bluuebunny/crossref_metadata_2025 huggingface dataset:
Static Crystal Effects on the Vibronic Structure of the Phosphorescence, Fluorescence, and Absorption Spectra of Benzene Isotopic Mixed Crystals
Authors: Bernstein E. R. , Colson S. D. , Tinti D. S. , Robinson G. W.
Published: February 2004

The phosphorescence, fluorescence, and absorption spectra of the isotopic benzenes C6H6, C6H5D, p-C6H4D2, and sym-C6H3D3, present as dilute guests in a C6D6 host crystal at 4.2°K, are obtained with sufficient spectral resolution to ascertain the magnitude of the crystalline site effects. The relative vibronic intensities in fluorescence and phosphorescence are compared. Two site effects are emphasized: site splitting of degenerate fundamentals and orientational effects. The former can occur for the isotopes C6H6 and sym-C6H3D3, while the latter is possible only for isotopes with less than a molecular threefold rotation axis. The observations show that both site-splitting and orientational effects do occur as a general rule on vibronic and vibrational states in benzene isotopic mixed crystals. An empirical correlation between the magnitudes of the site splitting, orientation effect and site (gas-to-crystal) shifts for in-plane and out-of-plane modes is noted. The phosphorescence of C6H6 and sym-C6H3D3 has been completely analyzed out to 0, 0 − (ν8 + ν1), while for that of C6D5H the analysis of only the more intense bands near the electronic origin has been carried out. Some ground-state vibrations of p-C6H4D2 are also presented but the phosphorescence spectrum, complicated greatly by both ground- and excited-state orientational effects, is not fully analyzed in the present work. Absorption spectra of these mixed crystals have yielded information concerning the orientational effect on the first excited singlet state of C6H5D and p-C6H4D2 as well as site splitting of the ν6′ vibrational levels of C6H6. On heavily exposed photographic plates it has been possible to assign a number of transitions in the 13CC5H6 emission spectra. The 13CC5H6−nDn0,0 absorption spectra have also been identified. New absorptions, in the region of the 0, 0 transition of C6H6 and C6H5D have been tentatively assigned on the basis of their intensity behavior as a function of guest concentration to resonance-pair lines and to lines from 13CC5H6-nDn and 13C2C4H6-nDn.
Mass-Spectrometric Study of Photoionization. IX. Hydrogen Cyanide and Acetonitrile
Authors: Dibeler Vernon H. , Liston Susan K.
Published: February 2004

Photoionization yield curves are obtained from threshold to 600 Å for the HCN+ and CN+ ions of HCN and for the principal ions of CH3CN. The first ionization energy of HCN is 13.59 eV. The threshold for the CN+ ion permits calculation of ΔHf0°(CN) = 100 kcal mole−1, D0(CN) = 182.5 kcal mole−1, D0(H–CN) = 119.2 kcal mole−1, and D0(NC–CN) = 126.6 kcal mole−1. Dissociative photoionization processes in acetonitrile do not produce methyl or cyanogen radical ions in sufficient abundance for direct verification of the above. Nevertheless, threshold values of the principal photoions of CH3CN are tabulated, and some thermodynamic values are calculated, including ΔHf0°(CH2) = 94 kcal mole−1.
Effect of Oxygen Atoms on the Vibrational Relaxation of Nitrogen
Authors: Breshears W. D. , Bird P. F.
Published: February 2004

The vibrational relaxation of nitrogen in the presence of oxygen atoms generated by the decomposition of ozone has been studied behind incident shock waves in the temperature range 3000°–4500°K. Relaxation of the nitrogen was followed by measurement of the postshock density gradient using a laser-beam deflection technique. Analysis of the data to yield PτN2–O, the relaxation time for nitrogen dilute in 1 atm of oxygen atoms, requires consideration of the simultaneous effect of molecular oxygen produced by the ozone decomposition The values obtained for PτN2–O are subject to some uncertainty, but clearly lie below those for pure nitrogen by nearly two orders of magnitude. The results are interpreted as evidence of a chemical effect.
Chapman–Enskog Method in Chemical Kinetics
Authors: Present R. D.
Published: February 2004

Nonequilibrium effects in gas-phase reactions associated with the perturbation of the Maxwell speed distribution by the reaction have been investigated by Prigogine and others using the Chapman–Enskog method in the lowest-order approximation. We have extended these calculations to the second order in the Burnett expansion of the perturbation in a series of Sonine polynomials. In the case of the reaction A + A→B + C in which the products B and C are removed and no inert gas is present, the appropriate elastic collision integrals have been evaluated for the model of rigid elastic spheres and the reactive collision integrals have been evaluated for two reaction cross sections, one corresponding to the simple collision theory of bimolecular reactions with activation energy ε* and the other to the “centrifugal barrier” theory of free-radical recombinations. For the activated reactions the detailed results show that the Chapman–Enskog method is useless when the reaction is fast (ε* / kT ≲ 5) because the perturbation method fails and is also useless when the reaction is slow because the Sonine polynomial expansion then diverges, as anticipated by Takayanagi. In free-radical reactions the Chapman–Enskog procedure is satisfactory and the nonequilibrium corrections to the reaction rate are negligibly small (<0.1%) in first and second orders.
Studies of Phase Transitions in Ammonium Salts and Barriers to Rotation of Ammonium Ions by Neutron-Scattering Cross Sections as a Function of Temperature
Authors: Leung P. S. , Taylor T. I. , Havens W. W.
Published: February 2004

