bluuebunny/crossref_metadata_2025 huggingface dataset:
Hollow-cathode copper-vapor laser
Authors: Fahlen Theodore S.
Published: February 2004

The design and operation of a hollow-cathode copper-vapor laser are discussed. The sole source of copper atoms is the pulsed glow discharge inside the hollow cathode, which generates copper vapor by sputtering and heating of the copper-plated cathode. With no optimization of the laser parameters, 270 mW of green output power have been obtained at a 12-kHz pulse repetition frequency from a 1-m-long tube.
Microwave Spectrum, Structure, Boron Quadrupole Coupling Constants, and Dipole Moment of Difluoroborane
Authors: Kasuya T. , Lafferty W. J. , Lide D. R.
Published: February 2004

The microwave spectra of H10BF2, H11BF2, D10BF2, and D11BF2 have been assigned. Rotational constants are 74 494.82, 10 496.74, and 9181.67 Mc/sec for H11BF2 77 244.25, 10 495.35, and 9221.49 Mc/sec for H10BF2 52 896.09, 10 498.29, and 8740.46 Mc/sec for D11BF2 and 54 081.82, 10 496.89, and 8771.57 Mc/sec for D10BF2. The structural parameters obtained from these constants and their estimated uncertainties are rBH = 1.311 ± 0.005 Å, rBH = 1.189 ± .010 Å, and ∠FBF = 118.3° ± 1°. The quadrupole coupling constants have been obtained. The dipole moment is 0.971 ± 0.010 D.
Heat Capacity of Deutero-Ammonium Bromide from 17° to 300°K
Authors: Stephenson C. C. , Karo A. M.
Published: February 2004

The heat capacity of deutero-ammonium bromide has been measured from 17° to 300°K. The heat-capacity curve is characterized by the appearance of two maxima. These are associated with polymorphic transitions in the crystal lattice and with the ordering of the ammonium ion tetrahedra with respect to the two equilibrium positions in the unit cell. The excess entropy associated with the maxima is found to be in agreement with the order-disorder nature of the upper transition. A frequency of torsional oscillation for the ammonium ion in good agreement with infrared data is obtained from the Debye-Einstein function representing the heat capacity below 100°K.
Viscosity and Its Temperature Dependence in Molten BeF2
Authors: Moynihan Cornelius T. , Cantor Stanley
Published: February 2004

The viscosity of molten beryllium fluoride has been measured with coaxial-cylinder viscometers over five orders of magnitude (limits: 979°C, 28.6 P; 574°C, 2.24 × 106 P). Over the experimental range of shear stresses, BeF2 behaves as a Newtonian fluid. Like SiO2, its high-temperature analog, BeF2 shows an Arrhenius temperature dependence over several orders of magnitude in viscosity. Reported heat-capacity data for BeF2 and SiO2 and the Adam-Gibbs theory indicate that the Arrhenius viscosity behavior of these liquids may be explained in terms of the configurational entropy which is virtually constant at temperatures above the glass-transition temperature.
Effect of Electric-Field-Gradient Inhomogeneity on Quadrupolar Satellite Intensities in Nuclear Magnetic Resonance Spectra in Solids
Authors: McCart B. R. , Barnes R. G.
Published: February 2004

A simple model of random electric-field-gradient inhomogeneity has been incorporated into the usual first-order treatment of quadrupolar satellites in nuclear magnetic resonance spectra in solids. Observed departures of experimental intensities from those expected strictly on the basis of transition probabilities are satisfactorily accounted for on the basis of this model.
Vapor Pressures of Tritium Oxide and Deuterium Oxide. Interpretation of the Isotope Effects
Authors: Jones Wesley M.
Published: February 2004

Measurements are reported on the difference in vapor pressures of H2O and T2O ( − 9°-114°C) and of H2O and D2O (4°-114°C). The relative vapor pressures of the pure liquids are represented by ln (pH2O / pT2O) = ( − 103.87 ± 0.57) / T + (46 480 ± 210) / T2 and ln (pH2O / pD2O) = ( − 70.87 ± 0.43) / T + (33 630 ± 160) / T2. The normal boiling points of T2O and D2O are 101.51° and 101.42°C. Isotopic differences in heats of vaporization are given from 10° to 110°C. Triple-point temperatures and pressures are summarized. Vapor-pressure crossover temperatures are: D2O–T2O, 116.2° ± 0.5°C; H2O–T2O, 190 ± 10°C (estimated); H2O–D2O, 220.7° ± 0.1°C (literature).

The data were also fitted to extensions of the above equations which included correction terms based on Bigeleisen's formulation of the vapor-pressure isotope effect and a uniformist harmonic-oscillator model of water. Estimates of the coefficients of 1 / T and 1 / T2 for H2O–D2O from Raman spectra are in reasonable agreement with coefficients from this data fit. Ratios of corresponding coefficients for H2O–D2O and H2O–T2O agree with theory.
Retarded Interaction Energies between Like Atoms in Different Energy States
Authors: Meath William J.
Published: February 2004

The long-range interaction energy between two like atoms in different energy states is discussed in general, through O (α2), using the Breit-Pauli approximation. Selection rules are derived for possible interactions where retardation or relativistic effects may be important. The S-P resonant interaction is considered as a specific example. The interaction energies for the resulting Σ and Π molecular states are calculated in both the Breit-Pauli approximation and from the exact dipole-dipole results of McLone and Power, Stephen and others. The R−1 expansion of the exact result and the validity of the Breit-Pauli approximation are discussed in detail. The interaction energies are also compared with the linewidths for the various molecular states. It is shown that the Breit-Pauli approximation can give a good representation (especially for the Σ states) of the interaction for quite large values of R <̃ λ, where λ is the characteristic wavelength for the S-P transition.
Electron Paramagnetic Resonance of Mn2± in K2SO4 Single Crystal
Authors: Chowdari B. V. R. , Venkateswarlu Putcha
Published: February 2004

