bluuebunny/crossref_metadata_2025 huggingface dataset:
Classical Monte Carlo Analysis of Four-Body Reactions: K + C2H5I System
Authors: Raff L. M.
Published: January 2005

The analysis of the classical four-body problem as applied by Monte Carlo techniques to chemical reactions of the type A+BCD→AB+CD is reported. Using a modified form of a Blais—Bunker interaction potential surface, the model is applied to the reaction of K with C2H5I by approximating the C2H5 radical as being two carbon atoms, one of mass 14 amu, the other of mass 15 amu. Hamilton's equations are solved numerically, and by Monte Carlo averaging over the initial variables for 1060 different trajectories, various attributes of the reaction are calculated; these include the total reaction cross section, the differential reaction cross section, and the distribution of the heat of reaction among the available degrees of freedom of the products. It is found that the total reaction cross section is 15.9 Å2. This result, which is less than that obtained by similar methods for the (K, CH3I) system, is interpreted as reflecting the increased steric hindrance present in the more bulky system.

The differential reaction cross section for C2H5 scattering is peaked at small angles, and an average of about 90% of the available reaction energy finds its way into internal degrees of freedom of the products. These results are in reasonable agreement with the available experimental data. It is also found that the C–C vibrational mode of the ethyl radical is important in absorbing the heat of reaction. On the average it accounts for about 14% of the available energy. Two modes of reaction are observed, one a direct interaction, the second through complex formation. This second mechanism is found to enhance the importance of the organic radical in absorbing the heat of reaction. This is interpreted as being due to the increased opportunity for energy exchange during complex formation.
Some Infrared Spectra of Matrix-Isolated Lithium Fluoride
Authors: Redington R. L.
Published: January 2005

Infrared spectra of LiF species suspended in solid Ne, O2, CO, and CH4 at liquid-helium temperature have been obtained. The monomeric LiF frequency (in cm−1) is 869 in Ne, a doublet at 819–824 in O2, 787 in CH4, and a doublet at 710–725 in CO, compared to 895 cm−1 in the gas phase. Some of these values seem consistent with Linevsky's statement that the solvent shift in LiF is primarily of electrostatic origin. Electrostatic calculations were made for the rare-gas matrices in order to observe the effects of asymmetric solute positions in the ideal lattice substitutional site and to test ideal lattice breakdown, or ``solvation'' of the monomeric LiF solute. For reasonable distance parameters, both types of calculation can account for most, or all, of the observed solvent shift. These simple calculations show ways to reduce the dispersive contributions to commonly observed values but likewise illustrate the presently unsatisfactory state of a genuine understanding of the LiF—matrix systems.
Experimental and Theoretical Studies of Photoionization-Efficiency Curves for C2H2 and C2D2
Authors: Botter R. , Dibeler V. H. , Walker J. A. , Rosenstock H. M.
Published: January 2005

Photoionization-efficiency curves for C2H2 and C2D2 have been remeasured in the wavelength region from onset of ionization to 600 Å, using a gold-coated grating and the Hopfield continuum as a photon source. The curve shapes of the molecule ions near threshold are compared with calculations of the Franck—Condon factors. Nearly exact agreement between experiment and calculation is obtained when taking into account hot bands. A general discussion is given for the shape of the molecule-ion curve and for that of the fragment ions, C2H+ and C2D+. The observed onsets of ionization for the latter ions are 17.22— and 17.34 eV, respectively.
Microwave Spectrum of Methylazide
Authors: Salathiel William M. , Curl R. F.
Published: January 2005

The microwave spectrum of methylazide (CH3N3) has been investigated, and a- and b-type transitions assigned. The dipole moment has been found to be 2.17±0.025 D. The barrier to internal rotation of the CH3 group has been found to be 714±20 cal/mole.
Exciton Impurity States in Molecular Crystals
Authors: Takeno Shozo
Published: January 2005

The effect of impurities on Frenkel excitons in molecular crystals is studied with particular attention to impurity levels appearing outside exciton bands and virtual impurity levels lying in the continuum. A study is made of a specific case in which the transition dipole moments of the impurities are parallel to that of the host molecules. A secular equation which determines the energies of impurity levels due to any number of impurities is obtained, and a resonance form of the inverse relaxation time of excitons scattered by an impurity is derived. In the one-impurity problem, a detailed discussion is made of the criterion for the appearance of impurity levels and virtual impurity levels. It is concluded that for excitons with fairly large effective masses these impurity states are very likely to occur. Numerical calculations are performed for a simple cubic lattice in which only interactions between nearest-neighbor molecules are important. The results are then applied to a study of the interaction of impurity levels due to small but finite concentrations of impurities. It is shown that there can exist long-range jumps of excitons from one impurity site to another due to the dipole—dipole interaction. An impurity-induced energy transfer is suggested.
Microwave Spectra, Dipole Moments, Structure, and Ring Puckering Vibration of Cyclobutyl Chloride and Cyclobutyl Fluoride
Authors: Kim Hyunyong , Gwinn William D.
Published: January 2005

