bluuebunny/crossref_metadata_2025 huggingface dataset:
New Theoretical Method for the Accurate Calculation of Expectation Values on Functions of Internuclear Separation in 1Σ-State Diatomic Molecules
Authors: Herman R. M. , Short S.
Published: February 2004

A new theoretical method for the calculation of expectation values on 1Σ-state diatomic molecular vibration-rotation states is developed. Using Dunham's theory of vibration-rotation energies, each integral can be expressed as a rapidly converging series of terms, each of which is given to high accuracy as an analytical function of the internuclear potential parameters. Results are presented which allow the rapid calculation of expectation values on any arbitrarily specified algebraic function of intermolecular separation, complete to four orders in the ratio of the rotational to vibrational constant of the molecule. We first apply the method to review and extend the theoretical calculation of rotational energies in H2. In these calculations, agreement with experiment to within the combined limits of accuracy is achieved, the value 60.837 cm−1 resulting for Dunham's rotational constant, Y01. As a further example, the expectation value on the υ = 0, J = 1 state of the inverse third power of the internuclear separation in H2 is calculated using theoretical potential constants on the one hand, and potential constants derived from spectroscopic measurements on the other. The greatest accuracy is achieved with the latter, the value 〈01 | R−3 | 01〉−1 / 3 = (0.74695 ± 0.00003) Å showing good agreement with the experimental value and a value obtained from direct numerical calculation by Wolniewicz.
Scattering of Thermal Neutrons by Liquid Solutions of Ortho- and Paradeuterium
Authors: Talhouk S. J. , Harris P. M. , White David , Erickson R. A.
Published: February 2004

The structures of two samples of liquid deuterium, one enriched in paradeuterium (85% para-D2) and the other enriched in orthodeuterium (the 20°K equilibrium concentration 96.9% ortho-D2), have been investigated by diffraction of 1-Å neutrons. The scattering data have been interpreted both as an assemblage of atom scatterers and, somewhat more exactly, as molecular scatterers. Fourier inversion of the intermolecular scattering yields a radial distribution interpretable for both samples as exhibiting approximately 10.3 nearest-neighbor molecules (cf. 12 for close packing of spheres). In the case of the converted sample (96.9% J = 0, nonrotating D2) the nearest-neighbor molecules are at a mean distance of 3.85 Å from the reference molecule; in the enriched sample (85% J = 1) the nearest-neighbor distance is 3.72 Å corresponding to a smaller molar volume attributable to the angular anisotropy of the intermolecular interactions when the rotations are hindered. Small-angle scattering also indicates a higher compressibility for the 96.9% para-D2 (J = 0) sample.
Collisional Energy Transfer in Thermal Unimolecular Systems. Dilution Effects and Falloff Region
Authors: Tardy D. C. , Rabinovitch B. S.
Published: February 2004

To assess further the operational meaning of efficiency, collisional activation-deactivation efficiencies β for thermal unimolecular reactions in the falloff region have been computed on a stochastic model with use of an iteration procedure. Stepladder and exponential collisional transition probability models were used; detailed balance and completeness were obeyed. Computations were made for the methyl isocyanide, nitryl chloride, and cyclopropane systems for which accurate values of the microscopic specific rate probabilities kE were also obtained. For a particular collisional model, the efficiency was calculated as a function of the average step size, temperature, the order of reaction, and the dilution of substrate by heat bath molecules. For the conventional definition of efficiency, β decreases as the pressure increases. The quasiuniversal efficiency-step-size relations found earlier in the second-order region have been extended. Correlations with several systems studied in the falloff are made. The nature of the dilution effect on β noted previously for the low-pressure regime [D. C. Tardy and B. S. Rabinovitch, J. Chem. Phys. 45, 3720(1966)] is further amplified, and examined in the falloff region. The resolution of β into population and transition probability factors is also extended. The comparative behavior of the Poisson and exponential factors relative to the stepladder values, when various amounts of energy are transferred on the average, is illustrated. Experimental β values in the low-pressure region for the nitryl chloride and methyl isocyanide systems are correlated with conclusions derived from the calculations.
Photolysis of Liquid Cyclohexane and Cyclohexane Solutions in the Vacuum Ultraviolet
Authors: Yang John Y. , Servedio Frank M. , Holroyd Richard A.
Published: February 2004

Liquid cyclohexane and cyclohexane solutions were photolyzed at 1236 and 1470 Å. The products and quantum yields for cyclohexane photolysis at 1470 Å are hydrogen (1.0), cyclohexene (0.94), dicyclohexyl (0.06), ethylene (0.003) and butadiene (0.001). Products and relative yields at 1236 Å are hydrogen (1.0), cyclohexene (0.93), dicyclohexyl (0.05), ethylene (0.06) and butadiene (0.02). The addition of benzene or cyclohexene as solutes caused drastic reductions in the rate of cyclohexane decomposition. A significant fraction of the decreases in the product yields is attributed to the scavenging of hydrogen atoms by the solute. The ratio of the rate constant for hydrogen atom addition to benzene to that of hydrogen abstraction from cyclohexane is about 300. Neutral excited cyclohexane molecules are found to be important intermediates, and the major effects of benzene and cyclohexene as solutes are accounted for by quenching of these excited species. The rate-constant ratio for energy transfer to the solute and dissociation of the excited intermediate is about 3.2 liter/mole.
Theoretical Study of the Rotational Barriers of Allene, Ethylene, and Related Systems
Authors: Buenker Robert J.
Published: February 2004

