bluuebunny/crossref_metadata_2025 huggingface dataset:
Uniform Microcrystals of Platinum and Gold
Authors: Wilenzick R. M. , Russell D. C. , Morriss R. H. , Marshall S. W.
Published: January 2005

Theories describing bulk properties of solids are simplified by neglecting the presence of a boundary; i.e., one usually assumes a crystal of infinite size. There are situations, however, in which it is not permissible to neglect the effects that crystal boundaries have on electronic and vibrational properties. Order-of-magnitude calculations show that for most properties, particles must be less than 1000 Å before size effects become manifest. To study physical properties which are crystal-size dependent it is often desirable to have a sample containing many distinct particles of a well-defined size distribution confined to a small volume. Hydrosols of platinum and gold have been prepared using various procedures in order to determine the optimum conditions required to produce a given crystal size with a uniform size distribution. Crystal size and morphology were analyzed by electron microscopy and electron diffraction. Uniform microcrystals were obtained with sizes ranging from 40 to 500 Å. Methods for dialyzing and dehydrating the hydrosols are also discussed.
Expansion about an Arbitrary Point of Three-Dimensional Functions Involving Spherical Harmonics by the Fourier-Transform Convolution Theorem
Authors: Silverstone Harris J.
Published: January 2005

Expansion of ψ(r)=ψ(r)YLM(θ,φ) in terms of spherical harmonics and radial functions, whose coordinates are measured from an arbitrary point in space, is obtained by use of the Fourier-transform convolution theorem. For a specific ψ(r), two integrals most be evaluated to determine the expansion explicitly: (1) the radial part ψ̄(k) of the Fourier transform of ψ(r); and (2) an integral of ψ̄(k) with spherical Bessel functions. The examples of noninteger-n and integer-n Slater-type orbitals are worked out by contour integration.
Tracer Study of the Reactivity of O(1D)
Authors: Katakis D.
Published: January 2005

The transfer of oxygen from water to oxygen in the uv photolysis of O3–H2O mixtures is studied as a function of the ozone and water vapor pressures using 18O-labeled H2O. It is shown that deactivation of the active species is generally competitive with the ordinary chemical reactions these species undergo. It is also shown that the reaction of O1D with H2O is about four times slower than its reaction with O3. The quantum yields at different O3 and H2O pressures are calculated from the exchange data. Some preliminary experiments on the exchange of O1D with N2O and in somewhat more detail on the CO2–O2 exchange during the uv decomposition of O3 are also reported.
Oxygen-17 NMR Linewidths as Influenced by Proton Exchange in Water
Authors: Rabideau Sherman W. , Hecht Harry G.
Published: January 2005

Linewidths for the 17O nuclear magnetic resonance have been obtained at 29.0°±0.2°C in 10% H217O as a function of acidity with the sideband technique at 8 MHz. Computer methods have been used to solve the set of coupled linear equations from which line shapes as functions of the residence time and 2δ, the proton—17O spin—spin coupling constant, have been calculated. It has been possible to obtain a linear relationship between k1, the specific rate constant for the proton catalyzed exchange process, and 2δ. The spin—spin coupling constant has been redetermined by the acetone-dilution procedure, and a value of 82±1 Hz has been obtained. Because of quadrupole relaxation of the 17O, the true coupling constant will be somewhat larger than the value obtained under these conditions of slow exchange. With the assumption of a value of 2δ of 580 rad sec−1, the acid and base catalyzed specific rate constants at 29.0°C are k1=8.2×109 mole−1 liter sec−1 and k2=4.6×109 mole−1 liter sec−1, respectively. However, it appears that the spin—spin coupling constant cannot be obtained in an unambiguous manner and accordingly, the values of the specific rate constants for the exchange processes are uncertain.
Electron Spin Resonance of γ-Irradiated Tetrafluoroethylene—Hexafluoropropylene Copolymers
Authors: Iwasaki M. , Toriyama K. , Sawaki T. , Inoue M.
Published: January 2005

Radicals produced in tetrafluoroethylene—hexafluoropropylene copolymers γ-irradiated at room temperature in vacuo have been studied by electron spin resonance. Besides the well-known spectra assigned to the radicals ···CF2–ĊF–CF2··· and ···CF2–CF2–O·, a poorly resolved eight-line spectrum was found and tentatively assigned to the tertiary carbon radical ···CF2–Ċ(CF3)–CF2···. Upon heating, this radical disappeared much faster than the others. This is probably because it is trapped in a region where the regular crystallization of the copolymer chains was perturbed by trifluoromethyl groups. The temperature and orientation dependence of the spectra were also examined and interpreted in terms of the proposed radical.
Photoinduced and Thermal Radical Conversions in γ-Irradiated Copolymers of Tetrafluoroethylene and Hexafluoropropylene as Studied by Electron Spin Resonance
Authors: Iwasaki Machio , Toriyama Kazumi
Published: January 2005

It was found that a perfluorinated tertiary-carbon radical ···CF2–Ċ(CF3)–CF2··· formed in γ-irradiated copolymers of tetrafluoroethylene and hexafluoropropylene is converted into the radical ···CF2–CF(ĊF)2–CF2··· by illumination of uv light at 77°K and the process is reversed by thermal annealing. This may be the first example of the photoinduced conversion of fluorocarbon radicals. The uv absorption spectra of perfluorinated tertiary-carbon radicals were also measured and a strong absorption was found at 2650 Å. The wavelength dependence of the radical conversion indicates that the photoisomerization of the tertiary-carbon radical is induced by the absorption of this light. The tentative assignment of the ESR spectra to the radical ···CF2–Ċ(CF3)–CF2··· in a previous paper was further confirmed by this experiment. In addition, it was found that γ irradiation at 77°K gives the radical ···CF2–CF(ĊF2)–CF2··· as a forerunner radical of the tertiary-carbon radical found in room-temperature irradiation.
Theory of Isotropic Nuclear Resonance Shifts in Octahedral Co2+ Systems
Authors: Jesson J. P.
Published: January 2005

