bluuebunny/crossref_metadata_2025 huggingface dataset:
Vibrational Energy Exchange of Highly Excited Anharmonic Oscillators
Authors: Benson Sidney W. , Berend George C.
Published: January 2005

The probabilities of dissociation Pdis, excitation Pex, de-excitation Pde, and the associated average energy exchanges were calculated theoretically for a highly energized, anharmonic oscillator (I2 or Br2) colliding classically with an inert gas atom C through a Morse-type potential. The effect of varying mass and well depth was investigated.

It was found that the effect of anharmonicity is to favor excitation and dissociation. However, the average ΔEv for these processes is about the same for harmonic and anharmonic oscillators and not much bigger than 1 to 2 RT. Pdis increases markedly with increasing mass. The well depth (V0) does not seem to have much effect in the range 0.004<V0/D0<0.14, where D0 is the bond dissociation energy. Exchange reactions are observed, but for shallow well depths they are rare events. From the results, it is possible to calculate λ, the probability of stabilizing an atom pair by a third-body collision. This turns out to be independent of temperature but depends strongly on the mass of the third body C. It is always in the range 0.1<λ<1.0 for the systems considered, and increases with increasing mass of C.

For the dissociation process, it is found that the average dissociation event gives rise to a pair of atoms with very little excess energy (∼0.10 RT) above the dissociation barrier. This implies an activation energy for dissociation of the order of D0°—2RT in the Benson—Fueno theory and also a T—2 dependence for the rate of recombination of atoms.
Electron Spin Resonance of Gamma-Ray Irradiated Single Crystals of Sodium Nitrite
Authors: Tateno Jun , Gesi Kazuo
Published: January 2005

Single crystals of sodium nitrite were irradiated with Co60 gamma rays of about 109 R at room temperature and studied by ESR method. The spectrum consists of a triplet and a quintet associated with different paramagnetic species; the former is believed to be NO2 and the latter N2O4—. From the analysis of the anisotropy of the hyperfine tensor the molecular plane of NO2 lies in the crystal ac plane, being different from the result obtained with irradiation at 77°K by Zeldes and Livingston. Molecular orbital of the unpaired electron of N2O4— was also calculated.
Excitation Energy Transfer from Toluene to Some Organic Scintillators
Authors: Melhuish W. H.
Published: January 2005

A general equation is derived for the light output of a liquid scintillator as a function of solute concentration, which includes both radiative and nonradiative excitation energy transfer. The rate constants for energy transfer from toluene to 2,5-diphenyloxazole, anthracene, 9,10-diphenylanthracene, perylene, and methyl anthranilate, were determined from this equation using oxygen-quenching data obtained by γ-ray and uv excitation. The correction of the observed scintillation intensities for reabsorption and re-emission of solute fluorescence is described. The corrected points were found to agree well with the general equation using transfer rate constants derived from oxygen-quenching studies.
Analysis of Charge Distributions: Hydrogen Fluoride
Authors: Kern C. W. , Karplus M.
Published: January 2005

Electron density maps and their appropriately weighted analogs (e.g., dipole-weighted density map) are found to provide a consistent and useful tool for the analysis and the comparison of atomic and molecular charge distributions obtained with different wavefunctions. Specific applications are made to hydrogen fluoride, for which a series of single-determinant SCF—LCAO—MO wavefunctions permit a study of the changes that occur in the electron density as the Hartree—Fock solution is approached. An examination of alternative basis-set functions of essentially the same size and the same energy shows that significantly different charge distributions can result; this points out the need for a careful selection of basis functions in large scale molecular calculations. It is found also that the charge density fluctuations from one basis set to another can be as large as the effects of chemical binding. Comparisons between density-map and population-analysis results indicate that considerable caution must be used in employing the latter for the interpretation of complicated wavefunctions.

Various methods for summarizing wavefunctions in terms of characteristic parameters of the charge distribution are considered. The forces acting on the nuclei are analyzed in relation to the Hellmann-Feynman theorem and a necessary condition on the exact molecular Hartree—Fock solution is obtained. Although none of the presently available wavefunctions for HF and LiF satisfy the condition to a high degree of accuracy, refinements in the wavefunctions are shown to yield improved results.
Liquid—Vapor Equilibrium in the System Normal Hydrogen—Helium
Authors: Streett W. B. , Sonntag R. E. , Van Wylen G. J.
Published: January 2005

Liquid—vapor equilibrium phase compositions for the binary system normal hydrogen—helium have been determined for 11 isotherms in the range 15.50°—32.50°K and at pressures up to 500 psia. The vapor recirculation method of obtaining equilibrium was used in conjunction with a liquid hydrogen vapor—pressure controlled cryostat. Analyses were made on a mass spectrograph. The results are presented in both tabular and graphical form, and the general behavior of the system discussed. An agreement with some previous investigations is demonstrated, and conflicts in existing data are resolved. Some problems of theoretical correlation of the data are discussed.
Experimental Determination of the Oscillator Strength of the Violet System of OH
Authors: Bennett R. G. , Dalby F. W.
Published: January 2005