The allene and ethylene rotational potential surfaces are investigated by means of ab initio SCF MO calculations employing a basis set of Gaussian group orbitals. It is pointed out that the MO's of both systems can be divided into two categories, σ or π, according to the behavior of their component carbon AO's upon rotation about the C–C bonds. A general qualitative theory capable of dealing with the barriers of allene and ethylene and related systems in the same terms is thus developed on the basis of two observations: First, that the π MO's in both allene and ethylene are essentially unchanged by hydrogen rotation and secondly, that there is a one-to-one correspondence between each of the four most stable π MO'x of the two molecules. Subsequently it is shown that the barrier description of both systems is significantly altered upon the introduction of CI techniques to the quantitative calculations and consequently the qualitative theory, based strictly upon consideration of the closed shell SCF wavefunctions, can be improved in a simple manner to take account of the modifications of the rotational potential surfaces dictated by configuration interaction. Finally, the resulting integrated theory is applied to the discussion of other geometrical phenomena in AnH4 systems and also to the study of related trends in molecules containing a different number of hydrogen atoms, such as acetylene, hydrogen peroxide, and ethane.
Alternative Explanation of Metal Orbital Energy Orders in Coordination Compounds with Strong Ligand-Ligand Interactions
Authors: Schmidtke Hans-Herbert
Published: February 2004

The relative order of d orbital energies in symmetrical molecules is determined in the case of highly interacting ligand-ligand orbitals. For most symmetries this sequence turns out to be the same as obtained from crystal-field or molecular-orbital theory. The method starts from the order of ligand orbitals gained by topological considerations. The central metal-ligand interaction is then treated by a perturbation in which the variation of Ed − Ex (energies for metal d and ligand x orbitals) is considered as the predominant factor.
Infrared Spectrum of Dichlorocarbene in Solid Argon
Authors: Andrews Lester
Published: February 2004

The matrix reaction of lithium atoms and carbon tetrachloride produces the CCl3 radical followed by secondary reaction of Li with CCl3 to yield a sufficient concentration of dichlorocarbene for infrared spectral study. Natural chlorine isotopes, carbon-13 and bromine substitution, and loss of CCl2 absorptions accompanied by growth of C2Cl4 absorptions on sample warming furnish convincing evidence that dichorocarbene is isolated in the argon matrix. Assignments of the C-Cl stretching vibrations for the 12C35Cl2, 12C35Cl37Cl, 13C35Cl2, and 12C35Cl37Cl species are supported by normal coordinate calculations. For the most abundant isotopic species, ν1 = 719.5 and ν3 = 745.7 cm−1, and ν2, the weak bending mode, was not detected. The stretching force constants Fτ = 2.86 mdyn / Å and Fττ = 0.27 mdyn / Å indicate that C-Cl single bonds are present in dichlorocarbene, making it unlikely that the electron deficiency of the carbon atom is relieved by pi bonding with chlorine.
Method of Diatomics-in-Molecules. VII. Excited Singlet States of H3+
Authors: Wu Ay-Ju A. , Ellison Frank O.
Published: February 2004

Diatomics-in-molecules theory is applied to the excited singlet-state functions of H3+ which are anti-symmetric to the molecular plane. If one uses only 1s and 2p AO's, it is possible to construct six covalent singlet valence-bond wavefunctions of this type, and this set reduces to A21″ + 1 A1″ + 21 E″ for equilateral triangles, 31 A2 + 31 B1 for isosceles triangles, or one component of each of 3 1Πg + 3 1Πu for linear symmetrical H3+. Potential-energy surfaces for all states have been computed. None of the states appear to be stable or metastable. For the lowest energy  A21″ state for equilateral H3+, the diatomics-in-molecules results agree with a previous extensive ab initio calculation by Conroy within 7 kcal.
Charge Transfer and Proton Transfer in Polyatomic Ion-Molecule Systems
Authors: Leventhal J. J. , Friedman L.
Published: February 2004

Ion impact mass spectra of some hydrocarbon molecules have been investigated using mass analyzed beams of H+, D+, H2+, D2+,H3+, D3+, ArH+, ArD+, Ar+ and Ne+ ions. Charge-transfer and proton- or deuteron-transfer mechanisms suffice to account qualitatively for the observed spectra. The energetics of the respective processes in the systems studied provide a basis for assigning various ion fragments and parent molecule ions to either charge-transfer or ion-molecule reaction formation mechanisms. The role of the neutral molecule as an energy sink in molecular charge transfer has been examined in detail for H2+ charge-transfer reactions. The distribution of recombination energies experimentally observed in H2+ collisions with a variety of molecular species is rationalized with the aid of a model that considers the neutralization reaction as a Franck-Condon process. Estimates are made of the distribution of excited neutral product H2 molecules from the squares of the overlaps of H2+−H2 vibrational wavefunctions. This model also accounts for relatively low cross sections for H3+ ion-impact reactions because of the production of vibrationally excited H2 which renders some processes endothermic. The necessity of formation of vibrationally excited neutral molecular products in ion-molecule reactions that proceed via stripping mechanisms accounts for energy barriers not predicted from usual thermochemical considerations. Cyclopropane and propylene spectra were the subject of extensive study. With ArH+ projectile ions the velocity dependence of the component of ion-impact spectra attributed to ion-molecule reactions was found to be in good agreement with the 1 / υ dependence of Langevin collision cross sections, and the magnitude of experimental cross sections were found in good agreement with those calculated from simple classical theory. Significant differences were observed in the ion-impact spectra of cyclopropane and propylene. The ion-molecule reaction component was attributed primarily to proton- or deuteron-transfer reactions which initially produce excited C3H7+ ions. Processes which superficially appeared to be hydride ion-transfer processes were plausibly explained as the loss of H2 from excited C3H7+, and this argument was supported by the isotopic exchange observed with deuterium-substituted projectile ions. Studies on hydrocarbons up to and including neopentane showed further consistency with predictions made for ion-molecule reaction cross sections based on the Langevin model.
Boron Trifluoride: The Analysis of ν2 and the Determination of the Molecular Geometry
Authors: Ginn S. G. W. , Kenney J. K. , Overend John
Published: February 2004

