relaxation times for “pure” CH4 less than 2 μsec·atm.
Pressure Dependence of Benzophenone Phosphorescence
Authors: Simpson J. D. , Offen H. W.
Published: February 2004

The phosphorescence spectrum, intensity, and lifetime of benzophenone have been studied at 77°K as a function of pressure (0–30 kbar) in EPA, polymethylmethacrylate (PMMA), and polyethylene (PE). At 30 kbar the tiplet energy is raised 90 cm−1 in EPA and lowered about 460 cm−1 in PMMA and PE, according to the pressure-induced, reversible shift of the band origin. The triplet lifetime in EPA is reduced from 5.8 to 4.5 msec at 30 kbar pressure. A decrease in phosphorescence intensity suggests that the radiative transition probability diminishes under pressure. The intensity decay becomes strongly nonexponential in polymer matrices under compression.
Explicit Formulas for the Nth-Order Wavefunction and Energy in Nondegenerate Rayleigh–Schrödinger Perturbation Theory
Authors: Silverstone Harris J. , Holloway Thomas T.
Published: February 2004

The wavefunction and energy in nth order of Rayleigh–Schrödinger perturbation theory are shown to be given by En =  ∑ σ1,σ2···,σn; (σ1+2σ2+···+nσn=n;σi≥0,i=1,2,···,n) (σ1!σ2!···σn!)−1(d / dE0)Σσi−1〈V〉σ1〈Va−1V〉2σ··· × 〈V(a−1V)n−1〉σn, χn = (a−1V)n| 0 〉 +  ∑ j=1n−1 ∑ (σ1+2σ2+···=n−j;σi≥0,i=1,2,···) (σ1!σ2···)−1(d / dE0)Σσi−1(V〉1σ〈Va−1V〉2σ·mc· × 〈V(a−1V)n−j−1〉σn−1(d / dE0) (a−1V)i| 0 〉. Here |0〉 is the unperturbed eigenfunction of H0 with energy E0, V is the perturbation, 〈V···V〉 denotes 〈0|V···V|0〉, and a−1 is (1 − |0 〉〈0 |) (E0 − H0)−1(1 − |0〉〈0|). The wavefunction is given in the socalled “intermediate normalization.” Partial summations of these formulas give exactly the wavefunction and energy in Brillouin–Wigner perturbation theory.
Microwave Spectrum of Monomethylfurazan
Authors: Saegebarth Ellen
Published: February 2004

The ground-state rotational spectrum of monomethylfurazan has been assigned, and splittings of the transitions into A and E components have been analyzed according to the principal axis treatment. All the terms in the effective Hamiltonian through fourth order are needed to explain the spectrum. Iα and s were obtained by a least-squares fit of the calculated splittings to the observed. This treatment gives Iα = 3.19 ± 0.01 amu·Å2 for the moment of inertia of the methyl group and V3 = 722 ± 4 cal/mole for the barrier to internal rotation.
ESR of the BC2 Molecule in Inert Matrices at 4°K
Authors: Easley Warren C. , Weltner William
Published: February 2004

The vapor in equilibrium with solid boron carbide at 2600°K, known to contain BC2, B2C, and BC molecules, has been trapped in argon and neon matrices and investigated by X-band ESR spectroscopy. A strong spectrum characteristic of an axially symmetric 2Σ molecule was observed. Isotopic 10B, 11B, and 13C substitution indicated that the molecule was either BC2 or BC, and the latter could be eliminated because its ground state is probably 4Σ. The molecules were found to occupy several distinct sites in the matrices with preferential orientation of the internuclear axis perpendicular and parallel to the condensing surface. A representative set of magnetic parameters for BC2 in neon is: g‖ = 2.0015, g⊥ = 1.9994, A‖(11B) = 826.8 MHz, A⊥(11B) = 750.3 MHz, A‖ (13C) = 42.0 MHz, A⊥(13C)=24.1 MHz. Approximately 80% of the spin is on the boron atom, and the electronic structure can be appropriately depicted as ·B=C=C:.
Nature of Two-Particle Correlations in Atoms: Calculation of Mass Polarization in the Two-Electron Atom for Large Nuclear Charge
Authors: Ruffa A. R.
Published: February 2004