The total scattering cross sections per hydrogen atom for NH4F, NH4Cl, NH4Br, NH4I, (NH4)2SO4, (NH4)2Cr2O7, and NH4ClO4 have been measured as a function of temperature using subthermal neutrons (λn = 8.5 Å). No significant change in the slope (Δσs / ΔT / H atom ≡ ST) is observed in the region of the λ-point transitions of the ammonium halides. At the first-order transitions of NH4Cl, NH4Br, and NH4I where the motion of the ammonium ions changes from torsional oscillation to relatively free rotation, the cross sections increase sharply by 18 to 20 b/H atom. The slope ST of the linear sections of the plot of σs / H atom vs T increases with decreasing torsional frequency or barrier to rotation of the ammonium ions. A plot of ST vs the barriers V0 for the ammonium halides and (NH4)2Cr2O7 gave an empirical curve, V0 = 48.83 − 424.2ST + 1364.5ST2 − 1575.5ST3(± 0.2)kcal / mole. This curve was used to obtain an average barrier for ammonium ions in (NH4)2SO4(ST = 0.25 b / °K / H atom, V0 = 3.4 kcal / mole) and in NH4ClO4 (ST = 0.34 b / °K / H atom, V0 = 0.4 kcal / mole). Calculations of the scattering cross sections using harmonicoscillator approximations for torsional and translation–vibration motions are in reasonable agreement with the experimental results. A comparison of calculations based on a model of free rotation above the first-order transitions of the ammonium halides indicates that there is significant hindrance to free rotation in the order NH4Cl > NH4Br > NH4I.
Ab Initio Calculations on 62 Low-Lying States of the O2 Molecule
Authors: Schaefer Henry F. , Harris Frank E.
Published: February 2004

Ab initio calculations have been made on the 62 low-lying states of molecular O2 which result from the combination of O atoms in P3, D1, and S1 atomic states. The calculations are done at nine different internuclear separations, and potential-energy curves are presented for all states. Twelve bound states were found: the lowest seven have been observed; two others have been predicted before; three are new. The state ordering agrees with experiment except for the c 1Σu− state. Possible reasons for this discrepancy are discussed. The remaining errors in the bound-state energy separations are rationalized. Data possibly bearing on the unobserved bound states are cited. Repulsive-state curves are used to discuss predissociation in the Schumann–Runge bands and to illustrate avoided-crossing phenomena.
SCF Matrix Elements for a Phosphorus Oxide Anion
Authors: Boyd Donald B. , Lipscomb William N.
Published: February 2004

The wavefunction and Hamiltonian matrix for hypothetical PO2− (isoelectronic with SO2) have been obtained from ab initio SCF calculations using a minimum basis set of Slater orbitals augmented with the important P3d orbitals (exponent 1.1). The charges are −0.61 on P and −0.19 on O and the P–O overlap population is 1.19, to which interactions of the P3d orbitals contribute 58%. The Hamiltonian matrix furnishes useful parameters for obtaining approximate LCAO–MO wavefunctions for phosphates by a new molecular-orbital method.
Microwave Spectrum of Dimethylamine
Authors: Wollrab James E. , Laurie Victor W.
Published: February 2004

Microwave spectra of 12 isotopic species of dimethylamine have been assigned for the ground vibrational state. Splittings arising from the inversion of the amino hydrogen have been observed and an inversion barrier of 4.4 kcal/mole has been estimated. From the rotational constants the structural parameters have been calculated and the conformation of the methyl groups has been determined. The structural parameters obtained are: r(CN) = 1.466 Å, r(NH) = 1.022 Å, r(CH) (average) = 1.09 Å, ∠CNC = 112.2°, ∠HCH (average) = 108.6°, ∠HNC = 108.8°. Evidence for an asymmetric methyl group is discussed. The 14N nuclear quadrupole coupling constants in the principal quadrupole axis system are χxx = 3.04 MHz, χyy = 2.01 MHz, and χzz = −5.05 MHz, where the x axis is normal to the symmetry plane. Analysis of the Stark effect gave a dipole moment of 1.01 D.
Dielectric Study of the Pressure Dependence of Intermolecular Association in Isomeric Octyl Alcohols
Authors: Johari Gyan P. , Dannhauser Walter
Published: February 2004

The equilibrium dielectric constant and density of 2-octanol, 3-octanol, 2-methyl-3-heptanol, and 5-methyl-3-heptanol have been measured as a function of pressure to 4 kbar from about 100°C to the freezing temperature. The isobaric temperature dependence and the isothermal pressure dependence of the dielectric constant are both sensitive functions of temperature, pressure, and the isomeric nature of the alcohol. Analysis of the data in terms of Kirkwood's dipole correlation factor clearly reveals the differences between isomers. It is proposed that the principal effect of pressure is to perturb the liquid structure. A model of intermolecular association involving monomeric, linear chain, and ring-dimer species is developed and thermodynamic parameters characterizing the various intermolecular associative equilibria are evaluated. ΔH of association is nearly independent of pressure. Thus, application of pressure favors formation of linear chains primarily because of entropic factors. The nature of the short-range order in these liquids is discussed.
Photoionization of the Lower Aliphatic Alcohols with Mass Analysis
Authors: Refaey Kamel M. A. , Chupka William A.
Published: February 2004

Relative photoionization cross-section curves have been determined for parent and fragment ions of methanol, ethanol, n-propanol, and isopropanol over the photon energy range from the ionization potential to 14.0 eV. Appearance potentials and heats of formation of some fragment ions have been determined. The data have been treated to give experimental breakdown curves which are compared with those obtained by charge exchange and with the results of theoretical calculations. Some details of the fragmentation processes are elucidated.
Nonempirical Calculations on Excited States: The Formaldehyde Molecule
Authors: Dunning Thomas H. , McKoy Vincent
Published: February 2004

