bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of Scattering Data for Mixtures of Amorphous Solids or Liquids
Authors: Pings C. J. , Waser J.
Published: February 2004

Results are derived which show that in the analysis of x-ray or neutron-scattering data from mixtures of amorphous solids or liquids, a meaningful scattering function, i(s), can always be computed without recourse to simplifying assumptions regarding the atomic scattering functions. Fourier inversion of i(s) yields a distribution function, H(r) = ΣΣxixjHij(r), where xi is the atomic fraction of species i, and Hij(r) is the convolution of the true net radial-distribution function, hij(r), with a particular function of the atomic scattering factors. The much-used assumption that all atomic-scattering factors are proportional to the same function yields an H(r) that is a weighted sum of the hij(r), but does not offer any means of ascertaining the individual hij(r) terms if only one scattering experiment is performed.
Vibrational Anharmonicity in the Methyl Halides
Authors: Reichman Sandor , Overend John
Published: February 2004

A simple model has been assumed for the anharmonic intramolecular potential function of the methyl halides; a quadratic potential in instantaneous curvilinear coordinates has been supplemented with Morse functions for the bond-stretching coordinates. All parameters in this potential function are known from other work, and the model could therefore be used to estimate the anharmonic spectroscopic parameters of the methyl halides. These are discussed and compared with the experimental values where the latter are known. Systematic differences in the calculated anharmonic constants Xss′ for the symmetric and asymmetric CH stretching vibrations are noted, and an explanation is offered. The concept of group anharmonicities has also been investigated.
X-Ray K-Absorption Edge of Yttrium in Some Yttrium Compounds
Authors: Bhide V. G. , Bhat N. V.
Published: February 2004

The x-ray K-absorption edge position and the extended structure of yttrium in several compounds have been investigated using 400-mm bent-crystal (mica) spectrograph. The absorption edge position and the extended structure for Y3 + in dilute aqueous solutions of several salts have been found to be identical indicating that Y3 + ions absorb as if they are in vacuum. The absorption edge position for the Y3 + ion in a solution has been taken as a reference with which the edge position for Y3 + ions in different compounds is compared. The shift of the absorption edge towards the lower-frequency side seems to be related to the covalency. If the near neighbors are unchanged, a change in the distant neighbors does not affect the absorption edge position appreciably.
Raman Spectrum and Structure of N2F4
Authors: Durig James R. , Clark James W.
Published: February 2004

The Raman spectra of liquid N2F4 at temperatures ranging from −80° to −150°C have been recorded. Depolarization values have been measured. The far-infrared spectrum of the vapor and solid has also been reinvestigated. Seventeen pronounced Raman lines have been observed whereas the C2 isomer of tetrafluorohydrazine has only 12 fundamentals. The large number of Raman lines suggests the presence of more than one isomer at −120°C. A comparison of the infrared and Raman bands below 800 cm− 1 shows the mutual exclusion principle is operative and it is concluded from this alternate forbiddeness that the trans-N2F4 isomer of C2h symmetry gives rise to these mutually exclusive bands. Assignment of the observed frequencies based on depolarization values, band positions, and infrared band contours are presented for the molecule in both the C2 and C2h configurations. It is shown that the data can only be interpreted in terms of an equilibrium mixture of the two isomers at both ambient and lower temperatures, and that these isomers differ little in energy.
Rotation–Vibration Interaction and Barrier to Ring Inversion in Cyclopentene
Authors: Scharpen LeRoy H.
Published: February 2004

The contributions to the effective rotational constants of cyclopentene originating in the term in the Hamiltonian which couples the ring-bending vibration with rotation are examined. After corrections which depend only on experimentally determined parameters are applied to the constants for υ = 0 and υ = 1, the ring-bending vibrational dependence of the constants is expressible as an expansion in expectation values of even powers of the bending coordinate. Analysis of the rotation–vibration interaction yields a ring-bending potential function which is in excellent agreement with results of far-infrared studies of other workers; both sets of data are consistent with a barrier to ring inversion of 232 ± 5 cm−1. The results given in this paper are also necessary for a correct interpretation of the dependence of rotational constants in methylenecyclobutane and trimethylene sulfide on the ring-puckering vibrational state.
Normal Coordinate Calculations as a Tool for Vibrational Assignments. I. Fundamental Vibrations of Simple Aliphatic Amines
Authors: Dellepiane Giovanna , Zerbi Giuseppe
Published: February 2004

Fundamental frequencies, normal coordinates, and force constants were calculated using an Overlay technique for CH3NH2, CD3NH2, CH3ND2, CD3ND2, (CH3)2NH, (CH3)2ND, (CH3)3N, and (CD3)3N. Both valence and Urey–Bradley force fields were adopted. The vibrational assignments previously reported on all these molecules have been partly confirmed and partly modified. The usefulness and limitations of normal coordinate calculations in problems of vibrational assignments is discussed.
Pi-Electron Hamiltonian. II. Inclusion of Self-Consistent Screening
Authors: Harris Robert A.
Published: February 2004

Pi-electron Hamiltonians are derived which contain self-consistent screening in zeroth order, and sigma–pi coupling through second order. It is shown that the Coulomb interaction between pi electrons is modified by a frequency-dependent inverse sigma dielectric matrix. The nature of the dielectric matrix is discussed.
Mass-Spectrometric Studies of Bonding in the Group IIA Fluorides
Authors: Hildenbrand D. L.
Published: February 2004