The radiative lifetime of the A 2Σ→X 2Π transition of OH has been measured. The apparent lifetime is dependent upon the pressure of the parent molecule from which OH* is produced by electron bombardment. Extrapolation to zero pressure yields a spontaneous radiative transition probability of 0.99×106 sec—1 corresponding to an oscillator strength f= (7.25±0.5) 10—4. This value assumes that the electronic transition moment is constant over the (0, 0) vibrational transition. Utilizing Learner's values of rotation—vibration interaction an f value for the rotationless molecule and the (0, 0) band is f= (8.0±0.8) 10—4. The collisional quenching cross sections between OH* and water or methanol are 70×10—16 cm2 and 110×10—16 cm2, respectively.
High-Temperature Heat Content of Tungsten Carbide and Hafnium Carbide
Authors: Levinson L. S.
Published: January 2005

The heat content of tungsten carbide was measured between 1276° and 2642°K and that of hafnium carbide between 1286° and 2805°K using a drop calorimeter.
Absorption Spectrum at 357 mμ in the Nitrogen Oxides—Water System
Authors: Waldorf D. M. , Babb A. L.
Published: January 2005

A previously unreported ultraviolet absorption spectrum has been observed in aged solutions of low acidity containing HNO2. It is similar to that of HNO2 without the vibrational substructure, and its presence was detected by a differential recording technique. Possible sources of the unidentified spectrum are considered in detail. A cyclic configuration of the ion HONONO+, which could be formed in the presence of NO+ and HNO2, can satisfactorily account for the properties of the unidentified absorber, but this hypothesis has not yet been tested experimentally.
Doppler Shifts in Light Scattering from Pure Liquids and Polymer Solutions
Authors: Pecora R.
Published: January 2005

A framework for interpreting experiments on Doppler shifts in light scattering from pure liquids and polymer solutions is presented. The spectral density of the light scattered into a given frequency range and angle by a liquid composed of identical, isotropic particles much smaller than the wavelength of the incident light is expressed in terms of the Fourier transform of the two-body space—time correlation function. The formalism is then applied to the problem of light scattering from dilute polymer solutions. The Doppler shifts are evaluated for a polymer molecule undergoing translational Brownian motion, and for a rigid rod-shaped molecule undergoing Brownian motion about its center of mass. It is concluded that for a pure liquid more accurate experiments are needed to determine the form of the long-range part of the space—time correlation function. For polymer solutions, for which Doppler shift measurements have never been done, Doppler shift measurements should yield information about the shape of the polymer molecule, and its translational and rotational diffusion coefficients. In addition, for flexible molecules, information would be obtained about the long wavelength internal modes of motion of the molecule. The recently developed optical maser has made such experiments practical.
Ionization of U, UO, and UO2 by Electron Impact
Authors: Mann Joseph B.
Published: January 2005

The first ionization potential of uranium and the first appearance potentials of UO and UO2 by electron impact have been measured in a mass spectrometer, using the retarding potential difference (RPD) method. Small modifications of the RPD source are described. Crucibles of zirconium diboride were found to be preferable to tantalum crucibles for vaporization of uranium metal. Correction is made to the uranium appearance potential for thermally excited low-lying levels of the uranium atom, and for the several possible ionization paths. The ionization potential for uranium is 6.11±0.05 eV; for UO and UO2 the appearance potentials are 5.72±0.06 eV and 5.5±0.1 eV. Ionization probability curves were determined for U and UO.
Infrared Spectra of Ices Ih and Ic in the Range 4000 to 350 cm—1
Authors: Bertie J. E. , Whalley E.
Published: January 2005

The infrared spectra of Ice Ih made from H2O, D2O, a mixture of 95% H2O and 5% D2O, and a mixture of 5% H2O and 95% D2O, and of Ice Ic made from H2O, D2O, and a mixture of 95% H2O and 5% D2O, have been recorded in the region 4000 to 350 cm—1 using low-temperature mulling techniques developed in these laboratories. The Ice Ic was made by transformation of Ices II and III, and was authenticated by its x-ray diffraction powder pattern. The spectra of Ices Ih and Ic are identical within experimental error. The spectra of Ice Ih, while similar in their main features to those reported by earlier workers, differ significantly in detail, probably largely because much of the previous work, particularly on D2O ice, has been done with partly vitreous ice. The usual interpretation of the bands in terms of the v1, v2, v3, and vR vibrations of isolated molecules is greatly oversimplified because intermolecular coupling is important. There are at least six (five infrared and one Raman) bands due to O—D stretching vibrations in the spectrum of D2O Ice I, but the detailed origin is unknown. The breadth of the O–H and O—D stretching bands of HDO in dilute solution in D2O and H2O is interpreted as indicating a disarrangement of the oxygen positions due to the disorder of the hydrogen atoms.
Microwave Spectrum of Propionaldehyde
Authors: Butcher Samuel S. , Wilson E. Bright
Published: January 2005

The microwave spectrum of propionaldehyde, CH3CH2CHO, has been investigated in the frequency region 8–38 Gc/sec. The existence of two stable rotamers has been demonstrated. The cis rotamer, in which the four heavy atoms are coplanar, is more stable by 900±100 cal/mole. An approximate treatment of the coupling of the —CH3 and C–C torsional motions in the cis rotamer is presented. Using this treatment the barrier to internal rotation in the cis rotamer is found to be 2280±110 cal/mole. The dihedral angle in the higher energy, gauche rotamer is about 131°. Evidence is given for coupling of the C–C torsional momentum and over-all rotational angular momentum in the gauche rotamer. Other aspects of the spectrum are also discussed.
Analytical Expressions for the Hartree—Fock Potential of Neutral Atoms and for the Corresponding Scattering Factors for X Rays and Electrons
Authors: Strand T. G. , Bonham R. A.
Published: January 2005