A series of calculations on the excited states of formaldehyde using excitation operator techniques are presented. As in ethylene, the effect of σ–π interaction on the “π→π*”(1A1) excitation is rather large, decreasing the calculated excitation energy from 14.89 to 12.03 eV and the oscillator strength from 1.01 to 0.30. The coupling has little effect on the corresponding triplet state (3A1). The next higher approximation reduces the excitation energy to 11.22 eV and the oscillator strength to 0.21. The effect of the coupling on the “n→π*”(1,3A2) excitations is not as large as that for the A11 state, lowering the excitation energies for both the singlet and triplet by ∼0.5 eV. Similar results were obtained for the “σ→π*”(1,3B1) excitations. Trends are observed in calculations on corresponding states in ethylene and formaldehyde. Numerous one-electron properties are claculated for the excited states. The results are in moderate agreement with experiment; a major source of error probably arises from the use of an unoptimized, minimum basis set LCAO(STO)–MO–SCF wavefunction.
Infrared Spectrum of Anthracene Crystals
Authors: Bree A. , Kydd R. A.
Published: February 2004

The infrared spectrum of anthracene is reported with the plane of the incident polarized light parallel to all three crystal axes. The measurements were extended to 50 cm− 1; thus the c polarized spectrum was recorded over a sufficient spectral range to cover all fundamentals. Some lattice modes and all the low-frequency infrared-active fundamentals (below about 600 cm− 1) were firmly assigned. Some earlier misassignments were corrected and a more probable; though, in part, still uncertain, assignment of the infrared-active fundamentals at higher energy was made.
Avoided Crossings in Bound Potential-Energy Curves of Diatomic Molecules: Derivation and Analysis of the Vibrational Hamiltonian
Authors: Lewis J. K. , Hougen J. T.
Published: February 2004

As a first step in analyzing the effect of an avoided crossing on the spectrum of a diatomic molecule, a formalism is presented for dealing with the vibrational problem. A mathematically well-defined procedure is given for going from potential curves exhibiting an avoided crossing (such as would be obtained by solving exactly the eigenvalue problem associated with the complete electronic Hamiltonian for fixed nuclei) to two crossing potential curves and an interaction function. These latter curves, though less meaningful physically than the former, lead to a pair of relatively simple coupled differential equations (similar to those arising in other vibronic problems) which must be solved to determine the vibrational wavefunctions and energy levels. The order of magnitude and mass dependence of the interaction terms in the coupled differential equations are examined.
Statistical-Mechanical Calculation of Surface Properties of Simple Liquids and Liquid Mixtures. I. Pure Liquids
Authors: Plesner Igor W. , Platz Ole
Published: February 2004

Statistical calculations of surface properties of simple liquids at two different reduced temperatures are presented. Alternatively, the results represent the properties of argon and nitrogen, respectively, at 84°K. The equation of state employed here is the Reiss–Frisch–Lebowitz equation of state for a hard-sphere fluid, on which is superimposed a van der Waals interaction term. The agreement between our values of the surface tension and the experimental values is satisfactory considering the limitations imposed by the model. The results are compared with those of earlier works.
Carbon Characteristic X-Rays from Gaseous Compounds
Authors: Mattson R. A. , Ehlert R. C.
Published: February 2004

Carbon spectra from CH4, C2H6, C3H8, C4H10, CCl4, CBr4, CF4, benzene, cyclohexane, ethylene, acetylene, CO, and CO2 have been measured in an ultrasoft x-ray spectrometer using electron-beam excitation, a lead stearate multilayer analyzer, and a thin window flow proportional counter. The spectra have been corrected for background and normalized so that the height of the largest peak of each spectra is the same. Similar molecular species exhibit similar spectra. Furthermore, for the alkanes, a correlation is observed between the position of the main peak and the first ionization potential of the molecule.
Numerical Solution of Quantum-Mechanical Pair Equations
Authors: McKoy Vincent , Winter N. W.
Published: February 2004

We discuss and illustrate the numerical solution of the differential equation satisfied by the first-order pair functions of Sinanoğlu. An expansion of the pair function in spherical harmonics and the use of finite difference methods convert the differential equation into a set of simultaneous equations. Large systems of such equations can be solved economically. The method is simple and straightforward, and we have applied it to the first-order pair function for helium with 1 / r12 as the perturbation. The results are accurate and encouraging, and since the method is numerical they are indicative of its potential for obtaining atomic-pair functions in general.
Electronic and Vibrational Exciton Structure in Crystalline Benzene
Authors: Bernstein E. R. , Colson S. D. , Kopelman R. , Robinson G. W.
Published: February 2004

The purpose of this paper is to lay a consistent theoretical framework for the discussion of a series of forthcoming experimental papers on the absorption and emission of light by benzene crystals. Emphasis will be placed not only on the usual Davydov splittings but also on k≠O states and band-to-band transitions in neat (pure) crystals, and on orientational effects, site splittings, shifts, and resonance pair spectra in isotopic mixed crystals. The role of translationally equivalent interactions will be discussed. The interchange-group concept is used in order to simplify the theoretical analysis. From the four possible interchange groups D2, C2υa, C2υb, C2υc, the D2 group is found to be the most convenient for the classification of benzene exciton functions. A differentiation between static and dynamic interactions is made in the limit of Frenkel excitons, and the concepts of site distortion energy and the ideal mixed crystal are introduced to aid in this distinction. Data pertaining to site shifts and splittings and resonance and quasiresonance interaction terms for the B2u1 electronic exciton band and the vibrational ν12(b1u), ν15(b2u), and ν18(e1u) exciton bands are discussed in order to illustrate briefly the theoretical concepts.
Even Moments of the End-to-End Distance of Polymeric Chains
Authors: Nagai Kazuo
Published: February 2004