The nature of two-particle correlations in atoms is examined within the framework of a formalism developed earlier which involves sum rules for one-particle transitions. Relations for the expectation values of certain two-particle operators which were derived with the aid of this formalism are shown to be exactly valid for the two-electron atom in the limit of large nuclear charge Z. Similar relations are derived for a more general class of two-particle operators, and these relations are used in a term by term evaluation of the series representation of the expectation value of the two-electron repulsion potential 1/r12. The terms in the series which are zero in the Hartree–Fock approximation are expressed, with the aid of these relations, in terms of the expectation value of the mass-polarization operator p1·p2 and the energy. In this way, with the aid of the expression for the correlation energy as a function of Z, one obtains an expression for the mass polarization in the two-electron atom as a function of Z. Comparison of the values for the mass polarization obtained in this way with those calculated by Hart and Herzberg by means of very accurate 20-term variational wavefunctions shows an agreement which improves with increasing values of Z. The difference for Z = 12 is only about 4%. The results of the calculation are used to draw some inferences concerning the nature of two-particle correlations in atoms.
Matrix-Isolation Study of the Water Dimer in Solid Nitrogen
Authors: Tursi Anthony J. , Nixon Eugene R.
Published: February 2004

The infrared spectra of H2O, D2O, and HDO in nitrogen matrices at temperatures from 20 to 4°K reveal no evidence of rotation of the water molecules. Absorption features attributed to water dimers and the vibrational force constants calculated therefrom are indicative of an open structure with a single moderately weak hydrogen bond. The absence of certain HDO absorptions in the observed spectra can be interpreted as the manifestation of a stronger deuterium-vs-hydrogen bond.
Mass-Spectrometric Observations of Argon Clusters in Nozzle Beams II. The Kinetics of Dimer Growth
Authors: Milne Thomas A. , Vandegrift A. Eugene , Greene Frank T.
Published: February 2004

Previously reported data on the growth of argon dimer in free-jet expansions of pure argon are given a simple kinetic interpretation. A third-order rate constant for recombination, coupled with consideration of the reverse process of dimer dissociation (assuming microscopic reversibility), is chosen for the kinetic description. The temperature–pressure–time history of the expanding gas is based on an ideal isentropic expansion to a terminal Mach number. A stepwise computer solution of the simple differential equation governing dimer growth is carried out with trial temperature-dependent rate constants. Those rate constants which most nearly reproduce the experimental data are kf = 0.8 × 10−30 / T2 and kf = 6.5 × 10−30 / T3cm6molecules−2·sec−1. The principal conclusions are that the rate constants are strongly temperature dependent, reverse reactions are quite important, dimer continues to be formed throughout the expansion, and the best correlating parameter for dimer growth is P02d. An argument is also made that dimers may play a crucial role in homogeneous nucleation by providing a fast, two-body route for the growth of clusters.
Proton and Deuteron Magnetic Resonance Study of Calcium Bromate Monohydrate
Authors: Cvikl B. , McGrath J. W.
Published: February 2004

The proton magnetic resonance spectrum of calcium bromate monohydrate was obtained. Results indicate that there are two orientations of the water molecule in the crystal. The p–p distances are 1.58 ± 0.02 and 1.59 ± 0.02 Å, respectively. Their orientations with respect to the crystallographic axes were determined. The protonic spin–lattice relaxation times were measured as functions of orientation at room temperature and of temperature in a single crystal of calcium bromate monohydrate. The b crystallographic axis was the axis of rotation of the crystal. The relaxation time was essentially independent of orientation of the crystal in the external magnetic field. The temperature dependence was characteristic of 180° flipping motion of the H2O molecule whose activation energy was 6.7 ± 0.4 kcal/mole. Quadrupole splittings of the Larmor resonance for the deuterons in Ca(BrO3)2·D2O were measured for single crystals at room temperature. The D2O molecules execute flipping motion at this temperature. The coupling constants and asymmetry parameters for both nonequivalent D2O molecules were determined to be 124.0 ± 1.5 kc/sec and 0.759 ± 0.015, respectively. No dipolar splittings of the quadrupole lines were observed. The H2O molecules were determined to be hydrogen bonded to the O(5) and O(2) atoms in the crystal.
Quantum Theory of the Intensities of Molecular Vibrational Spectra
Authors: Peticolas Warner L. , Nafie Laurence , Stein Paul , Fanconi Bruno
Published: February 2004