Approximate analytical expressions for the Hartree—Fock potential of neutral atoms to Z=36 have been obtained by fitting the radial electron density with an analytical expression by least squares. The expression for the radial density corresponds to the following form of the screening factor: Zp(r)Z= ∑ i=12γiaexp(−λiar)+r ∑ j=1mγjbexp(−bλjr),where m=2 for Z=2 to Z=18 and m=3 for Z=19 to Z=36. The corresponding expressions for the mean radius, the mean square radius, the diamagnetic susceptibility, and the atomic scattering factors for x rays, and for electrons according to the first Born approximation are given. The accuracy of the approximate expressions is discussed in relation to results obtained by numerical calculations from the Hartree—Fock wavefunctions for the atoms.
Collisional Transition Probabilities for Deactivation of Highly Vibrationally Excited Cyclopropane and Dimethylcyclopropane
Authors: Setser D. W. , Rabinovitch B. S. , Simons J. W.
Published: January 2005

Collisional deactivation of vibrationally excited cyclopropane and dimethylcyclopropane molecules, in their ground electronic states, has been studied with ethylene and cis-butene as the respective deactivators. Activation is to an energy region just above 100 kcal mole—1, which is reached by chemical activation. The activated molecules may isomerize, and the measurable cascade is to a reaction threshold at 60–65 kcal; below the threshold the excited molecules are stable with respect to reaction. The principle and characteristics of this steady-state method has been described in detail in Ref. 5.

The two substrate molecules offer an interesting difference in internal rotational degrees of freedom. Cyclopropane was investigated at 298°, 598°, and 723°K, and dimethylcyclopropane at 573° and 673°K. The observed behavior was compared with model calculations for various assumed functional forms of collisional transition probabilities pij which include stepladder, Gaussian, and skewed distributions. The data, unfortunately, are too inaccurate to distinguish between these models clearly; but they do show that ethylene removes energy from cyclopropane in average steps which are at least 7 kcal (and in one system, perhaps, as high as 30 kcal); butene removes energy from dimethylcyclopropane in steps of at least 10–14 kcal; there is an indication that a step or Gaussian distribution fits the data better than a skewed exponential model. There is some evidence that the average step size decreases with increase of ambient temperature.
Linewidth Studies in Electron Spin Resonance Spectra : The Para and Ortho Dinitrobenzene Anions
Authors: Freed Jack H. , Fraenkel George K.
Published: January 2005

Large variations have been found among the linewidths of the different hyperfine lines in the low-temperature electron spin resonance spectra of the p- and o-dinitrobenzene anions generated electrolytically in N,N-dimethylformamide solutions. The magnitude of the variations in the para compound is so great that the spectrum is superficially uninterpretable. Detailed analysis of the spectrum of this radical shows, however, that most of the linewidth differences can be accounted for by modulation through molecular tumbling of the intramolecular anisotropic dipolar and g-tensor interactions. There may also be a small contribution from modulation of the isotropic proton hyperfine splittings, the mechanism that accounts for the alteranting linewidth phenomenon in a number of radicals, but an alternation of the widths is not observed in the p-dinitrobenzene anion spectrum because the contribution from this interaction is small. The sign of the isotropic nitrogen hyperfine splitting aN has been determined by a new method involving only pure dipolar interactions with the nitrogen nuclei and protons and not depending on any assumptions about the magnitudes of the components of the g tensor. A number of features of the relaxation matrix determining the linewidths are discussed, and the problems encountered when the components of a degenerate line have different widths are analyzed. The spectra obtained in dimethylformamide solutions are much better resolved than those previously reported in acetonitrile solutions. Changes of hyperfine splittings with both solvent and temperature are observed.
Retarding Potential Measurements of Electrons Photoemitted by N2, CO, and O2
Authors: Schoen Richard I.
Published: January 2005

Retarding potential measurements have been made on electrons emitting during the photoionization of N2, O2, and CO. More than half of the ions produced by radiation in the 700 to 500 Å interval were observed to be in states of electronic excitation. Vibrational excitation of the ground states of CO+ and O2+ occurred in the wavelength intervals between the first and second ionization potentials. Part of the excitation of vibrational states was attributed to autoionization phenomena.
Spin—Lattice Relaxation in Some TCNQ Ion—Radical Salts
Authors: Jones M. T.
Published: January 2005

Spin—lattice relaxation as a function of temperature has been studied for the salts (φ3AsCH3)+(TCNQ)2—, (φ3PCH3)+(TCNQ)2—, and (Cs+)2(TCNQ)3=. A plot of spin—lattice relaxation time (T1) as a function of the inverse of temperature yields a V-shaped curve for the above salts. Correlation times are calculated from the spin—lattice relaxation data and are shown to vary as the inverse of the exchange frequency. Such measurements furnish an independent means to calculate exchange frequencies. This represents the first case in which a minimum in T1 due to random modulation of the dipolar interaction has been observed in ESR, although such phenomena are common in NMR.
Resolvent Operator Formulation of Stationary State Perturbation Theory
Authors: Yaris Robert
Published: January 2005

By starting with an exact operator equation and using different methods of expanding the resolvent operator, the Schrödinger, Wigner—Brilloin, similarity transformation, gauge transformation, and first-order perturbation iteration method, perturbation expansions are generated in a rigorous and straightforward manner. It is also shown how additional perturbation and perturbation iteration methods can be generated.
Calculation of Intensity Distribution in the Vibrational Structure of Electronic Transitions: The B 3Π+u—X 1Σ+g Resonance Series of Molecular Iodine
Authors: Zare R. N.
Published: January 2005