The paramagnetic resonance spectrum of divalent manganese ion in single crystals of potassium sulfate is described in detail over a large temperature range. Mn2± is found to substitute for K± and becomes associated with first-, second-, and third-neighbor potassium ion vacancies. The different spectra obtained at room temperature have been analyzed. Variation in the fine-structure spread with temperature has been studied for one of these spectra and the variation indicates a probable phase change at about − 130°C. This was supported by the observation that some of the resonance lines appear to begin to split into two as the temperature is lowered below − 130°C.
Theoretical Analysis of the Electronic Structure and Molecular Properties of the Alkali Halides. III. Sodium Chloride
Authors: Matcha Robert L.
Published: February 2004

Results of a theoretical investigation of the electronic structure of NaCl within the SCF-LCAO-MO approximation are discussed. Special emphasis is given to the computation of molecular properties. Computed values (followed by experimental values in parentheses) for the total energy E, equilibrium separation Re, spectroscopic constants ωe, ωexe, and Be, and dipole moment μ, are: E = − 621.4574 a.u.; Re = 4.485 a.u. (4.4601); ωe = 378.3 cm−1 (364.6); ωexe = 2.589 cm−1 (2.05); Be = 0.2155 cm−1 (0.2181); μυ = 9.1540 + 0.0580 (υ + 12) + 0.0003 (υ   12)2; and μυ (exptl.) = 8.9734 + 0.0570 (υ + 12) + 0.0005 (υ + 12)2. The computed Hartree-Fock dissociation energy (DeHF  =  0.117 a.u.) was coupled with estimated correlation and relativistic energy contributions (Decorr = 0.031 a.u., Derel = 0.002 a.u.), producing a lower limit value, Decalc = 0.146 a.u., a result somewhat smaller than the experimental value Deexptl. = 0.155 a.u. The discrepancy is due to neglect of small corrections discussed in this paper. The combination of calculated field gradients with experimental quadrupole coupling constants yielded the following electric quadrupole moments for sodium and chlorine: QNa = 0.0950 × 10−24cm2 and QCl35 = − 0.1171 × 10−24cm2.
Generalized Equation of Motion for a Gas Using the Quantum-Mechanical Green's Function Technique. I
Authors: Paul R. , Fowler G. N.
Published: February 2004

The quantum-mechanical Green's function technique of Kadanoff and Baym is extended to include non-Markowian effects in order to make contact with the results of Prigogine.
Ab Initio Studies of Small Molecules Using 1s Gaussian Basis Functions. III. LCGTO SCF MO Wavefunctions of the Three- and Four-Electron Systems He2+, He2, and Linear H3, H4+, H4
Authors: Schwartz Maurice E. , Schaad L. J.
Published: February 2004

The ground states of the three- and four-electron systems He2+, He2, and linear symmetric H3, H4+, and H4 are investigated using the linear combinations of Gaussian-type orbitals (LCGTO) self-consistent-field molecular-orbital (SCF MO) approach. The basis functions are 1s GTO's, not necessarily located at nuclear positions. Optimized, near-Hartree–Fock (HF) wavefunctions are presented for the isoelectronic H3 and He2+ systems, for which such results were not previously available. They are found to have similar correlation energies. With simpler wavefunctions, E-vs-R plots for H3 and He2+ give good bond lengths and shapes of the energy curve. It is found that previous SCF MO studies have not closely approximated the true HF function for He2. The H4+ calculations are the first SCF MO results available for the species, and indicate its instability with respect to H3+ + H, in agreement with recent experimental data. The GTO studies for H4 are the only rigorously executed ab initio calculations yet done for the system. E-vs-R data derived for H4 refute the best previous studies, which used integral approximations. The interaction potential of two H2 molecules (end to end) is derived from these H4 energies.
Reactions of Metal Atoms. I. The Combination of Mercury and Chlorine Atoms and the Dimerization of HgCl
Authors: Horne D. G. , Gosavi R. , Strausz O. P.
Published: February 2004

The combination reaction of mercury atoms with chlorine atoms from the mercury-sensitized flash photolysis of CF3Cl has been studied. The kinetics were followed by monitoring the band intensities of the Π1/22←2Σ and2Π3/2←2Σ systems of the HgCl transient with kinetic absorption spectroscopy. The absorption spectrum agrees well with the previously reported emission spectrum. The extinction coefficient for the 2790-Å band of the Π1/22−2Σ system has been measured to have the value of 1.6 ± 0.6 × 105M−1·cm−1. The second-order rate constant for the reaction is 3 and 0.9 × 1010M−1·sec−1 in 720 torr CF3Cl and 10 torr CF3Cl + 710 torr Ar, respectively, and is independent of temperature between 110° and 170°. The rate constant for the dimerization of HgCl is 3.0 ± 1.8 and 1.9 ± 1.3 × 1011M−1·sec−1 in the above mixtures. The reaction is second order in [HgCl].
Polarizability of Molecular Hydrogen
Authors: Wilkins Roger L. , Taylor Howard S.
Published: February 2004

A summation technique is used to calculate the static dipole electric polarizabilities of molecular hydrogen. The technique requires a complete set of single-particle Hartree–Fock states. The occupied Hartree–Fock orbitals for molecular hydrogen are bound, and the complementary set of Hartree–Fock orbitals all lie in the continuum. Such a basis set permits one to evaluate the required sums by integrating over the excited states. The uncoupled Hartree–Fock model is used to calculate the zero-order terms of the components of the polarizability tensor. The first-order corrections to the components of the polarizability tensor are calculated using double perturbation theory. At the equilibrium internuclear separation, R = 1.4 a0, the static parallel dipole polarizability α‖ and static perpendicular polarizability α⊥ are 0.941 Å3 and 0.728 Å3, respectively, which compare favorably with the values 0.944 Å3 and 0.677 Å3 calculated by Kolos and Wolniewicz using a variation–perturbation method. The results are also in satisfactory agreement with the experimental values.
Self-Consistent-Field Calculations for the Translawrencium Elements—Beginning of a 5g Transition Series
Authors: Larson Allen C. , Waber James T.
Published: February 2004