Expressions are derived for the dipolar and Fermi-contact contributions to isotropic nuclear resonance shifts for ligand nuclei in axially distorted octahedral Co2+ systems.
Electronic Structure of Diatomic Molecules. VI.A. Hartree—Fock Wavefunctions and Energy Quantities for the Ground States of the First-Row Hydrides, AH
Authors: Cade Paul E. , Huo Winifred M.
Published: January 2005

Hartree—Fock wavefunctions are presented for the LiH(X1Σ+), BeH(X2Σ+), BH(X1Σ+), CH(X2Πr), NH(X3Σ−), OH(X2Πi), and HF(X1Σ+) molecules. These are the analytic self-consistent-field wavefunctions obtained from the solutions of the Hartree—Fock—Roothaan equations. Large sets of Slater-type functions centered on both nuclei were used as the expansion basis, and extensive optimization of the orbital exponents has been carried out. The total energies obtained for Re(exptl) are −7.98731, −15.15312, −25.13137, −38.27935, −54.97806, −75.42083, and −100.07030 hartrees, respectively, for the AH hydrides listed above. The first ionization potentials, which are obtained from the Hartree—Fock energy differences between AH and AH+ systems, are 7.02, 8.14, 8.45, 10.08, 12.82, 11.44, and 14.54 eV, respectively. In addition, potential curves, spectroscopic constants, and certain other energetic quantities are presented. Crude estimates of the correlation energy of the first-row hydrides are made and such quantities are compared within the series and with their respective united and separated atoms. These results suggest that the changes in correlation energy of AH relative to the correct united atom is independent of which hydride is involved and the change is small.
Electronic Structure of Diatomic Molecules. VII.A. Hartree—Fock Wavefunctions and Energy Quantities for the Ground States of the Second-Row Hydrides, AH
Authors: Cade Paul E. , Huo Winifred M.
Published: January 2005

Hartree—Fock wavefunctions are presented for the NaH(X1Σ+), MgH(X2Σ+), AlH(X1Σ+), SiH(X2Πr), PH(X3Σ−), SH(X2Πi), and HCl(X1Σ+) molecules. These are the analytic self-consistent-field wavefunctions obtained from the solutions of the Hartree—Fock—Roothaan equations. Large basis sets of Slater-type functions centered on both nuclei were used and extensive optimization of the orbital exponents has been carried out. The total energies obtained for Re(exptl) are −162.3928, −200.1566, −242.4634, −289.4361, −341.2932, −398.1015, and −460.1103 hartrees, respectively, for the hydrides listed. The first ionization potentials, which are obtained from the Hartree—Fock energy differences between the AH and AH+ systems, are 6.14, 6.76, 7.36, 7.36, 9.65, 9.31, and 11.84 eV, respectively. In addition, potential curves, spectroscopic constants, and certain other energetic quantities are presented. Crude estimates of the correlation energy of the second-row hydrides are made and such quantities are compared within the series and to their respective united and separated atoms. These results suggest that the change in the correlation energy of AH relative to the correct united atom is independent of which hydride is involved. Among the different experimental data for the dissociation energies (De) of MgH and PH, a value of 2.3 for MgH and 3.34 eV for PH are supported by this calculation.
Collision Broadening of Rotational Absorption Lines. I. Theoretical Formulation
Authors: Murphy Joseph S. , Boggs James E.
Published: January 2005

An impact theory approach to the pressure broadening of microwave absorption lines is presented. A time-development matrix is evaluated to yield expressions which are averaged over all internal quantum states of the colliding molecule and the velocity distribution function to give half-width and frequency-shift parameters. The half-width parameter is then evaluated for dipole—dipole, dipole—quadrupole, quadrupole—quadrupole, and dispersion interactions. The dependence of the linewidths on the multipole moments, temperature, and the rotational state of the colliding molecule is discussed. The results are compared with previous theoretical treatments.
Matrix-Isolation Study of the Reaction of Carbon Atoms with Chlorine. The Electronic and Vibrational Spectra of the Free Radical CCl2
Authors: Milligan Dolphus E. , Jacox Marilyn E.
Published: January 2005

Studies of the photolysis of N3CN in the presence of Cl2 in Ar and N2 matrices at 14°K provide evidence for the formation of the free radical CCl2 by the reaction of photolytically produced C atoms with Cl2. The two stretching fundamentals of CCl2 appear at 721 and 748 cm−1. The corresponding fundamentals of 13CCl2 have also been observed. When the sample is warmed above about 30°K, these features disappear, and CCl4 features grow in intensity, indicating that CCl2 can react with Cl2 with little or no activation energy. The valence angle of CCl2 probably lies between 90° and 110°. A weak band system appearing between 4400 and 5600 Å, with an average band separation of 305 cm−1, may also be attributed to CCl2. Analogy with the electronic absorption spectrum of CF2 suggests that CCl2 possesses a ground singlet state and that this band system arises from a transition between the ground-state electronic configuration and the first excited electronic configuration of CCl2, involving an extensive progression in the upper-state bending vibration.
Self-Avoiding Walks on the Tetrahedral Lattice
Authors: Mark Philip , Windwer Stanley
Published: January 2005