A method is developed for calculating even moments 〈r2k〉 of the end-to-end distance r of polymeric chains, on the basis of the rotational-isomeric-state approximation for rotations about skeletal bonds. Expressions are obtained in a form which is applicable in principle to arbitrary k, but practical applications are limited by a tremendous increase in orders of matrices to be treated, with increasing k. The order of a matrix derived for 〈r2k〉 is Hk5s = (k + 4)!(4!k!)−1s, where s is the number of states in which each bond can exist. An application is made to the polyethylene chain by using the familiar, three-state (trans, gauche, and gauche prime) model. With a computer of relatively low ability, we have obtained even moments through 〈r12〉 for n through 400, where n is the number of C–C bonds. Approximate values of the distribution function Wn(r) of the end-to-end vector r, Wn(0), and 〈r− 1〉, are calculated from these even moments by a method previously developed, and mathematical implications of them are discussed.
CO Chemiluminescence from Flames
Authors: Becker K. H. , Bayes Kyle D.
Published: February 2004

The chemiluminescence from the reaction of oxygen atoms and carbon suboxide in a flow system has been reinvestigated. In addition to the “triplet” bands reported previously, two other band systems of CO were observed: the Herman bands, also in the red, and the Fourth Positive bands in the vacuum ultraviolet. The three electronic states show a common excitation limit of almost 9 eV above the ground state. The emission intensity in the red and in the vacuum ultraviolet vary together as the flame conditions are changed, showing that the three excited states are formed in a single reaction. Traces of hydrogen are not necessary for the chemiluminescence. The reaction responsible for the emission is probably O(3P) + C2O(X 3Σ)→CO(A 1Π, d 3Δ, e 3Σ) + CO(X 1Σ). Quenching of the CO emission depends on the ratios (NO) / (O) and (O2) / (O). NO is a more efficient quencher than O2, in agreement with the behavior found for C2O(X 3Σ) formed by the photolysis of C3O2. The vacuum-ultraviolet emission from a O + C2H2 flame was found to be identical to that of the O + C3O2 flame. As required by the single-reaction hypothesis, the “triplet” bands and probably the Herman bands were found in the spectrum of the O + C2H2 flame. The vacuum-ultraviolet photon yield from the O + C2H2 flame was 10−4.3 ± 0.5/C2H2. Possible reactions which could form C2O in these flames are discussed.
Re-examination of Homogeneous Nucleation Theory: Statistical Thermodynamics Aspects
Authors: Abraham Farid F. , Pound G. M.
Published: February 2004

An analysis of the equilibrium concentration of critical clusters in a supersaturated vapor is developed from the grand canonical ensemble representation of statistical mechanics, Callen's axiomatic formulation of thermodynamics and the standard capillarity approximation of nucleation theory. It is concluded that: (1) There is a small correction to the Kelvin equation for the equilibrium of a small droplet with the vapor; (2) The conclusion of Frenkel and Lothe and Pound in regard to the equilibrium concentration of critical nuclei is essentially correct for the case of no orientational degeneracy in the rigid-body rotation of a cluster; (3) For an orientationally degenerate cluster, the Lothe-Pound 1017 factor of correction to classical nucleation theory is no longer valid, but is replaced by a 108 correction factor; (4) The revision of nucleation theory proposed by Reiss and Katz is erroneous.
Lattice Perturbations in CaWO4 and CaMoO4
Authors: Scott James F.
Published: February 2004

Frequency assignments for the vibrational modes of species Bu in CaWO4 and CaMoO4 are made. Bu modes are both infrared inactive and Raman inactive in unstrained material, but become infrared active and exhibit Eu characteristics under xz or yz shear strain and Au characteristics under xy shear strain. In the present paper previously published infrared data are interpreted in terms of strain-induced mode mixing, and the nature of the crystalline strain is discussed. The assignment of the three Bu modes in CaWO4 completes the task of identifying the 18 internal modes of the WO4= ions.
Mössbauer Effect in Tin Compounds: Interpretation of Isomer Shifts and Determination of the Nuclear Radius Change in 119Sn
Authors: Lees Joseph K. , Flinn Paul A.
Published: February 2004

An interpretation of the isomer shift of 119mSn in its two ionic states [(2 + ) and (4 + )] and its one covalent (sp3) state is presented. Based on the values of the isomer shifts of the ideal configuration of  + 2.86 mm/sec for Sn(2 + ), − 2.36 mm/sec for Sn(4 + ), and − 0.075 mm/sec for Sn (sp3) all relative to Mg2Sn (77°K) and a Liberman-Waber-Cromer relativistic wavefunction calculation, a value of δR / R = + 9.21 × 10−5 is obtained. In addition, a calibration for the corresponding shift due to a single 5s electron, 3.06 mm/sec, the 5s − 5s screening effects, −0.20 mm/sec, the 5s − 5p screening effects, − 0.09 mm/sec, and the inner-shell screening due to the 5s electron, − 0.05 mm/sec is given.
Neutron Scattering in Normal and Deuterated Polyethylene
Authors: Lynch J. E. , Summerfield G. C. , Feldkamp L. A. , King J. S.
Published: February 2004

The one- and two-phonon amplitude-weighted directional frequency functions are calculated for normal and deuterated crystalline polyethylene. These results are compared to previously measured frequency spectra for stretch-oriented normal polyethylene and to new measurements on deuterated polyethylene. In addition, the Debye-Waller factors are calculated for oriented polyethylene and compared with elastic-scattering data.
ESR of N2− in uv-Irradiated Single Crystals of Anhydrous Barium Azide
Authors: Marinkas Paul L. , Bartram Ralph H.
Published: February 2004