The preferred electronic configurations of the very heavy synthetic elements in the vicinity of atomic number 126 have been deduced through nonrelativistic self-consistent Hartree calculations made for many configurations. The resulting wavefunctions were used to compute the total average Hartree–Fock energy of each configuration. The configuration 8s26f15gν emerges as more stable than either 8s27d15gν or 8s25gν+1. The principal chemical valences are 3+ and 2+; oxidation to 4+ would probably be difficult.
Ferroelectric Tungsten Bronze-Type Crystal Structures. I. Barium Strontium Niobate Ba0.27Sr0.75Nb2O5.78
Authors: Jamieson P. B. , Abrahams S. C. , Bernstein J. L.
Published: February 2004

Ferroelectric Ba0.27Sr0.75Nb2O5.78, with Tc = 348° ± 15°K, is a tungsten bronze-type structure crystallizing in the tetragonal system, with lattice constants a = 12.43024 ± 0.00002 and c = 3.91341 ± 0.00001 Å at 298°K, space group P4bm, and five formulas in the unit cell. The integrated intensities of 6781 structure factors were measured with PEXRAD, 875 symmetry-independent structure factors being significantly above background. The metal-atom positions were determined from the three-dimensional Patterson function and the oxygen atoms from subsequent Fourier series. The final agreement factor between measured and calculated structure factors is 0.0508. The structure consists of close-packed slightly puckered layers of oxygen atoms separated by nearly c / 2. The Nb atoms are slightly displaced from one layer, the Ba and Sr atoms from the other and in the same sense. The oxygen atoms in the Ba and Sr layer are disordered. Neither of the two independent sites occupied by the Ba and Sr atoms is fully filled. The 2a site is preferred by Sr, which is in distorted cubo-octahedral coordination; the Sr–O distances range from 2.547 ± 0.008 Å to 2.919 ± 0.008 Å. The 4c site, occupied by Ba and Sr, has distorted tricapped trigonal prismatic symmetry; the Ba/Sr–O distances range from 2.604 ± 0.009 Å to 3.035 ± 0.010 Å. The two independent Nb atoms fully occupy the 2b and 8d sites and are each in relatively regular octahedral coordination. The 2b site has Nb–O distances ranging from 1.92 ± 0.03 Å to 2.03 ± 0.03 Å; the 8d-site Nb–O distances range from 1.88 ± 0.03 Å to 2.11 ± 0.03 Å. A ferroelectric mechanism is proposed in which the metal atoms in the 2a, 2b, and 4c sites move, at the Curie temperature, into the oxygen layers. These metal atoms then acquire 4̄,222, or 2 point symmetry, respectively, as the space group transforms to P4̄b2. The remaining Nb atoms, in the 8d position, also rearrange so as to have half above and half below the oxygen layer. The absolute displacements of the metal atoms from their nearest mean planes of oxygen atoms, in space group P4̄bm, are directly related to the ferroelectric polarization sense.
Measurement of the Relative Abundances and Recoil Energy Spectra of Fragment Ions Produced as the Initial Consequences of X-Ray Interaction with C2H5I, CH3CD2I, and Pb(CH3)4
Authors: Carlson Thomas A. , White R. Milford
Published: February 2004

The fragment ions produced as the initial consequence of x irradiation of C2H5I, CH3CD2I, and Ph(CH3)4 have been measured with a specially designed mass spectrometer for their relative abundances and kinetic-energy spectra. The x rays used in this experiment should in the case of iodine-containing molecules give rise to photoionization primarily in the L shell, and in the case of lead, the M or L shells. As in the earlier studies on CH3I, the molecules decomposed nearly completely into their constituent elements as the result of the high degree of ionization resulting from the reorganization of the heavy atoms to an inner-shell vacancy by means of Auger processes. Calculations based on the Coulombic repulsion of point charges are compared with the experimentally determined recoil energies. The agreement is reasonable, although the experimental values are generally lower than the calculated ones. The relative recoil energies of H+ and D+ from the study on deuterated ethyl iodide suggest that the β carbon on the average loses as many electrons as the carbon next to the iodine; while the low recoil energy of Pb suggests that the decomposition of highly charged tetramethyl lead is essentially symmetrical.
Thermal Diffusion in Argon–Carbon Dioxide Gas Mixture
Authors: Batabyal A. K. , Ghosh A. K. , Barua A. K.
Published: February 2004

The composition dependence of the thermal-diffusion factor α of the argon–carbon dioxide system has been studied by a trennschaukel or swing separator at three different temperatures. The temperature dependence of α of this system has also been studied for a 1:1 mixture. The plot of α vs percentage of Ar shows a maximum at all the three temperatures whereas that of α vs temperature shows a negative gradient and the existence of a possible minimum. The results cannot at present be explained satisfactorily with the existing theories.
Statistical-Mechanical Calculation of Surface Properties of Simple Liquids and Liquid Mixtures. II. Mixtures
Authors: Plesner Igor W. , Platz Ole , Christiansen S. E.
Published: February 2004