Self-avoiding walks on the tetrahedral lattice were studied. By extending the excluded-volume condition to incorporate first nonbonded nearest neighbors one obtains a value of the polymer index γ to be 1.255. This is in agreement with the direct enumeration studies of Mazur and Joseph and is interpreted in terms of the intrinsic excluded volume and excess excluded volume. It is suggested that all real systems may have to be studied in their own right to obtain their molecular-weight configurational dependence.
Infrared Spectra of Cesium Bihalide Salts
Authors: Nibler Joseph W. , Pimentel George C.
Published: January 2005

Cesium bihalide salts, probably ClHCl−, ClDCl−, ClHBr−, ClHl−, and ClDl−, have been prepared and sharp infrared spectra obtained at 20°K. In addition, complex spectra which must be attributed to higher polymers such as H2Cl3− have been obtained. The 20°K infrared spectra of the cesium bihalide salts reveal an absorption at roughly half the frequency earlier assigned to ν2 for NR4+XHY− salts at room temperature. This requires a reinterpretation of the earlier bihalide spectra; the bands previously assigned to ν2 must be assigned instead to 2ν2. This reassignment obviates difficulties with previous assignments but requires an explanation for the high 2ν2 intensities. These can be explained in terms of the abnormally large dipole second derivative which occurs in hydrogen bonds because of the large charge mobility along the bond. In ClHCl− the occurrence of this enhancement shows that ClHCl− does not involve a centrally located proton in the cesium salt.
Deactivation of Vibrations by Collision in the Presence of Fermi Resonance
Authors: Herzfeld Karl F.
Published: January 2005

The rate of vibrational deactivation by collision of polyatomic molecules is discussed. Previous calculations for CO2 by the author are corrected. A systematic method to find the steric factor in complex collisions is proposed, and the best procedure for evaluation of such collisions is discussed. Mixture of vibrational wavefunctions may increase the rate appreciably, particularly in the presence of Fermi resonance. The agreement with experiment is good for the deactivation of the transversal vibration and for the effect of CO2 admixture on O2 deactivation, but the experimental rate of deactivation of the asymmetric longitudinal CO2 vibration is much greater (60 to 90 times) then the calculated one.
Free Volume and Shear Compliance of Hydrogen-Bonded Liquids
Authors: Madigosky W. M. , McDuffie G. E. , Litovitz T. A.
Published: January 2005

A phenomenological formulation for the shear compliance of hydrogen-bonded liquids is presented. It is based on the assumption that the compliance of these liquids is a linear function of the reciprocal density of hydrogen bonds. The bond density is expressed in terms of the free volume of the liquid and the equilibrium number of broken or bent bonds. This latter number is expressed in terms of a two-state model. Ultrasonic shear data in glycerol, 1, 3 butanediol, and 1-propanol are considered and good fits to the data are obtained when ΔH = 3.0 kcal/mole and ΔS = 5.0, 5.9, and 16 e.u., respectively. It is argued that these are quite reasonable values for hydrogen bonding. The above theory predicts that the difference in magnitude and temperature dependence of the shear rigidity found for different hydrogen-bonded liquids is determined to a large extent by differences in ΔS which in turn determines the relative importance of free energy and free volume effects. In general a large value of ΔS would lead to a low and highly temperature-dependent shear rigidity.
Photoselection Study of Charge-Transfer Complexes
Authors: Prochorow J. , Tramer A.
Published: January 2005

The polarization of the charge-transfer (CT) fluorescence excited in the charge-transfer and donor absorption band was measured for the complexes of tetracyanoethylene with benzene, toluene, ortho- and para-xylene, and those of s-trinitrobenzene and tetrachlorophthalic anhydride with anthracene in organic glass at 77°K. It was shown that (1) the fluorescence excited in the CT band is positively polarized, the degree of polarization (P) depending on the complex stability; (2) in the case of a single CT absorption band, P is independent of the wavelength of the exciting light and the case in that of a double absorption band, P is different for any subband; (3) polarization of the fluorescence excited in the donor intramolecular absorption band is negative or zero. These results are discussed on the basis of a model of a partially disoriented complex.
Ultrasonic Attenuation and Volume Viscosity in Liquid Nitrogen
Authors: Singer J. R. , Lunsford J. H.
Published: January 2005

The volume viscosity in liquid nitrogen has been calculated from ultrasonic attenuation measurements at temperatures between 73.6° and 113.8°K with pressures up to 141.5 kg/cm2. Measurements of attenuation as a function of pressure were made using single transducer, pulsed systems. The low-pressure apparatus employed a variable-path-length sample chamber while the high-pressure study was made with a fixed double-path-length cell. The measured attenuation depends linearly on the square of the frequency over the range 30–70 Mc/sec. The volume viscosity of liquid nitrogen increases with increasing density and shows the same density dependence as has been reported for liquid argon. The volume viscosity of liquid nitrogen ranges from 1.3 g/cm·sec at a density of 0.650 g/cm3 to 2.4 g/cm·sec at a density of 0.850 g/cm3 and has the same order of magnitude as the shear viscosity. The ratio of volume viscosity to shear viscosity at a temperature of 77.6°K and pressure of 1.67 kg/cm2 is 1.2. The results indicate that no internal molecular relaxation processes are involved in liquid nitrogen so that the bulk viscosity is the same as the volume viscosity.
Electron Spin Resonance of Oriented RĊHSR′ Sulfide Radicals
Authors: Griffith O. Hayes , Mallon Michael H.
Published: January 2005

Single crystals of the di-n-hexyl sulfide—urea and diethyl sulfide—urea inclusion compounds were x irradiated at 77°K and the long-lived free radicals produced were investigated by electron spin resonance. The free radicals observed in both crystals were of the type RĊHSR′. The value for the spin density on the carbon atom is 0.74±0.07. The unpaired spin distribution is discussed in terms of simple molecular-orbital models.
Energy of Interaction between Two Hydrogen Atoms by the Gaussian-Type Functions
Authors: Kim Hojing , Hirschfelder J. O.
Published: January 2005

