bluuebunny/crossref_metadata_2025 huggingface dataset:
Transition moments, band strengths, and line strengths for NaH
Authors: Sachs Edward S. , Hinze Juergen , Sabelli Nora H.
Published: February 2003

Electronic transition moments, as functions of internuclear separation, are calculated for the A1Σ+ → X1Σ+, B1Π → X1Σ+, B1Π → A1Σ+, c3Σ+ → a3Σ+, b3Π → a3Σ+, and b3Π → c3Σ+ transitions in NaH from ab initio molecular wavefunctions. Reduced line strengths, band strengths, band oscillator strengths, and band Einstein coefficients are calculated for the observed A1Σ+ → X1Σ+ transition, and are compared to experimental band intensities. Also calculated are Franck–Condon factors and R centroids, and the effects of various approximations used in treating experimental data are analyzed.
Calculation of the far-wing line broadening of the sodium D line induced by collisions with hydrogen atoms
Authors: Sachs Edward S. , Hinze Juergen , Sabelli Nora H.
Published: February 2003

Using ab initio potential curves and electronic transition moments we have calculated the far wings of the sodium D line emission spectrum broadened by collisions with hydrogen atoms. A classical–statistical model was used for this calculation. The calculated spectrum has two satellite peaks, one at 9683 cm−1, whose intensity diminishes with increasing temperature, and one at 21 641 cm−1, whose intensity increases with increasing temperature.
Lambda doublings and electric dipole moments of v=6 and 7 a 3Π carbon monoxide
Authors: Wicke Brian G. , Klemperer William , Field Robert
Published: February 2003

Precise Stark effects have been measured in CO a 3Π v=6 and v=7. The results of these measurements are in good agreement with extrapolation of Stark coefficients of lower (v=0–3) vibrational levels.
Optimized exponents in minimum basis atomic ground state wavefunctions
Authors: Weltin E. E.
Published: February 2003

The dependence on the nuclear charge of exponents minimizing the total energy of minimum basis ground state wavefunctions for first and second row atoms and some Ne-like and Ar-like ions is examined. Excellent linear correlations are found with correlation coefficients better than 0.999. Interpretation within a model of screened nuclear charges suggests, in agreement with the classical Slater rules, that s and p electrons with the same n are grouped together and that screening due to outer shell electrons is negligible. In disagreement with these rules, it is found that a multiplying factor different from unity is necessary for 2s and 3s exponents to correct for deficiencies in the functional form of the ns atomic orbitals.
New type of cluster theory for molecular fluids: Interaction site cluster expansion
Authors: Ladanyi Branka M. , Chandler David
Published: February 2003

A new cluster series, called the interaction site cluster expansion, is derived for classical molecular fluids. For a general class of molecular models, the series provides an exact formula for the equilibrium pair correlations between interaction sites on different molecules. In the models considered, each molecule contains m of these interaction sites. The total intermolecular potential between two molecules is the sum of m2 site–site potentials. A site–site potential depends on the separation between the sites only. However, because the sites are not necessarily located at the centers of molecules, the total molecular pair interaction can depend strongly on molecular orientations. Even though the interaction site cluster expansion is exact, the cluster integrals in the series involve the translational coordinates of the interaction sites only. The molecular orientational coordinates are removed by a transformation which introduces intramolecular correlation functions into the series. Thus, the new cluster series expresses the intermolecular site–site correlation functions in terms of diagrams involving site–site cluster bonds and intramolecular correlation bonds. The interaction site cluster expansions are used to derive several important results. It is shown that when the site–site interactions are hard core potentials, the pair correlation functions rigorously contain not only discontinuities but also cusps. The locations for these singularities are derived. A method is presented which shows how these singularities are smoothed when the hard core potentials are softened. The singularities as well as special limiting results derived herein are used to provide a justification for the reference interaction site model (RISM) equation.
Determination of the torsional potential function of 1,3-butadiene
Authors: Carreira L. A.
Published: February 2003

A series of 10 lines in the Raman spectrum of 1,3-butadiene has been observed and assigned as torsional overtones. An analysis of the data leads to a potential of the form V (φ) = 𝒥4i=1(Vi/2) (1 − cosiφ). The less stable species is found to be in the cis configuration with a cis–trans energy difference of 873 cm−1. The barrier for trans → cis interconversion was found to be 2504 cm−1.
Relaxation time of thermal diffusion columns nonactive volumes
Authors: Madariaga J. A. , Savirón J. M. , Brun J. L. , Mendí M. D.
Published: February 2003