A mass spectrometer was used to study high-temperature gaseous equilibria of the type M(g) + MF2(g) = 2MF(g), where M = Mg, Sr, and Ba. The heat of this reaction gives directly the difference between bond dissociation energies D (MF −F) − D (M −F). Results obtained for the above equilibrium were ΔH298 = 25.6, 2.1, and −6.7 kcal (all ±2 kcal) for Mg, Sr, and Ba, respectively. In addition, the dissociation energies, D°298, of MgF, SrF, and BaF were determined as 110.4 ± 1.2, 129.5 ± 1.6, and 140.3 ± 1.6. Although the bond dissociation energies of the lighter Group II fluorides are in qualitative accord with the simple s – p valence state scheme of covalent bonding, this model breaks down rather badly for the heavier metal fluorides. It appears, however, that the bond dissociation energies of these heavier fluorides can be accounted for quite well by an electrostatic model which considers each molecule as an assembly of polarizable ions. The measured dissociation energies of the metal monofluorides can be correlated reasonably well with the spectroscopic values of D0° if the degree of ionic character is considered.
Thermal-Diffusion Factors from the Measurements on a Trennschaukel:Ne–Ar and Ne–Xe
Authors: Saxena V. K. , Nain V. P. S. , Saxena S. C.
Published: February 2004

Measurements of the thermal-diffusion factor for Ne–Ar and Ne–Xe systems are reported at about 45°C as a function of composition. These were obtained on an eight-tube glass trennschaukel with the two ends maintained at 0° and 100°C. Certain previously drawn conclusions for the efficient design and operation of a trennschaukel are confirmed. The new data are compared with the existing one and also interpreted on the basis of the Chapman–Enskog kinetic theory and modified Buckingham exp-6 intermolecular potential. In general, the agreement between the new measured values and the other existing data is good. Independent measurements taken on a two-bulb apparatus and under similar experimental conditions also confirm the trennschaukel results. The theory is in approximate agreement with the experiments over the whole range of composition of the binary mixtures.
Vibrational Intensities. XVI. COF2, COCl2, and COBr2
Authors: Hopper M. J. , Russell Joel W. , Overend John
Published: February 2004

The integrated intensities of all the vibrational fundamentals of COF2 COCl2, and COBr2 have been measured. From these, the values of the dipole-moment derivatives have been found. A particularly interesting feature of these results is that numerical values of ∂μ / ∂r for the carbonyl bond can be found without resolving the well-known sign ambiguity of the ∂p / ∂Q's. We find for COF2, ∂μ / ∂rCO = 4.70 ± 0.7 D / Å; for COCl2, ∂μ / ∂rCO = 4.75 ± 0.2 D / Å; and for COBr2, ∂μ / ∂rCO = 5.25 ± 0.2 D / Å.
Microwave Spectrum of Acryloyl Fluoride
Authors: Keirns J. J. , Curl R. F.
Published: February 2004

The microwave spectrum of HF||H2C=C–C=O has been studied in the region 8–26 GHz. Two planar rotational isomers have been assigned. Only a-type transitions have been assigned for ground-state and first and second torsional excited states of the s-trans form. Both a- and b-type transitions have been assigned for the ground-state and first and second torsional excited states of the s-cis form. The ground-state energy difference between the two forms was found to be 90 ± 100 cal/mole with the s-trans the more stable form. The electric dipole moment of the s-trans form has been found to be 3.26 D oriented 29° from the carbon–oxygen bond. The dipole moment of the s-cis form was found to be 3.21 D oriented 53° from the carbon-oxygen bond.
Ion-Pair Theory of Concentrated Electrolytes. I. Basic Concepts
Authors: Stillinger Frank H. , Lovett Ronald
Published: February 2004

The statistical thermodynamics of symmetrical “primitive-model” electrolytes is formulated in such a way that all ions are uniquely paired. The behavior of the resulting fluid of “polar molecules” may conveniently be described by a wavelength-dependent dielectric constant ε(k). A rigorous formula of the Kirkwood type for ε(k) is derived. Since ion-atmosphere mean charge densities may be obtained from ε(k), this dielectric function is utilized in construction of an electrolyte free-energy expression [Eq. (50)], as well as to establish an exact second-moment condition on the ion atmospheres [Eq. (73)]. From the latter it is demonstrated that for rigid spherical ions of diameter a, the ion atmospheres necessarily each have nonuniform charge sign when κa > 61 / 2 (κ− 1 = Debye length).
Vibrational Spectra and Structures of Ionic Liquids. II. The Pure Alkali Metal Nitrates
Authors: Williamson Ken , Li Paul , Devlin J. Paul
Published: February 2004

Attenuated total reflection infrared spectroscopy has been used together with thin-film transmission measurements to obtain detailed spectra for the molten nitrates of lithium, sodium, and potassium in the 250–4000-cm−1 range. The techniques, which yield spectra approaching the ultimate in resolution and precision possible for salt melts, permit the detection of several features which, when combined with Raman data, definitely rule out a melt structure dominated by either ion pairs or simple 1:1 complexes. Rather, systems wherein important factors include both cation distortion of the nitrate symmetry (site effect) and vibrational coupling of neighboring anions (correlation field effect) are definitely suggested. Thus, an assignment based on a perturbed orthorhombic lattice structure is presented which accounts very satisfactorily for all observed features. Order in the melts seems to be slightly greater in LiNO3 than for the other salts.
Glory Scattering of Lithium by a Series of Molecules. I. Diatomics
Authors: Helbing Reinhard K. B. , Rothe Erhard W.
Published: February 2004