The parallel band ν2 of 10BF3 has been remeasured with a resolution of about 0.03 cm−1 and new values of the rotational constants have been determined. The values of B0 = 0.34474 ± 0.0005 (10BF3) and B0 = 0.34505 ± 0.0005 cm−1 (11BF3) are consistent with the geometry obtained in the electron-diffraction experiments of Kuchitsu and Konaka, but differ appreciably from the values previously reported by Nielsen. From our results we obtain r0 = 1.3096 ± 0.001 Å (10BF3), re = 1.3090 ± 0.001 Å (11BF3), and r0 = 1.3072 ± 0.002 Å (10BF3). From the analysis of the hot bands we have determined values of (B′ − B″) for ν4 and some of the anharmonic constants xss′.
Matrix-Isolation Study of the Hydrogen Cyanide Dimer
Authors: King Charles M. , Nixon Eugene R.
Published: February 2004

On the basis of the infrared spectra of HCN and DCN in Ar, N2, and CO matrices at temperatures from 4.5° to 20.5°K, it is concluded that there is no evidence for rotation of the monomeric species in these matrices and that the dimer has a linear or nearly linear HCN·HCN structure. The Lippincott-type potential is used to calculate frequencies for the stretching of the hydrogen bond and for the torsion about the hydrogen bond. These calculated frequencies are compared with our observed far-infrared spectra of dimers in the matrix and with available Raman data on crystalline HCN and DCN.
NMR Studies of Diffusion in Glassy and Crystalline Lithium Borates
Authors: Bishop S. G. , Bray P. J.
Published: February 2004

The 7Li NMR spectra from several lithium borate glasses have been examined as a function of temperature and found to narrow abruptly with increasing temperature in the range of temperatures from 250° to 475°K. The observed narrowing is a manifestation of the phenomenon of motional narrowing, and is attributed to diffusion of the lithium ions in the glasses. Activation energies for this diffusion, as deduced from the temperature dependence of the 7Li NMR linewidths, range from 0.22 eV in a glass containing 28.6 molar % Li2O to 0.12 eV in a 60 molar % Li2O glass. The 7B NMR lines from these glasses are reduced somewhat with increasing temperature because of the removal of the lithium-boron dipolar interaction with the onset of the lithium diffusion. The linewidths of the 7Li spectra from the crystalline lithium borates also decrease with increasing temperatures and the activation energies obtained from their narrowing rates range from 0.14 eV in the Li2O·4B2O3 compound to 0.43 eV in the 3Li2O·2B2O3; compound. It has been concluded that the ionic movement responsible for the narrowing of the resonance spectra is motion within limited regions, rather than the movement over long distances necessary for electrical conductivity.
Proton Affinities of H2S and H2O
Authors: Beauchamp J. L. , Buttrill S. E.
Published: February 2004

Ion cyclotron single- and multiple-resonance spectroscopy have been used to identify and examine the energetics of ion-molecule reactions in which H3O+ and H3S+ are involved either as product or reactant. The reactions observed provide narrow limits for the gas-phase proton affinities of these species, giving 164 ± 4 kcal/mole for H2O and 178 ± 2 kcal/mole for H2S.
Vibrational Relaxation of Anharmonic Oscillators with Exchange-Dominated Collisions
Authors: Treanor C. E. , Rich J. W. , Rehm R. G.
Published: February 2004

The terms in the master equation for vibrational relaxation of anharmonic oscillators are ordered according to the rates of the relaxation processes (vibrational exchange, vibrational-energy transfer to translation). The population distributions in the master equation are expanded about their values when the vibration-vibration mechanism is the only one present. An analytic expression is given for the distribution maintained by the vibration-vibration mechanism. In the limiting case of the simple harmonic oscillator, this distribution reduces to the usual Boltzmann-like distribution defined by a single vibrational temperature. The general solution also applies to a mixture of simple-harmonic-oscillator gases of different fundamental frequencies. For such a mixture, each gas relaxes in a Boltzmann-like distribution, but the different gases have different (but related) vibrational temperatures at any given time. The relaxation of the first moment of the distribution function also has been investigated. Anharmonicity causes a marked departure from the Landau-Teller model of vibrational relaxation under conditions of high vibrational energy, coupled with low translational temperature. For such conditions, the populations of the lower vibrational states can be considerably lower than those predicted by the Landau-Teller model. Furthermore, the over-all energy relaxation rate can be accelerated.
Statistical Study of Nonstationary Polymerization
Authors: Nanda V. S. , Jain R. K.
Published: February 2004