Analytical solutions for the time evolution of the separation factor Q of an isotopic binary mixture in a thermal diffusion column with small reservoirs (dead spaces) at its ends are given. The simple expression obtained is checked against the numerical solution of the evolution differential equation. This shows its reliability to predict the nonstationary separation factor of a column with dead spaces up to 40% of its active volume, and for equilibrium values of lnQ up to 2 with no restrictions in the isotopic composition of the mixtures. These conditions take account of most of the experimental range that corresponds to the one stage units operating under total reflux. The obtained results support an empirical relation for the relaxation time proposed in a previous work.
Rough hard sphere treatment of mutual diffusion in binary liquid mixtures
Authors: Bertucci Sidney J. , Flygare W. H.
Published: February 2003

Mutual diffusion in binary liquid systems is treated theoretically in terms of the hard sphere model of the liquid state. The necessity of amending the basic hard sphere (Enskog) theory of transport to allow for the transfer of angular momentum between colliding molecules is emphasized. For nearly ideal solutions the calculated diffusion coefficients are in excellent agreement with experiment. The breakdown of the theory for nonideal solutions provides insight on a microscopic level into the nature of nonideality in a large class of binary liquid mixtures.
Order fluctuation dynamics of nematic liquid crystal in a binary system: MBBA/biphenyl
Authors: Shaya Steven A. , Yu Hyuk
Published: February 2003

The twist mode of a nematic liquid crystal, composed of a nematogenic solvent (MBBA) and a nonnematogenic solute (biphenyl), is investigated by the spectral composition of quasielastically scattered light from uniformly oriented samples in the forward depolarized configuration. The twist diffusivity coefficient K22/γ1 as a function of temperature and composition is found to be separable into two factors, one involving solely the equilibrium nematic order and the other attributed to an additional composition-dependent term. With use of the twist viscosity data in the literature, the twist elastic constant K22 of pure MBBA over the entire nematic region is deduced, and is shown to remain finite at the nematic–isotropic transition.
Measurement of vibrational–vibrational energy transfer probabilities in CO–CO collisions by a fast flow approximation
Authors: Liu Yung S. , McFarlane R. A. , Wolga G. J.
Published: February 2003

The vibrational–vibrational (V–V) energy transfer probability P0,1v,v−1 in CO–CO collisions, CO(0)+CO(v) → CO(1) + CO(v−1), has been measured from the first overtone emission spectra for v=3 to v=9 from vibrationally excited CO* produced in the reaction of oxygen with acetylene at room temperature. Under fast flow conditions in which spontaneous radiative rates, collisional deactivation rates, and other loss rates are made much smaller than the volumetric pumping rate, we find that the solution of the master equations for the vibrational population can be simplified and V–V transfer rates can be accurately determined. We call this approach the ’’fast flow approximation.’’ The experimental results are compared with previous work and with a calculation that includes both long-range and short-range interaction potentials.
A study of the dynamic behavior of the vibrational population relaxation in carbon monoxide
Authors: Liu Yung S. , McFarlane R. A. , Wolga G. J.
Published: February 2003

The dynamic behavior of a relaxing CO–He mixture has been studied with a computer. The time evolution of the nonequilibrium vibrational population distribution was obtained by numerically integrating the master equations for the vibrational population including vibrational–vibrational (V–V), vibrational–translational (V–T), and spontaneous decay processes. The results show the characteristic relaxation through the V–V energy transfer of an anharmonic molecule. The calculations are compared with the vibrational population distribution measured from two different experimental works: (i) ir chemiluminescence data from chemically excited CO formed in the reactions O+C2H2 → CO*+CH2+51 kcal/mole, O+CH2 → CO*+2H+71 kcal/mole; (ii) vibrationally excited CO produced in an electrical discharge induced reaction O+CS2→SO+CS, O+CS→CO*+S+75 kcal/mole and measured using a pulsed delay technique.
Ultranarrow, forbidden, singlet–triplet anticrossings in H2
Authors: Miller Terry A. , Freund Robert S.
Published: February 2003