The velocity dependence of the total cross section has been measured for the scattering of lithium-7 by D2, N2, O2, CO, NO, HF, HCl, DCl, HBr, HI, ICl, Cl2, and Br2. Glory undulations are observed for all systems except Cl2 and Br2 although in some cases these undulations are considerably smaller than might be expected for comparable atom–atom scattering. Potential parameters are derived for these systems. Chemical reaction, time-dependent anisotropic potentials, and inelastic processes are discussed as possible mechanisms for the observed quenching.
Linewidths of the Rotational Spectra of Symmetric-Top Molecules
Authors: Roberts James A. , Tung T. K. , Lin Chun C.
Published: February 2004

Measurements of linewidths are reported for some 50 rotational transitions (J→J + 1) of the CH335Cl, CH337Cl, CH379Br, CH381Br, CH3I, CH3CN, and CH3CCH molecules. The CH3CN molecule has exceptionally wide lines (100 Mc/sec·torr) due to the large dipole moment (3.92 D). The experimental data are compared with the theoretical widths which are calculated using the Anderson theory with dipole–dipole interaction. With the exception of the CH3CCH molecule, the theoretical widths are larger than the experimental ones. The over-all agreement between theory and experiment is within 30%.
Group-Theoretical Analysis of Lattice Vibrations in Molecular Crystals
Authors: Chen S. H. , Dvorak V.
Published: February 2004

A practical method of analysing the external vibrations of molecular crystals according to the representation theory of space group is presented. The procedure, which is a direct extension of the method given for the ordinary crystal by one of the authors, is applicable to any complicated molecular crystal. The result should be useful to both neutron and Raman spectroscopy. Detail on hexamine, adamantane, and ammonium chloride crystals has been worked out, and the result for hexamine is compared with actual calculation by Cochran and Pawley.
Theoretical Calculations of the Kinetics of the Order–Disorder Transition in Carbon Monoxide and of the Energy Levels of a Double-Minimum Two-Dimensional Hindered Rotor
Authors: Curl R. F. , Hopkins H. P. , Pitzer Kenneth S.
Published: February 2004

The kinetics of the order–disorder transition in solid carbon monoxide by a tunneling mechanism are considered. The rate of the transition is found to be much smaller than the rate of barrier penetration. An estimate of the rate is made using the best current estimate of the twofold barrier to end-for-end rotation in solid carbon monoxide; it appears that the rate of ordering will be unobservably slow. The rate is very sensitive to the barrier height and might become observable if the barrier were smaller by a factor of 2. The energy levels of the two-dimensional double-minimum hindered rotor have been calculated as a function of barrier height and are tabulated.
n→π*
Transitions in a Diazine: Phthalazine
Authors: Hochstrasser Robin M. , Marzzacco Charles
Published: February 2004

The absorption spectrum of phthalazine single crystals and mixed crystals with naphthalene at 4.2°K are presented and analyzed. The near-uv region displays two nπ*1 states each having A2 electronic symmetry. The gap between the two states is 1657 cm−1 in the crystal, 1672 in the mixed crystal, and 1685 cm−1 for phthalazine-d4 in the mixed crystal. Both states display a1, b1, and a2 vibrations that correlate well with naphthalene modes of known symmetry. It is shown that this interpretation of the spectra is at variance with MO theory, and the results most probably dramatize the effects of charge reorganization in the nπ* excited states.
Stability and Uniqueness of the Equilibrium Point in Chemical Reaction Systems
Authors: Shear David B.
Published: February 2004

It has recently been established that equilibria are stable in the large for coupled chemical reaction systems of arbitrary complexity and arbitrary mixtures of orders, so long as the rates of change of the amounts of the species present are derivable from mass-action rate equations. The proof, employing Liapunov's direct method, is entirely kinetic. It is now shown that there can never be a continuum of equilibrium points accessible to a reaction system. An argument based on stability in the large is used to show that if there were a second equilibrium point accessible to a reaction system, there would have to be a continuum of equilibrium points connecting the two. Consequently, there cannot be more than one equilibrium point for any given reaction system. A proof that there must be at least one equilibrium point has also been given, based on Brouwer's fixed-point theorem. Thus, each reaction system has one, and only one, equilibrium point.
Harmonic Oscillator in Atomic and Molecular Physics
Authors: Moshinsky M. , Novaro O.
Published: February 2004

Harmonic oscillator states have played an important role in nuclear structure. This has encouraged nuclear physicists to develop elaborate mathematical techniques, based on group theory, for dealing with n-particle states in the harmonic oscillator (ho) potential. The n-particle ho states are used in this article to represent the electronic wavefunctions. The matrix elements of the physical Hamiltonians with respect to the n-particle ho states are explicitly evaluated. Applications to atoms and diatomic molecules of up to four electrons are given as well as a discussion of H3+. An analysis for closed shells in the ho potential, where the matrix elements can be reduced to those of one or two particles, is also given. The validity of the approximations involved and the possibilities of the method are discussed critically.
Nuclear Resonance in the Solid Methylamines. I
Authors: Haigh P. J. , Canepa P. C. , Matzkanin G. A. , Scott T. A.
Published: February 2004