Microwave spectra of nine isotopic species of cyclobutyl chloride and of the normal species of cyclobutyl fluoride have been studied. From the ground state moments of inertia, the structure of cyclobutyl chloride has been determined. Some of the more important structural parameters are: r(Cα–Cβ) = 1.525±0.005 Å r(Cβ–Cγ) = 1.550±0.005 Å, r(Cα–Cl) = 1.775±0.005 Å, ∠Cl–(CβCαCβ) = 135°±1°, and ∠(CβCαCβ)– (CβCγCβ) = 20°±1°. The chlorine atom is found at the equatorial position of the puckered ring, and the axial form was not observed. Quadrupole coupling constants of the chlorine atom for CH2CH2CH2CH35Cl species were found to be χaa = −56.58±0.10 Mc/sec and χcc = 23.60±0.1 Mc/sec. The transformed coupling constant along the C–Cl bond is −65.98 Mc/sec (assuming the quadrupole tensor was axially symmetric about the C–Cl bond). The moments of inertia of cyclobutyl fluoride calculated using r(C–F) = 1.37 Å, ∠F–(CβCαCβ) = 132° and the remaining structural parameters of cyclobutyl chloride agreed with the observed moments of inertia. The dipole moments of cyclobutyl fluoride were determined by the Stark effect: μa = 1.870±0.005 D, μc = 0.52±0.02 D, and μ = 1.94±0.01 D.
Interpretation of the Chemical Shift of C1F
Authors: Cornwell C. D.
Published: January 2005

The chemical shift of 19F in gaseous ClF, about 160 ppm above the estimated shift for the free ion F−, represents a striking discrepancy with simple fluorine chemical-shift theories, which generally predict fluorine resonance shifts to be paramagnetic relative to F−. This result can be accounted for satisfactorily in terms of a simple p-bonded model with the use of a relatively uncomplicated equation for shielding. In the second-order or excitation term, it is essential (1) to consider separate contributions from different excitations, (2) to include terms on both atoms for some matrix elements, and (3) to recognize the role of the π-bonding coefficient even though the π shell is filled. The anomaly for ClF arises from the valence shell π*→σ* excitation, which corresponds to electron circulation in opposite senses on the two atoms. No such effect occurs for F2, on account of symmetry restrictions, or for HF, because of the absence of π electrons on the H atom.
Electron Spin Resonance Linewidths of Manganese(II) Ions in Concentrated Aqueous Solutions
Authors: Hinckley C. C. , Morgan L. O.
Published: January 2005

ESR spectra of concentrated solutions of manganese(II) perchlorate (1–3.2M) do not indicate strong spin exchange and the dipole—dipole interaction is considered to be the predominant intermolecular-relaxation process. A model of the ESR spectrum is constructed using 30 Lorentzian distribution functions positioned according to a relation developed by Hurd, Sachs, and Hershberger. Ratios of the second moment for the various electron-magnetic transitions are used to approximate the linewidth ratios of the transitions and thereby reduce the number of linewidth parameters to one, ΔHD½, the dipolar-linewidth contribution to the −½→½ absorption. ΔHD½ is calculated from the experimental spectra by trial and error. The variations of ΔHD½ with increasing temperature indicates that for concentrations less than 1.9M a simple rapid-motion diffusion model is sufficient to explain the narrowing of the spectrum. Above 1.9M, ΔHD½ follows a modified exponential function, ΔHD½=AD—BD exp(—u/kT), in which AD varies linearly with concentration and BD and U are very nearly concentration independent. A weak exchange interaction is suggested for the more concentrated solutions.
Calculation of the Average Structure of Ethylene
Authors: Kuchitsu Kozo
Published: January 2005

The average structure of ethylene in the ground vibrational state has been calculated from the internuclear distances (rg) obtained from electron diffraction by making corrections for the effect of atomic displacements perpendicular to the equilibrium bond directions and the centrifugal distortion, and from the rotational constants A0, B0, and C0 obtained from infrared and Raman spectra by making corrections for the interactions of vibration and rotation. Good agreement is observed between the diffraction and spectroscopic average structures, and the following average structure of C2H4 has been determined: rz(C=C) = 1.335±0.003 Å, rz(C–H) = 1.090±0.003 Å, and ∠zC–C–H = 121.7°±0.4°.
Cross Sections for Ionization by Electrons. I. Absolute Ionization Cross Sections of Zn, Cd, and Te2. II. Comparison of Theoretical with Experimental Values for Atoms and Molecules
Authors: Pottie R. F.
Published: January 2005

Ionization cross sections for Zn, Cd, and Te2 vapors have been measured by collection of the total positive ion currents produced from electron impact by 50-eV electrons in the specially designed ion source of a mass spectrometer. The results: σi(Zn) = 5.03±0.45×10−16 cm2, σi(Cd) = 8.54±0.33×10−16 cm2, σi(Te2) = 17.46±0.48×10−16 cm2. These results are combined with available data to set up a compilation of absolute ionization cross sections for 27 atoms. Very limited agreement is found with theoretical ionization cross sections: It is shown that ionization cross sections of molecules cannot be calculated reliably by summation of the ionization cross sections of the constituent atoms.
Vibrational Spectra of Trioxane and Trioxane-d6
Authors: Kobayashi Masamichi , Iwamoto Reikichi , Tadokoro Hiroyuki
Published: January 2005

The infrared spectra of trioxane and trioxane-d6 have been measured in the region from 4000 to 300 cm−1 on the gaseous, solution, liquid, and solid samples. Polarized spectra have been taken on the oriented thin layer of crystal grown between NaCl or KBr plates. Group-theoretical analyses were made for a free molecule (point group C3v) and the crystal (site group C3 and space group R3c—C3v6). The symmetry species of the observed bands were determined on the basis of the polarized spectra of the crystal. The normal vibrations of a free molecule were calculated according to Wilson's GF matrix method by use of the Urey—Bradley potential field. The observed bands have been interpreted reasonably based on the calculated results. The band shapes of the gaseous spectra were found to be consistent with the dichroism of the polarized spectra of the crystal by taking into account the Coriolis interactions.
Molecular Constants for l-Uncoupled Electronic States of Diatomic Molecules
Authors: Ginter Marshall L.
Published: January 2005