We employ the continuum approach in order to study the statistical character of the polymer resulting from a nonstationary polymerization with a first-order termination process. Some authors have carried out theoretical investigations in connection with this problem by imposing conditions either on the monomer consumption or on the occurrence and nature of chain transfer. We deduce here the size distribution expression for the general case when spontaneous transfer and transfer through the monomer are simultaneously operative while the conversion is not limited to low values. The expressions for averages can be formally obtained from this result. Beyond the first average, however, the general expression gets too involved for convenient analysis. We investigate separately the effect of the two types of transfer on the size distribution and the averages in some typical cases. In the inhomogeneity versus conversion curves characteristic minima appear when only spontaneous transfer is operative, while the decrease is monotonic when transfer through the monomer alone is present. Finally, we compare the theoretical results for cumulative weight fraction with the experimental results of Pepper's group on the polymerization of styrene with strong sulphuric acid.
Neutron-Diffraction Refinement of the Crystal Structure of Barium Chlorate Monohydrate Ba(ClO3)2·H2O
Authors: Sikka S. K. , Momin S. N. , Rajagopal H. , Chidambaram R.
Published: February 2004

A single-crystal neutron-diffraction study has been made to determine the shape and coordination of the water molecule in Ba(ClO3)2·H2O. The intensities of 557 neutron reflections—partial three-dimensional data with sinθ / λ≤0.80—have been measured, and the structure has been refined to an R factor of 0.080. Although the earlier x-ray structure is basically correct, there are significant differences in the two sets of structural parameters. The structure contains Oω–H···O(2) hydrogen bonds of length 2.891 ± 0.014 Å, in which the Oω–H distance is 0.958 ± 0.011 Å (corrected for thermal motion) and the angle Oω–H···O(2) is 163.6 ± 0.9°. The orientations of the interproton vectors found in the present study agree with those determined by the proton magnetic resonance method to within 2.5°.
Statistical-Mechanical Theory of Polymers. I. An Integral Equation for the Excluded-Volume Effect
Authors: Naghizadeh Jamshid
Published: February 2004

Statistical mechanics of a single polymer in a continuous medium is considered. Partition function, the reduced distribution functions, and related statistical concepts are defined. Thermodynamic functions of the system are calculated in terms of the distribution functions. Finally, a Kirkwood-Born-Green integrodifferential equation is derived for the excluded-volume effect, and its approximate solution for the case of a ring polymer is given. The results show that the zeroth-order approximate solution of the integral equation is equivalent to the self-consistent approximation of Edwards and of Reiss. The mean-square radius of gyration in this approximation varies as 43 power of the molecular weight.
Fluorine and Proton NMR Study of Gaseous Hydrogen Fluoride
Authors: Hindermann David K. , Cornwell C. D.
Published: February 2004

The 19F and 1H resonances for gaseous hydrogen fluoride were measured over the range from low pressure to saturated vapor. In each spectrum, only a single line is observed, which shows an unusually large and monotonic change in chemical shift with HF density. The monomer chemical shifts were determined by extrapolation, to zero total pressure, of data for mixtures with various foreign gases. The 19F chemical shifts, in parts per million relative to SiF4 gas at zero pressure, are HF (g, monomer): 46.85 ± 0.35 ppm, DF(g, monomer): 49.35 ± 0.35 ppm, HF (liq, cylinder): 25.53 ± 0.04 ppm. The 1H shifts relative to CH4 gas at zero pressure are HF(g, monomer): − 2.10 ± 0.20 ppm, HF (liq, cylinder): − 8.67 ± 0.02 ppm. These data are for 34°C, but the extrapolated monomer shifts appear to be practically independent of temperature. The absence of spin-spin splittings, and the observation of only a single averaged resonance in HF-DF mixtures, proves that there are rapid monomer-breaking exchange processes in the vapor. This is evidence for the presence of a ring polymer.
Correlation of Electrons Within the Hydride Ion
Authors: Banyard K. E.
Published: February 2004

The hydride ion is one of the simplest systems possessing electrons with antiparallel spins and, therefore, it is ideal for a study of electron correlation. Five wavefunctions for H− have been analysed and compared. Two functions were based on the single determinant independent-particle model and three were correlated wavefunctions. The present article is devoted, in the main, to a discussion of radial correlation, hence, graphs are presented for the two-particle density ρ(r1, r2) and the radial density D(r) for each treatment. Values are determined for the coherent x-ray scattering contribution f00(X), the three-dimensional Dirac delta functions 〈δ3(r1)〉 and 〈δ3(r12)〉, and also for 〈rn〉 when −2 ≤ n ≤ 4. In this way, the effect of electron correlation on various physical properties could be examined. In particular, by comparing the results with those obtained from a more accurate wavefunction, it was possible to assess the usefulness of a limited configuration-interaction treatment which employed `floating' orbitals. On the whole, this treatment of H− proved to be good. Finally, it was observed that the inclusion of electron correlation effects within a wavefunction for H− causes the electron density to become more diffuse, the inner regions around the nucleus resembling, fairly closely, the density within an isolated hydrogen atom.
Assignment of the Second Singlet in Carbonyl
Authors: Johnson W. Curtis , Simpson William T.
Published: February 2004