Proton NMR lines have been studied in solid NH2CH3, NH(CH3)2, and N(CH3)3 from 4.2°K to the respective melting points. All the lines show a line-narrowing transition beginning, on warming, at about 40°, 65°, and 105°K, respectively. Second moments as well as peak-to-peak linewidths and line shapes have been measured in an attempt to determine the physical situation responsible for these transitions. Pure quadrupole resonances of 14N have also been observed in these compounds from 4.2°K to their melting points and the coupling constants and asymmetry parameters determined. A first-order phase change was detected in monomethylamine. This transition occurs at 55° ± 2°K on cooling and at 105° ± 2°K on warming. Two pairs of lines were seen in dimethylamine indicating two chemically inequivalent sites. Coupling constants (and asymmetry parameters) at 4.2°K are: monomethylamine 4.0180 MHz (0.3697), dimethylamine 4.6810 MHz (0.3339) and 4.6452 MHz (0.3228), and trimethylamine 5.2377 MHz (0).
Magnetothermodynamics of α-NiSO4·6H2O. III. Derivation of Spin-Hamiltonian–Molecular-Field Parameters from Experimental Data
Authors: Fisher R. A. , Hornung E. W.
Published: February 2004

Magnetothermodynamic data for α-NiSO4·6H2O, with magnetic fields along two axes, the c crystallographic axis ([001] direction) and the [110] direction, have been interpreted using a spin-Hamiltonian–molecular-field model for the NI(H2O)6+ 2 complexes. Best values for the spin-Hamiltonian parameters are D = 4.741 cm− 1 (singlet–doublet separation for H = 0); gz = 2.2158, gxy = 2.2495 (principal values for the g tensor of the Ni(H2O)6+ 2 complexes); φ = 39.00° (angle the z magnetic axes of the four Ni(H2O)6+ 2 complexes per unit cell makes with the c tetragonal screw axis—the x magnetic axes are perpendicular to the tetragonal axis); γ = 0.272 mole / cm3 (molecular field constant representing an isotropic combined ferromagnetic exchange and dipole–dipole interaction between Ni+ 2 ions); and λ = − 281 cm− 1 (the spin–orbit coupling constant). For the c axis the temperature-independent susceptibility α was computed to be 0.75 × 104, while for the [110] direction it was 0.98 × 10− 4 cm3/mole. However, a best fit to the magnetic-moment data for the [110] axis was obtained using only the diamagnetic susceptibility, −1.25 × 10− 4 cm3/mole. A detailed analysis of the methods used in obtaining the parameters from the data is given. The over-all fit to all of the magnetothermodynamic data is excellent, constituting a “textbook” example of the spin-Hamiltonian–molecular-field method.
Polarization of Atomic Fluorescence Excited by Molecular Dissociation
Authors: Van Brunt R. J. , Zare R. N.
Published: February 2004

Fluorescence from excited atomic fragments which arises from molecular dissociative processes can be shown in general to be polarized. The degree of polarization is related to the form of the anistropy in the angular distribution of dissociation products.
Dissociation of HCl Behind Shock Waves
Authors: Seery Daniel J. , Bowman Craig T.
Published: February 2004

The dissociation of HCl in HCl–Ar mixtures was studied behind incident shock waves over the temperature range 2900°–4000° using vacuum ultraviolet absorption spectroscopy. The experiments were conducted using gas mixtures of 1% HCl–99% Ar and 2% HCl–98% Ar. For the reaction HCl + Ar→H + Cl +  Ar, a rate constant k1 = 4.2 × 1013 exp (− 81 000/RT) cm3mole·sec gave the best fit of the experimental data. This result agrees with the results obtained by Fishburne and Jacobs et al. using infrared emission spectroscopy. The apparent activation energy for HCl dissociation was found to be less than the dissociation energy.
Interatomic Potentials for HeNe, HeAr, and NeAr
Authors: Konowalow Daniel D.
Published: February 2004

Semiempirical potentials for HeNe, HeAr, and NeAr are determined according to Nesbet's scheme from Hartree–Fock (H–F) repulsions and the experimental Boyle temperature in terms of the (exp-6) and Morse models. For the Morse model, the agreement with potentials determined entirely from experimental data is within about 10%; it is poorer for the (exp-6) model. However, both models afford poor agreement with the theoretical − C6r−6 dispersion attraction. Hybrid model potentials, constructed by equating the H–F repulsion with the repulsive term of the model potential and requiring a first-order contact with the theoretical dispersion, have much too shallow a well. Possible means for obtaining improved hybrids are explored.
Intra-atomic Magnetic Interactions in fn Configurations. I. Spin–Spin Interaction for f2 and f3 Configurations
Authors: Malli Gulzari , Saxena K. M. S.
Published: February 2004

The spin–spin interaction matrix elements have been evaluated for all the states arising from f2 and f3 electron configurations. These matrix elements have been used to calculate the spin–spin interaction for Ce(4f2) with Z = 58 and Pr(4f3) with Z = 59 using numerical Hartree–Fock wavefunctions.
Quantum Dynamics of Triatomic Molecules
Authors: Smyser William E. , Wilson David J.
Published: February 2004

The quantum dynamics of the bond-stretching motions of linear triatomic molecules with Morse bond potentials were studied. It was found that expansion of the energy eigenfunctions in terms of sums of products of eigenfunctions of Morse diatomic molecules was greatly superior to expansions in sums of products of simple-harmonic-oscillator wavefunctions, as expected. Vibrational energy levels calculated by second-order perturbation theory from the Morse basis set were essentially as good as those obtained by the linear variation method and were much easier to obtain; the wavefunctions showed some inaccuracy where accidental near-degeneracy of the corresponding energy levels occurred. The behavior of 〈r1(t)〉 and 〈r2(t)〉 was investigated for various initial wave packets. Rapid transfer of energy from one bond to the other was observed. It was noted that all motions having vibrational energies up to at least half the dissociation energy were combinations of stable symmetric and stable antisymmetric modes of oscillation.
Electron Spin Resonance of High-Spin d5 Systems
Authors: Dowsing R. D. , Gibson J. F.
Published: February 2004