Improved methods for the evaluation of the matrix elements in the usual energy expressions for l-uncoupled electronic states of diatomic molecules are discussed. The proposed approximations yield molecular constants which greatly improve the quantitative agreement between theory and experiment. The specific examples of the v = 0 levels of the 3d complexes of BH and He2 are considered in detail. Modifications in the off-diagonal (interaction) elements seem to be the major remaining considerations. Such modifications have only minor effects on the most important of the molecular constants (the electronic energies and B values), however, inclusion of such effects should substantially improve the determination of the higher-order rotational constants.
NMR Studies of Inorganic Fluorides. I. High-Resolution 19F Spectra of Si2F6 and (SiF3)2O
Authors: Johannesen Rolf B. , Farrar T. C. , Brinckman F. E. , Coyle T. D.
Published: January 2005

Fluorine NMR spectra of hexafluorodisilane and hexafluorodisiloxane have been recorded and analyzed. The 19F–19F and 29Si–19F spin coupling constants were obtained from the satellite spectra arising from the 29Si-substituted molecules present in natural abundance. The ``near'' and ``far'' 29Si–19F coupling constants in Si2F6 were found to be of opposite sign.
Stochastic Approach to First-Order Chemical Reaction Kinetics
Authors: Darvey I. G. , Staff P. J.
Published: January 2005

A stochastic model for the general system of first-order chemical reactions involving n chemical species is derived, from which the multinomial distribution is shown to represent the probability time course of the components of the reaction. The mean and variances of the numbers of molecules of the components present, at any time, are given and the correspondence between the stochastic model and the classical deterministic model is discussed.
Luminescence Processes Generated by Ionizing Radiation in KI and KI:Tl
Authors: Kaufman R. Gilbert , Hadley Wayne B.
Published: January 2005

Undoped KI and thallium-doped KI are irradiated with x rays at 78°K. Luminescence and energy storage, in the form of trapped electrons and holes, are produced during irradiation. After irradiation phosphorescence is observed at 425 mμ and stimulation with light gives an emission quite similar to that during irradiation with bands at 302, 370, and 425 mμ. It is suggested that the luminescence produced during irradiation is predominantly from recombination. In stimulation the 425-mμ band characteristic of thallium grows and decays slower than the 302- and 370-mμ bands characteristic of the KI host. It is suggested that the phosphorescence is the result of the direct recombination of I2− and Tl°, and that the same process is occurring during stimulation and irradiation. In addition it is observed that 370-mμ emission produced during irradiation decreases in intensity with increasing temperature and that the 425-mμ emission intensity increases. It is suggested that 370-mμ emission decreases because of a radiationless transition and that 425-mμ emission increases because of the increase of recombinations at thallium sites.
Influence of Temperature on the F-Center Absorption in Sodium Fluoride
Authors: Amenu-Kpodo Kwasi , Neubert Theodore J. , Youngblade Walter
Published: January 2005

The F-center absorption in NaF, x irradiated at CO2 temperature, has been studied as a function of temperature after a preanneal at 100°C. Three absorptions occur in such crystals: (a) an unnamed band at 5.70 eV (218 mμ), (b) the K band at 4.35 eV (285 mμ) whose peak position and half-width (1.0 eV) are not temperature sensitive, and (c) the F band which has its peak at 2.71 eV (334 mμ) at 80°K after correction for K-band overlap. The data for half-width of the F band as a function of temperature when fitted to the well-known hyperbolic-cotangent relation, indicate a value of H0=0.358±0.002 eV for the half-width at 0°K and a value of νg=(7.7±0.2)×1012 sec−1 for the effective frequency of the phonons which interact with the F-center electron in its ground state. That frequency (νg) appears to be approximately one-half the frequency (ν0) of the longitudinal optical modes, for NaF and for the five other alkali halides for which data are published.
Center of Dispersion Force in HCl Interacting with Rare-Gas Atoms
Authors: Herman R. M.
Published: January 2005

Variational calculations of the center of long-range forces in HCl are described. The calculations are performed in two ways. In the first, the center of polarizability is calculated through a consideration of the polarization energy for the molecule placed in an inhomogeneous electric field, and the center is assumed identical with that effective in long-range interactions. In the second, a direct calculation of the dispersion forces between HCl and the rare-gases Ar and He is made, and from their angular dependence, the position of the effective center of attraction of HCl to the rare-gas atom is deduced. The calculations, which take account of the anisotropy of the HCl orbitals, yield a value for the separation between the HCl center of mass and center of long-range force equal to 0.11 Å, with a small variation from one rare gas to another. The long-range isotropic force constant and the HCl polarizability components are also calculated through the present approach. Comparison of the calculated parameters with experiment is made whenever this is possible.
Energy Transfer between p-Benzoylbenzoate and Europium Ethylenediaminetetraacetate in Water Solution
Authors: Charles R. G. , Riedel E. P. , Haverlack P. G.
Published: January 2005

