bluuebunny/crossref_metadata_2025 huggingface dataset:
Reactions of Alkali-Metal Atoms with Carbon Tetrabromide. Infrared Spectra and Bonding in the Tribromomethyl Radical and Dibromocarbene in Solid Argon
Authors: Andrews Lester , Carver T. Granville
Published: February 2004

Simultaneous condensation at 15°K of beams of lithium atoms and carbon tetrabromide diluted in argon produces infrared absorptions which are identified as lithium bromide and the tribromomethyl radical. Comparisons within the series of radicals CCl3, CCl2Br, CClBr2, and CBr3 verify the molecular identity. Assignments to the carbon–bromine stretching vibrations are ν1 = 582 cm−1 and v3 = 773 cm−1, whereas the bending modes v2 and v4 were not observed. The stretching force constants Fr = 3.55 mdyn/Å and Frr = 0.70 mdyn/Å are compared with those of other bromocarbons and BBr3. The high carbon–bromine stretching-force constant can be rationalized by the fact that the tribromomethyl radical is resonance stabilized. Secondary reaction of lithium atoms with the tribromomethyl radical yields a sufficient concentration of dibromocarbene for infrared spectral study. Variation of the perbromochloromethane precursors and loss of CBr2 absorptions with attendant growth of the most intense C2Br4 absorption on sample warming furnish convincing evidence that dibromocarbene is isolated in the argon matrix. Assignments to the carbon–bromine stretching vibrations are v1 = 595.0 cm−1 and v3 = 640.5 cm−1, and the bending mode was not detected. The stretching-force constants Fr = 2.38 mdyn/Å and Frr = 0.18 mydn/Å indicate that C–Br single bonds are present in dibromocarbene, making it unlikely that the electron deficiency of the carbon atom is relieved by pi bonding with bromine.
Interpretation of the Optical Spectrum of Yb3+ in CdF2 with the Aid of ESR Spectroscopy
Authors: Abbruscato Victor J. , Banks E. , McGarvey B. R.
Published: February 2004

The optical absorption spectra of Yb3+ in CdF2 and of Yb3+ in CdF2 in the presence of various codopants such as Na+, Y3+, and Eu3+ were recorded, and the oscillator strengths of the main absorptions of the Yb3+ in the 10 000-cm−1 region were calculated. Also, the electron spin resonance (ESR) spectra of Yb3+ in CdF2 and Yb3+ in CdF2 in the presence of Na+, 2% Y3+, and 10% Y3+ were recorded. Noncubic spectra were observed only in the case of the Yb3+–Na+–CdF2 and Yb3+–10% Y3+–CdF2 samples. The former noncubic spectrum was interpreted assuming a rhombic distortion with the major distortion axis along the [110] direction, while the latter could not be interpreted due to the broadeness of the absorptions. From the results of these measurements and the comparison to the optical spectra of Yb3+ in other systems, it has been concluded that the previous interpretation of the optical spectrum of Yb3+ in CdF2 is incorrect. It is suggested that the main absorption line at 10 250 cm−1 is not due to an internal f–f transition but is due to some other mechanism. Possible mechanisms are proposed based on some of the unusual physical properties of trivalent rare-earth ions in CdF2. The interpretation of the optical spectra assuming the absorptions at 10 395 and 10 870 cm−1 are the main f–f transitions gives a reasonable fit to the theoretical calculations.
Optical Absorption Measurements of Ground-State CN in Active Nitrogen Flames
Authors: Iwai Tsuruji , Pratt D. W. , Broida H. P.
Published: February 2004

Concentrations of CN in the X 2Σ, υ = 0 level as low as 1 × 109 molecules cm−3 have been detected in active nitrogen flames at pressures from 0.5 to 20 torr by optical absorption spectroscopy using a CN discharge light source and a refined ac detection method. A systematic study of CN B 2Σ+ ↔ X 2Σ+ absorption and emission intensity as a function of pressure and fuel has provided additional information about the mechanisms of formation and removal of ground-state CN in these systems. An estimate of 3×10−14 cm3 molecule−1·sec−1 for the rate constant for removal of X 2Σ CN by H2 has been obtained by determining the effect of added gases on steady-state concentrations. High-resolution measurements have revealed that the rotational population distribution in the ground vibrational level is thermal at pressures as low as 0.5 torr; this result is consistent with the estimated lifetime of ground-state CN in active nitrogen flames.
Effects of Deuterium Substitution on the ESR Spectrum of the Benzene Negative Ion
Authors: Lawler Ronald G. , Fraenkel George K.
Published: February 2004