The interaction of two hydrogen atoms in their ground states is investigated with a Hirschfelder—Linnett type of wavefunction in which the exponentials are replaced by Gaussian-type functions. It is found that these functions do not properly describe the long-range interaction, although the same functions reasonably approximate the molecular energy near the equilibrium separation. The explicit formulas for the atomic integrals are tabulated.
Raman Effect of Corundum
Authors: Porto S. P. S. , Krishnan R. S.
Published: January 2005

The Raman effect of corundum (sapphire) was measured with an Ar+ laser source. The seven expected Raman active phonons were found and their symmetry characters determined. Assignment of the internal and external vibrations of the crystals was made and the effect of birefringence in the Raman selection rules is discussed.
Polarization of Triplet Factor Group States
Authors: Hochstrasser Robin M.
Published: January 2005

An account of the polarization of triplet factor group, or dimeric, states is given. It is shown that in the presence of a twofold axis the resulting plus (symmetric) and minus (antisymmetric) states are not generally uniquely polarized along the C2 and perpendicular to the C2, respectively. This arises because of the spin correlation induced by the exciton exchange interactions. The intensities can be reduced to geometric parameters and predictions and comparisons with experiment are made for naphthalene, anthracene, and phenazine crystals.
Exciplex Studies. II. Indole and Indole Derivatives
Authors: Walker Michael S. , Bednar Thomas W. , Lumry Rufus
Published: January 2005

An excited-state solute—solvent complex (exciplex) has been shown to be responsible for a large red shift and loss of vibrational structure in the fluorescence spectra of indole and indole derivatives in polar solvents. Solute—solvent stoichiometry of 1:2 and 1:1 is observed with associating and nonassociating solvents, respectively. Hydrogen bonding between the indole >N–H group and solvent is shown not to be responsible for the interaction. It is suggested that the exciplex state is a charge-transfer state and is an intermediate in the process of electron transfer from the solute to the solvent.
Asymptotic Relations between the Thomas—Fermi—Dirac and Thomas—Fermi Atom Models. I. Case of Low Atomic Number
Authors: Gilvarry J. J. , Hartle R. E. , March N. H.
Published: January 2005

An asymptotic relation between the pressure with exchange on the Thomas—Fermi—Dirac atom model and the corresponding pressure without exchange on the Thomas—Fermi model, obtained by Gilvarry for the limit of vanishing atomic number Z, is derived by a direct physical argument. As compared to the original derivation, this procedure obviates the need for solutions of the differential equations of the models and for discussion of termination of the series so obtained. The virial theorem is used to delimit the domain of validity of the result, and thus to indicate the circumstances under which correction terms are necessary from the solution of March and the general asymptotic solution of Rijnierse for the Thomas—Fermi—Dirac equation at small atom radius. The limiting form for the radius of an isolated Thomas—Fermi—Dirac atom as a function of the atomic number in the case where Z approaches zero is determined on the basis of the Jensen boundary condition. This expression yields an immediate interpretation of the parameter entering the connection between the pressures with and without exchange. The results are discussed in terms of homology transformations of the Thomas—Fermi—Dirac and Thomas—Fermi equations. Corresponding asymptotic forms for other thermodynamic functions (parameters associated with the energy and the equation of state, as well as the compressibility) are considered also for the case of vanishing atomic number.
Determination of Partial Photoionization Cross Sections by Photoelectron Spectroscopy
Authors: Blake A. J. , Carver J. H.
Published: January 2005

A photoelectron energy sepectrometer has been used to determine partial photoionization cross sections of molecular oxygen, nitrogen, and water vapor for monochromatic incident radiation in the wavelength range 584–900 Å. For each gas, cross sections have been determined for transitions to particular ionic states which have been identified by measuring the corresponding photoelectron energy. For molecular oxygen, cross sections have been determined for transitions to the X 2Πg, (a 4Πu+A 2Πu), b 4Σg−, and 2Σg− states of O2+; and at incident wavelengths longer than 680 Å a process of fluorescent autoionization involving quasi-stable states of the neutral oxygen molecule has also been observed. Molecular nitrogen cross sections corresponding to transitions to the X 2Σg+, A 2Πu, and B 2Σu+ states of N2+ have been determined. For water vapor, cross sections corresponding to transitions to the 2B1 and 2A1 states of H2O+ have been observed in addition to processes of dissociative ionization. In all cases the measurements illustrate the competition between various modes of decay which are energetically possible for incident radiation of a given wavelength.
On the Occurrence of Oscillations around the Steady State in Systems of Chemical Reactions far from Equilibrium
Authors: Lefever R. , Nicolis G. , Prigogine I.
Published: January 2005

The onset of oscillations around the steady state in systems of chemical reactions far from equilibrium is studied in certain specific cases. It is demonstrated that the appearance of oscillations is not followed by any kind of instability but comes progressively, and on modifying the thermodynamic constraints, continuously.
Analysis of ``Lock-In'' Detection of Modulated Molecular Beams Scattered from Solid Surfaces
Authors: Yamamoto S. , Stickney R. E.
Published: January 2005