Formulas for the transition probabilities and hence the absolute intensities of molecular vibrational spectra are obtained from a unified quantum field treatment. The theory of infrared, Raman, and hyper-Raman spectroscopy of molecular vibrations is developed by assuming these processes occur as time-ordered steps involving the creation or destruction of one quantum of vibrational energy and changes in the occupation number of one, two, or three photons, respectively. The formulas obtained by this method for ir transitions become equivalent to the earlier treatment of Jones and Simpson if the energy difference of the ground and first excited electronic energy levels are very large relative to that of the vibrational quantum. The formulas obtained for Raman transitions are very similar to those obtained by the method originated by Albrecht and developed further by Savin; we get not only the original terms of Albrecht but also the trace terms obtained by Savin. Furthermore by using third-order time-dependent equations from the start we avoid many of the difficulties of the earlier treatments; our equations predict different conditions for the resonant Raman effect than do the earlier equations, and experiments are suggested for testing the new equations. The formula which we give for the absolute intensity of the hyper-Raman effect appears to be the first ever given.
Angular Dependence of Raman Scattering Intensity
Authors: Nafie Laurence , Stein Paul , Fanconi Bruno , Peticolas Warner L.
Published: February 2004

The angular distribution of the intensity of Raman scattered light from a sample of randomly oriented molecules is calculated for all Raman active vibrational transitions for the common molecular point groups. Experiments of Damen, Leite, and Porto are presented.
Calculation of the Vapor-Pressure Ratio of the Isotopes of Solid Ne and Ar
Authors: Klein M. L. , Blizard W. , Goldman V. V.
Published: February 2004

The improved self-consistent phonon theory of Goldman, Horton, and Klein for the Helmholtz energy of anharmonic crystal is used to calculate the vapor-pressure ratios of the common isotopes of Ne and Ar. For both substances, a Mie–Lennard-Jones (m − 6) nearest-neighbor potential (m = 12 and 13) with parameters chosen to fit the zero-temperature latent heat and molar volume is found to give reasonable agreement with experiment.
Nitroxide Radical–Metal Chelate Interactions
Authors: Wilbur David , Kreilick Robert
Published: February 2004

We have investigated the interaction of some nitroxide radicals with a series of transition-metal acetyl-acetonate complexes by monitoring the linewidth of peaks in the ESR spectra of the radicals as a function of chelate concentration. The effect of the chelates on the NMR spectra of some diamagnetic materials was also investigated. The linewidths are found to vary with the number of spins on the metal and the geometry of the complexes.
New Model for the Study of Liquid–Vapor Phase Transitions
Authors: Widom B. , Rowlinson J. S.
Published: February 2004

A new model is proposed for the study of the liquid–vapor phase transition. The potential energy of a given configuration of N molecules is defined by U(r1, ···, rN) = [W(r1, ···, rN) − Nυ0]ε/υ0≤0, where W is the volume covered by N interpenetrating spheres each of volume υ0 and each centered on one molecule, and where ε is an arbitrary positive energy. This continuum model proves to have a line of symmetry comparable with those found hitherto only in lattice models. The line is that of the diameter, or mean orthobaric density ρ = 12ρ1 + 12ρg, below the critical point, and continues through the one-phase region to infinite temperature. The existence of this line allows some of the properties to be obtained explicitly, the most unusual of which is that the diameter has a singularity comparable with that in Cυ; hence the law of the rectilinear diameter is not obeyed. An exact solution of the model is obtained in one dimension, in which there is no phase transition, and a mean-field solution in three dimensions. The latter preserves the symmetry. The model is shown to be thermodynamically equivalent to a two-component system in which the pair potential between molecules of like species is zero, while that between molecules of unlike species implies a mutually excluded volume of υ0. In this transcription the symmetry of the model becomes obvious.
Non-Markovian Contributions to Rate Equations. IV
Authors: Laidlaw W. G. , Fabris A.
Published: February 2004

The magnitude of the non-Markovian contribution to the rate of a reaction is investigated for systems interacting through a potential having a finite extension in space. The investigation is carried out within the context of the field-theoretic Green's function approach to kinetics.
Ion Impact Spectroscopy: Inelastic Scattering of 150–500-eV H+ and H2+ from N2, CO, C2H2, and C2H4
Authors: Moore John H. , Doering John P.
Published: February 2004