An investigation has been made of the effects of deuterium substitution on the electron spin resonance spectrum of the benzene negative ion. Spectra of the benzene-1-d, benzene-1,3-d2, benzene-1,4-d2, benzene-1,3,5-d3, and benzene-d6 anion radicals have been obtained at −100° and −120°C, and a more extensive study of the temperature dependence of the spectrum of the benzene-1,4-d2 anion has also been carried out. The results for the benzene-1,3-d2 and benzene-1,4-d2 anions are in agreement with those reported previously for the benzene-1-d anion: The degeneracy of the benzene negative ion is removed by deuterium substitution. As expected, the degeneracy is not lifted in the benzene-1,3,5-d3 and benzene-d6 anions which have threefold or higher symmetry. The temperature dependence of the hyperfine splittings in those radicals which do not possess threefold or higher symmetry was found to be different from that of the unsubstituted benzene anion, and when compared to the benzene anion, some hyperfine splittings increase with temperature while others decrease. In addition, the proton–deuteron splitting-constant ratio was found to be approximately (aH / aD) = 6.18 in all of the radicals studied instead of the value (aH / aD) = 6.514 expected solely on the basis of the magnetic properties of the two isotopes. The effects of deuterium substitution are analyzed by assuming a rapid thermal equilibration between states corresponding to the symmetric and antisymmetric orbitals of the radicals, and estimates are made from the experimental data of the energy separations and relative populations of the two states. These depend on theoretical values for the spin densities; with a Hückel molecular orbital calculation they are −20, 22, and −38 cm−1, respectively, for the benzene-1-d, benzene-1,3-d2, benzene-1,4-d2 anions. The spin densities and energy separations of the symmetric and antisymmetric forms have been calculated using the Hückel MO method without including vibronic interactions by using both a Coulomb and resonance-integral perturbation for the effects of deuterium substitution.
Studies in Raman Intensity Theory
Authors: Tang J. , Albrecht A. C.
Published: February 2004

Raman intensity theory is investigated with the Kramers–Heisenberg dispersion theory as a basis. The sum over excited states is transformed into an infinite series in ground-state matrix elements involving an average energy. Particular choice of this average energy and neglect of all terms N ≥ 2 amount to the same approximations as in a variation–perturbation approach used by others. This truncated series, after a transformation through a quantum mechanical identity, assumes a particularly simple form. Calculations using this simple expression are presented for both the H2+ ion and the H2 molecule for several approximate wavefunctions. In several additional calculations for the H2 molecule, a more drastic approximation is employed where it is assumed that the major contribution to the derived polarizability is from the normalization factor of the wavefunction rather than from the detail of the wavefunction itself. The results of these calculations are compared with other calculations and, in the case of H2, also with experimental data. The qualitative success is encouraging. Finally, tentative explanations, based on the present approximation, are offered for some common empirical rules in Raman spectroscopy. These concern (1) the additivity properties for various bond types, (2) the fact that highly ionic bonds tend to exhibit weak Raman intensity while covalent bonds exhibit strong intensity, and (3) that totally symmetric vibrations almost always exhibit significantly greater intensity than do nontotally symmetric vibrations.
Photoionization of High-Temperature Vapors. IV. TlF, TlCl, and TlBr
Authors: Berkowitz J. , Walter T. A.
Published: February 2004

The vapors of TlF, TlCl, and TlBr have been studied by photoionization mass spectrometry. From the thresholds for formation of Tl+, the dissociation energies obtained are 4.57 ± 0.02, 3.82 ± 0.02, and 3.42 ± 0.02 eV for TlF, TlCl, and TlBr, respectively. The TlF value provides confirmation for the existence of barriers in the potential energy curves of its π0+3 and π13 states. The ion pairs in TlF and TlCl are formed with considerable kinetic energy, probably by a predissociative mechanism.
Dynamic Behavior of the Oxygen–Peroxide Couple on Platinum
Authors: Bowen R. J. , Urbach H. B.
Published: February 2004

The near-reversible nature of the oxygen–peroxide couple on platinum is demonstrated by substantial exchange currents. The transition between current by reduction of oxygen to peroxide and the reduction of peroxide to hydroxide ion is shown. Diagnostic criteria for determining the mechanism have been measured. The cathodic behavior of oxygen–peroxide systems in 1M potassium hydroxide is determined by the reduction of oxygen to peroxide when the concentration of peroxide is relatively low, and by the reduction of peroxide to water when its concentration is relatively large. At low peroxide concentrations Tafel slopes of approximately −2.3(2RT / 3F) are observed. With increasing oxygen activity these Tafel curves are translated towards increased currents in direct proportion to the pressure. In contrast, peroxide concentration changes do not influence the Tafel slopes in low concentration ranges. At high concentrations of peroxide, peroxide reduction becomes the predominant source of the observed current. The diffusion-limited currents are translated toward higher currents in direct proportion to the concentration of peroxide. A mechanistic interpretation of the reduction of oxygen to peroxide indicates that a fast one-electron step in quasiequilibrium precedes a slow one-electron rate-determining step. This latter may be a slow proton transfer to a superoxide species or a slow desorption of peroxide. The computed and observed diagnostic derivatives are in good agreement. The specific rate constant based on the proposed mechanisms show good constancy with change over two orders of magnitude in oxygen and peroxide concentration.
Critical Solution Behavior in a Binary Mixture of Gaussian Molecules. II
Authors: Helfand Eugene , Stillinger Frank H.
Published: February 2004

The critical solution properties of a model mixture have been examined. The system is composed of two gases (A and B) such that there are no AA or BB molecular interactions. The AB interaction is repulsive, with a negative Gaussian Mayer f function. The Mayer series for the free energy has been calculated through tenth power of the density (11-point graphs). By methods of Padé approximants nonclassical critical singularities have been found in the second composition derivative of the free energy (related to composition fluctuations), fourth composition derivative of the free energy, and the compressibility. An infinity in cp and a cusp in cυ are inferred. Thermodynamic questions discussed are the relations among the properties with pressure, density, or temperature as the independent variable; and the scaling laws. The critical fluctuations are also examined from the point of view of correlation functions.
Vibrational Energy Transfer in a System of Radiating Oscillators
Authors: Zitlau Carl F. , Moore William M.
Published: February 2004