Calculation of density transition curves and surface tension in a series of mixtures of argon and nitrogen at 84°K are presented. The densities of the two components as a function of position in the interface furnish insight in the structure of the transition region and predict certain features in regard to the (excess) surface tension, which are confirmed experimentally. The calculated values of surface tension as a function of liquid mole fraction are in satisfactory agreement with experiment. Certain problems pertaining to the numerical solution of simultaneous nonlinear integral equations are discussed.
X-Ray Emission Spectra from Chlorinated Methanes and Fluorochloromethanes
Authors: Ehlert R. C. , Mattson R. A.
Published: February 2004

The carbon K, fluorine K, and chlorine L spectra are presented for the chlorinated methanes (CCl4, CHCl3, CH2Cl2, CH3Cl) and fluorochloromethanes (CFCl3, CF2Cl2, CF3Cl, CHFCl2, CHF2Cl). Comparisons are made with the spectra of methane and carbon tetrafluoride. Multiplet structure is observed in every case. The position and intensity of the various lines is dependent on the type and number of halogens present in the molecule.
Phase Diagrams of H2O and D2O at High Pressures
Authors: Pistorius Carl W. F. T. , Rapoport Eliezer , Clark J. B.
Published: February 2004

The VIII/VII phase boundaries of solid H2O and D2O were studied by means of differential thermal analysis. The thermal hysteresis of the transition decreases with increasing pressure, but the presumed equilibrium temperatures are independent of pressure to 40 kbar. The transition is of the first order, and the average transition temperature is −3°C in both cases. The ice VI/VII transition pressure at 25°C is 21.39 ± 0.05 kbar, in good agreement with other recent studies, but considerably lower than Bridgman's value. The heavy ice VI/VII and VI/VIII transition lines are located ∼1.4 kbar below the ice VI/VII and VI/VIII transition lines. The heavy ice VI/VII transition at 25°C occurs at 19.90 ± 0.07 kbar. Bridgman's melting curves of ice VI and ice VII are shown to be correct. The melting curve of heavy ice VI is ∼2°C above that of ice VI, but the heavy-ice VI/VII/liquid triple point is located at 78°C, 20.6 kbar as compared with 81.6°C, 21.97 kbar for H2O. The melting curve of heavy ice VII appears to have a stronger curvature than the melting curve of ice VII.
EPR Study of the Equilibrium between Peroxydisulfuryl Difluoride and Fluorosulfate Free Radicals in the Gaseous State
Authors: Stewart R. Allan , Fujiwara Shizuo , Aubke F.
Published: February 2004

The EPR spectrum of the fluorosulfate radical SO3F· in the gaseous state was observed as a single broad line at temperatures between 390° and 480°K. The linewidth between points of maximum slope was found to be 41.5 G, with a g value of 2.010. The change in free energy ΔF of the reversible reaction S2O6F2⇆2SO3F· was found to be 10.6 ± 1.0 kcal/mole from the temperature dependence of the resonance line amplitude, and the energy of dissociation ΔE estimated to be approximately 27 kcal/mole.
Internal Rotation Spectra of Methylamines. I. CH3NH2 and CH3ND2
Authors: Tamagake Keietsu , Tsuboi Masamichi , Hirakawa Akiko Y.
Published: February 2004

Infrared absorption spectra of methylamine (CH3NH2) and methylamine-d2 (CH2ND2) have been observed in the gaseous states in the region of 500–80 cm–1 (20–125 μ). A complicated, irregular structure is observed all over the spectral region, which is attributable to the internal rotation coupled with an over-all rotation of the molecule. The internal and over-all rotation energy levels were calculated on the basis of the previously determined molecular parameters and a potential function for the internal rotation (x) with the form of V(x) = 12H3(1-cos3x) + 12H6(1-cos6x). The frequencies and intensities for radiative transitions between these energy levels were then calculated. On comparing the results of the calculation with the observed spectra, it has been found that we need to revise the values of the potential constants and one of the molecular constants C2 (the moment of inertia of the methyl group around its own symmetry axis) from what were determined previously with microwave data. The new set of values is H3 = 683.2 cm−1, H6 = −2.0 cm−1, and C2 = 5.273 × 10−40g·cm2 for CH3NH2. For CH2ND2, a set of values: H3 = 671.6 cm−1, H6 = 0, and C2 = 5.273 × 10−40g·cm2, has been proposed. The band center of the fundamental band (n = 1←0) is found to be at 263.9 cm− 1 for CH3NH2 and at 224.5 cm− 1 for CH3ND2.
Neutron-Diffraction Study of Lithium Sulfate Monohydrate
Authors: Smith H. G. , Peterson S. W. , Levy H. A.
Published: February 2004

A neutron-diffraction study of Li2SO4·H2O has shown the water molecule to be weakly hydrogen bonded to the oxygen atom (O5) of an equivalent water molecule (O5–O5′ = 2.95 ± 0.01 Å) and to an oxygen atom (O1) of a sulfate ion (O5–O1 = 2.87 ± 0.02 Å). The O5–H2···O5′ and O5–H1···O1 angles are 151.0 ± 1.0° and 152.6 ± 3.4°. The dimensions of the water molecule (after correction for thermal motion) are: O5–H1 = 0.99 ± 0.03 Å, O5–H2 = 1.00 ± 0.55 Å, H1–H2 = 1.64 ± 0.05 Å, and H1–O5–H2 = 110.6 ± 2.4°. The R factor (for F2) based on the hk0, h0l, and 0kl reflections is 6.1%.
Irreversible Transformation of Hexagonal Boron Nitride by Shock Compression
Authors: Coleburn N. L. , Forbes J. W.
Published: February 2004

Shock-wave compression measurements from 20 to 300 kbar are reported for hexagonal boron nitride. A phase transition occurs at 122 kbar and 230°C in good agreement with static data. The volume decrease is approximately 19% and the estimated slope of the phase line for the solid–solid transition is −3.6 × 10−2kbar °C−1. Crystallites of the dense phases recovered after shock compression above the transformation pressure were identified by x-ray diffraction as zinc blende cubic with traces of wurtzite.
Satellite Bands in the Emission Spectrum of Cesium
Authors: Gwinn Joel A. , Thomas Paul M. , Kielkopf John F.
Published: February 2004