A high-resolution ion impact spectrometer has been constructed to measure the energy lost by ions which have been inelastically scattered from molecular targets. Inelastic collisions between 150–500-eV H+ and H2+ and N2, CO, C2H2, and C2H4 were observed in which the energy lost corresponded to electronic transitions in the target molecules. Most of the observed energy losses were assigned to known transitions in the targets. The cross sections for the observed electronic excitations are large. Ion impact excitation in the cases studied appears to be a very specific process because only certain types of transitions are excited in molecules which have a large number of available electronic states. Proton impact was found to excite only singlet–singlet transitions while H2+ impact preferentially excited certain types of singlet–triplet transitions. The implications of the specific nature of the observed excitation as well as the general spectroscopic utility of the method are discussed.
Range Relaxation. IV. Optimal Series Expansion Coefficients for Molecular Potential Curves and Surfaces
Authors: Empedocles Philip
Published: February 2004

A simple many-dimensional (multiple) perturbation–variation scheme is invoked to generate the coefficients in the expansion of an energy curve or surface about some origin, to arbitrary small order. These expressions appear in a form in which it is unnecessary to start with a full set of eigenvectors and eigenvalues of the Hamiltonian. This permits their use in conjunction with large-scale configuration-interaction calculations. The relaxation of both linear and nonlinear parameters in the wavefunction from their values at the origin is taken into account. The expansion can be used as a basis for the development of both range and pass relaxation functions. The approach abridges the more conventional two-step procedure of calculating the energy at a set of points which must subsequently be fitted to a polynomial. It eliminates thereby the repeated laborious solution of the eigenvalue problem. For the particular case of a one-dimensional coordinate representing a uniform scaling of the nuclear positions it is trivially easy to generate matrix-element derivatives by scaling. In application to several small molecules using a Gaussian-type basis in both SCF–MO and CI frameworks such simple scaled matrix elements are shown to provide a reasonably good basis over a useful range of coordinates. In the particular case of a 20 configuration wavefunction for H2+ the scaled and conventional curves are partically indistinguishable over a range 0.25–15.0 a.u. The results are reproduced over a more limited section of the curve using the perturbation expansion in the inverse of the internuclear distance.
Ultraviolet Absorption Spectrum of Carbonyl Sulfide
Authors: Breckenridge W. H. , Taube Henry
Published: February 2004

The absorption coefficients of gaseous carbonyl sulfide have been measured in the spectral region 2000 to 2650 Å. Band structure has been observed superimposed on apparently continuous absorption. The bands can be arranged into four progressions, one of which arises from population of an excited vibrational level of the ground electronic state. It is concluded from the temperature dependence of the long wavelength portion of the spectrum that the “continuous” absorption is due to a transition to a bent upper state of OCS, namely (1Δ)1A′ or (1Σ−)1A″.
Lifetime Studies of Na(32P) and Tl(72S) Produced by Photodissociation and Quenched by Halogens
Authors: Brus L. E.
Published: February 2004

The time dependence of Na(32P) fluorescence produced by pulsed, far-ultraviolet photodissociation of NaI vapor at 600°C has been directly observed via the method of single-photon counting. The experimental apparatus and procedure are described. Sodium iodide molecules photodissociate in a time much less than 1 nsec, and the fluorescence decay is exponential with τ = 16.0 ± 0.2 nsec. No evidence of collision-induced fluorescence is seen, and quenching of the fluorescence by NaI vapor itself is not observed. Quenching by iodine vapor is studied as a function of pressure, and I2 molecules are shown to be at least 30 times more effective quenchers than I atoms. The velocity dependence of the I2 cross section in the range ∼ 12 − 25 × 104 cm/sec is studied by varying the photodissociation pulse wavelength. The fluorescence of Na(32P) following photodissociation of NaBr and of Tl(72S) following photodissociation of TlI are also observed. An average cross section for the quenching of Na(32P) by Br2 is reported. Both TlI and I2 are observed to quench Tl(72S) quite strongly, with I2. having a cross section of ∼ 490 Å2 at ∼ 4 × 104 cm/sec. The quenching process is discussed, principally in terms of the “harpooning” mechanism. Comparison is made with analogous molecular beam experiments.
ESR Study of Quantum Tunneling of a Methyl Group: A Simple Tunneling Model
Authors: Davidson R. B. , Miyagawa Ichiro
Published: February 2004