Forbidden singlet–triplet anticrossings have been observed between different MN levels of the i (3d) 3Πg, v=1, N=6 state and the W (?) 1Σ+g, v=1, N=4 state of H2. As these anticrossings are rigorously forbidden in the absence of magnetic field mixing of rotational states, their widths are quite narrow, ranging from <10 to ∼30 G. Such narrow lines allow measurements of their center positions to approximately 3 MHz. These measurements are analyzed to yield values for the zero-field separation of the singlet and triplet levels as well as linear and quadratic Zeeman parameters. Analysis of the widths and intensities of the nine observed anticrossings yields the radiative lifetimes of the singlet and triplet states as well as the spin–orbit perturbation between them. The spin–orbit coupling between the singlet and triplet states is found to be much larger than expected from measurements of diagonal fine structure in similar triplet states.
Singlet–singlet electronic energy transfer: Dipole–dipole and exchange contributions
Authors: Loper Gary L. , Lee Edward K. C.
Published: February 2003

Singlet–singlet electronic energy transfer rates from p-difluorobenzene to acetone and its methyl-substituted derivatives have been measured in the gas phase. The results are compared to the data previously obtained with benzene as the donor, within the theoretical framework of the long range Coulombic and the short range exchange mechanisms. It is shown that the small energy transfer rates obtained with the highly substituted ketones can be attributed to the steric hindrance effect associated with the exchange mechanism; the steric hindrance factor in di-t-butyl ketone is ∼0.1 compared to acetone. No steric hindrance effect is observed for the dipole–dipole mechanism, as expected.
On the relation between the collision operator in the Liouville representation and the Lippmann–Schwinger transition operator
Authors: Eu Byung Chan
Published: February 2003

Fano obtained a relation between the tetradic collision operator W (z) in the Liouville representation and the transition operator T which is the solution of the Lippmann–Schwinger equation in scattering theory. Fano’s formula involves a convolution integral over the entire energy range. In this paper we propose an alternate for the relation, which does not include such a convolution integral and is more algebraic. We obtain the formula by suitably rewriting the ’’Lippmann–Schwinger equation’’ for W (z) and thereby obtaining a set of coupled integral equations. We discuss the formula obtained by Snider and Sanctuary in the light of Fano’s and the present formulas.
Kinetic equations for reacting chemical system: Exchange reaction
Authors: Eu Byung Chan
Published: February 2003

The Waldmann–Snider kinetic equations are generalized to a chemically reacting system AB+C ⇄ AC+B ⇄ A+BC ⇄ AB+C. In the formulation Kirkwood’s time averaging is introduced, which provides in a natural and concise way a route to exploit time-independent scattering theoretic technique. The master equations for the reacting system are obtained from the derived kinetic equations and the rate coefficients are identified.
Determination of the proton affinity from the kinetics of proton transfer reactions. V. The equilibrium H+3+Kr ? KrH++H2 and the relative proton affinity of Kr and H2
Authors: Payzant J. D. , Schiff H. I. , Bohme D. K.
Published: February 2003

The position of the equilibrium in the proton transfer reaction H3++Kr ? KrH++H2 was investigated with a flowing afterglow apparatus at 296±2 °K. Lower limits of ≳ 1×10−10 and ≳ 1×10−11 cm3 molecule−1⋅sec−1 were determined for the rate constants of the forward and reverse directions, respectively. Equilibrium was achieved in both directions and a value of 17±3 was determined for the equilibrium constant at 296±2 °K. This corresponds to a ΔG°296 = −1.67±0.12 kcal mole−1 and leads to a proton affinity difference PA(H2)−PA(Kr) = −0.017±0.012 eV molecule−1.
Susceptibilities, polarization fluctuations, and the dielectric constant in polar media
Authors: Fulton Robert L.
Published: February 2003

A procedure which avoids the necessity of the artificial introduction of cavities has been used in a previous paper to relate the dielectric constant ε of polar media to polarization and orientational fluctuations calculated in the absence of the transverse electromagnetic field. Here the arguments are extended to relate ε to the polarization fluctuations calculated with the inclusion of the transverse fields. This modification leads to the appearance of a propagating mode in the expression for the fluctuations. For a system of nonpolarizable molecules, the polarization fluctuations are directly related to the orientational fluctuations. The expression for the propagating mode of these latter fluctuations agrees with that given by Titulaer and Deutch when the media is nonmagnetic. The expressions for the short and long range fluctuations are the same as previously obtained. It is pointed out that it is quite common to ignore the transverse fields in a microscopic calculation of the orientational fluctuations. Such calculations should not give a propagating mode if the conventional macroscopic Maxwell equations are to be obeyed.
Species produced by the isolation of Na+ ions in solid C6H6
Authors: Duley W. W. , McCullough J. D.
Published: February 2003