Franck—Condon overlap integrals have been calculated which predict within experimental error the intensity distribution of the sixty measured lines in the visible fluorescence spectrum of molecular iodine, B 3Π0+u(v′ = 15, 16, or 26)→X 1Σ0+g(v″ = 0 to 69). Rydberg—Klein—Rees potentials were used for both electronic states, and exact vibrational eigenfunctions were obtained by direct numerical solution of the radial Schrödinger equation, including vibration—rotation interaction. The electronic transition moment was assumed to be independent of internuclear distance. Overlap integrals derived in the same way for Morse potentials fail to give even qualitative agreement with experiment for lines with v″≳10. Because of the rapid oscillation of the vibrational wavefunctions for high v′ and v″, a shift in the potential of only 0.002 Å is found to alter appreciably the calculated intensity distribution; thus the agreement obtained provides a very severe test of the RKR potentials and the Franck—Condon principle. The radiative lifetime of the B state has also been calculated from the absolute intensity of a single line and the integrated intensity of the band system, and the results compare favorably with direct lifetime measurements.
Simple Basis Set for Molecular Wavefunctions Containing First- and Second-Row Atoms
Authors: Clementi Enrico
Published: January 2005

The self-consistent field functions for the ground state of the first- and second-row atoms (from He to Ar) are computed with a basis set in which two Slater-type orbitals (STO's) are chosen for each atomic orbital. The reported STO's have carefully optimized orbital exponents. The total energy is not far from the accurate Hartree—Fock energy given by Clementi, Roothaan, and Yoshimine for the first-row atoms and unpublished data for the second-row atoms. The obtained basis sets have sufficient flexibility to be a most useful starting set for molecular computations, as noted by Richardson. With the addition of 3d and 4f functions, the reported atomic basis sets provide a molecular basis set which duplicate quantitatively most of the chemical information derivable by the more extended basis set needed to obtain accurate Hartree—Fock molecular functions.
X-Ray Diffraction and Nuclear Quadrupole Resonance Studies of Chromium Trichloride
Authors: Morosin Bruno , Narath Albert
Published: January 2005

The infinite-layer compound CrCl3 is found to undergo a first-order phase transformation near 240°K. The crystal structures of the high- and low-temperature phases have been elucidated by detailed x-ray diffraction and 35Cl nuclear quadrupole resonance studies. The previously reported structure for CrCl3 is shown to be incorrect. The present single-crystal diffraction results at 298° and 225°K give monoclinic (C2/m: a0=5.959 Å, b0=10.321, c0=6.114 Å, β=108.49°) and rhombohedral (R3̄: a0=5.942 Å, c0=17.333 Å) structures, respectively. The 35Cl quadrupole resonance frequencies, measured in polycrystalline samples, have been compared with results of field-gradient calculations based on the ionic point-charge model. The ionic contribution accounts for a large fraction of the total gradient making it impossible to evaluate the covalency parameters of the Cr–Cl bonds from the measured quadrupole coupling constants.
Studies on the Residual Lines of Mica
Authors: Sato Kenzo
Published: January 2005

By the measurement of the residual lines of cleaved mica (muscovite), using an incident beam of unpolarized infrared radiation of 9–28 μ, where anomalous dispersion is seen, some information about the characteristic properties of the residual lines are obtained.

(1) Intensity of the residual lines of the 10- and 20-μ groups change regularly with a period of 2π by the change of the incident direction.

(2) Intensity of the residual lines of a sheet of cleaved mica changes almost alternately by the change of sample planes.

(3) Extreme values of the reflectivity of the residual lines are observed when the incident angle is set in the range of 15°—19° for the two groups commonly.

(4) The oscillators as origins of the residual lines are assumed to be oriented not parallel to the surface planes but declined about 15°—20°.
Nuclear Magnetic Resonance Determination of Some Microscopic Parameters of LiAl5O8
Authors: Stauss George H.
Published: January 2005

Quadrupole coupling data have been obtained from analysis of NMR spectra of 7Li and 27Al in single crystal and polycrystalline ordered LiAl5O8. On axially symmetric sites, values of | νQ | for 7Li and 27Al are, respectively, 41±2 kc/sec and 284±6 kc/sec. On 27Al sites with octahedral coordination, | νQ |=683±25 kc/sec, η=0.347±0.025, and the orientation of principal axes has been found. An ionic model calculation gives estimates of distortions of the crystal from the ideal spinel form and possible signs for the νQ values. A convenient general expression for second-order shifts is given, together with results for the positions of the prominent second-order features in the line shapes of polycrystalline samples.
Surface Effects in the Production of Ozone in the Silent Discharge
Authors: Bersis D. , Katakis D.
Published: January 2005

The discharge rate in a closed ozonizer filled with O2 or air, as measured by the radio-frequency current passing through it or the light emitted, was found to decrease with the time during which the discharge is maintained, reaching eventually a minimum value. It is concluded that this decrease is due to species formed during the discharge and adsorbed on the glass surface. It is also concluded that the ionization in the gaseous phase is small, and that the discharge occurs by a sudden release of a cascade of electrons from the cathode, these electrons being responsible for ozone formation through an oxygen-atom mechanism. It is pointed out that some of the discrepancies in the literature may be removed if a better understanding of the role of the state of the surface is achieved.
Infrared Spectra of Crystalline C2H2, C2HD, and C2D2
Authors: Bottger G. L. , Eggers D. F.
Published: January 2005