The ``lock-in'' technique (i.e., narrow-band amplification and phase-sensitive detection) for detecting modulated molecular beams is analyzed for the case of scattering from solid surfaces. A general method is described for computing An and Φn, the amplitude and phase of the output signal. Since this computation requires the assumption of a gas—solid collision model, we have selected three different models for a comparative study. Special consideration is given to the ``hard-cube'' model [Logan and Stickney, J. Chem. Phys. 44, 195 (1966)]. Numerical results are presented (a) to illustrate the dependence of An and Φn on the nature of the collision model and the experimental conditions, and (b) to indicate the limitations of present interpretations of experimental data.
Scattering of Low-Energy Electrons from Polar Molecules
Authors: Crawford Oakley H.
Published: January 2005

Differential and total cross sections are predicted for low-energy collisions of electrons with polar molecules. The potential is due to a point dipole fixed to the molecule at its center of mass, the molecule is treated as a rigid rotator, and the first Born approximation is used. Each type of polar rigid rotator is treated: linear, symmetric top, and asymmetric top; and free radicals are discussed briefly. Reference is made to swarm experiments to indicate the validity of the theory.
Semiempirical Molecular-Orbital Calculations. IV. Some Metallocenes
Authors: Armstrong A. T. , Carroll D. G. , McGlynn S. P.
Published: January 2005

Charge self-consistent semiempirical calculations including all valence sigma orbitals of the ligands are reported for ferrocene, aminoferrocene, chloroferrocene, and nickelocene. The computations follow the Wolfsberg—Helmholz scheme, and use Slater atomic orbitals which mimic the overlaps, including distance dependence, of the SCF atomic orbitals. An attempt is made to assign electronic excitation energies in a manner consistent with computation and experiment. The only assignment which may be considered reasonably secure is that of the very intense absorption at 51 200 cm−1 which is taken to be the allowed component of the e1g←e1u orbital excitation (fcalc/fobs=0.549/0.691). The ionizing orbital in ferrocene was found to be a1g (−9.78 eV) and in nickelocene was e1g (−6.874 eV). The formal charge on the metal was found to be positive in all cases. A discussion of metal—ligand bonding is included.
Nuclear Spin Relaxation in Methanol. The Effect of Proton Exchange
Authors: Cocivera Michael
Published: January 2005

For liquid methanol, the longitudinal relaxation of the OH and CH3 proton magnetic moments was found to depend on the rate of OH proton exchange between methanol molecules. This exchange dependence is explained quantiatively in terms of cross relaxation between the OH and CH3 protons resulting from the scalar interaction J(t)I·S. The good agreement obtained between experiment and theory indicates that measurement of the longitudinal relaxation rate can be used to obtain accurate values for the rate of proton exchange in methanol. In addition, for the range of rates where the longitudinal relaxation is affected, the spin—echo determination of T2, the transverse relaxation time, was found to be reliable for the CH3 proton but not for the OH proton.
Surface Tension and Energy of Liquid Xenon
Authors: Smith B. L. , Gardner P. R. , Parker E. H. C.
Published: January 2005

The surface tension of liquid xenon was measured in the temperature range 189°—286°K by a capillary-rise method. The results may be represented by γ=γ0[1 − (T/289.74) ]p, with γ0=54.6±0.1 dyn cm−1 and p=1.287±0.017.

The experimental method is discussed and the results compared with existing theory and experimental data.
Nuclear Quadrupole Resonance of (NH4)2[InCl5H2O]
Authors: Carr S. L. , Garrett B. B. , Moulton W. G.
Published: January 2005

The nuclear quadrupole resonance frequencies of 35Cl and 115In have been measured in (NH4)2[InCl5H2O] as a function of temperature. The lattice contribution to the field gradients was calculated using a point-charge model, and a bonding analysis was made in the temperature region where the rigid lattice approximation appears to apply. The individual chlorine resonances were assigned to specific chlorine sites in the lattice. The results of the calculation show that the complex is predominantly ionic with greater covalency for the indium—water bond than for the indium—chlorine bond. It is also shown that the antishielding factor for chlorine must be greater than, or equal to, −13 for this complex.
Influence of Charge Compensation on uv Excitation of Rare-Earth Fluorescence
Authors: Viehmann Walter
Published: January 2005

Excitation spectra for the fluorescence transitions of Tb3+, Eu3+, and DY3+, were obtained at room temperature on single crystals of the tungstates and molybdates of Ca, Sr, Pb, and Cd, having the Scheelite structure, and on terbium-doped crystals of CaF2 and SrF2. Rare-earth concentrations were nominally 1 at.% and charge compensation was provided by vacancy formation or interstitials, by substitution in cation sites or by anionic substitutions. Strong uv-excitation bands were found for Tb- and Eu-doped crystals and weaker bands for Dy-doped matrices. The bands generally occur in the vicinity of the host-lattice absorption edge but their intensities and energy positions are strongly influenced by the charge-compensating defects in the vicinity of the active ion. The long-wavelength peaks of the bands occur at energies coinciding with 4f-level positions of the rare-earth ions, thus suggesting a strong perturbation of 4f levels by charge transfer states. The short-wavelength regions of the excitation bands are ascribed to exchange transfer from uv-absorbing groups.
Molecular Schrödinger Equation. V. A Correlated Polyelectronic Wavefunction
Authors: Conroy Harold
Published: January 2005

Our earlier method for obtaining accurate solutions to the molecular Schrödinger equation for one and two electrons has been improved and extended, at least in principle, to the general polyelectronic case. The discussion includes development of the theory and examples of specific numerical results obtained with systems containing up to four electrons.
Molecular Schrödinger Equation. VI. Results for H3 and Other Simple Systems
Authors: Conroy Harold , Bruner Buddy L.
Published: January 2005