The distribution function and the total band intensity for a system of excited oscillators that can both exchange vibrational energy among themselves through collisions and emit their energy through radiative transitions has been obtained for several pressure conditions. The nonequilibrium solution for an initial Boltzmann distribution is not a time-dependent Boltzmann distribution as has been obtained for non-radiating models. This solution is investigated for (1) very low pressures in which there are no interactions between the oscillators and (2) pressures high enough that collisional exchanges are much more rapid than the radiative transitions but not so high as to involve collisional deactivation or reabsorption. Both of these cases yield identical solutions, namely, a Boltzmann distribution with a time-dependent temperature. The solution for the second condition is also obtained by assuming a Boltzmann distribution is maintained at all times and solving for the temperature as a function of time. Although the non-equilibrium solution is not Boltzmann, it is very close, deviating at most 2% for CO. The solution for an initial delta-function distribution is also non-Boltzmann under nonequilibrium conditions, being given by a hypergeometric function. The total band intensity which is proportional to the first moment is exponential with respect to time and is independent of the initial distribution and the pressure. Also, the effect of first overtone transitions on both the distribution function and the total band intensity is bound to be negligible, the deviation for CO being less than 1%.
Kinetics of Hydrogen Halides in Shock Waves. III. The Reactions Cl + HCl→Cl2 + H and Cl + Cl2→3Cl
Authors: Jacobs T. A. , Giedt R. R. , Cohen N.
Published: February 2004

The decomposition of HCl via the chlorine exchange reaction Cl + HCl⇆Cl2 + H was studied in the shock tube by monitoring the infrared emission from the fundamental band of HCl. Mixtures of 0.2% HCl, 5% Cl2 (balance Ar) and 2% HCl, 5% Cl2 (balance Ar) were employed. Over the 3500°–5200°K temperature range of the experiments, the added Cl2 dissociated rapidly behind the shock waves; the HCl reaction mechanism thus proceeded in a large excess of Cl atoms and was dominated by the chlorine exchange reaction. We found the rate constant for the chlorine exchange reaction to be consistent with the low-temperature value of Klein and Wolfsberg. The study also yielded the efficiency of Cl atoms in decomposing Cl2. Compared to Ar, Cl was found to be 10 times more efficient.
19F Nuclear Magnetic Resonance Chemical Shift of Alkali Fluorides in Light- and Heavy-Water Solutions
Authors: Deverell C. , Schaumburg K. , Bernstein H. J.
Published: February 2004

Fluorine-19 chemical shifts of alkali fluorides dissolved in mixtures of light and heavy water are reported. The 19F isotopic shift of the fluoride ion is relatively insensitive to the cation, salt concentration, and temperature. There is a linear variation of shift with isotopic composition of the solvent and a total shift of approximately 3 ppm to high field on going from light- to heavy-water solutions. It is found that the results can be interpreted in terms of alterations in the vibrational energy of the fluoride ion, F− (H20)x, resulting from isotopic substitution. This leads to a change of the average excitation energy 〈ΔE〉 which occurs in the paramagnetic term of the nuclear magnetic shielding constant and results in a high-field shift with the heavier isotope. Similar effects were found for solutions of potassium fluoride in deuterated alcohols.
Scattering of Velocity-Filtered Atomic Beams of Ar and Xe from the (111) Plane of Silver
Authors: Smith Joe N. , Saltsburg Howard , Palmer Robert L.
Published: February 2004

The scattering of nearly monoenergetic atomic beams of Ar and Xe from the (111) plane of silver has been studied as a function of the nominal velocity υ0 transmitted by a slotted-disk velocity selector (SDVS) used as a velocity filter on the incident thermal-energy (Maxwellian) beam. The selector has a velocity spread of ±0.19 υ0 and studies were carried out over a range of υ0 from 2.2 × 104 to 5.3 × 104 cm/sec. The scattered beam distributions were found to be directed, corresponding closely to those of Maxwellian beams when υ0 = ῡ = 34(2πkTB / M)1 / 2, the average velocity of the corresponding Maxwellian beam of temperature TB. These results, together with the results of earlier scattering studies, imply that the thermal motion of the lattice is the dominant factor in producing the spatial dispersion as well as the velocity dispersion in the scattered beam that has been observed by other investigators. The most likely origin of these dispersive effects is the languidness of the collision in the sense used by Goodman to describe gas atom–lattice collisions.
Effect of Adsorbate–Adsorbate Interactions on the Net Charge of an Alkali Atom on a Metal Substrate
Authors: Bennett Alan J.
Published: February 2004

A previous calculation of the effective charge of an isolated alkali atom on a metal substrate is generalized, in the low-coverage limit, to include interactions between adsorbed atoms. The long-range Coulomb field traditionally invoked to explain the decrease in net charge with increasing coverage is incorporated into our self-consistent procedure. The complex nature of the dependence of this decrease on coverage is emphasized. Short-range interactions due to the overlap of adsorbate atomic orbitals are included by allowing for both monatomic and diatomic adsorbate species. The effect of the long-range Coulomb and overlap interactions is illustrated by numerical results for K adsorbates on a (100) W surface at various coverages. Several factors combine to cause a similar net charge per nucleus on the two species.
Hydrogen–Chlorine Explosion Laser. II. DCl
Authors: Corneil Paul H. , Pimentel George C.
Published: February 2004