Na+ ions trapped in C6H6 at 55 °K are shown to produce the ion C6H6+. An electronic transition of this ion showing extensive vibrational structure has been observed near 5600 Å. Na0 trapped in C6H6 at the same temperature yields a broad absorption feature that may be due to an electronic transition in the benzene anion C6H6−. The possibility that Na0 is incorporated in a C6H6 matrix by forming a Na+ C6H6− charge transfer complex is discussed.
PNO–CI (pair natural-orbital configuration interaction) and CEPA–PNO (coupled electron pair approximation with pair natural orbitals) calculations of molecular systems. III. The molecules MgH2, AlH3, SiH4, PH3 (planar and pyramidal), H2S, HCl, and the Ar atom
Authors: Ahlrichs R. , Keil F. , Lischka H. , Kutzelnigg W. , Staemmler V.
Published: February 2003

PNO–CI and CEPA–PNO calculations are performed for the molecules MgH2, AlH, AlH3, SiH4, PH3, H2S, HCl, and the Ar atom. Two types of Gaussian basis sets are used; both sets contain one p-set on H. The ’’small’’ set includes one d-set on the heavy atom, the ’’standard’’ basis two d-sets and one f-set. Both for MgH2 and Ar, a ’’large’’ and a ’’very large’’ basis are used as well, which contain additional polarization functions. The energy improvement due to the different polarization functions is analyzed. Hartree–Fock limits for the molecular energies are estimated. The computed valence shell correlation energies are analyzed in terms of quantities defined in part I, in particular in terms of the IEPA (independent electron pair) correlation energies εμIEPA and the error ΔEIEPA of the IEPA scheme. Both the valence shell interorbital pair correlation energies and the IEPA error are smaller in absolute value than those of the corresponding first row hydrides, provided that one uses the localized representation. MgH2, AlH3, and SiH4 are ’’good IEPA molecules’’, i.e., ‖ΔEIEPA‖ is unusually small for them. For Ar, calculations that include the L and M shell, and the K, L, and M shell correlation energy are reported. The best known variational energy of the Ar atom is obtained as −527.2592 a.u., the (nonvariational) CEPA energy being −527.2916 a.u. For the unknown molecules MgH2 and AlH3, binding energies, equilibrium geometries, and symmetric-stretching force constants are predicted. MgH2 has a binding energy of 104 kcal/mol referred to Mg+2H; it is hence expected to be unstable with respect to Mg+H2. The predicted binding energy of AlH3 is ? 205 kcal/mol referred to Al+3H. The inversion barrier of PH3 which amounts to ? 38 kcal/mol on SCF level is reduced by electron correlation to ? 35 kcal/mol.
Feshbach resonances associated with Rydberg states of the hydrogen halides
Authors: Spence David , Noguchi Tetsushi
Published: February 2003

Using an electron transmission spectrometer we locate Feshbach resonances in the hydrogen halides HF, HCl, HBr, and HI. These resonances consist of two Rydberg electrons bound to a positive ion core grandparent state. By analysis of previously published data, we determine the electron configurations of resonances observed in the isoelectronic rare gases and hence deduce the electron configurations of the resonances observed in HCl, HBr, and HI. We find that most of the observed resonances whose grandparent positive ion states have term value X 2Π are associated with Rydberg parent states of symmetry [X 2Π]nsσ, [X 2Π]npσ, and [X 2Π]ndλ. In HF, only one resonance series, associated with the [X 2Π]3sσ 1,3Π Rydberg state is observed.
’’Impurity’’ induced localized hole states of a one dimensional linear chain: Magnus green salt
Authors: Silverman B. D. , Scott B. A.
Published: February 2003

The effect of an interstitial (off chain) negative halide ion on the one dimensional molecular orbital or ’’tight binding’’ states of a 20 site metal ion linear chain is examined. It is assumed that the halide ion shifts the chain site potentials an amount given by the Coulomb potential resulting from a negative point charge placed at the halide ion site. The eigenvalues and eigenvectors of the 20 site problem have been obtained numerically. For an initially unperturbed metal 5dz2 bandwidth of 1 eV and a background dielectric constant ε=1, the binding energy of a 5dz2 hole is found to be 0.46 eV. This value is in good agreement with twice the observed conductivity activation energy, ? 0.6 eV, in extrinsic samples of the linear chain platinum compound Magnus’s green salt. The general dependence of the eigenvalues and eigenvectors will also be presented as a function of bandwidth and background dielectric constant.
Localized hole pair states on a one dimensional linear chain: Magnus green salt
Authors: Silverman B. D. , Scott B. A.
Published: February 2003