The infrared absorption spectra of polycrystalline films of C2H2, C2HD, and C2D2 have been examined at 63°K in the frequency range between 4500 and 450 cm—1. The spectra of the solid state and the gas phase of the various acetylenes are compared and the appropriate vibrational assignments are made. Several absorptions attributable to combinations of lattice modes and molecular fundamentals were found. The observed multiplet structure of the fundamental vibrations indicates that in the low-temperature modification of C2H2 and C2D2 the molecules are located at sites of C2h symmetry. Spectra of various solid solutions composed of mixtures of isotopic species were obtained and their significance discussed. The effect of isotopic substitution on the splittings in the ν5 region led to the conclusion that the dipole—dipole coupling model is sufficient to explain the observed spectra.
Microwave Spectrum of Methyl Hypochlorite
Authors: Rigden John S. , Butcher Samuel S.
Published: January 2005

The microwave spectra of the normal species and some isotopically substituted species of methyl hypochlorite (CH3OCl) have been investigated in the frequency region 9 000–38 000 Mc/sec. Analysis of the results indicates the following structural parameters: d(CH)av=1.099 Å, <HCHav=109.4°, d(OCl) = 1.674 Å, d(OC) = 1.389 Å, and <COCl=112.8°. The quadrupole coupling constants for CH3O35Cl are eQq=—84.34 Mc/sec and η=0.408. The coupling constants for CD3OCl and the structural data indicate that the quadrupole tensor is probably cylindrically symmetric. The barrier to internal rotation calculated from splittings in the vtorsion = 1 state for CH3O35Cl is 3060±150 cal/mole.
Microwave Absorption and Molecular Structure in Liquids. LVI. Dielectric Behavior of Water and Heavy Water in Dioxane
Authors: Clemett Colin J. , Forest Edward , Smyth Charles P.
Published: January 2005

The dielectric constants and losses of seven water—dioxane mixtures and six heavy-water—dioxane mixtures ranging in concentration from 5 to 58 mole % of water have been measured at wavelengths from 0.44 to 10.0 cm. The results are interpreted in terms of two partly superimposed noninteracting Debye dispersions. The high-frequency dispersion region for the water—dioxane mixtures corresponds to a relaxation time 4×10—12 sec, which is concentration independent, while the low-frequency dispersion region corresponds to a relaxation time which is concentration dependent and rises to a maximum at about 70 to 80 mole % water. The relaxation time 5.6×10—12 sec associated with the high-frequency dispersion region of the heavy-water—dioxane mixtures differs from the corresponding relaxation time for water—dioxane mixtures by a factor of (½)½. The low-frequency concentration-dependent relaxation time was found to be about 1.2 to 1.5 times greater than the corresponding relaxation time of the water—dioxane system. The high-frequency dispersion region is attributed either to the rotation of the OH (or OD) group about its hydrogen (or deuterium) bond or to over-all molecular relaxation. The low-frequency dispersion is attributed to the partial breaking and reforming of the hydrogen (or deuterium) bond. The rotational mechanism becomes a molecular libration in the extrapolating to pure water and contributes to the large atomic polarization observed.
Absolute Correlations of Nuclear Spin—Spin Coupling Constants with Atomic Number. III. JX—H in Isoelectronic Series and the Lighter Elements
Authors: Reeves Leonard W.
Published: January 2005

The equation (JX—H/γXγH)½ = AZX+B is obeyed for the isoelectronic series BH4-, CH4, and NH4+. The molecular hydrides of the first period can be considered in terms of the deviation parameters from this as suggested previously. The slope of the equation, ``A'', for an isoelectronic series is considerably greater than the line obtained from a similar correlation of the Group IV molecular hydrides. Terminal and bridge hydrogen coupling with boron in the molecule diborane is considered in terms of deviation parameters from the point for the tetrahedral species BH4-. All ions and molecules considered show consistently positive deviation parameters with the s character of the X—H bond exceeding the tetrahedral value and negative deviation parameters for less s character than true tetrahedral.
On the Semiclassical Expansion of Scattering Phase Shifts
Authors: Choi Sang-il , Ross John
Published: January 2005

A relation between the canonical density matrix and scattering phase shifts is obtained and applied to the derivation of the semiclassical expansion of scattering phase shifts. The method differs from that used by Curtiss and Powers, but the results are shown to be identical.
Quantum Effects in Small-Angle Molecular-Beam Scattering
Authors: Mason E. A. , Vanderslice J. T. , Raw C. J. G.
Published: January 2005

Quantum-mechanical calculations of the differential cross section for the small-angle elastic scattering of heavy particles are carried out to establish more definitely the region of validity of the classical approximation. Four results are discussed: (1) The Massey—Mohr phase-shift formula corresponds to the Kennard small-angle scattering formula in the semiclassical limit. (2) The Schiff approximation for the cross section is exactly the same as the semiclassical approximation at small angles, for any central potential. (3) At very small angles the semiclassical limit for the differential cross section varies as exp (—cθ2), where c is a function of velocity for which explicit expressions are given. (4) The first quantum deviation from the classical limit, which is proportional to ℏ2, can be combined with the preceding result to give a reasonable representation of the differential cross section over the entire range of small angles for which quantum deviations are appreciable. Detailed calculations for some specific systems are made, and it is shown that Wu's misgivings over the classical interpretation of the experimental results of Amdur and co-workers are unjustified.
One-Center Basis Set SCF MO's. I. HF, CH4, and SiH4
Authors: Moccia Roberto
Published: January 2005

One-center SCF MO ground-state wavefunctions are reported for HF, CH4, and SiH4. The molecular orbitals are expressed in terms of Slater-like functions all centered at a common origin. The basis sets employed contain more than 25 functions including, for the spherical harmonics, values of l up to 3. The results of the calculations here reported, performed by the use of a large electronic computer, refer to the geometrical configurations which, among many others considered, gave the minimum of the total energy.