Ultraviolet radiation absorbed by the p-benzoylbenzoate (p-BB−) ion in solution is transferred to an appreciable extent to the europium ethylenediaminetetraacetate (EuEDTA−) ion and is re-emitted as the visible red fluorescence characteristic of Eu3+. Fluorescence intensity is greater in D2O than in water. The fluorescence is quenched by dissolved O2. Although evidence for mixed ligand complexes involving p-BB− and EuEDTA− was obtained, fluorescence seems to result from ultraviolet absorption by free p-BB− ions followed by intermolecular energy transfer to free EuEDTA− ions. The analogous water systems containing o-BB− or m-BB− are nonfluorescent, although all three of the solid hydrated salts Eu(o-BB)3, Eu(m-BB)3, and Eu(p-BB)3 fluoresce brightly at room temperature.
Electric, Magnetic, and Magnetic Resonance Properties of the Nonstoichiometric Sodium—Vanadium Bronzes
Authors: Sienko M. J. , Sohn J. B.
Published: January 2005

Electric and magnetic studies have been carried out on the system NaxV2O5 (0.24<x<0.33). Single-crystal electrical-conductivity measurements on Na0.33V2O5 show semiconducting behavior from 77° to 500°K. A room-temperature conductivity of 230 Ω−1·cm−1 with an activation energy of about 0.02 eV is observed. Thermoelectric power amounts to −116 μV/K° and is constant from 273° to 500°K. The Hall voltage is too small to be observed, indicating >1019 carriers/cc. Gouy-susceptibility measurements have been carried out on a series of bronzes of variable Na/V ratio in the range 1.5° to 300°K. All specimens are highly paramagnetic and follow a Curie—Weiss law between 63° and 300°K. Weiss constants vary from −139° to −157°K; Curie constants from 0.119 to 0.159. The effective magnetic moments range from 1.94 to 2.01 Bohr magnetons. Below 63°K, the reciprocal susceptibility decreases more rapidly than linearly with temperature. No evidence of an antiferromagnetic transition is observed. The results, together with other electrical, ESR, and NMR data, cannot be explained by a hopping model but are consistent with a 3d t2g band model in which a majority of V4+ donor sites remain un-ionized over the temperature range investigated.
Shock-Tube Measurement of the Rate of Dissociation of Nitrogen
Authors: Byron Stanley
Published: January 2005

The rate of dissociation of nitrogen behind strong shock waves in nitrogen—argon mixtures was determined using time-resolved interferometric measurements of gas density. Dissociation rates for impact by N2, N, and Ar were found by varying the mixture composition from 5% N2 to 100% N2. Temperatures from 6000° to 9000°K were covered in the experiments. The effectiveness of the N atom in causing N2 dissociation was found to be more than that of the N2 molecule by a factor of 10 to 15, whereas that of the argon atom was found to be less than that of N2 by a factor of 2.5. A large discrepancy between these results and those reported recently by Cary is partially resolved by an alternative interpretation of his data. A difficulty in fitting all of the data by using a single set of rate constants is described and several possible explanations are suggested.
Vibration—Rotation Spectra of Monomeric HCl, DCl, HBr, DBr, and HI in the Rare-Gas Lattices and N2-Doping Experiments in the Rare-Gas Lattices
Authors: Bowers M. T. , Flygare W. H.
Published: January 2005

Extensive experiments are performed on trapping of the HCl, DCl, HBr, DBr, and HI molecules in rare-gas lattices. Concentration, deposition rate, and temperature-dependent studies yield the monomer spectra of the molecules. The HCl and DCl monomers in Ar, Kr, and Xe show hindered rotational spectra that is interpreted on the basis of 0h site symmetry. HCl in Ne also appears to rotate. HBr and DBr in Ar shows additional splitting which is attributed to either site splitting due to loss of one of the near-neighbor atoms or site distortion toward D3h symmetry. HBr and DBr in the larger Kr lattice give spectra similar to the HCl spectra. The spectra indicate the predominant local symmetry is 0h and the barriers to rotation in the lattices are given from an interpretation of the spectra. The barriers to rotation are interpreted by extension of an electrostatic model.

Calculations of rotational energy levels have been performed for the linear molecule in a lattice site of D3h symmetry. The perturbed rigid-rotor levels are given as a function of lattice—molecule coupling constants. No experimental evidence was found in these studies for D3h site symmetry.

N2-doping experiments are performed with HCl in the argon lattice. N2 doping (1%—4%) is found to give predominately two sites for the HCl molecule; one site similar to the pure HCl in Ar case and another site in which the rotation is frozen out giving a single transition for HCl. The frozen site is attributed to the nearest-neighbor presence of N2.

Detailed discussions are given in interpreting the spectra in terms of a hindered rotor or a librator. Most of the spectra is interpreted on the basis of a hindered rotor but some spectra such as the N2-doping experiments require the librator analogy similar to CO in Ar and CN− in KCl.

The vibrational shifts of the monomers in the rare-gas lattices are given for all cases studied where the predominant shift is to lower energy. These shifts are also qualitatively explained by localized nonbonded dispersion and overlap repulsion effects.
Infrared Spectra of VOF3 and POF3
Authors: Selig Henry , Claassen Howard H.
Published: January 2005

The infrared spectrum of VOF3 has been studied and interpreted in terms of a C3v molecular symmetry. All six fundamentals have been observed: the a1 frequencies are 1057.8, 721.5, and 257.8 cm−1 and the e frequencies are 806, 308, and 204.3 cm−1. The infrared spectrum of POF3 has also been studied and the lowest e fundamental, earlier observed in the Raman spectrum, has been confirmed.
Nuclear Magnetic Relaxation in Ionic Solution. I. Relaxation of 23Na in Aqueous Solutions of NaCl and NaClO4
Authors: Eisenstadt Maurice , Friedman Harold L.
Published: January 2005

The relaxation time of the nuclei of sodium ions has been measured for aqueous solutions of sodium chloride and sodium perchlorate at 25°. The longitudinal and transverse relaxation times are equal and depend on solution composition according to the rate law T1−1=17.55+0.55cNaCl+11.95cNaClO4±0.30,with T1 in seconds and cX in moles of X per liter, for single and mixed electrolyte solutions at concentrations less than 1M. Deviations from the equation are small up to 3M total concentration, and also in D2O if the coefficients are first multiplied by the ratio of solvent viscosities.