Satellite bands near the atomic lines of the emission spectrum of cesium in the presence of heavy noble gases were observed and their positions measured. For the series which also appear in absorption, the measured positions of the band maxima are in general agreement with those previously reported. Several interesting regularities in the data are noted and a simple interpretation is suggested.
Shock-Tube Study of Nitrogen Dissociation using Vacuum-Ultraviolet Light Absorption
Authors: Appleton J. P. , Steinberg M. , Liquornik D. J.
Published: February 2004

A shock-tube investigation of the dissociation of nitrogen diluted in argon is described which utilizes vacuum-ultraviolet absorption at 1176 Å to monitor the disappearance of molecular nitrogen. Measurements of the dissociation rate coefficients for the process kd(M)N2 + M→2N + M were obtained over the temperature range 8000° to 15 000°K where the collision partner, M, was Ar, N2, and N. The temperature dependence of the individual rate coefficients was found to be the same and was obtained with good precision. The magnitudes of the rate coefficients were generally lower than the currently accepted values obtained in previous shock-tube investigations, especially the value for kd(N) which, although it was found to be about 10 times greater than kd(Ar), was six times less than two previous measurements. The results of the investigation may be summarized by the following expressions for the dissociation rate coefficients: kd(Ar) = (2.3 ± 0.2) × 10−3T−1.6exp( − 1.132 × 105 / T) cm3sec−1, kd(N2) = (6.2 ± 1.6) × 10−3T−1.6exp( − 1.132 × 105 / T) cm3sec−1, kd(N) = (2.7 ± 1.0) × 10−2T−1.6exp(−1.132 × 105 / T) cm3sec−1.

Encouragingly good agreement between the recombination rate coefficients, kr(Ar), inferred from the measurements of kd(Ar), with predictions of kr(Ar) obtained from the theories of Benson and Fueno and Keck and Carrier, were obtained.
Field-Emission Study of the Adsorption and Decomposition of Ammonia on Tungsten
Authors: Dawson P. T. , Hansen Robert S.
Published: February 2004

The catalytic decomposition of ammonia on tungsten has been investigated by field electron-emission microscopy. Physisorbed ammonia causes a large lowering of work function (∼ − 2.8 eV). Ammonia chemisorbs at low temperatures by the formation of a coordinate bond and the heat of adsorption and activation energy for decomposition appear to be highest on planes of highest clean work function. Decomposition to nitrogen and hydrogen occurs in the interval 200°–400°K. Interaction of ammonia with a clean tungsten surface at higher temperatures causes the successive appearance of three species, presently interpreted as N, NNH2, and NNH3+. The interaction of ammonia with nitrogen adatoms to produce the additional species will proceed at lower temperatures and therefore requires little activation energy. The rate-limiting step in the decomposition of ammonia on tungsten is the decomposition on the surface of NNH2. The proposed scheme for decomposition satisfies the existing kinetic data for tungsten. The implication of these results on the structure of nitrogen adatoms is discussed.
Ultrasonic Absorption and Velocity near the Critical Region of Nitrobenzene-n-Hexane Mixtures
Authors: D'Arrigo G. , Sette D.
Published: February 2004

Ultrasonic absorption and velocity measurements have been performed in nitrobenzene-n-hexane mixtures over wide ranges of temperatures and frequencies, and over the full range of compositions. The general behavior of the absorption coefficient is found to be similar to the one shown by other binary critical mixtures. The results are discussed in connection with Fixman's theory. An attempt is also made to explain the composition dependence of the absorption coefficient by using the Flory-Huggins approximation for the long-range correlation function (κ−1) in the Fixman theory.
Decorated Lattice Model of a Binary Mixture
Authors: Clark Ronald K.
Published: February 2004

A binary lattice gas model is described whose properties can be exactly transformed into those of a reference one-component lattice gas. The model lattice contains regular lattice sites occupied by one component and decorated bond sites occupied by the second component. Multiple occupancy of sites is not allowed. All other interactions between like molecules are zero but there is a finite repulsion between unlike nearest neighbors. The complete two-phase region of the binary system is described by means of the two-phase behavior of the reference system. The two-phase region in a constant temperature plane is enclosed in a closed-loop binodal curve with two plait points. The binodal curve near the plait point is found to be of degree (1-α′) / β while the degree of the top of the coexistence surface is 1 / β, where α′ and 1 / β are the exponents of the divergence of the constant volume heat capacity in the two-phase region and the degree of the coexistence curve, respectively, of the reference system. The heat capacity at constant volume and composition in the one-phase region is found to remain finite near the plait point and to diverge as the −α power of the distance from the top of the coexistence surface at the critical composition. Fluctuations in the composition in the one-phase region diverge as the −γ / (1 − α) power of the distance from the plait point and as the −γ power of the distance from the top of the coexistence surface, where −γ is the power of the divergence of the reference system compressibility in the one-phase region near the critical point.
Generalized Susceptibility Theory. II. Optical Absorption Properties of Helical Polypeptides
Authors: Barnes D. G. , Rhodes William
Published: February 2004