The results of calculations on the ground state of the H3 system are presented, and potential-energy surfaces are constructed for the linear and isosceles triangular configurations. The path of minimum energy along these surfaces for the H+H2→H2+H reaction passes through a maximum 7.74 kcal above the reactants at a linear symmetric configuration with an H–H separation of 1.76 bohrs. Calculations on the ground states of He2+, He2++, the lowest 1Π state of equilateral triangular H3+, and a number of one-electron states of H3++ and He2+++ are also summarized.
Molecular Schrödinger Equation. VII. Properties of the Energy Variance Function: The Estimation of Energy Eigenvalues
Authors: Conroy Harold
Published: January 2005

The energy variance function U2 is defined in terms of the eigenfunction expansion for a trial wavefunction ψ. The relationship of U2 to certain upper- and lower-bound formulas for the energy and purity functions associated with ψ is discussed. The concurrently allowed values of U2 and the energy function ε fall within a bounded region, the shape of which depends partly upon the Schrödinger equation and partly upon those restrictions imposed by the incompleteness of the basis set used for the representation ψ. A number of exact relationships governing the behavior of ε, U2, and their derivatives along the boundary curve are worked out. The concept of the derivative wavefunction along the boundary is introduced, and an explicit prescription for its computation is given. Ways and means for the estimation of the true energy eigenvalue from the properties of an imperfect wavefunction are presented and discussed.
Vibrational Spectrum of Cyclopropene
Authors: Eggers D. F. , Schultz J. W. , Wiberg K. B. , Wagner E. L. , Jackman L. M. , Erskine R. L.
Published: January 2005

The infrared spectra of gaseous cyclopropene and a partially deuterated cyclopropene, and the Raman spectrum of liquid cyclopropene have been determined. The majority of the fundamentals and several overtones and combinations have been assigned. Some force constants based on a simple valence-force potential function have been calculated.
Raman and Infrared Spectra of the 10BF3 and 11BF3 Complexes with Dimethyl Sulfide and the Isotopic Exchange of This Complex with BF3
Authors: Begun G. M. , Palko A. A.
Published: January 2005

The Raman and infrared spectra of liquid BF3·dimethyl sulfide have been recorded for both the 10B and 11B compounds. Assignments of the observed bands have been made using analogies with those of BF3·dimethyl ether. The isotopic data have been used to calculate theoretical equilibrium constants for isotopic exchange between the complex and BF3. The calculated values are compared with published experimental values.
Uniform Localization of Atomic and Molecular Orbitals. I
Authors: Magnasco V. , Perico A.
Published: January 2005

A general procedure for a nonarbitrary external localization of atomic and molecular orbitals given in the form of a general LCAO expansion is introduced by imposing an extremum principle on the sum of certain local orbital populations which are required to be localized in given regions of space, in particular around atoms or between pairs of atoms in the molecule. The localization, which is uniform insofaras these local electron populations are simultaneously maximized in all the available orbitals, yields well-defined inner-shell, lone-pair and bond orbitals. The orthogonal transformation which maximizes the localization function is obtained through an iterative sequence of 2 × 2 rotations between all N (N − 1)/2 possible pairs of molecular orbitals. Convergence was found to be excellent. The method turns out to be exceedingly simple, the coefficients in the LCAO expansion and the overlap integrals between the basic atomic orbitals only being required, and general enough to be valid for the localization of atomic orbitals as well of molecular orbitals, either for exact LCAO—SCF—MO's or for approximate LCAO—MO's constructed from nonorthogonal as well from orthogonal basic sets. The localized orbitals obtained in this paper starting from some unsymmetrically orthogonalized atomic orbitals and from the minimal-basis-set LCAO—SCF—MO wavefunctions given by Ransil for LiH, BH, NH, FH, LiF, BF, CO, Li2, Be2, N2, F2 prove to be very close to the energy localized orbitals recently obtained by Edminston and Ruedenberg by maximizing the sum of the orbital self-repulsion energies.
Electronic States of the Amide Group
Authors: Basch Harold , Robin M. B. , Kuebler N. A.
Published: January 2005

The presence of a moderately strong band falling between the n→π* and π→π* (N→V1) transitions of the amide group has been observed for the first time. All-electron SCF calculations in Gaussian bases aimed at assigning the bands of formamide suggest that the new band is an n→σ* excitation in which the σ* orbital is Rydberg-like. A second π→σ* big-orbit transition follows the π→π* (N→V1) excitation. In a basis containing expanded orbitals, the usual virtual orbital—configuration interaction calculations predict that every upper state will be of Rydberg-orbital dimensions. However, this obvious error can be avoided by indirect SCF calculations on the upper states, which show that in formamide, all states below 13 eV terminating at π* are valence-shell transitions, whereas all states terminating at σ* are big-orbit Rydberg states.
Polyhedral Clathrate Hydrates. XII. The Crystallographic Data on Hydrates of Ethylamine, Dimethylamine, Trimethylamine, n-Propylamine (Two Forms), iso-Propylamine, Diethylamine (Two Forms), and tert-Butylamine
Authors: McMullan R. K. , Jordan Truman H. , Jeffrey G. A.
Published: January 2005