Marked increases in extinction going from crystalline to melted samples are observed for the electronic absorption at ∼1850 Å (second singlet) in various appropriately selected aliphatic ketones. These changes probably indicate that the transition moment in the crystal is perpendicular to the plane of incidence. Taken together with the crystal geometry this leads to assignment of the second singlet as n→σCO*. The polarized spectrum of 9-heptadecanone is extended from 56 to 65 kK and extinction coefficients are included. A dichroic ratio anomaly observed in the polarized spectrum is interpreted as involving different amounts of hypo- (hyper-) chromism for parallel and perpendicular polarization directions.
Nuclear Magnetic Double Resonance: Systems of Two- and Three-Spin 12 Nuclei
Authors: Wakefield R. H. , Memory J. D.
Published: February 2004

Nuclear magnetic double resonance measurements have been made on the AB proton spin system in dehydro-α-lapacone and the ABX proton spin system in dipotassium malate, in conjunction with density matrix calculations using the Baldeschwieler formalism. The principal relaxation mechanisms were RFC (correlated random field) for the AB system and RFUC (uncorrelated field) for the ABX system, and relative signs of all coupling constants were found in the ABX case.
Raman Spectrum of Strontium Titanate
Authors: Nilsen W. G. , Skinner J. G.
Published: February 2004

The Raman spectrum of single-crystal SrTiO3 has been investigated as a function of temperature down to about 25°K. The lattice dynamics of this crystal have been extensively studied in recent years primarily because of its unusual dielectric and acoustic properties. Both nominally pure and impure samples were examined since these properties seem to be sensitive to small amounts of impurities. An argon-ion laser served as the exciting source and an in-tandem grating spectrometer was used to disperse the scattered light. These instrumental techniques provided rather complete data including the polarization characteristics of the individual lines and peaks. The above data, together with the known phonon dispersion curves of SrTiO3, made it possible to obtain a reliable interpretation of the Raman spectrum. At room temperature we find the Raman spectrum to be entirely second order, in agreement with the selection rules for the cubic perovskite structure. Further, the phonons contributing to the second-order scattering have wave vectors at or near the Brillouin zone boundary and are for the most part transverse polarized. The same combinations and overtones tend to give intense peaks in both SrTiO3 and KTaO3, but the different dispersions of the phonon branches in the two crystals make their spectra appear different. On cooling nominally pure SrTiO3 below the phase transition at 110°K, three sharp lines appear in the spectrum which are due to scattering from local modes rather than from the polar transverse-optic modes. The energy shifts measured for these three sharp lines do not agree with those for the polar TO modes. In the impure sample at low temperature (15°K) scattering from local modes and the polar transverse-optic modes are observed simultaneously. Measurements on the impure sample at 78°K yield scattering from the three polar transverse-optic modes but not from the local modes. These results illustrate the great sensitivity of Raman scattering to crystal structure and show that pure and impure SrTiO3 undergo different phase transitions as the temperature is reduced. Since no ferroelectricity or first-order Raman scattering is found in the tetragonal phase of pure SrTiO3, the point group of this phase is most probably C4hor D4h. If the impure sample is tetragonal at 78°K, as is likely the case, then the Raman measurements show the point group to be S4, C4, or C4V. At lower temperatures the crystal structure is undoubtedly of lower symmetry than tetragonal.
Collision of an Atom and a Diatomic. The Distorted Wave Expansion
Authors: Thiele Everett , Weare John
Published: February 2004

Higher-order terms are considered in Mott and Jackson's distorted wave treatment of the atom-diatomic collision problem. In addition to the physically realistic requirement of a soft interaction, it is shown that the expansion is best for light incident atom with low kinetic energy. It is also shown that for an n-quantum transition, it is necessary to go to at least the nth order in the expansion in order to obtain a reasonably accurate result. A simple second-order formula is given for two-quantum transitions. Numerical evaluation of the second- and third-order terms has been carried out for a number of transitions and the results compared with Secrest and Johnson's exact values. A rearrangement of the distorted wave expansion for one-quantum transitions which leads to a wider range of applicability is presented.
Nonradiative Energy Transfer in Systems in which Rotatory Brownian Motion is Frozen
Authors: Steinberg Izchak Z.
Published: February 2004

The effect of the complete restriction of rotatory Brownian motion of donor and acceptor molecules on the extent of nonradiative energy transfer in systems containing many donors and acceptors has been investigated. It is assumed that the molecules under discussion are randomly distributed and randomly oriented in space at the moment of excitation. The number of donor molecules which retain their excitation energy at time t after excitation is found to decrease exponentially with the sum of two terms: one proportional to t and the other proportional to t1 / 2. This time dependence is similar in form to that found by Förster for systems in which donor and acceptor molecules undergo rapid rotatory diffusion. While the coefficient of −t in the exponent is the same in both cases, the coefficient of −t1 / 2 is smaller for systems in which molecular rotation is frozen than for systems in which rotatory Brownian motion is rapid.
Transport Properties of Polar Gas Mixtures. II. Heat Conductivities of Ammonia-Methylamine Mixtures
Authors: Gutweiler J. , Raw C. J. G.
Published: February 2004

The thermal conductivities of ammonia, methylamine and binary mixtures of these polar gases have been measured in the temperature range 66° − 258°C, using a “potential-leads” hot-wire apparatus. For the pure gases, the Mason-Monchick theory is found to give reasonably good agreement with experiment when the average rotational collision number in the temperature range is treated as a disposable parameter. For the mixtures, good agreement is obtained between the experimental data and the values calculated from the Hirshfelder-Eucken formula, provided that the pure component heat conductivities are replaced by the corresponding experimental values.
Field-Electron-Microscopy Studies of Cesium Layers on Various Refractory Metals: Work Function Change
Authors: Swanson L. W. , Strayer R. W.
Published: February 2004