Further work on the H2–Cl2 explosion laser shows that the emission occurs in υ = 2 → 1 vibration–rotation transitions P2(4) to P2(8) instead of 1 → 0 transitions, as concluded earlier. The laser emission is intensified with higher flash energy and with shorter flash duration. The effects of reactant pressures reflect the factors that influence the rate of the first reaction in the explosion chain. Raising temperature raises the laser gain, again due to acceleration of the Cl + H2 reaction, despite Doppler broadening, pressure broadening, and increased rotational dilution. With all conditions optimized, the D2–Cl2 explosion laser was successfully operated giving DCl 2 → 1 transitions P2(7) to P2(9). With HD–Cl2 mixtures, both HCl and DCl emissions were obtained. By mixing HD, H2, and D2 we were able to deduce for the first time the relative rates of the two reactions Cl + HD →  lim kHHCl + D and Cl + HD →  lim kDDCl + H: kH / kD = 1.9. The important processes in this chemical laser are becoming clear. A crucial datum needed for the determination of energy distribution among the vibrational levels is the rotational temperature at the time laser threshold is reached, since Tr rises during the explosion.
Quadrupole Coupling in Dirhenium Decacarbonyl
Authors: Segel S. L. , Anderson L. A.
Published: February 2004

The quadrupolar coupling of the two rhenium isotopes, 185Re and 187Re, in dirhenium decacarbonyl has been investigated as a function of temperature. Between the temperatures 350° and 77°K the coupling constant increases from 132–139 MHz while the asymmetry parameter in the electric field gradient increases from 0.58–0.86. The four allowed transitions have approximately the same linewidth of 17 KHz as measured with an induction spectrometer. Further evidence has been found for a solid-state phase transition at a temperature of 92°C.
Variational Upper Bounds to Second-Order Energies for Excited States
Authors: Epstein Saul T.
Published: February 2004

The second-order perturbation theory analog of the Hylleraas–Undheim theorem is derived and discussed. In particular it is shown that with the use of a sufficiently flexible trial function in the Hylleraas variation principle, one can get an upper bound to the second-order energy of an excited state without needing to know either the exact zero-order energies or wavefunctions of the lower states.
Specific Heat near the Critical Point
Authors: Mistura L. , Sette D.
Published: February 2004

A theory is given for the specific heat of a simple fluid in the critical region in the homogeneous phase above Tc. The excess heat capacity is related to the long-wavelength contribution to the mean-square fluctuation of internal energy. The derivation is based on the assumption that the Planck function of a fluid system in thermal equilibrium in a nonuniform state above the critical point is an analytic functional of the density distribution. The result obtained agrees with the predictions of the scaling laws. A discussion of the relationships between our theory and some recently published works is also included.
Effect of Lone-Pair Hybridization on the Stability of Weak Hydrogen Bonds
Authors: van Duijneveldt F. B.
Published: February 2004

In the past, various explanations have been given for the fact that hydrogen bonds involving a common proton donor become stronger as the acceptor lone-pair orbital contains less s character (e.g., amines form stronger H bonds than nitriles). Calculations are now presented which provide a more coherent rationalization for this phenomenon. The calculations are based on Murrell's second-order perturbation theory of intermolecular forces—including exchange—and they have been carried out for a linear model system A–H···B which was described previously. The results show that there are three contributions to the H-bond energy which favor the formation of H bonds with low lone pair s character, viz., the penetration part of the Coulomb energy, the exchange energy, and the charge-transfer energy. Differences in dipolar interaction are less important except for very polar A–H bonds. A comparison with some experimental data is given in the final section.
Medium-Dependent Intermolecular Potential for Liquids and Its Use in Obtaining Free Energy and Entropy
Authors: Halicioğlu Timur , Sinanoğlu Oktay
Published: February 2004

It has been found that even in nonpolar liquids an intermolecular pair potential derived from gas properties may be affected by as much as 10%–40% due to the medium effect of the liquid, and many-atom forces. An effective intermolecular pair potential for liquids was recently derived. It takes into account the local solvation structure around the two molecules in an analytical form with an explicit dependence on the relative sizes of the solute and solvent molecules. Its parameters are specified mainly in terms of some macroscopic properties. The potential is defined so as to reproduce the total thermodynamic energy of the system correctly. In the present paper, based on a statistical-mechanical perturbation theory, it is shown that the effective pair potential may be used as though it were an ordinary two-body potential, not only in the total energy, but also in quantities like free energy and entropy.
Isotope Exchange Rates. V. The Homogeneous Reaction between H2S and D2
Authors: Burcat Alexander , Lifshitz Assa , Lewis David , Bauer S. H.
Published: February 2004

Single-pulse shock-tube data were obtained for the homogeneous isotopic exchange reaction between deuterium and hydrogen sulfide, highly diluted in argon, over the temperature range 1260–1590°K. Three sets of experiments were performed independently in two laboratories. H2S/D2 ratios were varied over the range 4/1–1/4, at total reaction densities from 6 × 10−6 to 5 × 10−5 moles/cm3. The agreement among the three sets of data is generally good. An average activation energy of 52 ± 3 kcal/mole was deduced from them. All three sets of data may be fitted by a second-order power rate expression which is first order in D2 and roughly 12 order with respect to H2S and to Ar. These data support a mechanism, suggested previously for similar isotopic exchange reactions, in which metathesis reactions during collisions between H2S and D2 occur with significant probability only when the deuterium molecule contains at least a critical amount of vibrational energy. The rate-limiting process is the maintainance of an adequate population in the 4th and 5th vibrational levels of deuterium. The relative efficiencies for excitation of deuterium by collisions with the various species present, as determined from the kinetics data, are in reasonable agreement with values determined directly from vibrational relaxation studies.
Effects of X- and Γ-Ray Radiation on the Thermal Decomposition of Solid Orthorhombic Ammonium Perchlorate. I. Experimental and Results
Authors: Herley P. J. , Levy P. W.
Published: February 2004