The electron spin resonance spectra of polycrystalline samples of some sideramines (coprogen, ferrichrysin, ferricrocin, and ferrirubin), transferrin, and conalbumin are reported both at 9.3 and 36 kMc/sec and at various temperatures. These results have been interpreted in terms of a spin Hamiltonian of the form H = gβH·S + D[Sz2 − 13S(S + 1)] + E(Sx2 − Sy2). The application of this interpretation to other high-spin d5 systems both in single-crystal and polycrystalline form is discussed.
Polymorphic Behavior of Titania under Dynamic Loading
Authors: Linde Ronald K. , DeCarli Paul S.
Published: February 2004

Single-crystal and polycrystalline specimens (including powder compacts of various densities) of titanium dioxide have been subjected to shock-wave pressures in the 150–1000–kbar range. Hugoniot measurements have disclosed a phase transition commencing below 200 kbar, and x-ray diffraction studies of specimens recovered after shocking to various pressures above 150 kbar have shown the presence of an orthorhombic phase with the α-PbO2 structure. Calculated lattice parameters are a = 4.55 Å, b = 5.46 Å, and c = 4.92 Å, which correspond to a crystal density of 4.34 g/cm3. The orthorhombic phase appears to result on release of pressure from a considerably denser phase of TiO2 (postulated to have approximately 8:4 oxygen-titanium coordination) that dynamic measurements indicate is formed under shock. Yields of the α-PbO2 phase as high as about 90% have been obtained from [001]- and [111]-oriented rutile crystals shocked to 450 kbar. At atmospheric pressure this phase can be retained indefinitely at temperatures below 340°C, but reverts to rutile rapidly at 550°C. An activation energy of 66 ± 5 kcal/g-mole has been computed for reversion of specimens containing predominantly the orthorhombic phase but also containing some nuclei of rutile. The average crystallite size of shocked material is typically as small as 100–200 Å, and crystallites obtained from initially single-crystal rutile exhibit preferred orientation. Shocked specimens of rutile and of the orthorhombic phase have ESR spectra that exhibit surface-sensitive behavior, but which do not appear to be dependent upon the relative amounts of rutile and orthorhombic phase present. Petrographic and electron microscopy observations of shocked material are also reported.
Semigrand Isobaric–Isothermal Ensemble Distribution Functions and Their Use in Solution Theory
Authors: Keizer Joel E.
Published: February 2004

Thermodynamic distribution functions are defined in the semigrand isothermal–isobaric ensemble. It is shown that Hill's constant-pressure solution theory can be rewritten in terms of these distribution functions. An expression for the solvent chemical potential for a two-component solution is obtained using certain pair distribution functions and the intermolecular potential. A simple relationship between distribution functions and Stockmayer's concentration fluctuation term for the turbidity is derived.
Exciton-Controlled Proton Relaxation Times in Some Ion Radical Salts of TCNQ
Authors: Nyberg Graeme , Chesnut D. B. , Crist Buckley
Published: February 2004

Proton spin-lattice relaxation times in several ion–radical salts of TCNQ have been measured over a range of temperature. The temperature dependence of T1 in these materials (which contain thermally activated triplet excitons) suggests that ψc, the correlation time of the relaxation mechanism, may be written as ψc−1 = ψ0−1ρ, where ρ is the exciton density per lattice site and ψ0 a time characteristic of the system. This assertion is supported by a very close agreement of correlation-time activation energies and triplet-exciton activation energies.
Anisotropy of Molecular Rotations Measured by NQR Relaxation
Authors: Tzalmona A.
Published: February 2004

The highly anisotropic spin–lattice relaxation times in pure nuclear quadrupole resonance of 14N in piperazine are investigated in terms of anisotropic molecular rotations with respect to the principal axes of the electric-field-gradient tensor. A sudden approximation is used to obtain relations between the geometrical parameters of the molecular rotations and the correlation time involved. The double resonance technique is used to determine the relaxation times of the three-energy-level system.
Hole and Particle Distribution in Water
Authors: Ben-Naim A.
Published: February 2004

The hole–particle and the hole–hole correlation functions were calculated for water at several temperatures and compared with the corresponding functions for liquid argon. The unique structure of liquid water as revealed in these results is discussed.
Fine Structure of the X-Ray K-Absorption Spectrum of Yttrium
Authors: Bhide V. G. , Bhat N. V.
Published: February 2004

The x-ray K-absorption spectrum of metallic yttrium has been investigated using a 400-mm bent crystal (mica) spectrograph. The extended fine structure has been explained in the light of Hayasi's theory. The bond lengths have been computed for the yttrium metal and five of its compounds using Lytle's analysis. Plasma oscillation theory seems to explain satisfactorily the first two absorption maxima close to the absorption edge.
Deuteron Magnetic Resonance Study of Cupric Sulfate Pentahydrate
Authors: Soda Gen , Chiba Takehiko
Published: February 2004