The variation of work function φ with Cs coverage θ is investigated for W, Mo, Re, and Ni substrates. Single-crystal-face studies of the φ(θ) relationship performed on the (100) and (110) planes of W show a greater affinity of the (110) plane for mobilely adsorbed Cs at low values of θ. Coverage anisotropies are reduced as θ→1. An empirical relationship between the maximum work function change Δφm and substrate work function φs, and adsorbate ionization potential Ia, of the form Δφm = k1(k2Ia − φs), is established. The constants k1 and k2 are independent of the substrate and adsorbate for periodic Group Ia and IIa. Measurement of the temperature variation of the work function for Cs-coated Mo and W substrates show a negative temperature coefficient of ∼ − 1 × 10−4 eV/deg in the temperature interval 77° − 270°K. The average values of the adsorbate polarizability measured for the (110) and (100) planes of W are 23 ± 2 and 13 ± 0.2 Å3, respectively. The presence of oxygen coadsorbed with Cs on W greatly alters the emission distribution and reduces the minimum work function φm from 1.52 to 1.10 eV; also, the Cs coverage at which φm occurs is decreased from 1.9 to 0.9 × 1014 atoms/cm2.
Dipole Spectrum of Lithium
Authors: Stacey G. M. , Dalgarno A.
Published: February 2004

Variational methods based upon a multiconfiguration representation of the lithium eigenfunction are used to calculate a model dipole spectrum of lithium. From the model spectrum, values are obtained of the refractive index of lithium at wavelengths longer than 6600 Å, the mean excitation energy controlling the absorption of fast particles, and the van der Waals interactions of lithium with various gases.
Absolute Transition Probabilities in Ultraviolet Molecular Spectra
Authors: Hesser James E.
Published: February 2004

The radiative lifetimes of seventeen excited states in H2, N2, N2+, CO, CO+, NO, NO+, BF, CF, BCl, and CO2+ have been measured by the phase-shift technique of Lawrence. The measured lifetimes were derived from transitions in the 960-4500-Å region and range from 0.6 nsec in H2 to 118 nsec in CO2+. Particular attention has been paid to the understanding and elimination of possible sources of systematic errors in the absolute phase shift measurements. The lifetimes have been combined with measured and calculated emission intensities to derive electric dipole transition moments and absorption oscillator strengths for the diatomic band systems.
Temperature Dependence of Paramagnetic Relaxation of Mo5+ in TiO2
Authors: Chang Tetse , Yang George C.
Published: February 2004

The relaxation rate of Mo5+ in TiO2 was measured by the measurement of linewidth at temperatures between 77°K and 240°K, and by the saturation and recovery method at temperatures at and below 4.2°K. The linewidth is about 300 G at 240°K, and 0.5 G at 77°K. The relaxation time is about 5 sec at 4.2°K and about 100 min at 1.05°K. The temperature dependence of the relaxation rate is T9 between 3° and 200°K, T5 between 1.5° and 3°K, and T below 1.5°K. At the linear dependence region, i.e., ∼1°K, the magnetic field dependence is H4 as verified by experiments.
Trap–Trap Triplet Energy Transfer in Isotopic Mixed Benzene Crystals
Authors: Colson S. D. , Robinson G. W.
Published: February 2004

The phosphorescence and fluorescence spectra of three-component isotopic mixed benzene crystals, containing two different guests in a C6D6 host crystal, are studied as a function of guest concentration, excitation lamp intensity, and temperature. The energy relaxation processes in these systems are discussed, and it is established that few, if any, host-triplet excitons are produced during the interconversion of “trapped” singlet excitation into “trapped” triplet excitation. Triplet–triplet excitation transfer from one guest (trap) to a lower-energy guest (supertrap) is observed at temperatures where the host–guest ΔE is greater than 30KT. The concentration dependence of the trap–supertrap triplet energy transfer is interpreted in terms of a Perrin model and indicates that the energy can be transferred over no more than ∼20 Å in this system. At high lamp intensities, the phosphorescence intensity is found to depend upon the square root of lamp intensity. This is discussed in terms of excitation-annihilation models. Evidence is also presented for the photogeneration of impurities at these high lamp intensities.
Composition Dependence of the Thermal-Diffusion Factors in He–CO2, Ne–CO2, and Xe–CO2 Mixtures
Authors: Batabyal A. K. , Barua A. K.
Published: February 2004

The composition dependence of the thermal-diffusion factor in mixtures of carbon dioxide with helium, neon, and xenon has been studied with the help of an all-glass eight-tube trennschaukel or swing separator. In the case of He–CO2 and Ne–CO2 mixtures, α is found to increase with increasing concentration of the lighter component while in the Xe–CO2 mixture, α plotted against CO2, reaches a maximum value near 40% CO2 and falls off to a minimum value near 70% concentration of CO2. The theoretical composition-dependence curves calculated on the Lennard-Jones (12:6) model are found to reproduce qualitatively the shape of the experimental curves for the He–CO2 and Ne–CO2 systems.
Evidence of a Glass–Liquid Transition in a Gold–Germanium–Silicon Alloy
Authors: Chen H. S. , Turnbull D.
Published: February 2004