The hole pair ground state of a 20 atom linear tight binding chain and the excitation energy to the first excited hole pair state have been calculated for several configurations of two halide ions. Except for a small number of configurations, the ground state has been generally found to exhibit greater delocalization along the chain than the single hole state and an excitation energy to the first excited state that is less than the excitation energy for the single hole. These results These results are consistent with the observation that the activation energy for conduction in the doped ’’one dimensional’’ compound Magnus green salt appears to shift to lower energy as the dopant level is increased. They also provide a glimpse into the initial stages of the formation of extended hole orbitals that could lead to the formation of a one dimensional metallic state at higher dopant levels.
Vibrational relaxation of HCl(v=1,2,3,6) by H and Cl atoms
Authors: Wilkins Roger L.
Published: February 2003

Rate coefficients are calculated for the collisional de-excitation of vibrationally excited HCl molecules by H and Cl atoms. Three-dimensional classical trajectories of the collisional dynamics of these reactions are calculated by using London–Eyring–Polanyi–Sato (LEPS) potential-energy surfaces. The results indicate that (1) the rapid deactivation of vibrationally excited HCl by H and Cl atoms can be explained if bound complexes are postulated for both HClH and ClHCl; (2) H- and Cl-atom exchange are efficient mechanisms for relaxing vibrationally excited HCl by Cl and H atoms, respectively; (3) multiple quantum transitions are important in these de-excitation processes; and (4) the major energy transfer processes are vibration to translation in the deactivation of HCl by H atoms and vibration to rotation in the deactivation of HCl by Cl atoms. The vibrational relaxation of HCl by H atoms is faster than vibrational relaxation of HCl by Cl atoms. Room-temperature over-all relaxation rates kv from level v for HCl(v) by H atoms are k2/k1=1.7, k3/k1=2.2, and k6/k1=2.6, where k1=3.0×1013 cm3 mole−1⋅sec−1; for deactivation of HCl(v) by Cl atoms, they are k2/k1=1.7, k3/k1=2.2, and k6/k1 =8.4, where k1=4.5×1012 cm3 mole−1⋅sec−1. For v=1,2, and 3, these over-all rates show a linear dependence with v. The potential-energy wells of 3.8 kcal/mole predicted for the HClH surface and 0.77 kcal/mole predicted for the ClHCl surface have an effect on the collision dynamics corresponding to these surfaces as vibrational energy in the reagent is increased. The collision dynamics on the surface with the deeper potential-energy well are such that the deactivation rate for reaction H+HCl(v=6) shows a much smaller enhancement than that for reaction Cl+HCl(v=6), where the potential-energy well is not as deep. Increased vibrational energy in the reagents does not necessarily enhance the over-all reaction rates in reactions that occur mostly by formation of collision complexes rather than by direct interaction. The results of the calculations are compared with the experimental rates for the de-excitation of HCL (v=1,2,3) by Cl atoms and HCl(v=1) by H atoms. Rate coefficients are provided for many reactions that were not measured experimentally.
Random walk with two interacting walkers
Authors: Schwarz Martin , Poland Douglas
Published: February 2003

Using the method of images, exact solutions are given for various random walk models involving two interacting walkers on a finite one dimensional lattice. We extend the method of images to treat nonsymmetric walks with both reflecting and absorbing boundaries. One application of the models treated is the reversible unraveling (with a final irreversible step) of helical macromolecules.
Short-range He–Xe interaction from molecular-beam scattering
Authors: Amdur I. , Engler M. J. , Jordan J. E. , Mason E. A.
Published: February 2003

The short-range interaction potential between He and Xe has been determined from elastic scattering of beams of fast He atoms with room temperature Xe. The results are compared with previous experimental and theoretical results. (AIP)
The fluorescence spectrum of NH2 excited by a cw dye laser
Authors: Kroll M.
Published: February 2003