A deuteron magnetic resonance study is made of single crystals of CuSO4·5D2O between 130° and 360°K. The electric quadrupole coupling constant, the asymmetry parameter, and the directions of the principal axes of the field-gradient tensor are determined for each deuteron at 133.2° and 294.8°K. At low temperatures ten pairs of lines are observed, corresponding to five nonequivalent stationary water molecules. At temperatures above room temperature, five pairs of lines are observed; these are shown to result from fast molecular reorientation about the bisecting axis of each water molecule. An activation energy for the 180° reorientational motion is derived for each water molecule and is discussed in relation to the lonepair coordination of the oxygen atom of the water molecule and the hydrogen-bond strength. The field-gradient tensor for each stationary water molecule is discussed in relation to the structure of the hydrogen-bond system. For relatively weak asymmetric hydrogen bonds of O–H···O, an empirical equation, eQq/h = 310.0 − 3.0 × 190.6 / R(O···H)3 (kHz), is found to represent the observed values well, where R(O···H) is the O···H distance in angstrom units. For strong hydrogen bonds, there is a significant deviation from the above relation, indicating that the covalent effect is of importance in these cases. Coordination to a paramagnetic ion has no marked effect on the quadrupole coupling constant, but it appears to cause a rotation of the directions of principal x and y axes about the O–H bond. Two possible cases of the principal y-axes directions for the field-gradient tensor of the reorienting water molecule are analyzed in detail, and the available experimental data are classified into two groups. Theoretical formulas for the DMR spectra in the paramagnetic crystals are derived and compared with that in diamagnetic crystals. A local field due to the cupric ions is derived from the observed paramagnetic shift at 133.2°K for each deuteron and is found to be due to the electron nuclear spin dipole coupling. The spectra are observed at temperatures up to the dehydration point, and it is found that the free rotation of the water molecule does not occur in this temperature range.
Ab Initio Bond-Orbital Calculations. II. An Improved Procedure for Saturated Hydrocarbons
Authors: Hoyland James R.
Published: February 2004

The bond-orbital approach to calculations on saturated hydrocarbons given previously is improved by use of a more optimum basis set and through a more judicious choice of the bond orbitals. Calculations are carried out on methane, ethane, propane, and butane. Energy values, population analysis, and various computed properties are given and compared with the results of SCF calculations utilizing the same basis set.
Theory of Isotropic Hyperfine Interactions in Pi-Electron Free Radicals. I. Basic Molecular Orbital Theory with Applications to Simple Hydrocarbon Systems
Authors: Melchior M. T.
Published: February 2004

The general molecular orbital configuration interaction approach formulated by McConnell and others is used to express the hyperfine coupling matrix QA in terms of the properties of localized sigma bonds. [QA relates the coupling constant aA, A being 1H or any first row element, to the pi-electron spin-density matrix ϱπ through the expression aA =;trace (ϱπQA).] An important step is the inclusion of all overlap in the basis-set inner- and valence-shell atomic orbitals; failure to do this leads to artificial sensitivity of QA to sigma-bonding details. An orthonormal set of localized sigma-bond orbitals is generated from “equivalent” (two-center) orbitals by a transformation involving various overlap matrices. An approximation to this transformation is used to examine the salient features of QA. The theory supports the first approximation for aA in terms of diagonal elements of QA and ϱπ: aA≈QAAAρAAπ + ΣXQXXAρXXπ, where ρAAπ and ρXXπ are the pi-electron “spin densities” on atom A and its nearest neighbors. Contributions from inner-shell orbitals and interactions between sigma bonds are very important. It is shown that QAAA is particularly insensitive to environmental effects. The adjacent atom parameter QXXA involves contributions from all substituents on A (if any) and on X. If A is a multivalent atom these contributions occur with both positive and negative signs so that the ratio QXXA / QAAA is quite small and can, in principle, be either positive or negative, contrary to previous predictions. Application of the theory to the CH3 radical gives results which agree with experiment to well within the inherent uncertainties in the calculation. The CH3 results are used to choose semiempirical “excitation energies” for a calculation of QC and QH in a hypothetical CH2CH2±ion. For CH2CH2± the large diagonal elements of Q̄C and Q̄H (which include a zero-point “vibrational contribution”) are estimated as (in gauss) : Q̄CCC = +37.8 ± 3.0, Q̄C′C′C = −9.0 ± 1.0 and Q̄CCH = −27.2 ± 1.8. The first and last of these can be compared with the values observed in CH3, +38.3 and −23.0 G, respectively, showing that Q̄CCC is quite insensitive to the substituents on C but that Q̄CCH increases significantly with substitution on C. It is shown that these values of Q̄CCC and Q̄C′C′C give excellent agreement with experimental 13C data on selected aromatic radicals. The smaller elements of Q̄C and Q̄H are estimated (in gauss) : Q̄CC′C = +1.8, Q̄CC′H = −3.0, Q̄C′C′H = +1.8. The estimate of the off-diagonal element QCC′His in good agreement with empirical values which have been obtained for aromatic systems. Using CH3 as a model, the derivatives of QCCH and QCCC with respect to bond length and the effective nuclear charge of carbon are calculated and found to be an order of magnitude smaller than the results obtained by neglecting overlap.
Experimental Measurements of the Diffusion Coefficients of H Atoms in H2 and in H2–He and H2–Ar Mixtures
Authors: Khouw B. , Morgan J. E. , Schiff H. I.
Published: February 2004

The catalytic sink technique previously described was used to measure the diffusion coefficients of H atoms in H2 over the temperature range 202°–364°K and in H2–He and H2–Ar mixtures at 275°K. The rigid-sphere collision diameters of H atoms in H2, He, and Ar were 1.89, 1.94, and 1.84, respectively. However, the temperature dependence of the H–H2 diffusion coefficients does not fit the rigid-sphere equation but can be represented by the use of the Lennard-Jones parameters ε / k = 85°K and σ′H,H2 = 2.32 Å. Comparisons are made with values derived from viscosity data and with theoretical calculations.
Structure of the Alkali Hydroxides. III. Microwave Spectra of RbOH and RbOD
Authors: Matsumura Chi , Lide David R.
Published: February 2004