Gold-rich (73–81 at.% Au) alloys of gold–germanium–silicon were “splat” cooled to an amorphous solid form. Thermal and rheological evidence of a glass-liquid transition in the Au0.77Ge0.136Si0.094 alloy is reported. The transition was manifested thermally by an abrupt rise of 5.5 cal/g-atom·°K in specific heat, Cp, as the alloy was heated from 285° to 297°K. Just above 297°K, Cp starts to fall with increasing T on a reasonable extrapolation of the high-temperature Cp–T relation of the liquid alloy. This thermal behavior could be repeated on the same sample after it had been carried through the transition and chilled again. The apparent glass-transition temperature was increased by 1°–3° by increasing the heating rate by a factor of 16. The viscosity η of the amorphous alloy increases rapidly with falling temperature from 0.9 × 109 P at 305°K to 1.4 × 1013 P at 285°K and is described by the equation: η = 0.52 exp [136 / (T − 241.3)] P. The steady isothermal viscosity is independent of stress over the range 3–140 kg/cm2. Our finding that abrupt temperature changes in the high-viscosity regime shifts η rather little initially indicates that η depends primarily on configuration rather than temperature per se. We have also measured the enthalpy and resistivity of the alloy in its various states.
Experiments on N2(A 3Σu+). III. Excitation of Hg
Authors: Young Robert A. , St. John Gilbert A.
Published: February 2004

The rate coefficients of the reaction N2(A 3Σu+) + Hg→N2(X 1Σ) + Hg(3P10) have been measured for υ′ = 0 and 1 as k(0) = 8 × 10−12cm3 / sec and k(1) = 9 × 10−12cm3 / sec. The total rate coefficient for de-excitation of N2(A 3Σu+) by Hg is 1.4 × 10−11 cm3/sec.
Decorated Lattice Model for Ternary Systems
Authors: Clark Ronald K. , Neece George A.
Published: February 2004

A decorated lattice model for two- and three-component liquid systems proposed by Widom and extended by Clark and Neece is used to discuss the phase behavior of ternary systems. The binodal curves with their associated plait points are investigated for several systems lying within the framework of the model. Some results on the degree of the binodal curve, the heat capacity, and the composition fluctuations in the vicinity of the plait point, as found by Widom and Clark, are shown to hold in general for all systems discussed.
Temperature Dependence of Chemiluminescent Reactions. II. Nitric Oxide Afterglow
Authors: Gross Rolf W. F. , Cohen Norman
Published: February 2004

Using the glow discharge shock tube developed in this laboratory, we measured the temperature and density dependence of the β, γ, and δ bands for the NO recombination afterglow. We also determined the absolute rate constants for each of the vibrational transitions of the three bands at room temperature. Our results for the total band intensities are Iβ = 3.09 × 10−34(T / 300)−1.40[N][O][N2] photons / cm3·sec, Iγ = 1.18 × 10−17(T / 300)−0.35[N][O] + 2.12 × 10−34(T / 300)−1.24[N][O][N2] photons / cm3·sec, Iδ = 6.75 × 10−18(T / 300)−0.35[N][O] photons / cm3·sec. The results are critically reviewed and compared with previous experiments in the final part of the paper.
Interaction of Anthracene and Biacetyl at Different Excitation Wavelengths
Authors: Dubois J. T. , Behrens H.
Published: February 2004

It has been observed that anthracene in degassed n-hexane interacts with biacetyl in the presence of visible light. The molecular data of disappearance, biacetyl to anthracene, is 1.14:1. By the use of appropriate filters it is shown that only light above 435 mμ is responsible for the interaction. Pure anthracene in n-hexane is not decomposed in the presence of oxygen, whereas it is rapidly decomposed in degassed solutions. A mechanism is suggested to explain the results involving singlet excited oxygen, singlet biacetyl, and triplet anthrancene.
Nuclear Quadrupole Resonance Studies of Charge-Transfer Complexes of Carbon Tetrabromide with Methyl-Substituted Benzenes and Pyridines
Authors: Gilson D. F. R. , O'Konski C. T.
Published: February 2004

The 81Br nuclear quadrupole resonance spectra have been examined for a series of complexes of CBr4 with methyl-substituted benzenes and pyridines. The p-xylene−CBr4 complex gives two lines as expected from the known structure, and the benzene–CBr4 spectrum is the same, with a lower splitting. The spectra of a number of other complexes of unknown structure do not correlate simply with these. Estimates of the direct crystal-field gradients due to the charge distribution in the aromatics suggest that the direct field gradient effects are much too low to account for observed shifts in quadrupole frequencies. The temperature dependencies of the resonances in the p-xylene and durene complexes have been studied. The p-xylene complex follows the Bayer equation, but the durene complex requires the inclusion of a temperature dependence of the torsional frequency. Both complexes show a fading of the resonances at about 50° below the melting points.
Selective Photochemistry of Bromine Using a Ruby Laser
Authors: Tiffany W. B.
Published: February 2004

Gas-phase photochemical addition of bromine to olefin molecules has been studied by inducing the reaction with monochromatic light near 6940 Å from a pulsed, tunable ruby laser. All previous photochemical reactions of bromine were induced with light at wavelengths shorter than 6800 Å, and were found to proceed by means of free radical chains. The Br atoms initiating these chains are produced by direct dissociation of Br2 molecules upon absorption of light in the continuum. The present investigation shows that free-radical chains are responsible for the reaction at 6940 Å, also. However, direct dissociation at this wavelength is found to be negligible, and the Br2 molecules are excited to individual bound levels 500 to 800 800 cm− 1 below the dissociation energy. Kinetic and isotopic evidence shows that the additional energy is furnished by subsequent collisions, so that about 1% of the excited Br2 molecules become dissociated and can initiate the reaction. The remaining excited Br2 molecules relax by collisions to the ground state at a rate somewhat higher than the gas–kinetic-collision rate.
Proton Second Moment of an Isolated Tunneling Methyl Group
Authors: Allen P. S.
Published: February 2004