The limiting value of T1 at low concentration agrees roughly with the calculation of the effect of fluctuating electric-field gradients due to reorientational Brownian motion of water molecules coordinated to the sodium ion, but there are some very uncertain factors in the calculation. The coefficients of the rate law may be related to the distance of closest approach of the ions in various ways, with the result that this distance is much smaller for Na+ClO−4 than for Na+Cl−.
Method of ``Magnetophotoselection'' of the Lowest Excited Triplet State of Aromatic Molecules
Authors: El-Sayed M. A. , Siegel Seymour
Published: January 2005

The unique intensity distribution as a function of the angles between the principal magnetic axes and the applied magnetic field of the Δm=±1 ESR transitions of a collection of randomly oriented photoexcited triplet-state molecules has been used as a magnetoselection device, to observe only the molecules whose principal magnetic axes are parallel to the magnetic field. The latter is possible because the shape of the derivative of the Δm=±1 ESR absorption curve gives special prominence to those resonant fields corresponding to transitions of molecules possessing a canonical orientation. Changes in the relative intensities of the derivative ESR lines of the magnetophotoselected collection of molecules were observed as a function of the angle between the external field and the polarization direction of the exciting monochromatic light. The results obtained for glasses of naphthalene-d8 and quinoxaline were analyzed in terms of the known ESR spectra and polarization of the electronic absorption bands; the conclusions agree very well with theoretical predictions. The known directions of polarization of the electronic absorption bands of phenanthrene-d10 were then used to assign the Δm=±1 ESR spectrum of phenanthrene-d10 in EPA glass at 77°K. The assignment is found to agree with the first-order spectrum calculated using the published D and E values determined from single crystal studies. A simple procedure based on the magnetoselection method, and making use of the symmetry properties of π,π* and n,π* states, is then outlined by which assignments can be made for randomly oriented aromatic hydrocarbon or N-heterocyclic molecules, of the Δm=±1 ESR lines corresponding to those molecules which have their molecular plane either perpendicular or parallel to the magnetic field. The polarization of the electronic transitions used to excite these molecules to their triplet states need not be predetermined. A discussion is given of the advantages of using the method of magnetophotoselection instead of the normal photoselection method (where optical luminescence is used for analysis) to such problems as the assignment of optical electronic transitions and the mutual orientation of donor and acceptor in triplet—triplet transfer processes.
Radial Distribution Functions for Binary Fluid Mixtures of Lennard-Jones Molecules Calculated from the Percus—Yevick Equation
Authors: Throop Gerald J. , Bearman Richard J.
Published: January 2005

Using the Lennard-Jones 6–12 potential and the Percus—Yevick equations, the radial distribution functions for a number of binary mixtures have been calculated as a function of the Lennard-Jones parameters and the thermodynamic state. These are compared with one-component distribution functions and with those for binary hard-sphere fluids. The effect of a hard-sphere core, a softer attractive portion, and deviations from the combining rules ε12= (ε1ε2)½ and σ12= (σ1+σ2)/2 are also discussed. We find that the distances from the central molecules to the peaks of the distribution functions are entirely similar to those in the corresponding hard-sphere systems. The peak heights are considerably different, however. These are most sensitive to the nature of the repulsive potential and to the combining rule for σ12.
Dielectric Relaxation in the Electric Double Layer
Authors: Bockris J. O'M. , Gileadi E. , Müller K.
Published: January 2005

There are two groups of phenomena that can cause frequency dispersion of capacity and resistivity at a perfectly polarizable interface. The first comprises artifacts which lead to the observation of an apparent frequency dispersion: Of these, penetration of the electrolyte to shielded parts of the electrode and the resulting transmission line phenomena are discussed. The second group comprises processes which lead to an inherent frequency dispersion of the double-layer impedance: among these are, in particular, the relaxation phenomena of polar double-layer constituents.

Experimental results have been obtained for the interface: Hg (dropping) /6NHCl aq., in terms of parallel capacity, Cpd1, and resistivity, Rpd1, of the electric double layer as a function of frequency, v. These results are consistent with the occurrence of dielectric relaxation of the water dipoles adsorbed at the interface, and characterized by a certain distribution of relaxation times around τ0≃10−6 sec. The results are not consistent with the values ∂ lnRpd1/∂ lnv expected from the effect of a possible penetration of electrolyte into the capillary.