The microwave spectra of gaseous RbOH and RbOD have been measured with a high-temperature spectrometer. The spectra are generally similar to those observed in CsOH and indicate an essentially linear structure for rubidium hydroxide. The variation of rotational constant with excitation of the bending mode shows anomalies similar to those found in CsOH. The Rb–O bond length is found to be 2.305 Å, while the O–H distance is 0.965 Å. Analysis of the nuclear quadrupole hyperfine structure gives eqQ values of − 67.9 Mc/sec in 85RbOH and − 35 Mc/sec in 87RbOH.
Measurement of Ion–Molecule Reaction Rate Constants Using Ion Cyclotron Resonance
Authors: Buttrill S. E.
Published: February 2004

The theory of ion cyclotron resonance line shapes has been developed for the case where the ion does not suffer any collisions with the neutral gas molecules. Experimental results are in very good agreement with the theoretical line shape. Expressions have been derived for the single resonance signal intensities of both primary and secondary ions at low pressure. Ion–molecule reaction rate constants obtained for the following reactions were CH4++CH4→CH5++CH3, 9.5 × 10−10cm3/mole·sec, CH2D2++CH2D2→CH3D2+CHD2, 5.1 × 10−10, CH2D2++CH2D2→CH2D3++CH2D, 4.1 × 10−10, C2H2++C2H2→C4H2+H2, 3.9 × 10−10, C2H2+C2H2→C4H3++H, 8.3 × 10−10, and are in good agreement with rate constants obtained by other techniques.
X-Ray Diffraction Study of Some Concentrated Cobalt(II) Chloride Solutions
Authors: Wertz D. L. , Kruh R. F.
Published: February 2004

Diffraction results, interpreted in light of colligative measurements, indicate that the environment of Co(II) differs drastically when CoCl2 is dissolved in water and in alcohols. In H2O, the predominant cation species is Co (H2O)62+ with the Co–O distance being about 2.1 Å. In methanol and ethanol, the solute species is highly associated and each Co(II) has four chloride nearest neighbors at about 2.30 Å. The relative co-ordinating abilities of the potential ligands towards Co(II) are H2O > Cl− > CH3OH≃C2H5OH. Crystal radii serve to interpret bond distances.
Ion–Molecule Reactions in Alpha-Particle-Irradiated Methane and Water Vapor
Authors: Fluegge Robert A.
Published: February 2004

Ion–molecule reactions in methane and water vapor are investigated for the various primary, intermediate, and secondary species formed in parent gases bombarded by 1–3.5-MeV alpha particles. Reaction rates for CH4+ and CH3+ colliding with methane gas and for H2O+ and OH+ colliding with water vapor are given and compared to similar data obtained by others using electron ionization. Single alphas are detected, counted, and their number compared to the number of ions formed in the reaction chamber. A pulsed time-of-flight type of mass spectrometer is used to vary ion–molecule reaction times and to separate ions according to their mass to charge ratios. The well-defined “zero” time of interaction in this pulse counting experiment allows one to estimate a “lifetime” for shortlived intermediates; the results indicate a lifetime near 0.18 μsec for the excited (C2H7+)* ion formed as a collision complex of CH3+ and CH4. These experiments also reveal that collisions between either the OH+ or H2O+ ions with water vapor result in intermediates that have lifetimes far shorter than the 10−7 sec measured for (C2H7+)*.
Interferometric Investigation of Line Shapes in the Spectra of Rare-Gas Afterglows
Authors: Edwin R. P. , Turner R.
Published: February 2004

A search was made for line broadening in afterglows of krypton and neon. A previously reported case of dissociative recombination broadening in neon was observed. No other broadening due to recombination was found. Provided that momentum and excitation transfer is small, the absence of such broadening was interpreted as indicating that either the excited atoms are formed in upper atomic states or that the kinetic energy of dissociation is small for all atomic lines investigated.
Semiempirical Determination of the Hydrogen Bond Energy for Water Clusters in the Vapor Phase. I. General Theory and Application to the Dimer
Authors: Bolander Richard W. , Kassner James L. , Zung Joseph T.
Published: February 2004

A simple semiempirical method is given for determining the hydrogen bond energy for water clusters in the vapor phase. This method is based on a general statistical-mechanical theory of clustering. The partition function for a system of clusters is used to determine the equilibrium distribution of clusters. In conjunction with available thermodynamic and spectroscopic data, the cluster equilibrium constants can be used to calculate the cluster potential energy and the hydrogen bond energy. Results for the water dimer agree quite well with other reported values obtained either by quantum-mechanical calculations or approximate thermodynamic estimates. A correct temperature dependence of the bond energies is found.
Positronium Chemistry in Aqueous KMnO4 Solutions
Authors: Williams Thomas L. , Ache Hans J.
Published: February 2004

The reaction of positronium was studied in aqueous KMnO4 solutions at various concentrations and pH. Lifetime measurements show a distinct decrease of τ2 and increase of I2 with increasing temperatures, as expected for chemical reactions in which thermalized positronium is involved. No dependence on the pH of the solution could be observed. The activation energy calculated from the temperature dependence of τ2 is rather small and about 0.1–0.2 eV. The free positron annihilation lifetime was found to be approximately 0.55 nsec, which is in good agreement with the value obtained by using Dirac's formula, 0.5 nsec for water.
Absorptivity of Ice I in the Range 4000–30 cm−1
Authors: Bertie J. E. , Labbé H. J. , Whalley E.
Published: February 2004