In an attempt to find an explanation for the reduced proton second moments in methyl-bearing compounds at low temperatures, the rather simple model of an isolated methyl group has been considered. By taking account of the quantization of the molecular motion, an energy-level scheme is obtained for the nuclear spin system which is different from that obtained if the molecular motion is treated as a classical rotation. The intramolecular methyl contribution, M2, to the second moment of the proton spectrum is calculated from the energy-level scheme for various barrier heights, V3, at very low temperatures. For V3 ≲ 3 kcal mole− 1, M2 is one-quarter of its rigid-lattice value. However, as V3 increases from ∼3 kcal mole− 1, M2 does not increase monotonically to its rigid-lattice value. M2 decreases to about one-fifth of the rigid-lattice value in the region of 3.5 kcal mole− 1 before increasing to its full value for barriers, probably in the region of 5 kcal mole− 1. If the barriers are assumed to be temperature independent, it follows that if the energy-level scheme predicts a reduced M2 at helium temperatures, then it should stay reduced down to ∼10− 2 °K.
Neutron and X-Ray Diffraction Study of Ca3Al2(O4D4)3, a Garnetoid
Authors: Foreman Dennis W.
Published: February 2004

Deuterated hydrogrossular, Ca3Al2(O4D4)3, has been prepared in order to investigate, by neutron and x-ray diffraction, the isomorphic substitution of (O4H4)4− for (SiO4)4 −. A polycrystalline specimen yielded the cubic-cell edge, 12.5755 ± 0.0009 Å (28°C) and oxygen parameters x = 0.0303(3); y = 0.0547(4); z = 0.6430(3). Diffraction experiments show no phase change from 301° to 77°K, although deuterium atoms shift to more symmetrically located general positions at the lower temperature. Deuterium parameters are x = 0.149(1); y = 0.086(1); z = 0.792(1) at 301°K and 0.148(2); 0.087(2); and 0.798(2) at 77°K. The shortest O–D distance is 0.95 Å at 301°K and 0.94 Å at 77°K, indicating hydroxyl bonding.
Polymer Dynamics: Boson Representation of Gyration Radius
Authors: Stidham Howard D. , Fixman Marshall
Published: February 2004

The expansion parameter aR2 for the gyration radius of a linear polymer molecule exhibiting excluded-volume effects and dissolved in a theta solvent is approximated by the boson operator representation technique. The approximation scheme gives the known coefficient in the expansion of aR2 as a function of expansion parameter z exactly. Agreement of the approximate theory with a recently reported exact value for the coefficient of the term quadratic in z in this expansion is poor. Comparison with light-scattering results shows that the qualitative features of the experiment are accurately reproduced by the approximate theory for all values of z.
Statistical Mechanics of Hard-Particle Systems
Authors: Meeron Emmanuel , Siegert Arnold J. F.
Published: February 2004

The concept of the equivalence of a hard particle (depending on the number of dimensions: hard sphere, disk, or rod, with no attractive interaction) of diameter a in a system of hard particles, and a spherical cavity of radius at least a, is extended to define distribution functions, γn(r1, ···rn), for sets of n cavities in a hard-particle system. A new theorem, relating the excess chemical potential of a hard-particle system to the distribution function of two cavities at zero separation, γ2(r12)|τ12–0, as well as corresponding theorems for higher-order distributions, are derived. The theorems for γ2(r12) and γ3(r1, r2, r3), and some simple physical arguments are used to obtain an approximation to the exact Born–Green–Yvon equation for γ2(r12), the “pair stress approximation” (PSA). The resulting simple equation of state yields very good approximate values for the fourth and fifth virial coefficients for hard disks, and for the fourth virial coefficient for hard spheres. The corresponding zero-separation theorems for higher-order distribution functions yield successively higher- and higher-order approximations to the equation of state and pair distribution function of hard-particle systems. The next-order approximation after PSA results in an integral equation whose solution would yield equations of state exact through the fourth virial coefficient. A rough approximation to the solution of that equation results in an equation of state which agrees very well with molecular dynamics computer calculations, within the entire fluid range, both for hard spheres and hard disks. The equation of state yields minimum specific volumes for both systems, between the fluid and crystal specific volumes at phase transitions observed by molecular dynamics computer calculations. All these approximations become exact for hard rods in one dimension, and the method yields the known expressions for the equation of state and pair distribution function for this system in a particularly simple way.
Theory of Phase Transitions in Solid Methanes. I. Electrostatic Multipole–Multipole Interaction
Authors: Yamamoto Tsunenobu
Published: February 2004

A systematic method of studying the electrostatic interaction between two multipoles is presented. It is based on the quantum theory of angular momentum. A system of two interacting multipoles which have tetrahedral symmetry is worked out in detail. New expressions for the octopole–octopole, octopole–hexadecapole, and hexadecapole–hexadecapole interaction potentials are found which will be applied to the study of the molecular dynamics in solid methanes in the articles to follow.