The thermal decomposition kinetics of unirradiated, x-ray and gamma-ray irradiated orthorhombic ammonium perchlorate have been determined in the temperature range of 193°–238°C. Both millimeter size and powdered crystals were used. When all of the decomposition gases are allowed to collect, the pressure vs time curves consist of the following stages: First, an induction stage with a puff or burst superimposed on it; second, an acceleratory stage followed by a third, or decay, stage. When only the noncondensable gases, i.e., gases not condensed in a trap at −23°C or lower, are allowed to accumulate, the puff or burst, but not the induction period, is eliminated. Irradiation prior to decomposition reduces the induction period and increases the acceleratory period decomposition rate. Both of these effects increase as the dose is increased. If the decomposition is interrupted before the decay period, the sample irradiated with a fixed gamma-ray dose, and the decomposition resumed, the following changes occur in the pressure vs time curves. First, the decomposition proceeds along the curve for unirradiated material but only for a constant period of time equivalent to the induction period for irradiated material. Second, at the end of this period, the decomposition rate abruptly increases to the approximate value obtained for irradiated material. The subsequent decay stage is similar to that observed with irradiated crystals. In addition to the kinetic studies the decomposition gases were analyzed with a mass spectrometer and preliminary measurements made on the low-temperature thermoluminescence of gamma-ray irradiated material.
General Internal Motion of Molecules, Classical and Quantum-Mechanical Hamiltonian
Authors: Meyer R. , Günthard Hs. H.
Published: February 2004

The dynamics and the Hamiltonian of a general asymmetric-top molecule undergoing almost arbitrary deformations are discussed. s vector notations are used for translational, rotational, and internal-velocity coordinates. The kinetic energy is formulated by generalizing the G-matrix technique known from the theory of molecular vibrations. A geometrical definition of the rotational coordinates referring to the instantaneous principal axis system is compared with a dynamical definition involving the over-all angular momentum. States of general internal motion are associated by definition with zero linear momentum and zero over-all angular momentum.
Electron Attachment to Halogenated Aliphatic Hydrocarbons
Authors: Blaunstein R. P. , Christophorou L. G.
Published: February 2004

Mean attachment cross sections as a function of mean electron energy are reported and discussed for 22 halogenated aliphatic hydrocarbons.
Quantum Corrections for the Second Gas-Surface Virial Coefficient
Authors: MacRury T. B.
Published: February 2004

The quantum corrections for the second gas–surface virial coefficient are derived and applied to the experimental data for H2, D2, CH4, and CD4 in the external field provided by a uniform graphite surface. These corrections cause quite sizable differences in the interaction energies and areas obtained for the hydrogen pair, but the differences are, of course, small in the case of the methanes. Quantum effects have been measured in dilute adsorption systems and found to be of considerable importance. Theoretically, Yaris and Sams have developed the second gas–surface virial coefficient BAS from the Wigner–Kirkwood expansion to order ℏ4 and examined three different models for the gas–surface interaction potential, using the data of Constabaris et al. Due to a misprint in the ℏ4 term of Uhlenbeck and Beth, which has been carried through in the calculations of Yaris and Sams, we have recalculated the quantum corrected BAS and fitted it to the data mentioned above.
Bimolecular Ionization of the Triplet State of Aromatic Hydrocarbons in Solution
Authors: Gary L. P. , de Groot Klaas , Jarnagin R. C.
Published: February 2004

The production of free ionic carriers due to bimolecular triplet encounters of anthracene, naphthalene, phenanthrene, and pyrene in solvents methyltetrahydrofuran (MTHF), tetrahydrofuran (THF), benzonitrile (C6H5CN), and acetonitrile (CH3CN), whose dielectric constants fell between 6.2 and 36.7, was verified. The probability of producing free carriers per triplet–triplet collision from phenanthrene was found to be 1.9 × 10−4, 1.9 × 10−3, and 0.41 in MTHF, THF, and CH3CN, respectively. The probability of free carrier production in fluid THF was found to be 1.4 × 10−2, 1.3 × 10−2, and less than 10−4, respectively, for triplets of anthracene, pyrene, the tetracene. The significance of escape of carriers from a Coulomb well was delineated and shown to be of maximal concern for media whose dielectric constant was less than 15. Similarly, carrier escape was shown to be primarily responsible for the lack of observed photocurrents from these aromatic hydrocarbons in n-hexane and cyclohexane.
Electrolysis of SiO2 on Silicon
Authors: Jorgensen Paul J.
Published: February 2004

The application of an external voltage across a layer of SiO2 on silicon causes a reduction in the thickness of the oxide layer by electrolysis when the applied voltage exceeds the theoretical cell voltage of the cell O2, Pt/SiO2/Si and the electric field is oriented such that the silicon–silicon dioxide interface is negative with respect to the oxide–gas interface. A measurement of the stopping voltage reveals that four equivalents are involved in the reaction, thus indicating that O= ions or some similarly charged defect could be involved in the electrolysis. Further evidence shows that the transport of uncharged oxygen species is negligible during the electrolysis of SiO2.
Effusion. II. Angular Number Distributions of Gaseous Cadmium from a Right-Circular Cylindrical Orifice into Vacuum
Authors: Wahlbeck P. G. , Phipps T. E.
Published: February 2004