The crystallographic data for nine alkylamine hydrates are reported. The hydrates of C2H5NH2 and (CH3)2NH are isostructural with the 12 Å cubic gas hydrates and have unit cells with symmetries Pm3n and Pm3, and dimensions a=12.17 and 12.55 Å, respectively. Those of (CH3)3N and n-C3H7NH2 have symmetry P6/mmm and unit cell dimensions a=12.41 Å, c=12.50 Å and a=12.20 Å, c=12.38 Å, respectively, while that of iso-C3H7NH2 has symmetry P63/mmc and cell dimensions a=12.42 Å, c=25.22 Å. These hexagonal hydrates are related in their water structure to (iso-C5H11)4N+F−·38H2O. n-C3H7NH2 forms a second hydrate with monoclinic symmetry P21/n and unit cell dimensions a=12.58 Å, b=21.20 Å, c=17.47 Å, β=89.3°; (C2H5)2NH forms two hydrates, one of orthorhombic symmetry Pbcn and unit cell dimensions a=13.44 Å, b=11.77 Å, c=27.91 Å, and one of monoclinic symmetry P21/c and cell dimensions a=13.86 Å, b=8.44 Å, c=10.93 Å, β=97.5°; (CH3)3CNH2 forms a cubic hydrate with a unit cell of symmetry I4̄3d and dimensions a=18.81 Å. The total mass contents of the unit cells, calculated from the cell dimensions and experimental densities, are used to derive the probable stoichiometric formulas.
Polyhedral Clathrate Hydrates. XIII. The Structure of (CH3CH2)2NH·8⅔H2O
Authors: Jordan Truman H. , Mak Thomas C. W.
Published: January 2005

A three-dimensional single crystal x-ray analysis of (CH3CH2)2NH·8⅔H2O has been carried out. The crystals are orthorhombic, with a=13.44 Å, b=11.77 Å, c=27.91 Å, and space group Pbcn. The compound is a clathrate hydrate, and the most notable feature of the water framework is a novel polyhedral cage, the 18-hedron (octakaidecahedron), which has twelve pentagonal and six hexagonal faces. The 18-hedra form a two-dimensional network by sharing faces. The networks are then linked together by additional water molecules in a manner which gives rise to additional ``irregular'' cages having quadrilateral, pentagonal, and hexagonal faces. Diethylamine molecules are enclosed in two types of cages and in both the amine groups are hydrogen bonded to the water lattice. In the case of the 18-hedra, this bonding somewhat distorts the cage from its ``ideal'' D3d shape. In marked contrast to previous clathrate structures involving polyhedra with pentagonal and hexagonal faces, where the dodecahedron could be considered to be the basic structural unit, the pentagonal dodecahedron does not appear in this structure.
Molecular Dynamics of Weakly Coupled Electric Dipoles on a Rigid Lattice. I. The Approach to Equilibrium
Authors: Köhler M. , Bellemans A.
Published: January 2005

The approach to equilibrium of a finite two-dimensional system of 400 rotating dipoles located on the sites of a square lattice is investigated by the technique of molecular dynamics. For all dipoles initially oriented at random and rotating in the same direction with equal velocities, it is verified that the system goes to its equilibrium state and that the relaxation time of the fourth moment of the angular momentum distribution is inversely proportional to the eighth power of the dipole moment, as expected from theory. A particular situation, such that the system does not approach its equilibrium state, is discussed.
Comments on Friction Constant Formalism
Authors: Collings A. F.
Published: January 2005

Expressions for the molecular friction constant based on the acoustic continuum and small-step diffusion models have been compared with experimental data. The integral describing ζ was evaluated by assuming an (n, m) potential and by substituting internal energy and pressure for terms involving integrals of the radial distribution function. The experimentally estimated values of the friction constant, from which a hard-core contribution is removed, do not yield consistent or realistic values of the potential parameters n and m. The successful prediction of the coefficient of thermal conductivity and shear viscosity for liquid argon using the Rice—Allnatt theory is based on the extrapolation of experimental data for self-diffusion. Statistical analysis of these data indicates that they do not permit a reliable test of the theory. Predicted values of the bulk viscosity coefficient of liquid argon are 40%—50% lower than recent experimental data, and the pressure dependence of the bulk viscosity coefficient at constant density calculated from the Rice—Allnatt theory is of the wrong sign.
Evaluation of Long-Range Retarded Interaction Energies
Authors: Johnson Robert E. , Epstein Saul T. , Meath William J.
Published: January 2005

The most important contributions to the expansion of the exact long-range retarded interaction energy, between two nondegenerate atoms, are evaluated accurately for the H–H, H–He, and He–He interactions.
Integrated and Integral Hellmann—Feynman Formulas
Authors: Epstein Saul T. , Hurley Andrew C. , Wyatt Robert E. , Parr Robert G.
Published: January 2005

For an isoelectronic molecular process X→Y, the energy change ΔW = WY—WX may be computed from any one of three equivalent formulas if the exact molecular wavefunctions, ψX and ψY, are known: the expectation-value difference, the integrated Hellmann—Feynman formula, and the integral Hellmann—Feynman formula. Should only approximate wavefunctions be available, Ψ̃X and Ψ̃Y, these formulas give different estimates of the energy change. If the Hamiltonians for X and Y differ in values of some parameter or parameters λ, say λ = 0 for X and λ = 1 for Y, one has HX=H(0), HY=H(1), H=H(λ), Ψ̃X=Ψ̃(0), Ψ̃Y=Ψ̃(1), Ψ̃=Ψ̃(λ), and the three formulas are as follows: ΔWed=〈Ψ̃(1) |H(1) |Ψ̃(1)〉/〈Ψ̃(1) |Ψ̃(1)〉−〈Ψ̃(0) |H(0) |Ψ̃(0)〉/〈Ψ̃(0) |Ψ̃(0)〉,ΔW̃d= ∫ 01dλ〈Ψ̃(λ) |∂H(λ)/∂λ |Ψ̃(λ)〉〈Ψ̃(λ) |Ψ̃(λ)〉,ΔWl=〈Ψ̃(0) |H(1)−H(0) |Ψ̃(1)〉/〈Ψ̃(0) |Ψ̃(1)〉.Relative advantages and disadvantages of these formulas are discussed, and illustrations are given of their use. Conditions for the equivalence of the formulas are established. It is shown that if Ψ̃X and Ψ̃Y are selected by the linear variational method from a fixed basis set, the three formulas give the same ΔW̃. If each of Ψ̃X and Ψ̃Y is selected variationally from a given class of functions, as is the case when each is an exact Hartree—Fock function, ΔW̃ed and ΔW̃d are equal, but possibly different from ΔW̃l. Examples are included which show that ΔW̃l sometimes gives a better estimate of an actual energy change than does ΔW̃ed. Implications for the energy of interaction between two ions or ionic fragments in a molecule are discussed.
Aromatic Carbonyl Spectra at High Pressures
Authors: Kadhim A. H. , Offen H. W.
Published: January 2005