The equilibrium bond length thus determined for HF is 1.728 a.u. with a corresponding value of the energy of — 100.0053 a.u. and of the electric dipole moment of 2.104 D. For CH4 and SiH4 the equilibrium configurations were found to possess tetrahedral symmetry with bond lengths of 2.08 and 2.787 a.u. and energies of — 39.86597 and — 290.1024 a.u., respectively.

The general features and capabilities of the one-center expansion approach to molecular systems are discussed.
Perturbed Hartree—Fock Calculations. II. Further Results for Diatomic Lithium Hydride
Authors: Stevens Richard M. , Lipscomb William N.
Published: January 2005

The previous calculations for the susceptibility and shielding of lithium hydride are extended and refined. It is shown that the basis sets for the first-order wavefunction are invariant under small variations of the other parameters and that the basis sets used in the final calculations are essentially complete. Results from calculations at three internuclear distances have yielded vibrational corrections. The computed rotational magnetic moment is —0.667 nuclear magnetons, and the computed spin rotational constants of lithium and hydrogen are +9.45 and —9.38 kc/sec, respectively, in substantial agreement with experiment. The method is also applied to the perpendicular component of the electric polarizability, which has a calculated value of 4.063 Å3.
Statistical Model for the Beta Zirconium Hydrides
Authors: Douglas Thomas B.
Published: January 2005

It appears reasonable to consider the hydrogen as bonded covalently to zirconium in the zirconium hydrides. After consideration of the known structure of ZrH2, the hypothesis is made that the nonstoichiometric ``beta'' (bcc) Zr–H phases have four symmetrical (tetrahedral) hydrogen sites on each face of the unit cell, with simultaneous occupancy restricted to pairs not closer than the shortest H–H distance in ZrH2. The complex configurational problem is solved for all concentrations by developing a simple process of building up the lattice, after making tests of the amount of detail required for accurate solutions in one and two dimensions. The total entropy, when decreased by the corresponding configurational entropy, corresponds to values of the hydrogen vibration frequency averaging 1440 cm—1 and showing no consistent trend with temperature or with a fourfold change in hydrogen concentration. A semiempirical energy model is constructed by introducing the hypothesis that zirconium bonded to no hydrogen is ``abnormally stable,'' and the two energy parameters are derived from the experimental data. The agreement with the curves derived from thermodynamic data is fairly good for the partial molal entropy and energy of hydrogen, and excellent for the hydrogen equilibrium pressures. Alternative models, however, are not eliminated unambiguously.
Absorption Coefficients of Carbon Monoxide in the 1006–600-Å Wavelength Region
Authors: Huffman R. E. , Larrabee J. C. , Tanaka Y.
Published: January 2005

Absorption coefficients, or cross sections, of carbon monoxide have been measured in the 1006–600-Å wavelength region at a bandwidth of 0.5 Å using the Hopfield helium continuum as background and a photoelectric technique. Strong bands (up to k∼4500 cm—1) were observed from 1006 Å to about 715 Å and weaker bands were found at shorter wavelengths. These bands agree well in location and relative intensity with absorption spectra previously available. Continuous absorption begins at about 960 Å and continues to 600 Å. At wavelengths less than the first ionization potential at 884.7 Å, intense ionization continua are observed. There is one maximum in the continuum of k=710 cm—1 at about 870 Å associated with the CO+X2Σ+ state and another maximum of k=950 cm—1 at about 724 Å associated with the CO+A2Πi state.
Raman Spectral Studies of Oleums
Authors: Walrafen George E.
Published: January 2005

Relative integrated Raman intensities of oleums reported earlier [G. E. Walrafen and T. F. Young, Trans. Faraday Soc. 56, 1419 (1960)] have been redetermined, and the measurements have been extended to other Raman bands. The new intensity data indicate low degrees of dissociation of H2S2O7, and they constitute evidence for the presence of small amounts of H2O3O10.

When X(SO3), the stoichiometric mole fraction of a mixture of sulfur trioxide and sulfuric acid, is increased from zero to 0.3, relative integrated intensities of Raman bands of H2SO4 and of H2S2O7 are observed to decrease or to increase, respectively, in nearly perfect agreement with corresponding variations of Σ[H2SO4] and Σ[H2S2O7], the stoichiometric sulfuric or disulfuric acid molarities. These agreements indicate that [HS2O7—] is small, and they provide an explanation for the observed low electrical conductivities. When X(SO3) is increased above 0.3, however, SO3 and H2S3O10 appear and increase in concentration, while [H2S2O7] attains a maximum value of 9.8 mole·liter—1 at X(SO3)≈0.5, and [H2SO4] approaches zero at X(SO3)=0.6. Above X(SO3)=0.6, S3O9 makes its appearance and increases in concentration as [H2S3O10] attains a maximum value of ∼1.4 mole liter—1 at X(SO3)≈0.74. [SO3] and [S3O9] continue to increase until X(SO3)=1.0, at which composition [SO3]≈17.4 mole·liter—1 and [S3O9]≈2.1 mole·liter—1.