On the basis of a molecular model of the relaxation process, a rough estimate of the energy of activation for the process which results in a change of direction of the water dipole is made which is consistent with the mean relaxation time, τ0, estimated on the basis of the dielectric properties of double-layer water. It is shown that the frequency variation of the double-layer capacity is less than the detection limits of most ac bridges up to very high frequencies, as long as the high-atom polarization of water remains unchanged, and only dipole polarization is gradually reduced to zero with increase of frequency.
Significant-Structure Theory Applied to Water and Heavy Water
Authors: Jhon Mu Shik , Grosh Joe , Ree Taikyue , Eyring Henry
Published: January 2005

Significant-structure theory has been successfully applied to water and heavy water. The thermodynamic and transport properties have been calculated and the theory gives maximum density at near 4°C for H2O and at near 11.23°C for D2O. Further, the calculated results for entropy of vaporization, vapor pressure, molar volume, heat capacity, and the critical values are in good agreement with the observed values. The calculated curve for viscosity under pressure above 1 atm shows the observed minimum and is in satisfactory numerical agreement with the experimental values. According to our model, clusters of Ice-I-like molecules are in equilibrium with Ice-III-like molecules. The lifetime of the Ice-I-like cage structures is long compared to the relaxation time in viscous flow but fast compared to the relaxations observed in NMR.
Electron Paramagnetic Resonance of Oxygen on ZnO and Ultraviolet-Irradiated MgO
Authors: Lunsford Jack H. , Jayne John P.
Published: January 2005

A study has been made of the interaction of oxygen with samples of zinc oxide and ultraviolet-irradiated magnesium oxide using electron paramagnetic resonance techniques. Adsorption of oxygen at room temperature results in the rapid formation of a radical species, having gxx=2.077, gyy=2.0011, and gzz=2.0073 for oxygen on irradiated MgO and gxx=2.051, gyy=2.0020, and gzz=2.0082 for oxygen on ZnO. The radical is stable to temperatures of 200°C. The nature of this species is discussed and it is postulated that O2− is the entity adsorbed on the surface.
Study of CO Radicals on Magnesium Oxide with Electron Paramagnetic Resonance Techniques
Authors: Lunsford Jack H. , Jayne John P.
Published: January 2005

It has been determined that a fraction of the carbon monoxide which is adsorbed on magnesium oxide is in a paramagnetic state. Magnesium oxide was degassed at 850°C and 10−5 Torr for 16 h, cooled to room temperature, and then exposed to 150 Torr of high-purity carbon monoxide. The resulting paramagnetic spectrum grew slowly for several weeks.

This paper describes the spectrum of the adsorbed CO radical (g∥=2.0021, g∂=2.0055, ax=27 G, ay=11 G, az=0 G), the probable type of site on which the molecule is adsorbed, its bonding, and the effect of evacuating at elevated temperatures.
Resonance Transfer of Electronic Excitation Energy in Solution. I. Influence of Brownian Motion
Authors: Feitelson Jehuda
Published: January 2005

Förster's theory of electronic excitation transfer between molecules in solution treats a donor-acceptor system of constant intermolecular distances. However, in most solvents, at room temperatures, the relative diffusion path of donor and acceptor over the time of excitation is of the order of magnitude of their average separation. It is shown how the change in intermolecular distances can be incorporated into Förster's theory. An expression is derived for the fractional decrease of donor fluorescence due to resonance transfer in dilute solution where the diffusional displacement does not exceed the average distance between donor and acceptor molecules. It is shown that the effect of Brownian movement, though not great, should be detectable by experiment.
Resonance Transfer of Electronic Excitation Energy in Solution. II. The System p-Terphenyl−9-methylanthracene
Authors: Feitelson Jehuda
Published: January 2005

Excitation resonance transfer between p-terphenyl (donor) and 9-methylanthracene (acceptor) was measured using methanol, ethanol, iso-propanol, tert-butanol, cyclohexanol, and cyclohexane as solvents. Förster's theory and the influence of Brownian motion on the process, as outlined in Part I, were tested. It was found that energy transfer occurred somewhat more readily than predicted. The acceptor concentration at which the fluorescence yield decreased to half its original value was c0.5=6.0×10−3M instead of the calculated 8.3×10−3M. This corresponds to a critical distance R°=31 Å instead of 27.8 Å. The influence of the diffusional movement of donor relative to acceptor as reflected by solvent viscosity was found to agree with the calculated value within the experimental error limits. A method for the separation of radiative and nonradiative energy transfer is described.
Luminescence and Energy Transfer in Some Aliphatic α-Diketones
Authors: Richtol H. H. , Klappmeier F. H.
Published: January 2005

Strong phosphorescence is observed in all aliphatic α-diketones in rigid media at 77°K. In fluid solution at 25°C there is a decreasing phosphorescence intensity with the increasing length of one of the side chains. This effect is shown to be due to the increased probability of radiationless deactivation with increasing chain length. All the aliphatic α-diketones are good acceptors in triplet—triplet energy transfer and can be studied by diffusion-controlled sensitized phosphorescence techniques.
Mass-Spectrometric Determination of the Dissociation Energy of Beryllium Monofluoride
Authors: Hildenbrand Donald L. , Murad Edmond
Published: January 2005

A mass spectrometer was used to study high-temperature equilibria among vapor species produced by the fluorination of elemental beryllium with CaF2 and BF3 in a Knudsen effusion cell. The beryllium species Be, BeF, and BeF2 were identified in the effusing vapor from appearance potential measurements; Ca and CaF were also found in the Be–CaF2 system. Ion intensities were measured at a number of temperatures in the range 1320° to 1600°K with low ionizing voltages, and the intensities were used to calculate the equilibrium constants of several isomolecular reactions involving BeF. Derived thermodynamic data are for Be(g)+BeF2(g)=2 BeF(g), ΔH298=28.7±2 kcal, and for Be(g)+CaF(g)=BeF(g)+Ca(g), ΔH298=−8.0±2 kcal. These data yield a heat of formation at 298°K of −40.0±1.5 kcal/mole and a dissociation energy D0° of 5.85±0.10 eV for BeF(g). Several check measurements of equilibria in the Be–Al–F system confirmed these results. The derived dissociation energy is discussed in terms of corresponding values obtained from electronic spectra.
Kinetics of Unimolecular Breakdown. I. The Formal Solution
Authors: Hall G. G. , Levine R. D.
Published: January 2005

A quantum-mechanical discussion of the kinetics of unimolecular breakdown is presented using the Green's operator formalism. Experimentally, chemical reactions are characterized by their products and the theoretical discussion starts from this fact in an attempt to define the activated state. A scheme is indicated for the calculation of experimental results such as rate constants or yields of products. The concept of a natural line shape of a process is employed in discussing the separation of excitation and breakdown stages and the limitations on such a description are noted.