The absorbance of several samples of ice Ih has been measured in the range 4000–30 cm−1, and scaled to that of a particular film of unknown thickness. The thickness of the film has been calculated by two methods, first from the known absorptivity at 4940 cm−1, and second by equating the appropriate Kramers–Kronig integral to the known infrared contribution to the microwave refractive index. The two thicknesses agreed well and allowed the absorptivity to be obtained in the range 4000–30 cm−1. The complex refractive index and permittivity and the normal incidence reflectivity have been calculated from the absorptivity. About three-quarters of the infrared contribution to the microwave refractive index is caused by the translational lattice vibrations and about 15% by the rotational vibrations; the O–H stretching bands which absorb very strongly contribute relatively little. The maximum of the density of states in the transverse acoustic branch is at 65 cm−1 rather than below 50 cm−1 as reported earlier. Below 50 cm−1 the absorptivity is roughly proportional to the fourth power of the frequency. This arises because the vibrations here are short-wavelength sound waves with a density approximately proportional to the square of the frequency, and the integrated intensity of absorption by one vibration is proportional to the square of the frequency. A theory of the contribution of the translational lattice vibrations to the microwave permittivity is given based on the theory of the absorption by orientationally disordered crystals given in an earlier paper. From the theory and the experimental measurements reported in this paper the dipole-moment derivative for the relative displacement of two water molecules in ice along their line of centers (or equivalently the effective charge of a water molecule) is about 0.3 electronic charges.
Fermi–Thomas Response of a Metal Surface to an External Point Charge
Authors: Newns D. M.
Published: February 2004

The dielectric response of a semi-infinite metal to a point charge a short distance outside its surface is calculated in the linearized Fermi–Thomas approximation. The general form of the potential in the metal and vacuum is discussed. A generalization of the classical image theorem is given. The energy change on bringing up the charge to the surface is calculated, and found to be in good agreement with a previous approximation due to Gomer and Swanson.
Molecular Energetics of Borane Carbonyl and the Symmetric Dissociation Energy of Diborane
Authors: Ganguli P. S. , McGee H. A.
Published: February 2004

Large concentrations of borane, BH3, are produced upon the pyrolysis of borane carbonyl. Ionization efficiency measurements using a fast inlet mass-spectrometric technique, have led to I(BH3) as well as A(B+), A(BH+), A(BH2+), and A(BH3+) from BH3CO. These numbers permit a complete development of the molecular energetics of BH3CO and a confirmation of the symmetric dissociation energy of diborane of 59 kcal/mole. Earlier equilibrium data on the BH3CO decomposition, combined with these electron-impact data, also confirm D(BH3–BH3) = 59 kcal/mole. Earlier kinetic studies that suggest a very much lower dissociation energy are shown to be equivocal at best.
Steady-State Random Walks with Application to Homogeneous Nucleation
Authors: White George M.
Published: February 2004

The kinetics of steady-state random walks on the positive integers, between a source of 0 and a sink at i*, are treated with elementary techniques from the theory of stochastic processes. It is shown that the steady-state flux of random walkers past any point i is equal to the steady-state number density at i multiplied by the probability that a random walker at i will never return to i after taking a forward step. The mean time it takes a random walker to traverse integers is derived and related to the flux. For physical processes such as membrane transport and nucleation, the steady-state number density at i is shown to be equal to the equilibrium number density at i multiplied by the probability that a randomly walking particle at i will return to zero. Homogeneous nucleation in the vapor phase is dealt with at length and serves to demonstrate the connection between physical processes and the present treatment of random walks. An exact, discrete expression for the Zeldovich factor is derived. It is shown that the traditional expression for the Zeldovich factor which uses continuous functions is quite accurate.
Crystal Structure of NiCl2·6H2O at Room Temperature and 4.2°K by Neutron Diffraction
Authors: Kleinberg Robert
Published: February 2004

Atomic parameters in paramagnetic NiCl2·6H2O have been determined at room temperature from a single-crystal neutron-diffraction study in which the intensities of 100 independent reflections of the h0l and hk0 zones were measured. Isotropic least-squares refinement of the structure gave a final value of 0.104 for the reliability factor R and yielded the hydrogen parameters x, y, z, = (0.100, 0.299, 0.269); (0.444, 0.232, 0.225); (0.181, 0, 0.549); and (0.260, 0, 0.839). Parameters for the heavy atoms agree with the results of the x-ray structure analysis. Atomic parameters were also determined for the antiferromagnetic state (TN = 5.3°K) at 4.2°K from 108 h0l reflections. Final R after isotropic least-squares refinement is 0.070, and a comparison of the two sets of atomic parameters shows that the crystal structure is the same at both temperatures. At 4.2°K the hydrogen parameters are (0.107, *, 0.280); (0.441, *, 0.227); (0.184, 0, 0.549); and (0.261, 0, 0.828), and the unit-cell parameters are a = 10.20, c = 6.50 Å, and β = 122°32′.
Selection of the Intermolecular Potential Function. III. From the Isotopic Thermal Diffusion Factor
Authors: Hanley H. J. M. , Klein Max
Published: February 2004

A method developed previously to evaluate quantitatively the relationship between intermolecular potential functions and macroscopic properties is extended to the isotopic thermal diffusion factor. As before, the relationship between function families has been clarified. In particular, the insensitive temperature range, here about 2 ≤ T*12−6 ≤ 4, was found in which the data do not permit the selection of a potential function. The function families studied were the m–6, Kihara, and exp-6. A quantitative evaluation of the sensitivity of the thermal diffusion factor to the potential function is presented.