Single crystals of anhydrous barium azide have been irradiated at room temperature with 2537 Å ultraviolet light. Upon cooling to 77°K, an ESR spectrum is observed, the angular variation of which is expressed by the spin-Hamiltonian H = βH·g·S + I·A·S with gx≈gy = 1.997 ± 0.001, gz = 1.979 ± 0.0001, Ax = 3.6 ± 0.2 G, Ay = 20.0 ± 0.2 G (see text), Az = 4.1 ± 0.2 G. The spectrum is interpreted in terms of the theoretical predictions of Gelerinter and Silsbee for an N2− molecular ion in a field of rhombic symmetry. The ESR data are used to speculate on the orientation of the azide ions in the Ba(N3)2 lattice, the structure of which is as yet unknown. The optical absorption spectrum of thin single crystals in the range 200-300 mμ has been measured at room temperature and is correlated with the wavelength threshold for production of the paramagnetic center. It is postulated that the initial step in production of the center is the creation of an excited azide ion by the ultraviolet light.
Mean Displacement of Surface Atoms in Palladium and Lead Single Crystals
Authors: Goodman R. M. , Farrell H. H. , Somorjai G. A.
Published: February 2004

The intensity of specularly reflected [(00) reflection] low-energy (5-500-eV) electrons has been measured as a function of temperature for the (100) and (111) faces of palladium and for the (111) face of lead in the temperature ranges 25°-600°C and 25°-225°C, respectively. From the data, the root-mean-square displacements, 〈u⊥〉, of surface atoms perpendicular to the surface planes and the surface Debye temperatures have been calculated. The mean vibrational amplitudes of surface atoms are 40%→100% larger than for bulk atoms. There is little difference between the surface mean displacements of different crystal orientations; 〈u⊥〉 appears to be relatively insensitive to changes of surface structure or surface density. The experimental results correlate well with those obtained for platinum and silver single-crystal surfaces. It is believed that all monatomic face-centered cubic crystal surfaces should have mean displacements markedly larger than those in the bulk.
Magnetic Excitations in Charge-Transfer Complexes. I. p-Phenylenediamine–Chloranil
Authors: Hughes R. C. , Soos Z. G.
Published: February 2004

The electron magnetic resonance of single crystals of p-phenylenediamine–chloranil (PDC) at 160 Mc/sec, 9.5, and 35 Gc/sec is reported. The thermally accessible (activation energy 0.13 ± 0.01 eV) magnetic excitations for the linear chains of exchange-coupled, alternately PD cation and chloranil anion radicals (S = 12) are described by a single, almost axially symmetric g factor, with g‖ = 2.0024 ± 0.0002, g⊥ = 2.0054 ± 0.0002, and | gx − gy | ∼ 0.0001. Temperature-dependent g-factor splittings are observed below 315°K, while a single, strongly exchange-narrowed line (width ∼ 250 mG) is observed above 315° for any orientation of the crystal. The angular dependence of the splittings below 270°K corresponds to three magnetically inequivalent, independent free-radical chains related to each other by a threefold axis parallel to the chain axis, with a 6° angle between the chain axis and the normal to the molecular planes of the radicals. The collapse of the splittings between 270° and 315° is explained qualitatively in terms of electron–electron dipolar interactions between magnetic excitations on inequivalent chains. Evidence is presented that the magnetic excitations in organic charge-transfer crystals based, like PDC, on planar, strong electron donors and acceptors are Wannier spin excitons above a diamagnetic, completely ionic ground state. Delocalized magnetic excitations are indicated by the single, averaged g factor for each chain, by the absence of nuclear hyperfine splittings, and by the strongly exchange-narrowed, Lorentzian lines observed. Evidence that the pairs of spins forming a Wannier spin exciton are independent is obtained from the temperature and pressure dependence of the resonance linewidth and from the absence of fine-structure splittings. The observed near independence of the magnetically inequivalent, exchange-coupled free-radical chains vindicates the usual description of spin excitations in organic free radicals by one-dimensional models.
Applications of Diatomics-in-Molecules Theory. I. Prediction of Stable LiH2 and Li2H Molecules
Authors: Companion Audrey L.
Published: February 2004

The semiempirical diatomics-in-molecules approach developed by Ellison is applied to the molecules LiH2 and Li2H, both unobserved experimentally. For LiH2, an isosceles triangular A12 state with the diatomic component H2 at its equilibrium internuclear distance is predicted most stable, bound by 13.5 kcal/mole with respect to Li+H2(1Σg+). A linear symmetrical Σu+2 state of Li2H is stable by 19.6 kcal/mole with respect to Li+LiH(1Σ+). Ionization energies, characteristics of potential surfaces, and fundamental vibrational frequencies are predicted for both molecules.
Delayed Luminescence of Organic Mixed Crystals. VII. Intermolecular Triplet Decay Processes
Authors: Kinoshita M. , Stolzle K. , McGlynn S. P.
Published: February 2004

Mixed single crystalline specimens of various host-guest systems have been studied. Host materials were biphenyl, durene, and phenanthrene; guest materials were naphthalene-hs and ds, phenanthrene-d10 and h10, and chrysene. Primary attention was paid to the temperature dependence of first-order guest phosphorescence decay rates. It has been shown that the guest triplet depletive route is intermolecular and that it involves a thermally stimulated process T1G↝T1H. No other temperature-dependent T1G depletive process of any significance has been detected.
Adiabatic Rapid-Passage Experiments in Some Solids
Authors: Janzen W. R. , Cyr T. J. R. , Dunell B. A.
Published: February 2004