Applications are made to model theories of chemical reaction rates and to results of computer simulation studies.
Kinetics and Equilibria of the Difluorocarbene Radical Decomposition Behind Shock Waves
Authors: Modica A. P.
Published: January 2005

The thermal decomposition of the difluorocarbene radical diluted in argon has been studied behind incident shock waves over the temperature range from 2600° to 3700°K at a total pressure around 0.5 atm. The progress of the reaction has been followed by monitoring the time rate of change of CF2 molecules in absorption at 2536 Å. The observed rate data for the disappearance of CF2 are interpreted by the dissociation—recombination mechanism, −d[CF2]/dt=kf[Ar][CF2]−kr[CF][F][Ar],with kf=(4.20±0.67)1026 T−2.85±0.62exp (−106 000±5700/RT) cc/mole·sec,kr=(6.57±1.79)1026 T−2.85±0.62cc2/mole2·sec.Experimental equilibrium constants based on the reaction, CF2=CF+F, are calculated and fitted by the van't Hoff equation, yielding log Kc=−103 000±57002.303 RT−0.41±0.11 (Kc in mole/cc),for the temperature interval between 2600° and 3500°K. From the heat of reaction (107.3±5.7 kcal/mole) and the heat of formation of CF2 (−39.6±3 kcal/mole) at 298°K, the heat of formation of CF at 298°K is estimated to be 49.2±8.7 kcal/mole.
Solid Rotator Phase in Polar Liquids
Authors: Krishnaji  , Mansingh Abhai
Published: January 2005

Rotational behavior of five liquids having nearly spherical molecules has been studied by measuring their dielectric constant over a wide temperature range extending from liquid state to the solid state. Nitrobromoform and trimethylacetealdehyde show the existence of solid rotator phases. Different criteria of classifying polar liquids into two classes, Class I, not having a solid rotator phase and, Class II, having a solid rotator phase, have been discussed and 24 liquids have been examined in the light of these classifications. It has been shown that for Class II liquids x (the ratio of enthalpies from the dielectric relaxation and viscosity processes) is less than 0.45 and for Class I liquids x is greater than 0.55. The liquids which have x lying between 0.45 and 0.55 may show free rotation or may have a restricted rotation in the solid phase.
Computer Calculations of Ion—Molecule Reactions
Authors: Wolf Fred A.
Published: January 2005

A computer program has been developed which follows Light's phase-space theory of three-body ion—molecule reactions. The program predicts cross sections for 10 possible reaction branches as functions of the relative kinetic energy of the colliding particles in the range from thermal energies up to 20 eV. It also yields partial cross sections for the populations of the vibrational levels of the diatomic molecules in the product channel. Included in the results are reactions for the following ion—molecule pairs: [O++N2], [N++O2], [O+N2+], [He++N2], and [18O++O2]. The effects of varying the level of excitation, both vibrationally and electronically, of the reactants are presented. Increasing the excitation level always results in greater cross sections for reactions which are otherwise endothermic and slightly smaller cross sections for reactions which are otherwise exothermic.

All endothermic cross sections reach maximum values as functions of the barycentric kinetic energy of the reactants. All exothermic cross sections decrease with increasing barycentric kinetic energy at rates faster than predicted by the Gioumousis and Stevenson theory. This is due to the greater competition between the products for the available phase space which occurs at elevated energies. Good agreement is found between the theory and experiment in the high-energy region above 5 eV and in some cases throughout the whole energy range. Disagreement is most pronounced for low energies. It is felt that this indicates the presence of a small activation energy or, in the case where the products differ from the reactants by a charge transfer A++BC→A+BC+, the neglect of including resonance forces in the calculation.
Measurements of Collisional Energy Transfer between Rotational Energy Levels in CN
Authors: Evenson K. M. , Broida H. P.
Published: January 2005

A microwave-optical technique which selectively populates a single rotational level of CN and permits the observation of the redistribution of this population was utilized to measure the rates of collisional energy transfer between rotational energy levels of the B2Σ state of CN. CN was formed in the A 2Π state by the addition of CH2Cl2 to the afterglow of a nitrogen discharge. The near coincidence of the K=4, v=10 level of the A 2Π state with the K=4, v=0 level of the B 2Σ state permits microwave transitions near 10 GHz from the more populated Π level to the Σ level. The increased population in the rotational levels neighboring the K=4 level of the B 2Σ state was detected by measuring the increased optical emission due to the B 2Σ—A 2Σ transition near 3875 Å. Collisional energy transfer was measured over a pressure range from 0.1 to 5 Torr for changes in rotational quantum number ranging from one to ten. It is shown that rotational transitions having changes in rotational quantum number greater than unity take place with high probability, contrary to the optical selection rule ΔK=±1, and that approximately every gas kinetic collision produces a rotational transition. The relaxation time for the fourth rotational level was found to be 1.2×10−7 (±30%) sec at a pressure of 1 Torr.
Gas-Phase Radiolysis of Cyclobutane
Authors: Doepker R. D. , Ausloos P.
Published: January 2005