Vibrational frequencies of S2O72—, HS2O7—, and H2S2O7 obtained from studies of molten K2S2O7 and (NO2++HS2O7—), and from studies of oleums, have been compared, and the vibrations have been assigned and correlated with the aid of polarization data. The intensity data obtained from studies of molten (NO2++HS2O7—) provide additional evidence that HS2O7— concentrations are generally low in oleum solutions. Vibrations of SO3, H2S3O10, and S3O9 are also considered briefly.
CO Adsorption and Interaction with Oxygen on (110) Nickel
Authors: Park Robert L. , Farnsworth H. E.
Published: January 2005

The interaction of oxygen and carbon monoxide on the (110) surface of nickel has been studied by LEED. CO is adsorbed with one molecule to each atom of the clean nickel surface. Thus the two-dimensional surface unit cell of the CO structure has the same dimensions as the nickel substrate. Exposure of clean (110) nickel to O2 produces a sequence of oxygen—nickel structures terminating with NiO. The intermediate structures which are most easily reproduced have been designated the (1×2) and (1×3), and occur in that order during exposure. Both are quite stable in vacuum. Exposure of the (1×2) structure to CO results in a new structure having the same surface spacings as the (1×3) nickel—oxygen. However, this change was reversible and the surface returned to the (1×2) on standing in vacuum for several hours. CO preadsorbed on the clean (110) surface was readily replaced by oxygen, although the exposure required to produce the (1×2) nickel—oxygen structure was greater than in the corresponding case of the clean surface.
Energy Band Structure of Polynucleotides in the Hückel Approximation
Authors: Ladik J. , Appel K.
Published: January 2005

Taking as model systems the polynucleotides poly A, poly T, poly G, poly C, and poly U in a stereo arrangement according to the Watson—Crick model of DNA, we have calculated the energy bands of these macromolecules in the Hückel approximation. Simple polynomial expressions were found for the energy values as functions of cosk, and with the aid of these the limits of all the occurring energy bands were determined. Further in the paper we discuss some features of the obtained band structures.
Extended Hückel Theory. III. Compounds of Boron and Nitrogen
Authors: Hoffmann Roald
Published: January 2005

The extended Hückel theory is applied to compounds of boron and nitrogen, with emphasis placed upon similarities and differences with isoelectronic and isosteric carbon analogs. The barrier to internal rotation in borazane is predicted to be ∼1.5 kcal/mole and the torsional barrier in aminoborane∼10 kcal/mole. The internal charge-transfer nature of the expected electronic transitions is stressed. The highest occupied orbitals in aminoborane and borazine are computed to be σ type, with important consequences for the reactions of these molecules. It is proposed that the accepted valence picture of borazine is incorrect and that in all B–N molecules N is more negative. Stabilization due to nonbonded electrostatic interactions is studied. Predictions are made regarding the geometry of B–N analogs of cyclobutadiene and cyclooctatetraene. Borazine is calculated to be inefficient in transmitting electronic effects. Computations of the relative stabilities of heteroaromatic B–N compounds are made.
Threshold Laws for Processes of Autoionization
Authors: Morrison J. D.
Published: January 2005

An examination is made of some new data obtained by photon and electron impact, in an attempt to determine more accurately the threshold laws for processes of autoionization. In the cases of Kr and Xe, it is found that marked interference can occur between the two competing processes of direct and autoionization. The results, and also some of the apparently anomalous ionization efficiency data obtained by electron impact for several of the metals, can be interpreted in terms of configuration-interaction phenomena involving excited states of very short lifetimes.
Electron Spin Resonance of Ultraviolet-Irradiated Compounds. II. Peroxide-Initiated Radicals in Straight Chain Alkenes
Authors: Beasley Edward E. , Anderson Roy S.
Published: January 2005

Selected low molecular weight hydrocarbon glasses at approximately 77°K were irradiated with ultraviolet light, producing trapped radicals which were studied by ESR. Straight chain alkenes exhibited spectra which were demonstrated, through tests with 1-hexene, to be the result of free radical reactions initiated by the photolysis of peroxide impurities. Other experiments with 1-hexene are reported.

Symmetric alkene spectra were interpreted in terms of the following model: (A) Primary (peroxide) radicals, formed by uv photolysis, react with molecular end groups by abstraction or terminal addition to produce the observed spectra. (B) In the π-electron radicals assumed to be formed, the isotropic proton hyperfine coupling constants (which determine the observed approximate component separations) are taken to have the fixed values: α protons, 22 G; methylene protons, 22 G (β1) and 44 G (β2); methyl protons, 22 G. (The α-proton anisotropic splitting is manifested only as a broadening of the components.) In terms of this model, interpretations of the spectra obtained from 2-pentene, 1- and 2-hexene, 1-, 2-, and 3-heptene, 1- and 2-octene, and 1-decene are presented.
Zero-Field Exciton Magnetic Resonance
Authors: Thomas D. D. , Merkl A. W. , Hildebrandt A. F. , McConnell H. M.
Published: January 2005