The electric dipole polarizability of helical polypeptides is discussed in terms of a previously derived closed-form approximation of the generalized susceptibilities of molecular systems. Although helical symmetry leads to complications in the formulation of the helix polarizability, the absorption spectrum is determined by considering only the appropriate diagonal element of the polarizability in momentum space. In addition, evidence is given for a new absorption band in substituted amides, located between the n→π* and π→π* bands. This band is included in the calculation of the absorption spectrum of the α helix and of poly-l-proline II. The results for the α helix agree well with the observed spectrum as far as band positions, polarizations, and relative intensities are concerned, but they do not predict the magnitude of the observed hypochromism. The calculated relative intensities of the perpendicular and parallel components of the perturbed π→π* band is in much better agreement with experiment than the results of perturbation theory. Of particular interest is the fact that the calculated perturbed new band (mystery band) corresponds to an observed long-wavelength band (perpendicular polarization) which previously was given an n→π* assignment.
Infrared Absorption by Hydrogen Bonds in Single Crystal KH2PO4, KD2PO4, and KH2AsO4
Authors: Hill R. M. , Ichiki S. K.
Published: February 2004

The infrared absorption spectrum of KH2PO4, KD2PO4, and KH2AsO4 single crystals has been measured from 3000-1000 cm−1 over a temperature range from 20°-300°K. Three broad absorptions are found at 2670, 2360, and 1720 cm−1 which are associated with the hydrogen bonds. The two upper frequencies are stronger for light polarized perpendicular to the polar axis but are also found for light polarized along the polar axis. These absorptions have counterparts in the deuterated crystal with a frequency ratio νH / νD≃1.35. The lower-frequency absorption is strongest for light parallel to the polar axis and shows intensity changes at the Curie temperature, accompanying the appearance of a sharper absorption at 1850 cm−1 which has a Curie-law behavior above Tc. It is concluded that the uncoupled hydrogen-bond vibrations which give rise to the absorption at 2670 and 2360 cm−1 show no observable splitting of the ground or first vibrational state. This eliminates a double minimum potential with appreciable tunneling between minima as a model for this bond. In addition these motions appear to make an angle of several degrees with the x, y plane of the crystal. The 1720-cm−1 absorption is a hydrogen-bond vibration primarily along the polar or z axis with the 1850-cm−1 line representing coupled motion along z among locally ordered bonds.
Prompt and Delayed Fluorescence of X-Ray-Excited Anthracene Crystals
Authors: Perkins W. G.
Published: February 2004

The fluorescence of anthracene excited by x rays from a 600 keV pulsed source was investigated. An x-ray dose of 7.6 × 1012 eV cm−3 produced a prompt fluorescence output of 1.4 × 1011 photons cm−3, as well as an intense delayed fluorescence. Analysis of the time dependence of the delayed fluorescence, based on the diffusion kinetics of triplet excitons in tracks, indicated that the above dose produced 7 × 1010 singlet excitons by direct excitation (S0→Sn transitions) and 2.7 × 1011 short-lived ion pairs, of which 7 × 1010 recombined to form singlet excitons and 2 × 1011 recombined to form triplet excitons. In these calculations, the value of the triplet exciton diffusion coefficient was found to be (1 ± 0.5) × 10−4 cm2 sec−1.
Infrared Spectrum of the Trichloromethyl Radical in Solid Argon
Authors: Andrews Lester
Published: February 2004

The primary products of the reaction of lithium atoms and carbon tetrachloride in solid argon at 15°K are lithium chloride and the trichloromethyl radical, which are identified by infrared spectral studies. Natural chlorine isotopes, carbon 13 and bromine substitution, and loss of CCl3 absorptions with attendant growth of absorptions due to C2Cl6 on sample warming verify the molecular identity. Assignments to the carbon–chlorine stretching vibrations ν1 = 674 and ν3 = 898 cm−1 are supported by normal coordinate calculations, and the weak bending modes ν2 and ν4 were not detected. The stretching force constants Fτ = 3.83 mdyn / Å and Fττ = 0.43 mdyn / Å are compared with those of other chlorocarbons and BCl3 This comparison supports proposed resonance stabilization of the trichloromethyl radical.
Covalency Parameters in MnO, α-MnS, and NiO
Authors: Fender B. E. F. , Jacobson A. J. , Wedgwood F. A.
Published: February 2004

The intensities of low-angle neutron-diffraction peaks have been measured for the antiferromagnetic solids MnO, α-MnS, and NiO. From the reduced intensities of the (111) magnetic peaks the following covalency parameters have been derived: Aσ2 + 2Aπ2 + As2 = 3.5% (MnO); 7.6% (α-MnS); Aσ2 + As2 = 3.8% (NiO).
Dielectric Behavior of Ice with HCl Impurity
Authors: Young I. G. , Salomon R. E.
Published: February 2004

The complex dielectric behavior of ice doped with HCl has been measured in the concentration range 2 × 10−6 to 2 × 10−4M. The dissociation of HCl in ice was calculated as a function of temperature for ice doped at 2 × 10−6M. The results at 1 × 10−5M and below conform to the Debye model with a single relaxation time. The data suggest that, in a limited concentration range, HCl is substitutionally incorporated into the ice lattice.
Kinetic and Spectroscopic Constraints on the Origin of the N2 Afterglow
Authors: Benson Sidney W.
Published: February 2004

The large transition probability (10−1 to 10−2) for curve crossing such as that which occurs in N2 pre-dissociation, N2 (3B) ⇆N2(5Σ), guarantees that the rotationally hot members of the 12th vibrational level of the B state (3B(12))* will always be in equilibrium with free N atoms without the intervention of a third body. A kinetic scheme is suggested for these species that includes rotational and vibrational quenching in competition with electronic quenching. Fast rotational quenching gives rise to pseudoequilibrium population of normal B(12)3 species. The equilibrium constant KB for 2N⇆N2(2B(12)) is estimated at 10−1.2 liter/mole = 10−22.9 cc/particle at 300°K with a negative activation energy of − 2.2 kcal/mole, in good accord with recent data. Using 105.0±0.3 sec−1 as the measured radiative rate constant of the 12-8 transition yields an absolute emission intensity for this band of 102.9±0.3 liter/mole·sec = 10−17.9±0.3 cc/molecule·sec, again in good accord with observation. It appears from this that the 11th, 10th, and 9th vibrational levels are populated by successive collisional deactivation of the 12th level. This collisional deactivation is in competition with electronic quenching.
Use of the CNDO Method in Spectroscopy. I. Benzene, Pyridine, and the Diazines
Authors: Bene Janet Del , Jaffé H. H.
Published: February 2004