The angular number distributions of Cd(g) atoms effusing from a Pyrex right-circular cylindrical orifice have been studied by use of a condensation target. The profile of the deposit on the condensation target was analyzed by an interferometric means. Only qualitative agreement with the Clausing prediction for the angular number distribution could be obtained. A high-pressure limit for molecular flow was found to be 3.9 < K (Knudsen number; ratio of mean free path to orifice diameter) <4.6. At higher pressures in the transition region, the probability of effusion in the forward direction decreases with increasing pressure.
Infrared Study of the Adsorption of Methanol and Ethanol on Magnesium Oxide
Authors: Kagel R. O. , Greenler Robert G.
Published: February 2004

The adsorbed species which result when magnesia is exposed to methanol or ethanol vapor are reported. Five different surface species have been identified for both methanol and ethanol. At 25°C a tightly bound layer of liquid alcohol is observed. When this is removed by heat and evacuation, another species appears which is identified as a surface methoxide in the case of methanol and ethoxide in the case of ethanol. When the magnesia sample is heated to 165°C in alcohol vapor, a formatelike surface compound is formed from methanol and an acetatelike compound from ethanol. At temperatures near 430°C, two more surface species are observed to form after the disappearance of surface formate (or acetate). They are identified as a surface methyl carbonate from methanol (ethyl carbonate from ethanol) and surface carbonate which is formed from both methanol and ethanol. Both the surface alkyl carbonate and surface carbonate are attributed to a low-temperature (<240°C) reaction between surface alkoxide and CO2 which is liberated by dicarboxylation of the surface carboxylate. The interpretation of surface structures has been checked by using CD3 methanol and 13C enriched methanol. Proposed mechanisms for the formation of the different surface species (followed by mass spectrometry) are discussed.
Evaluation of the 57mFe Nuclear Quadrupole Moment
Authors: Harris C. B.
Published: February 2004

A value for the 57mFe nuclear quadrupole moment of 0.175 ± 0.02 has been determined from a comparison of the quadrupole splittings in the Mössbauer data of ferrocene and the pure nuclear quadrupole resonance of 59Co in cobalticinium perchlorate. The value is in good accord with recent calculations of Fe(II) complexes in the solid state.
Secular Behavior and Friedman's Multiple-Time-Scale Theory of Irreversible Processes
Authors: Wilson Hugh R. , Rice Stuart A.
Published: February 2004

The functional integral representation of statistical mechanics is used to derive the multiple-time-scale theory of irreversible processes. It is shown that the functional integral representation inherently removes secular behavior in the description of the irreversible process. This observation is related to the nature of the auxiliary conditions introduced by Frieman and to the properties of perturbation expansions in general.
Electron Paramagnetic Resonance Studies of VO2+ in KNO3 and CsNO3 Single Crystals
Authors: Rao K. V. S. , Sastry M. Dattatreya , Venkateswarlu Putcha
Published: February 2004

The electron paramagnetic resonance spectra of the VO2+ ion doped in KNO3 and CsNO3 single crystals have been investigated over a wide temperature range. Room-temperature studies reveal that there is a very fast readjustment of VO2+ ion, in both crystals, which is manifested in the presence of a single isotropic octet, thereby exhibiting a low viscous “liquidlike” nature. At low temperatures an anisotropic spectrum is obtained due to the hindered rotation of the VO2+ ion. The effect of CsNO3 in hindering the rotation of a vanadyl ion is found to be greater than that of KNO3. The linewidths at room temperature are found to depend upon the mI quantum number, and an attempt is made to fit the linewidth data of the present study in the theoretical expressions of Kivelson. It is found that Kivelson's theory can qualitatively explain the observed variation of linewidth with nuclear quantum number mI, but the experimental data could not be fit quantitatively into the theory. All the spectra are analyzed using the usual spin-Hamiltonian method.
Emission Properties of p-Hydroxybenzaldehyde with Particular Regard to Proton Transfer
Authors: Baba Hiroaki
Published: February 2004

The emission properties of p-hydroxybenzaldehyde have been studied in a hydrocarbon solvent in the presence of ether or triethylamine as a proton acceptor. At room temperature no emission is detected, and the absorption spectra indicate that a simple hydrogen-bonded complex is formed between p-hydroxybenzaldehyde and either of the two acceptors. The n→π* transition is shifted to the blue by the formation of the hydrogen bond, whereas the π→π* transition is shifted to the red. At liquid-nitrogen temperature, the p-hydroxybenzaldehyde–ether system shows a single phosphorescence spectrum with a vibrational fine structure, the spectrum being ascribable to the simple hydrogen-bonded complex. The p-hydroxybenzaldehyde–triethylamine system exhibits either a similar phosphorescence spectrum or a structureless phosphorescence spectrum accompanied by a broad fluorescence spectrum, depending on the region of excitation. It is concluded that, at liquid-nitrogen temperature, the latter system involves a proton-transferred complex (ion pair) as well as the simple hydrogen-bonded complex. The structureless phosphorescence and fluorescence spectra are assigned to the ion pair. In contrast to the case of the usual phenolic compounds, the proton transfer does not take place from p-hydroxybenzaldehyde to the amine during the lifetime of the excited state. This is attributed to the fact that the lowest singlet-excited state of the p-hydroxybenzaldehyde molecule is of an (n, π*) type, where the proton-donating power of the molecule is relatively weak.
Heat Capacity of Manganese Titanate from 30° to 300°K
Authors: Stephenson Clark C. , Smith David
Published: February 2004