The ESR absorption of the intermediate radical CH3⋅CHR from l-alanine was studied at 4.2°K. It was found that the methyl group spectrum for the a axis was different than that for the c axis. While Freed's theory J. Chem. Phys. 43, 1710 (1965)] failed to explain this fact, a simple quantum-tunneling model was found to account for the observations satisfactorily, attributing the observed difference to an anisotropic dipole–dipole interaction. It was shown that an hfs splitting having any functional dependence on the angle of twist Θ results in the characteristic splitting of the E states. A methyl proton which has the cos2Θ dependence assumed by Freed was found to be a special case exhibiting this E state splitting.
ESR Study of the Kinetic Isotope Effect in the Reaction of H and D Atoms with CH4
Authors: Kurylo Michael J. , Hollinden Gerald A. , Timmons Richard B.
Published: February 2004

ESR atom detection has been employed to determine the kinetic isotope effect involved in the reactions: H+CH4→H2+CH3, D+CH4→HD+CH3.New data were obtained for Reaction (1) leading to a slightly revised value for k1 of (6.25 ± 2.00)  ×  1013exp[− (11 600 ± 150) / RT] in units of cm3 mole−1·sec−1. Assuming that the ratio of pre-exponential factors for Reactions (1) and (2) is 1.38 we compute a value for k2 of (4.5 ± 2.0)  ×  1013exp[− 11 100 ± 150) / RT] cm3 mole−1·sec−1. The observed kinetic isotope effect is compared with those calculated from absolute rate theory using the semiempirical Sato potential energy surface, or that obtained from the empirical bond-energy–bond-order (BEBO) method. These two methods give equally good predictions of the value of k1 / k2. Application of a one-dimensional tunnel correction results in poorer agreement between theory and experiments.
Enthalpies of Mixing in Binary Liquid Alkali Iodide Mixtures
Authors: Melnichak M. E. , Kleppa O. J.
Published: February 2004

The enthalpies of mixing of the binary liquid alkali iodide mixtures have been measured at 740°C. The results are compared with similar data for the binary alkali bromide, chloride and fluoride mixtures. They indicate that it is not possible to represent the enthalpies of mixing for a wider range of binary fused salt systems by any simple general formula. However, the results for all the considered binary iodides alone are well represented by a single semiempirical expression ΔHM = N1N2(U0++ − 540δ122kcal/mole. In this expression N1 and N2 are the mole fractions of the two components; δ12 = (d1 − d2) / d1d2, where d1 and d2 are characteristic interionic distances in the two salts, while U0++ represents a numerical estimate of the positive contribution to the enthalpy of mixing which arises from the London–van der Waals interaction between second nearest neighbor cations.
Heat Capacity, Enthalpy of Fusion, and Thermodynamic Properties of NpF6 from 7 to 350°K
Authors: Osborne Darrell W. , Weinstock Bernard , Burns John H.
Published: February 2004

Measurements of the heat capacity of NpF6 from 7 to 350°K by adiabatic calorimetry are reported. No anomalies were observed in the heat-capacity curve. The triple point is 327.91 ± 0.02°K, and the enthalpy of fusion is 4188.4 ± 4.0 cal mole−1. Thermodynamic functions are tabulated at selected temperatures. At 298.15°K, CP°, S°, H° − H°0, and (G° − H°0) / T for solid NpF6 are 40.02 ± 0.08 cal °K−1·mole−1, 54.76 ± 0.11 cal °K−1·mole−1, 7436 ± 15 cal mole−1, and 29.82 ± 0.06 cal °K−1·mole−1, respectively. At 340°K, S°, for gaseous NpF6 is 94.09 ± 0.38 cal °K−1·mole−1 from the calorimetric and vapor-pressure data, if Rln2 is added to the entropy obtained by extrapolation of the observed heat-capacity curve from 7 to 0°K. This value is in excellent agreement with S° calculated from statistical mechanics and molecular data.
Adsorption of Oxygen on Tungsten: Field Emission from Single Planes
Authors: Engel T. , Gomer R.
Published: February 2004

Work-function and Fowler–Nordheim pre-exponential changes for incremental oxygen adsorption at 20 and 100°K have been measured on the (120), (111), (100), (211), and (110) planes of a tungsten field emitter. On the (110) plane Δφ = 0.6 eV at full coverage, while Δφ = 1.2–1.4 eV on most other planes. A model of O adsorption based on the partial filling of an affinity band is presented to account for this and other features of the results. Diffusion into various planes was also investigated. It was found that low-temperature boundary diffusion at 25°K leaves the (110) plane bare. Diffusion in the chemisorbed layer starts at 400°K on (110) with an activation energy of 15 kcal, and on other planes at temperatures of ∼ 500°K.
Theory of Inelastic Collisions: The WKB-Type General Solutions
Authors: Eu Byung Chan
Published: February 2004