Two types of adiabatic rapid-passage experiments are considered for measuring spin-lattice relaxation times in solids, and results are shown for calcium fluoride, stearic acid, and lithium stearate. Although rapid-passage experiments using a symmetric-sweep method give shorter T1 values in the substances examined than do experiments using a sequence of two rapid passages spaced at varying times, the two values may be brought together by applying a correction to the symmetric-sweep results for possible failure to invert completely the magnetization in the fast passage. For calcium fluoride and stearic acid, recovery from saturation experiments were also done and the T1 values obtained from these experiments agree very well with the relaxation times found by rapid-passage methods.
Nonequilibrium Effects in Free-Radical Recombination and Ion-Molecule Reaction Kinetics
Authors: Pyun Chong Wha
Published: February 2004

Distortion of the molecular velocity distribution functions from the Maxwellian form and the resulting deviation of the reaction-rate coefficients from the values calculated with the equilibrium assumption of conventional chemical kinetics are considered for two types of reactions in dilute, isothermal, spatially uniform gas mixtures: free-radical recombination reactions and ion-molecule reactions, both proceeding without an activation energy. The reactive collision cross sections used are those derived from the attractive potentials of the reacting pairs, which are inversely proportional to the sixth and the fourth powers of interparticle distances, respectively. The treatment is based on generalized Boltzmann equations which take into account the effects of reactive collisions, as well as elastic collisions, on the change of the velocity distributions with time. For free-radical recombination reactions, a first-order perturbation approximation analogous to that of Chapman and Enskog is used to derive the composition dependence of nonequilibrium effects. This differs from Mahan's earlier calculation; and, contrary to Mahan's result, the present calculation shows that the deviation of the rate coefficient from the equilibrium value remains small for any mole fraction of free radicals and typical values for various molecular parameters. The possible origin of the difference between the two calculations is analyzed. For the ion-molecule reactions, it is first shown that there is no distortion of the Maxwellian distribution by first-order perturbation theory irrespective of the choice of the series expansion. Next it is proved, without using a perturbation scheme, that nonequilibrium effects in the reaction rates vanish exactly for the ion-molecular reactions. The last conclusion is reached without an explicit assumption about the form of the velocity distribution, just as in the case of the transport properties of Maxwellian molecules which interact according to an inverse fourth-power repulsion potential. The reason for small or vanishing nonequilibrium effects in these reactions without activation energy is discussed.
Evaluation of Molecular Quadrupole Moments from Broadening of Microwave Spectral Lines. I. Measurements
Authors: Berendts B. Th. , Dymanus A.
Published: February 2004

The antimodulation method has been applied in a Stark cavity spectrometer to obtain pressure-broadening constants of OCS, CHF3, and N2O both for self-broadening (Λaa) and for foreign-gas broadening (Λab) with H2 HD, D2 N2 NO, and CO2 as (nonabsorbing) broadeners. The results are (in megahertz torr−1) J = 1→2 transition of OCS:ΛOCS,OCS= 6.44, ΛOCS, H2= 6.10, ΛOCS,HD= 6.10, ΛOCS,D2= 5.57, ΛOCS,N2= 4.41, ΛOCS,NO= 4.15, ΛOCS,CO2= 5.13; J = 0→1 transition of CHF3: ΛCHF3: ΛCHF3,CHF3= 34.2, ΛCHF3,H2= 4.9, ΛCHF3,D2= 4.3, ΛCHF3,N2= 4.1, ΛCHF3,NO= 3.55, ΛCHF3,CO2= 6.65; J = 0→1 transition of N2O: ΛN2O: ΛN2O,N2O= 5.22, ΛN2O,H2= 5.15, ΛN2O,D2= 4.20, ΛN2O,N2= 3.89, ΛN2O,NO= 3.65, ΛN2O,CO2= 4.12. As a byproduct of these measurements, peak intensities (αmax) of the above transitions were obtained. In a subsequent paper, molecular quadrupole moments will be derived from the measured broadening constants.
Melting-Curve Maxima at High Pressure. II. Liquid Cesium. Resistivity, Hall Effect, and Composition of Molten Tellurium
Authors: Rapoport Eliezer
Published: February 2004

Hall effect and electric-conductivity data for liquid tellurium are analyzed by means of the two-species model. Liquid tellurium is proposed to consist of two species, the normal form and another, metallic, form similar to one of the high-pressure phases of tellurium. The analysis yields a value for the interaction energy w which explains the irregularity in the high-pressure melting curve reported by Stishov, Tikhomirova, and Tonkov. Isoconcentration lines in the p-T plane are constructed for liquid tellurium and also for liquid cesium.
Binding and Field Desorption of Individual Tungsten Atoms
Authors: Ehrlich Gert , Kirk C. F.
Published: February 2004

The binding energy of individual tungsten atoms on different planes of a tungsten crystal, heretofore inaccessible to measurement, has been explored by field desorption at 20°K. Tunneling, rather than evaporation over a Schottky saddle, is the limiting step under these conditions. The appropriate relations between desorption field and atomic binding are derived and tested by establishing the evaporation field for tungsten at 6.1 V / Å. Desorption measurements on single adatoms lead to the following binding energies: (110), 5.3 eV; (211), 7.0; (310), 6.7; (111), 6.0; (321), 6.7; (411), 6.2. On low index planes such as (110), (211), and (310), agreement with the energetics estimated from Morse and Lennard-Jones potentials is reasonable. For rougher surfaces, however, the experimental quantities are significantly smaller than expected, suggesting a fundamental limitation on such potentials. Comparison of binding energies with activation energies for diffusion over the (211) and (321) planes also leads to the view that fluctuations in the position of lattice atoms play an important role in surface migration.
Double-ζ LCAO SCF MO Calculations for NO2 and OF2
Authors: Bonaccorsi Rosanna , Petrongolo Carlo , Scrocco Eolo , Tomasi Jacopo
Published: February 2004