The heat capacity of antiferromagnetic manganese titanate was measured between 31° and 300°K. The magnetic heat capacity of MnTiO3 was determined by subtracting the lattice heat capacity from the observed heat capacity. The lattice heat capacity of MnTiO3 may be represented by a sum of Debye and Einstein functions. The characteristic temperatures of MnTiO3 were estimated from the characteristic temperatures of isomorphous diamagnetic compounds. The entropy associated with the antiferromagnetic transition was calculated to be 3.51 cal deg−1, which is in good agreement with Rln6. Only 55% of the magnetic entropy is acquired by the Néel temperature at 62.3°K. The thermodynamic functions Cp, S° (H° − H0°) / T, and −(F° − H0°) / T of MnTiO3 in cal deg−1·mole−1 at 298.15°K are: 23.93, 25.08, 13.38, and 11.70.
Effects of Molecular Identity on Intermolecular Forces
Authors: Kromhout Robert A. , Linder Bruno
Published: February 2004

The free energy of interaction between two (nonoverlapping) molecules at finite temperature has been treated by quantum-statistical perturbation theory. This has been applied to the interaction between neutral molecules which may be rigid-rotor dipoles. It is shown that, in the absence of retardation, the leading term in the free-energy expansion varies as the inverse sixth power of the intermolecular distance r. This is true in spite of the existence of r−3 corrections to the energies of the pure states for pairs of identical molecules. The leading term in the free energy consists of two parts. One of these is associated with the adiabatic interaction of the two molecules and is expressible in terms of the isolated molecule susceptibilities; the other part is a correction arising from the redistribution of the molecules among the states and is not expressible in terms of the isolated molecule susceptibilities. The adiabatic part is always present and is identical with previously derived expressions for the van der Waals interaction. The second part, the resonance part, is present only when the molecules are identical; it vanishes when the temperature is zero and is negligible in the classical limit. It is concluded that the usual formulations for the dispersion (corresponding to T = 0), induction (T → ∞), and orientation (T → ∞) potentials are essentially correct.
Nature of the Rotational Phase Transition in Paraffin Crystals
Authors: McClure David W.
Published: February 2004

An attempt has been made to calculate the change in lattice energy accompanying the rotational phase transition cocurring in the paraffins. The calculation is based on the assumption that the change in the lattice energy corresponding to the discontinuous change in the crystal structure may be approximated by the difference in the theoretical lattice potential energies of the crystal before and after the transition has occurred. A specific model for the rotation mechanism has been postulated, and a method devised for calculating the average repulsive energy of a system of cooperatively rotating rigid chains. The results of the calculation indicate that the change in lattice energy is of the same order as the experimental heat of transition.
Conductivity, Dielectric Relaxation, and Viscosity of NaCl–Glycerol Solutions
Authors: Bartoli F. J. , Birch J. N. ,   Nguyen-Huu-Toan, McDuffie G. E.
Published: February 2004

Values of conductivity (σ), viscosity (ηs), and dielectric relaxation time (τD) are reported over several decades for various concentrations of NaCl–glycerol solutions as a function of temperature and concentration. The specific conductivity exhibits a non-Arrhenius temperature dependence of the form A exp[B / (T − T∞)] similar to that of ηs and τD. The dielectric relaxation time was found to be linear with mole-fraction concentration whereas the conductivity saturated at high concentrations (0.07 mole fraction NaCl). The product σηs exhibited a stronger temperature dependence than the product στs, where τs is the shear relaxation time. This suggests that the diffusion of ions is limited by the dynamic structural rearrangement of the solvent rather than simply by a continuous viscous retarding force.
Structures of Solid Deuterium above and below the λ Transition as Determined by Neutron Diffraction
Authors: Mucker K. F. , Harris P. M. , White David , Erickson R. A.
Published: February 2004

Reproducible neutron diffraction patterns were obtained from samples of powdered deuterium with para (J = 1) concentrations equal to 3%, 33%, 63%, and 80%. The diffraction patterns were obtained at various temperatures in the range 1.9°–13°K and for the 80% sample at temperatures both above and below the λ anomaly in the heat capacity. The deuterium powdered samples were randomly oriented except for an estimated preferred orientation of 8% or less. All of the samples froze from the liquid to a hexagonal structure with the molecules at the close-packed sites. In the case of the 80% paradeuterium sample a transformation from the hcp structure to a cubic structure occurred at a lower temperature than has been observed for the λ anomaly in the heat capacity. Observations of the transformation between the hexagonal and cubic phases, on warming or cooling, have shown a large hysteresis effect. The cubic-phase diffraction patterns corresponded to space group Pa3 with four molecules per unit cell and a = 5.074 Å. Absolute integrated intensities of the five observed lines were calculated and are in excellent agreement with observed values. The hexagonal-phase lattice parameters for the above samples are presented. An analysis of the integrated intensities of the six observed hexagonal lines indicated a disordered structure. Four of the five structural models under consideration gave an average site symmetry which is equivalent to that produced by a molecule precessing about the z direction with a mean precession angle δ. In general, δ was found to increase with increasing para concentration except for 63% paradeuterium, at 2°K, where a spherical average site symmetry (i.e., complete disorder) was indicated.
Proof of Two Conjectures of Mulliken Concerning the Electronic Energy of Diatomic Molecules for Small R
Authors: Bingel Werner A.
Published: February 2004