Fluorescence of the free radical NH2, produced in the gas phase in a flow system at a total pressure of ∼1 torr, has been excited by a cw dye laser operating in the region 5600–6300 Å. Values have been obtained for the vibrational energies G0 of the (0,1,0), (0,2,0), (1,0,0), (1,1,0), and (0,4,0) levels in the ground electronic state from an analysis of the emission which extends from 6300 to 8700 Å; approximate rotational constants (A, B, and C) have also been derived for these levels. The effects of collision-induced transitions are observed experimentally and the selection rules which govern these transitions are discussed.
Matrix elements of the tight-binding method for lattices with D144h symmetry
Authors: Jouanin C. , Gout C. , Albert J. P.
Published: February 2003

We have evaluated the matrix components of the Hamiltonian in the LCAO approximation for crystals with D144h symmetry.
Light scattering and pseudospinodal curve of the system polystyrene–cyclohexane in the critical region
Authors: Kojima J. , Kuwahara N. , Kaneko M.
Published: February 2003

The angular distribution of scattered light intensity from polystyrene (Mw = 1.1×105, Mw/Mn<1.02) in cyclohexane has been measured over a range of temperatures using a specially designed light-scattering photometer and then a ’’pseudospinodal curve’’ Tsp(φ) described by Tc − Tsp(φ) ∝ (φ(1) − φ(2))1/β+, where φ is the volume fraction of polymer on the spinodal curve, has been investigated for various equilibrium states in the critical neighborhood of the temperature–concentration diagram. An empirical equation of the form (Ic,0/T)−1 ∝ (T−Tsp)γ, in which Ic,0 is the extrapolated zero-angle scattering intensity, is used to effect an extrapolation for the determination of Tsp inside the coexistance curve. The temperature dependence of Ic,0 obeys the same relation with γ=1.20–1.24 for several samples. The long-range correlation length ξ obeys a relation ξ∝ (T−Tsp)−ν with ν=0.59∼0.64. As expected on the ground of the homogeneity hypotheses, the value of β+?0.38 found in the present work is essentially the same as the value of the critical exponent β=0.34±0.01 for the coexistence curve near its critical mixing point.
Nitrogen and chlorine NQR in paraelectric and ferroelectric tris-sarcosine calcium chloride
Authors: Blinc R. , Mali M. , Osredkar R. , Seliger J.
Published: February 2003

The pure nuclear quadrupole resonance spectra of 14N have been measured in tris-sarcosine calcium chloride (TSCC), deuterated TSCC, and sarcosine using nuclear double resonance in the laboratory frame. In TSCC two chemically nonequivalent nitrogen sites have been found at room temperature, one with a quadrupole coupling constant e2Qq/h =1040 kHz and an asymmetry parameter η=1 and another one with e2Qq/h = 940 kHz, η=1. The 14N results in deuterated TSCC differ from those in undeuterated TSCC by less than 10%. The corresponding 14N data for sarcosine are e2Qq/h = 1440 kHz, η=1 and e2Qq/h = 1470 kHz, η=0.79. In the ferroelectric phase at 77 °K only one nitrogen site has been found in TSCC with e2Qq/h = 1010 kHz and η=0.89. In TSCC, ν (35Cl) =2160 kHz and ν (37Cl) =1710 kHz, and deuterated TSCC 35Cl and 37Cl quadrupole resonance lines were found in the paraelectric phase, whereas in the ferroelectric phase no chlorine lines could be observed.
Radiationless relaxation of rare-earth ions in solids: Phenomenological effects of f→f and f→d transitions and the origin of multiphonon relaxation in first-order perturbation theory
Authors: Fong Francis K. , Lauer Howard V. , Chilver Charles R. , Miller Marvin M.
Published: February 2003

In this paper, the phenomenological effects of d→f and f→f processes are examined. The relationship between radiationless multiphonon decay and excitation processes is obtained in terms of the first-order adiabatic relaxation theory. A detailed analysis is given of the experimentally observed temperature dependence of the lifetimes and intensities of Sm2+ 5D0 fluorescence in KCl and SrF2. From this analysis, rate constants for the nonradiative d?5D0 processes are evaluated. The observed characteristics of radiationless f→f and f→d relaxation processes are compared in terms of the theoretical dependence of the rate constant on the energy gap, on temperature, and on the frequencies of the phonon modes of the host crystals. The main features of the first-order relaxation theory are compared with those of an earlier high-order treatment in the crude Born–Oppenheimer approximation. The role of potential-surface displacements (signifying coupling strengths) in the first-order perturbation treatment of multiphonon relaxation is discussed. It is shown that in the zero-displacements limit, the first-order multiphonon rate constant is identically zero. In this limit, multiphonon processes can only arise from high-order terms in the perturbation expansion.
Self-diffusion of oxygen in polycrystalline MgAl2O4
Authors: Oishi Y. , Ando Ken
Published: February 2003