The zero-field magnetic resonance spectrum of triplet excitons in the solid ionic free radical (φ3AsCH3)+(TCNQ)2— has been observed in the 75°—140°K temperature range using marginal oscillator spectrometers. Zero-field transition frequencies of 61.4, 163.8, and 225.4 Mc/sec were observed at a temperature of 111°K. The transition frequencies decrease by roughly 0.1%—1% per 10° in the 75°—130°K range. The transition frequencies are in good agreement with the frequencies that can be calculated from the earlier high-field spectra of this compound obtained by Chesnut and Phillips. At low temperatures where exciton—exciton spin exchange is weak, the dominant temperature dependence of the zero-field transition frequencies is shown to be due to molecular torsional oscillations that are quite similar to those that are known to produce temperature-dependent transition frequencies in nuclear quadrupole resonance. In a sample contaminated with spin ½ free radicals, small temperature-independent frequency shifts are found and are attributed to second-order exciton—free radical spin exchange. An analysis of exciton linewidths in terms of an exciton diffusional motion leads to a site-to-site jump rate of the order of τ∼1012 sec—1.
Fluorescence of Chlorophyll a in Monolayers
Authors: Tweet A. G. , Gaines G. L. , Bellamy W. D.
Published: January 2005

An apparatus has been constructed which permits observation of the fluorescence of pigment molecules spread in monomolecular films on aqueous surfaces. It is found that while the emission from pure chlorophyll films is strongly concentration quenched, relative fluorescence yield increases nearly 1000-fold when the chromophores are effectively separated by a two-dimensional diluent. Factors affecting the efficacy of several diluents are discussed. The emission spectrum of diluted chlorophyll a monolayers is presented. Measurements of relative yield as a function of pigment concentration in mixed films containing chlorophyll and oleyl alcohol are consistent with a model involving energy migration to nonfluorescent centers in the monolayer. The present results, however, cannot demonstrate the quantitative validity of any specific mechanism for the migration process.
Spectra Excited in an Argon Afterglow
Authors: Prince J. F. , Collins C. B. , Robertson W. W.
Published: January 2005

The selective excitation of electronic spectra of gases by collisions of the second kind with energetic species in an argon afterglow has been investigated. A discharge was excited by a dc source in a high-velocity argon stream which was allowed to interact subsequently with 14 different gases in a reaction chamber several centimeters downstream. The nonluminous argon stream entering the reaction chamber through a nozzle formed cone-shaped diffusion flames in the chamber. Results of the spectroscopic investigation of the flames are presented together with the reaction mechanisms. The observed states of excitation as well as the conditions of the discharge indicate that the exciting species are the argon metastables 3P2 and 3P0.
Raman Spectrum of the Liquid PbCl2–KCl System
Authors: Balasubrahmanyam K. , Nanis L.
Published: January 2005

The Raman spectra of PbCl2, 2PbCl2·KCl, PbCl2·KCl, and PbCl2·2KCl were recorded both in the molten state and in the solid state. The spectrum of solid PbCl2 exhibits three Raman lines which are explainable on the basis of linear structure for PbCl2 molecules in the lattice. The spectra of 2PbCl2·KCl and PbCl2·KCl are interpreted on the basis of a predominance of PbCl3— ions with pyramidal structure C3v. For PbCl2·2KCl, a distorted tetrahedral structure for the PbCl42— ion (C2v) is found. Force constants for the ionic species are calculated using valence force potentials.
Theoretical Investigations on the Light Scattering of Spheres. XV. The Wavelength Exponents at Small α Values
Authors: Heller Wilfried
Published: January 2005

Both theoretical and empirical expressions are derived for the wavelength exponent of lateral scattering and turbidity expected for isotropic nonabsorbing spheres which are small compared to the wavelength (α≤1.5). Use of these equations eliminates the need of interpolations between Mie data previously given or the computation of Mie data for small α values not considered before (α<0.4). The data cover all m values≤1.33. Reasons are given for their prospective usefulness in investigating spherical or quasispherical scattering bodies of unknown low concentration located at large distances from the observer.
Studies in Molecular Dynamics. III. A Mixture of Hard Spheres
Authors: Alder B. J.
Published: January 2005

For an equimolar mixture of hard spheres differing in radius by a factor of 3 it is shown that the numerical method gives the thermodynamic properties within 1% accuracy in the fluid region but generates metastable states at solid densities. The Percus—Yevick theory for mixtures is shown to be as accurate as for pure systems, which makes it plausible that no two-fluid phase region exists for mixtures of spheres. The volume of the mixture is found to be always smaller than the volume of the two pure fluid components, however, at high pressures when a solid and fluid must be mixed to give a fluid mixture, the excess volume is positive. The excess properties are small so that the assumption of ideal mixing (no excess volume) leads to an accurate prediction of the properties of hard sphere mixtures. Furthermore, the conclusion can be drawn that the excess properties in mixing ordinary liquids are primarily determined by differences in the attractive potentials rather than solely by the molecular sizes of the pure components.
Negative Nuclear Spin-Spin Coupling Constants for Aromatic Protons
Authors: McConnell Harden M.
Published: January 2005

Valence bond theory and observed hyperfine splitting data are used to calculate proton-proton spin-spin couplings that arise through long range correlation of π-electron spins in even alternate aromatic hydrocarbons. In benzene and naphthalene calculated spin coupling constants are positive for protons separated by an odd number of carbon-carbon bonds and are negative for protons separated by an even number of carbon-carbon bonds.