The CNDO method has been modified by substitution of semiempirical Coulomb integrals similar to those used in the Pariser-Parr-Pople method, and by the introduction of a new empirical parameter κ to differentiate resonance integrals between σ orbitals from those between π orbitals. The CNDO method with this change in parameterization is extended to the calculation of electronic spectra and applied to the isoelectronic compounds benzene, pyridine, pyridazine, pyrimidine, and pyrazine. The results obtained were refined by a limited CI calculation and compared with the best available experimental data. It was found that the agreement was quite satisfactory for both n→π* and π→π* singlet-singlet transitions. The relative energies of the pi and lone-pair orbitals in pyridine and the diazines are compared and an explanation proposed for the observed orders. Also, the nature of the “lone pairs” in these compounds is discussed.
Paramagnetic Resonance and Optical Study of Cupric Amine Complexes
Authors: Chiang Teh-ching
Published: February 2004

The EPR spectra of complexes of CuCl2, CuBr2, CuF2, and Cu (NO3)2 with primary, secondary, and tertiary amines were obtained at 77°K and room temperature. In a nonpolar solvent, 1:1 ether/ethanol, the g value and the hyperfine splitting constant were found to depend on both the amine ligands and the anion, whereas in water, the g value and hyperfine constant depend on the amine ligands but do not depend on the anions. Optical spectra of these systems taken at room temperature also show the same amine ligand and anion dependence. The anion dependence of the spin-Hamiltonian parameters can be explained by admitting admixtures of excited states with 4s character into the singly occupied orbital through vibronic coupling. This vibronic coupling assumption is also consistent with the effect of the amine ligands on the contact hyperfine interaction.
Dependence of the Rate of Electrodic Redox Reactions on the Substrate
Authors: Bockris J. O'M. , Mannan R. J. , Damjanovic A.
Published: February 2004

The steady-state velocities of an electrodic redox reaction have been determined on noble metals and some of their alloys. They are expressed in terms of the exchange current densities i0. Correspondingly, measurements of i0's as a function of temperature are recorded. The heats of activation at the reversible potential are independent of the properties of the substrate. However, log (reaction rate at the reversible potential) is linear with the work function of the substrate. Reactions in Cl− containing solutions have velocities greater than those in SO4– – solutions, and the ratio υCl– / υSO4– – depends upon the substrate in the order Pd > Au > Pt. The lack of dependence of the heat of activation upon the substrate is consistent with an electron transfer and not an atom-transfer model for the electrodic redox reactions. It is consistent with a weak interaction model. The dependence of the exchange current densities upon the substrate can be shown quantitatively to depend on the change of electrokinetic potential with the change of substrate-solution PD (potential difference) which occurs by carrying out the same reaction at a series of interfaces at which the metal-solution PD's are different, while the reversible potentials are the same. The anion effects cannot be due to blocking or bridging. They may be due to change in the φ2–b potential arising from a differing contact adsorption of the anions.
Best Choice for the Coupling Operators in the Open-Shell and Multiconfiguration SCF Methods
Authors: Levy Bernard
Published: February 2004

The meaning of the nonunique solution for the equations derived by Das for the extended Hartree-Fock problem is explored and a new set of equations is suggested. This set has a unique solution and leads to an easier calculation than the additional condition used by Das. It can be applied also to the so-called CMC-SCF method.
Effect of Diffusion on Transfer of Electronic Excitation Energy
Authors: Elkana Yehudit , Feitelson Jehuda , Katchalski Ephraim
Published: February 2004

The transfer of electronic excitation energy between naphthalene, acting as donor, and anthranilic acid, acting as acceptor, in a variety of alcohols, was investigated. The efficiency of energy transfer in all of the solvents used was different from the value to be expected according to the theory of Förster. The transfer efficiency was considerably higher in alcohols of low viscosity than in alcohols of high viscosity. This was attributed to the variation of intermolecular distance between donor and acceptor, as a result of Brownian motion, during the lifetime of the excited donor. Fair agreement was found between the experimental data and the values calculated according to theoretical treatments of nonradiative energy transfer in which diffusion has been taken into consideration.
Semiempirical Theory of Excimer Luminescence
Authors: Chandra A. K. , Lim E. C.
Published: February 2004

A semiempirical theory based on limited configuration interaction has been developed for the excimer luminescence of alternant hydrocarbons. The theory adequately accounts for (1) the energy of excimer luminescence (fluorescence and phosphorescence), (2) the linear relationship between the energies of the excimer fluorescence and the p band of the monomer, and (3) the near constancy of the energy difference between the monomer and excimer fluorescence.
Quantum Mechanics of the H2–H2 Interaction. V. The Importance of Intermolecular Charge-Transfer States
Authors: Magnasco V. , Musso G. F.
Published: February 2004

In a preceding paper a one-configuration wavefunction of strong orthogonal group functions was found to give a rather poor description of the orientation dependence of short-range intermolecular forces in H2–H2. As an alternative to the necessity of relaxing the strong orthogonality condition, it is suggested that the introduction of a small amount of the charge-transfer state H2−–H2+ describing one-electron transfer between the two molecules should improve the interaction energy and its change with the relative molecular orientation. Ab initio calculations in a region of intermolecular separations ranging from two to four times the internuclear equilibrium distance of an isolated H2 molecule show that less than 1% of such a charge-transfer state gives interaction energies which are in substantial agreement with those obtained with a complete configurational interaction.
Spectra of Polycrystalline Phthalocyanines in the Visible Region
Authors: Lucia Emmanuel A. , Verderame Frank D.
Published: February 2004