The gas-phase radiolysis of cyclo-C4H8 and cyclo-C4D8 has been investigated in the presence of O2, NO, H2S, NH3, and several organic compounds. From the products formed, it could be inferred that the following fragmentation processes occur: C4H8+→C3H5++CH3,C4H8+→C2H4++C2H4,C4H8+→C2H5++C2H3,C4H8+→C3H4++CH4.At 20 Torr, the ion-pair yields which can be ascribed to some of these processes are lower than the corresponding ion-pair yields observed in the mass spectrometer at a pressure of 10−5 Torr.

When compounds such as NO (I.P.=9.25 eV) or (CH3)3N(I.P.=7.8 eV) are added to cyclobutane, butene (I.P.=9.13–9.58 eV) is a major product. On the other hand, when organic or inorganic compounds whose ionization energy is higher than that of butene are added to cyclobutane, the yield of butene is, in most cases, negligibly small. The formation of butene can be tentatively accounted for by a ring opening of the parent ion followed by charge transfer. On the basis of this mechanism, a minimum value of 0.42±0.02 can be ascribed to M(C4H8+)/N.

When an electrical field is applied in the saturation current region, during radiolysis of cyclobutane—NO mixtures, the yields of methane, ethane, and butene which have the parent ion or fragments thereof as precursors, remain unchanged. On the other hand, the yields of products such as ethylene, allene, acetylene, and 1,3-butadiene whose formation is, in part, attributed to the decomposition of neutral excited molecules, are seen to increase due to increased excitation by electron impact. In the absence of an electrical field, the number of neutral excited molecule decompositions per ion pair is estimated to be ≤0.65±0.05.
Crystal Structure by Neutron Diffraction and the Antiferroelectric Phase Transition in Copper Formate Tetrahydrate
Authors: Okada K. , Kay M. I. , Cromer D. T. , Almodovar I.
Published: January 2005

The hydrogen positions in the crystal structure of copper formate tetrahydrate have been determined, and some new data on the antiferroelectric phase transition at −38.9°C are presented. It is shown that the orientation of the water molecules is disordered in such a way as to permit all possible short 0–0 contacts to be hydrogen bonded all of the time. The disorder is similar to that observed in ice. The phase transition probably occurs because of hydrogen motion.
Role of Interaction Constants in Force-Constant Calculations
Authors: Lehmann Walter J. , Beckmann Leo , Gutjahr Liselotte
Published: January 2005

The five in-plane vibrational frequencies of X2CO molecules are used to determine nine independent force constants of a general quadratic force field.

Instead of the usual arbitrary assumptions about the four supernumerary force constants (which four?), yielding simpler force fields, a minimum of very mild constraints was applied to the interaction constants (e.g., assumptions about some signs and the setting of reasonable limiting values). Some of these constraints in turn produced further constraints on the other force constants.

A specially designed analog computer allowed these calculations to be performed in a reasonable time. It was possible to vary continuously any of the force constants and to observe directly the effects on the frequencies and on the other force constants. Thus very quickly some ``feeling'' was developed for the molecule and the interrelation of the force constants.

The result then is not a unique set of force constants (which might be recorded in the literature with several decimals), but rather a nine-dimensional hypersurface of solutions, whereon each of the nine GFF constants occupies a range of values. For example, f(C=O) in Br2CO ranges from 12.9 to 14.2 mdyn/Å, and the C–Br stretch/opposite-angle interaction from −0.25 to −0.34 mdyn.
Reactive Scattering in Molecular Beams: Velocity Analysis of KBr Formed in the K+Br2 Reaction
Authors: Birely J. H. , Herschbach D. R.
Published: January 2005

The velocity distributions of scattered K and KBr from collisions of crossed thermal beams of K+Br2 have been measured over the range 200–850 m/sec at four laboratory angles Θ=10°, 15°, 20°, 30°. The results confirm that most of the energy released in the reaction (∼45 kcal/mole) appears in internal excitation rather than in translational motion of the products, as inferred previously from qualitative kinematic analysis of angular-distribution measurements. An approximate transformation to the center-of-mass coordinate system is carried out to evaluate for each Θ the distribution of the final relative translational kinetic energy E′ of the products. These distributions have a roughly Maxwellian shape (broader by ∼20%). The position of the peak varies from E′=1 to 4 kcal/mole for Θ=30°→10° (as compared with E=1.2 kcal/mole for the most probable initial relative kinetic energy of the reactants); the integrated intensity of cumulative yield with E′≳5 kcal/mole is ∼25% at 10° and ∼50% at 30° and with E′≲15 kcal/mole it is ∼75% at 10° and ∼90% at 30°. The distribution of the vibrational excitation Wv′ of the KBr for Θ=30° is also estimated by combining these results with data from electric-deflection experiments which provide an estimate of the rotational excitation. The vibrational excitation peaks near Wv′ ∼43 kcal/mole and the cumulative yield with Wv′≳30 kcal/mole is ∼90%. The ``electron-jump'' mechanism suggested by previous results, K+Br2→K++Br2−→K+Br− +Br, again offers plausible qualitative interpretations (perhaps not unique) for the main features of the observed energy distributions.