The ground-state wavefunctions for NO2− and OF2 are obtained by using the free-atom-ζ double-ζ STO set in the LCAO SCF MO approximation. Comparisons are made with the corresponding minimal STO set SCF wavefunctions and, for OF2, also with a Gaussian set SCF wavefunction.
Abundance of Excited Ions in O+ and O2+ Ion Beams
Authors: Turner B. R. , Rutherford J. A. , Compton D. M. J.
Published: February 2004

A method has been developed to determine the fraction of excited ions present in an ion beam formed using various energies E8of the electrons in the ion source. The determination is made ∼20 μsec after formation of the ions so that only long-lived states remain in the beam, as is usual in beam experiments. The method consists of attenuating the ion beam in a gas-filled reaction chamber, where different states of the ions suffer different attenuations. Results have been obtained for O2+ and O+ ion beams. In each case only one excited state appears to be important: For O2+ the fraction f of this excited state was found to be 0.22, 0.30, and 0.33 for E8 values of 25 eV, 50 eV, and 100 eV, respectively. For O2+, f is 0.27 for E8 = 50 eV and 0.30 for E8 = 100 eV. The use of these results is illustrated by combining them with crossed-beam measurements of charge transfer to determine separately the cross sections for the ground state and the excited-state ions of O+ and O2+.
Microwave Spectrum, Conformation, Dipole Moment, and Barrier to Internal Rotation in Methyl Vinyl Ether
Authors: Cahill Patrick , Gold L. Peter , Owen Noel L.
Published: February 2004

The microwave spectrum of methyl vinyl ether, CH3OCH=CH2, has been studied in the frequency region 8 to 40 Gc/sec. Absorption lines have been assigned to a planar cis isomer, with a barrier to internal rotation of the methyl group of 3830 ± 100 cal/mole. The components of the dipole moment along the principal axes of inertia were measured and found to be μa = 0.294 D, μb = 0.915 D (μ total = 0.96 D). Spectra were observed of the excited methyl torsional state and of two additional excited vibrational states, corresponding, respectively, to vibrations at about 240, 205, and 327 cm−1. These findings are confirmed by far-infrared and Raman spectra.
Theory of Neutralization of an Isolated Ion Pair: Application of the Method of Prescribed Diffusion to Random Walk in a Coulomb Field
Authors: Mozumder A.
Published: February 2004

The problem of random walk of an ion pair in their mutual Coulomb field is formulated here in the framework of “prescribed diffusion.” The solution of this problem, when integrated over volume, gives the probability that the ion pair will remain unneutralized at a given time. In the limit t→∞, this probability calculated by the present method gives exactly the same expression as the Onsager formula. Half-life for neutralization is computed and its variation is studied with time, temperature and thermalization length. Case of an entire track is also discussed and possible application to neutralization of charges produced by ionizing radiations is indicated.
Low-Temperature Viscosity Cross Sections Measured in a Supersonic Argon Beam
Authors: Knuth E. L. , Fisher S. S.
Published: February 2004

An exact translational-relaxation equation is derived from the Boltzmann equation for the special case in which (a) the flow is spherically symmetric source flow, (b) the velocity distribution is ellipsoidal, and (c) the atoms are hard spheres. It is shown that, at least for small temperature differences, the appropriate cross section is the thermal-conductivity (or viscosity) transport cross section. This relaxation equation is used then to calculate values of argon cross sections from velocity distributions near the centerline of a free jet measured by molecular-beam techniques. These values (a) agree with the values obtained from viscosity measurements in the temperature range in which the two sets of data overlap, (b) continue to increase as the temperature decreases to about 25°K, and (c) decrease as the temperature decreases to about 10°K. The observed decrease in values as the temperature decreases from about 25°K was not expected and has not been explained.
Quantum-Mechanical Pair-Correlation Function of Hard Spheres
Authors: Larsen Sigurd Yves
Published: February 2004

The density-independent part of the quantum-mechanical direct and exchange pair-correlation functions for hard spheres has been calculated for λT / σ = 1.4, 2, 2.93761, 4, 6, 8, and 10. In addition, points were obtained very near the surface of the sphere for λT / σ = 0.025 and 0.05. The results delineate the approach of the direct (Boltzmann) correlation function to the classical limit and emphasize the rapid disappearance of the effects of statistics with increasing temperature. These features are explained using Wiener (path) integrals. Analytical expressions valid near the surface of the sphere are derived and compare well with numerical results. Virial coefficients obtained from the correlation functions are in satisfactory agreement with very precise value calculated by Boyd, Larsen, and Kilpatrick.
Theory of the Solvated Electron in Polar Liquids. I. Oriented Dipole Model
Authors: Iguchi Kaoru
Published: February 2004

A model is proposed for the solvated electron in polar liquids, in which molecular dipoles are assumed to orient spherically around the electron. The potential field due to this orientation, the energy levels, the absorption peak and its temperature dependence, and the heat of solvation are calculated at various temperatures. Calculated absorption peak E = 1.69 eV (300°K), 1.89 eV (180°K), and ∂ΔE / ∂T = 0.16 eV deg−1 are compared with experimental data, and they show a fairly good agreement.
Magnetothermodynamics of α–NiSO4·6H2O II. Heat Capacity, Entropy, Magnetic Moment, and Internal Energy, from 0.4 to 4.2°K, with Fields 0-90 kG Along the Bisector of the a, b Axes
Authors: Fisher R. A. , Brodale G. E. , Hornung E. W. , Giauque W. F.
Published: February 2004