Transmission spectra of sublimed thin films of the α-crystalline forms of H2PC, CuPC, NiPC, CoPC, and ZnPC in the 0.5 to 0.9-μ region changed sharply as a result of α→β transformation induced by heat treatment above 300°C. The VOPC was unaffected. In the β-crystalline forms the absorption maxima (cm−1) were: H2PC 13 970, 15 500; CuPC 13 800, 15 540; NiPC 14 430, 15 900; CoPC 14 120, 15 730; and ZnPC 13 340, 15 430. The positions and contours of these bonds were to be expected on the basis of polarized single-crystal results reported by Lyons, Walsh, and White and Fielding and MacKay. Digital computer calculations of Davydov splittings for finite-sized “block”- and “bar”-shaped crystallites of CuPC based upon pairwise dipole–dipole interactions compared well with earlier results for the infinite sphere model in H2PC. Assignments for the four observed exciton components in β-H2PC must not only correctly predict the band positions and relative intensities, but should also be in accord with a red shift of each of the B2u and B3u vapor components. In the β crystal of the metal complex an intramolecular distortion or site symmetry should split the Eg molecular states. These in turn should also be red shifted and split by the crystal environment. The results, including studies of mixtures of several phthalocyanines in CuPC, are consistent with the interpretation.
Effect of Partial Deuteration and Temperature on Triplet-State Lifetimes
Authors: Lin S. H. , Bersohn R.
Published: February 2004

The lifetime of the triplet state of aromatic molecules increases when deuterons are substituted for its protons. For naphthalene, our experiments and others show that the decay rate is linear with the number of protons and independent of the position of substitution. This result is shown to follow from Lin's theory of nonradiative decay of excited states.
Dissociation Energies of Group VIa Gaseous Homonuclear Diatomic Molecules. III. Tellurium
Authors: Budininkas P. , Edwards R. K. , Wahlbeck P. G.
Published: February 2004

The dissociation energy of Te2(g) has been determined by the simultaneous Knudsen-torsion effusion method. The equilibrium, Te2(g)⇄2Te(g), has been studied with a double-oven alumina effusion cell; one oven contained elemental tellurium and supplied vapor to the hot oven from which effusion occurred. The value of D0° found in this study is 61.3 ± 1.1 kcal/mole. The electronic ground state of Te2(g) is most probably nondegenerate.
Spin–Orbit Coupling in Many-Electron Atoms
Authors: Thorhallsson J. , Fisk C. , Fraga S.
Published: February 2004

Spin–orbit splitting factors have been calculated from existing analytical Hartree–Fock functions for a number of isoelectronic series. It is found that there is an excellent agreement with the values obtained from experimental data, whenever available.
Infrared Matrix-Isolation Studies of Nuclear-Spin-Species Conversion
Authors: Hopkins H. P. , Curl R. F. , Pitzer Kenneth S.
Published: February 2004

Studies of the time evolution of intensities in the fine structure of infrared bands of CH3D, H2O, and NH3 isolated in rare-gas matrices in the temperature region 6.5°–20°K have been made. The molecule CH3D exhibits a fine structure at 6.5°K with time-dependent intensities. The data are interpreted in terms of nuclear-spin-species conversion. Because of rapid reconversion at 20°K it is concluded that CH3D cannot be obtained at room temperature with a nonequilibrium distribution of spin isomers by low-temperature equilibration. The time dependence of the fine structure of the H2O bending mode at 6.5°K has been reinvestigated. The essence of the previous work is confirmed. The rate of nuclear-spin conversion is found to be rapid at 30°K. The fine structure of the NH3 umbrella motion exhibits a time dependence which indicates that most of the fine structure observed is not due to rotation.
Crystal Structure and Molecular Motion of Solid Carbon Disulfide
Authors: Baenziger Norman C. , Duax William L.
Published: February 2004

The crystal structure of CS2 was determined at two temperatures from intensity data measured with a proportional counter and a modified Weissenberg apparatus. The orthorhombic cell [(a) 6.3437(8), (b) 5.5244(4), (c) 8.9971(7), 143°K, Cmca, Z = 4] exhibited marked anisotropic thermal expansion, the coefficients of thermal expansion being αa = 630 × 10−6 °C−1, αb = 570 × 10−6 °C−1, αc = −630 × 10−6 °C−1. Positional and anisotropic thermal parameters were refined using upper-angle data (sinθ / λ ≥ 0.35) and the x-ray results were compared with data from spectroscopic sources on the molecular motion of CS2 in the solid. The unweighted reliability indices for the two refinements were 0.039 (148°K) and 0.056 (133°K). The carbon–sulfur bond length corrected for foreshortening due to libration was 1.560(3) Å (133°K) and 1.559 Å (148°K), in agreement with calculations of the length in the gas from spectral data (1.558 ± 0.0005) and electron diffraction (1.559 ± 0.002).
Polyhedral Clathrate Hydrates. XV. The Structure of 4(CH3)3N·41H2O
Authors: Panke D.
Published: February 2004

The crystal structure determination of 4(CH3)3N·41H2O shows that the trimethylamine guest molecules are hydrogen bonded within voids formed by a polyhedral host lattice of hydrogen-bonded water. The water framework consists mainly of sheets formed by face-sharing dodecahedra which are linked by additional water molecules. The amine molecules occupy large irregular cages between the layers of dodecahedra. The amine and the linking water molecules are statistically disordered so that a hexagonal structure is observed, whereas an ordered arrangement would have monoclinic symmetry.