This paper deals with the coefficient E2 in the R expansion of the electronic energy of diatomic molecules for the manifold of molecular states (characterized by the quantum number Λ or Ω) originating from a given state of the united atom. Explicit expressions for E2(Λ) and E2(Ω) are derived, which generalize two conjectures of Mulliken concerning the Λ (or Ω) dependence of E2. As an example, the six lowest states of the BH molecule, which originate from the three lowest states of the carbon atom, are treated numerically.
Principal Field-Gradient Tensor in 1,1-Difluoro-2-Chloroethylene and Bonding in the Substituted Ethylenes
Authors: Stone R. G. , Flygare W. H.
Published: February 2004

The microwave spectrum of F2C=CH35Cl has been re-examined to determine the off-diagonal element of the nuclear quadrupole coupling tensor. The rotational constants are A = 10 710.72 ± 0.02 MHz, B = 2297.12 ± 0.01 MHz, and C = 1890.17 ± 0.01 MHz. The nuclear quadrupole coupling constants in the principal inertial axis system are χaa = −55.05 ± 0.10 MHz, χbb = +18.29 ± 0.08 MHz, and χcc = +36.76 ± 0.10 MHz. Second-order quadrupole coupling effects have been used to measure the nonzero off-diagonal element in the χ tensor (in the molecular plane) as χab = ±46.3 ± 4 MHz. The in-plane C–Cl bond-axis coupling constants are also given as χαα = −77.40 MHz and χββ = +40.64 MHz which agree well with similar molecules. The quadrupole coupling constants in several substituted chlorethylene molecules are interpreted in terms of effects on the carbon–chlorine bond.
Luminescence and Radiations Transitions in Sulfur Dioxide Gas
Authors: Strickler S. J. , Howell Daniel B.
Published: February 2004

The luminescence spectrum of SO2 gas has been measured at pressures from 0.003–1.0 torr. At low pressures, only a fluorescence from the lowest singlet state is observed. At higher pressures a phosphorescence from the lowest triplet state is also observed. The kinetics of production, luminescence, and quenching of these two states are analyzed, and certain ratios of rate constants are determined. The results are discussed in terms of current views of radiationless transitions.
Electron-Impact Ionization Cross Section in Cesium
Authors: Nygaard Kaare J.
Published: February 2004

The total ionization due to the passage of an electron beam in cesium vapor has been measured with a Tate and Smith-type apparatus. The retarding potential difference method was used in the electron gun to obtain energy resolution better than 0.1 eV. The density of Cs atoms was determined from the Taylor and Langmuir formula and also measured with a surface-ionization detector. The two methods gave the same density to within ±3% when the apparatus was in thermodynamic equilibrium with the Cs reservoir. The cross section for production of Cs+ has been determined from threshold to 100 eV. For energies above 28 eV, the results agree closely with those of McFarland and Kinney. At threshold the slope of the cross-section-vs-energy curve was measured to be 2.7 Å2/eV.
Use of Green Functions in Atomic and Molecular Calculations. III. Second-Order Perturbation of the Hydrogen Molecular Ion
Authors: Pan Yen-chi , Hameka Hendrik F.
Published: February 2004

We have derived analytical expressions for the second-order perturbation energy of a hydrogen atom, perturbed by a point charge λ at a distance R. Here the charge λ is taken as the perturbation parameter. The calculations make use of Green-function techniques and of the hydrogen-atom Green function that we derived in a previous publication.
Modified Perturbation Theory for Atoms and Molecules Based on a Hartree–Fock φ
Authors: Silverstone Harris J. , Yin Moon-Lung
Published: February 2004

The improvement of Hartree–Fock wavefunctions by perturbation theory is hampered by slow convergence with the usual choice of H0 =  ∑ i = 1N F(i), where F denotes the one-electron Hartree–Fock Hamiltonian. The slow convergence is usually attributed to the unphysical nature of the excited states of F, which do not describe electrons moving in the field of the nuclei, shielded by N-1 electrons. It is shown how to redefine F so that the zeroth-order wavefunction still remains the Hartree–Fock wavefunction but so that the excited states of F correspond to an electron moving in the field of the nuclei screened by N-1 electrons. The redefined F thus results in a more appropriate H0. Calculations of some second-order polarization and semi-internal correlation energies in first-row atoms are given to illustrate the use of the redefined F.
Abundance of Excited Ions in an NO+ Ion Beam
Authors: Mathis R. F. , Turner B. R. , Rutherford J. A.
Published: February 2004

A study of a beam of NO+ ions has been undertaken to determine the relative abundances of excited-state ions and ground-state ions. The experimental procedure involved the attenuation of the ion beam in a gas-filled reaction chamber where different states of the ion were attenuated at different rates. The ions were produced from NO by impact of electrons with energies of 25, 50, and 100 eV. The abundances were determined ∼20 μsec after the ions were formed, so that only ions in long-lived states remained in the beam. Several gases, H2, N2, O2, H2O, and Ar, were employed in the attenuation chamber to assess the importance of de-excitation processes and to reduce the possibility of identical-loss cross sections for excited and ground states. It was found that high pressures in the ion source, as well as the electron energy, could influence the abundance of excited-state ions. A typical result was that, using 50-eV electrons and low source pressures, 42% of the ions in the beam were excited.