The WKB-type general solutions to a set of two and three coupled Schrödinger equations are obtained. A set of rules of obtaining the WKB general solutions for an arbitrary number of coupled Schrödinger equations is conjectured. These rules reduce the solution of the coupled equations to a problem of linear algebra. The special cases of the solutions for the two and three coupled equations are considered.
Statistical Mechanics of Rodlike Particles. I. A Scaled Particle Treatment of a Fluid of Perfectly Aligned Rigid Cylinders
Authors: Cotter Martha A. , Martire Daniel E.
Published: February 2004

In order to test the suitability of the scaled particle approach for anisotropic fluids of nonspherical particles (this approach had not previously been used with systems of markedly nonspherical particles or with anisotropic fluids of any sort), a scaled particle treatment is applied to a fluid of rigid cylinders of radius a and length l with cylindrical axes all constrained to lie in the same direction but with centers of mass free to move translationally throughout a volume V. Expressions for the equation of state and chemical potential are obtained through consideration of the reversible work W (α, λ, ρ) necessary to add a scaled cylinder of radius α and length λ at some arbitrary fixed point in the fluid. Because of the simple particle shape, the complete arguments used by Reiss, Frisch, and Lebowitz in their original scaled particle treatment of rigid spheres can be extended to aligned cylinders without making any additional approximations, permitting the equation of state to be obtained by two independent methods. Identical expressions for (p / ρkT) are derived from both, demonstrating that the scaled particle approach is capable of yielding self-consistent results for an anisotropic fluid of markedly nonspherical particles.
Variational Principles from the Schwarz Inequality
Authors: Kim Chin Hyung , Kern C. William
Published: February 2004

The Schwarz inequality is used to generate variational principles for evaluating perturbation sums. By constructing two suitable kets and applying Schwarz's inequality to them, a bound results which contains an arbitrary (variational) operator. The method is illustrated with reference to a family of frequency-dependent sums for which the corresponding bound is shown to be a generalized form of Hylleraas's variation–perturbation principle. It is also pointed out that the Schwarz inequality provides bounds on simple matrix elements.
Collisional Stimulation of the O(1S)–O(1D) Emission of Oxygen Atoms Formed in Vacuum-Ultraviolet Photolysis of Nitrous Oxide
Authors: Hampson R. F. , Okabe H.
Published: February 2004

Oxygen atoms in the S1 state have been produced by the vacuum-ultraviolet photolysis of N2O and observed by their emission at 5577 Å in the S–1D1 transition. The stimulation of this emission by collision with added gases has been studied. The emission has been found to be proportional to the pressure of the added gas. Xenon is the most efficient stimulator of the gases used, followed in order of decreasing efficiency by Kr, Ar, N2, H2, and He. Data gotten by photolysis of NO2 and CO2 have been used to estimate their quantum yields for formation of O(1S).
Approximate Molecular Orbital Calculations for the Transition-Metal Carbonyls, Ni(CO)4, Co(CO)4−, Fe(CO)4=, Fe(CO)5, and Cr(CO)6
Authors: Hillier Ian H.
Published: February 2004

The nature of the bonding in five transition-metal carbonyls is investigated by means of self-consistent charge molecular orbital calculations. The inclusion of ligand field terms is shown to have a critical influence on the results obtained. The results are compared with available ionization data for the transition-metal carbonyls.
Some Structural Aspects of IF6+AsF6− from NMR Data
Authors: Hon J. F. , Christe K. O.
Published: February 2004

Broad-line NMR spectra obtained from polycrystalline IF6+AsF6− show that the IF6+ cation is slightly distorted, but no evidence is found for distortion of the AsF6− anion. Approximate chemical shifts were obtained for the 19F and 127I resonances.
Infrared and Raman Spectra of ClHCl− and BrHBr− Ions in CsCl·13H3OHCl2and CsBr·13H3OHBr2
Authors: Schroeder LeRoy W.
Published: February 2004

Infrared and Raman spectra of CsCl·13H3OHCl2and CsBr·13H3OHBr2 have been measured in the 50–4000- cm−1 region. The spectra show the bands expected for the oxonium ion plus bands due to the XHX− ion. The XHX− ions are in a symmetrical environment, and a consistent interpretation of the spectra suggests that the XHX− ions have a centrosymmetric structure in these salts.