The spectra of benzophenone (Snπ*←S0; Tnπ*→S0), fluorenone (Sππ*←S0; Sππ*→S0), and anthrone (Tnπ*→S0) have been studied as a function of pressure to 25 kbar. The π*←n absorption band of benzophenone shows a blue shift in compressed polar and hydrogen-bonding plastics, in contrast to the absorption of fluorenone. The fluorescence of fluorenone shows a red shift for all plastics which is greater than the corresponding red shift in absorption at the same isobar. The phosphorescence also shifts red except for benzophenone in polyethylene, polyacrylonitrile, and polyvinyl alcohol, where an initial blue shift is observed. These plastics are evidently capable of restraining geometrical changes in the benzophenone molecule.
Temperature Dependence, Orientation Correlation, and Molecular Fields in Second-Harmonic Light Scattering from Liquids and Gases
Authors: Weinberg D. L.
Published: January 2005

The properties of second-harmonic light scattering in fluids are derived in terms of the molecular polarizabilities, orientation correlation among molecules, and the molecular field Fα. Measurements of scattering intensity in CCl4 and water, from about 10° to 60°C, are reported. The variations with temperature, and therefore apparently the effects of changes of orientation correlation, are slight. The influence of preferred orientation in CCl4, of the type deduced from x-ray diffraction, is calculated. The third-rank molecular polarizability tensor consists of a fourth-rank tensor contracted with Fα, in addition to the term previously known, which is independent of Fα. With Fα arising from molecular multipole moments, the new term explains some measured depolarizations in liquids, and accounts for the spectral line, but not the background, observed in methane gas. In the case of molecular dipole moments, the new term can cause spectral narrowing.
Use of Optical Pumping to Detect Free Radicals during a Gas-Phase Photolysis
Authors: Crosley David R.
Published: January 2005

An optically pumped system of rubidium has been used as a probe to measure the concentration of free radicals present during the vacuum-ultraviolet photolysis of five hydrocarbons. The mechanism for this measurement is the reduction of the relaxation time of the oriented rubidium in the presence of radicals, due to the large spin exchange interaction between the two species. Measurements were made at two different pressures each on methane, ethane, propane, butane, and isobutane; from this both relative and absolute approximate quantum yields for radical production are determined. Separate detection of hydrogen atoms during the photolysis, through spin exchange coupled electron spin resonance, was reported briefly in an earlier note and is discussed more fully here. This method of directly detecting free-radical intermediates appears to be a useful complement to standard experiments in which reaction mechanisms are deduced from analysis of final products of the photolysis.
Vapor Condensation in a Shock Tube; Condensation Coefficient for sec-Butyl Alcohol
Authors: Kicska Paul A. , Smith Wesley R.
Published: January 2005

The condensation of sec-butyl alcohol vapor has been observed in a glass shock tube instrumented to observe the variations in monochromatic light transmittance caused by the growth of a liquid film of sec-butyl alcohol on the shock-tube walls. The film thickness was obtained from the transmittance. The gas pressure during condensation was monitered by strain gages, and the wall temperature and shock-wave velocity were measured with the resistance gages. The observed supersaturation ratios at the liquid—vapor interface ranged from 1.1 to 3.2 and the observed net condensation rates ranged from −0.015 to −0.67 g cm−2·sec−1. The interface temperatures ranged from 25° to 50°C. The condensation process was analyzed in terms of an equilibrium condensation coefficient. The gas at the interface was assumed to be uniform, in motion toward the interface, and have a Maxwellian velocity distribution. Using the measured values of net condensation rate, pressure, and temperature, the calculated condensation coefficients were not constant, but varied linearly with net condensation rate. When extrapolated to zero condensation rate, the condensation coefficient had a most probable value of 0.25 with a 65% probability of lying between 0.02 and 0.08. The value of the condensation coefficient calculated by the method of Mortenson and Eyring is in good agreement with the above value.
Exchange-Charge-Model Calculation of the Born—Mayer Repulsive Potential in Ionic Gases and Crystals
Authors: Hafemeister D. W. , Zahrt J. D.
Published: January 2005

By considering the deformation of the free ions and within the framework of the exchange charge model (ECM) of Dick and Overhauser and the technique of symmetrical orthoganalization of Löwdin, we have calculated the radial dependence of the repulsive potential for ionic gases and solids. The repulsive potential is considered to be a summation of the electrostatic energy between effective nuclear charges and the exchange charges, and it very closely fits the form of the Born—Mayer repulsive potential, B exp(—r/ρ). We have shown that the ECM values of the potential for the gases do not depend on the size of the effective nuclear charge and the values of ρ agree to within 10% with the experimental data. The crystalline values of ρ agree with the data reasonably well, but deviations are noted. The calculation of ρ depends only on the Hartree—Fock free-ion functions whereas calculations of dissociation energies, molecular force constants, vibrational frequencies, cohesive energies, compressibilities, and Debye temperatures depend also on the equilibrium spacing. The alkali hydride and hydride—hydride overlap integrals and their radial dependence are tabulated.