The heat capacity and magnetic moment of a 4-cm-diam single crystal of α-NiSo4·6H2O have been measured with stabilized fields 0-90 kG along the bisector of the a, b axes. The temperature range was about 0.4 to 4.2°K. Magnetic saturation was not reached even at 0.4°K and 90 kG although there was no temperature coefficient of the magnetic moment below 0.7°K and any field. The heat capacity approached zero at the lower temperatures and all fields. Although idealized calculation indicates a nuclear-spin contribution to the heat capacity in a field of 90 kG between 0.4 and 1°K, there was no evidence that this component was in equilibrium with the lattice, such as was observed when the field was directed along the c axis. The rapid decrease of electronic heat capacity to zero near 1°K at 90 kG indicates that the electron system was unable to serve as a mechanism to bring the nuclear spins into equilibrium with the lattice at temperatures where the nuclear-spin heat capacity should have made a substantial contribution. With the assistance of temperature observations during adiabatic magnetization the entropy was evaluated over the experimental region. The entropy and its change with field, the isentropic change of temperature with field, the differential magnetic susceptibility, the internal energy, enthalpy, and magnetic work are tabulated.
Dissociative Electron Attachment to Molecules
Authors: Christophorou L. G. , Stockdale J. A. D.
Published: February 2004

Dissociative-electron-attachment cross sections (some unpublished) for 30 molecules are summarized, evaluated, and discussed within the framework of the resonance scattering theory. The dissociative-attachment peak cross section, σc(εmax), is found to be a strong function of the peak (resonance) energy, εmax, with a break in this dependence at the energy where electronic excitation of the neutral molecule begins to occur. Based on the experimental data, three groups of molecules have been distinguished: (i) those where εmax is less than the energy, εN, of known electronic excited states of the neutral molecule, and the negative-ion state is purely repulsive in the Franck-Condon region, (ii) those where εmax ≥ εN, and (iii) those with exceptionally small σc(εmax) for which a vertical onset for dissociative attachment occurs. For the molecules in group (i) σc(εmax) varies almost as (εmax)−1, while for group (ii) σc(εmax) is a much stronger decreasing function of the resonance energy εmax. For group (i) the effect of autoionization on σc(εmax) is small, and isotopic effects on σc(εmax) are contained within the square root of the inverse ratio of the reduced masses of the products. For group (ii) and especially group (iii) the effect of autoionization on σc(εmax) is large and so are the isotopic effects on σc(εmax).
Extension of the CN Red and Violet Band Systems
Authors: LeBlanc F. J.
Published: February 2004

The wavelengths and intensity distributions for the red (A 2Π→X 2Σ) and violet (B 2Σ→X 2Σ) bands which were observed in a mixture of active nitrogen and CH4 are given. Bands which originate in the A 2Π and B 2Σ states with excitation energies in the range 4.5-6 eV are well developed. The wavelength range studied was 3000-6700 Å. About 20 of the violet bands and 30 of the red bands have not been reported previously.
Atomic Integrals Containing r23λ r31μ r12v
Authors: Perkins J. F.
Published: February 2004

S states of atoms may be calculated to high precision by means of expansions containing correlation factors of the form rijν. Resulting integrals may be expressed as sums of auxiliary functions which are evaluated by algebraic methods. Explicit expressions, suitable for computer programing, are given for such integrals for three-electron atoms; these include integrals containing correlation factors with linked indices, r23λ r31μ r12ν, with any set of (integral) values λ, μ, ν. Expressions are based on an expansion of rijν in terms of Legendre polynomials in cosθij; coefficients of this expansion are represented by a conveniently evaluated formula and some numerical values are given. The expressions given here have been found quite convenient in preliminary calculations of lithium ground state.
Studies of IBr, ICl, and I2Cl6 Crystal Properties by Means of the Mössbauer Effect in 129I. I. Chemical Bonds
Authors: Pasternak M. , Sonnino T.
Published: February 2004

Using 129I as Mössbauer nucleus, the properties of ICl, IBr, and I2Cl6, as well as I2Cl4Br2, were investigated. From the well-resolved spectra of the quadrupole splitting, the e2qQ, the η parameter, and the isomer shift with respect to the standard 66Zn129Te source are derived. These data are used to deduce the 5p electron population of I. On the basis of the sensitivity of the isomer shift to the s character of the bond, it is shown that no sp hybridization occurs. The linear dependence of the isomer shift on the p holes is found to extend to hp values higher than 1. A relationship is derived to include hs as well as hp when iodine is in a high valence state.
Ca(OH)2 and Ca(OD)2 Vibrational Crystal Spectra, Normal Coordinate Analysis, and Assignment
Authors: Oehler O. , Günthard Hs. H.
Published: February 2004

In this paper further experimental studies of the vibrational spectra of Ca(OH)2 and its deutero-modification are reported. Furthermore, a normal coordinate analysis of the crystal spectrum in harmonic approximation is given, based on a method for construction of symmetry coordinates and factorization of the eigenvalue problem given in a preceding paper. Numerical calculation of a considerable part of the dispersion surface is included, using force constants derived from a lattice model with Coulomb and repulsive forces. An assignment of the infrared spectrum is given. In particular the OH-stretching region is discussed in terms of transitions between critical points of the dispersion surface.