Self-diffusion coefficients of oxygen in polycrystalline MgAl2O4 were determined over the temperature range 1310–1694 °C by a gas–solid isotopic exchange technique using 18O as a tracer and the results were compared with those of single crystal MgAl2O4. The apparent diffusion coefficients for the polycrystal were greater than those of the single crystal. These results were interpreted as being due to oxygen diffusion enhanced by grain boundaries.
Heteronuclear diatomic scattering from solid surfaces: A hard-cube model
Authors: Nichols William L. , Weare John H.
Published: February 2003

A classical mechanical hard-cube model for the scattering of heteronuclear diatomic gas beams from well-defined solid surfaces is presented. The diatomic gas molecule is approximated by an ellipse. The geometric center of the ellipse differs from the center of mass of the gas molecule. The gas–surface interaction is impulsive, and the mechanics are developed with the classical conservation equations of energy, momentum, and angular momentum. Scattering patterns are computed numerically after an examination of the collision process. The influence of the physical parameters of the scattering process upon the shapes of scattering patterns is discussed.
An electron spin resonance study of the diphenyliminoxy radical. A photoproduced radical from benzophenone oxime in benzophenone crystals
Authors: Lin Tien-Sung
Published: February 2003

The anisotropic magnetic parameters of the diphenyliminoxy radical, photoproduced from the benzophenone oxime embedded in a benzophenone crystal, have been measured by ESR spectroscopy. The principal values of the 14N hyperfine interaction are Txx = 25.4, Tyy = 26.2, and Tzz = 42.5 G. The hyperfine principal axes are x perpendicular to a plane containing the CNO group, y in the plane and perpendicular to the bisector of the CNO bond angle, and z the bisector of the CNO bond angle. The g-tensor components are gxx = 2.0054, gyy = 2.0104, and gzz = 2.0031. The principal axes of the g tensor do not coincide with the hyperfine axes except for the x axis. The isotropic values, obtained from the iminoxy in a supercooled benzophenone liquid, are aN = 31.5 G, g = 2.0063, and aH = 1.5 G (ortho protons). The p:s ratio for the unpaired electron at the N atom is calculated to be 5.7. The spin density on 14N is 0.38. The bond angle of the CNO bond is 136°. The unpaired electron is in a pseudo ?u orbital with increasing s character at the N atom as the CNO bond deviates from a linear structure.
Temperature dependence of bimolecular ion molecule reactions. The reaction C2H5++CH4 = C3H7++H2
Authors: Hiraoka Kenzo , Kebarle P.
Published: February 2003

The reaction C2H5++CH4 = C3H7++H2 [Reaction (1)] was observed in pure methane in a pulsed electron beam high pressure ion source mass spectrometer. The rate constants k1 determined in the temperature range 250–650 °K were found to increase with temperature. An Arrhenius plot of k1 gave a straight line which yields 6×10−13 cm3 molecule−1⋅sec−1 for the preexponential factor and 2.5 kcal/mole for the activation energy E1. At temperatures below 250 °K, Reaction (1) was gradually replaced by (8): C2H5++2CH4 = C3H9++CH4. It is concluded that both (1) and (8) proceed by the excited intermediate (C3H9+) * which may back react to C2H5++CH4, decompose to C3H7++H2, or be stabilized to C3H9+. The positive temperature dependence of (1) arises from an internal energy barrier B between the three center bonded structures: x x x x The lowest energy structure IV is formed by the addition of C2H5+ to CH4. The H2 elimination from C3H9+ must proceed via structure III. The barrier B = ΔH8+Ea(1) = 6.6+2.5 kcal/mole is larger than the barrier A for back dissociation of C3H9+ to C2H5++CH4, where A = ΔH8 = 6.6 kcal/mole. Thus at low temperature back dissociation predominates, while at higher temperatures H2 elimination becomes competitive.
A theory of spontaneous fluctuations in macroscopic systems
Authors: Keizer Joel
Published: February 2003

A theory is developed for the dynamics of spontaneous fluctuations in systems which, on the average, obey nonlinear transport equations. The theory is a generalization of the Ornstein–Uhlenbeck theory of near equilibrium fluctuations (Langevin-type theories) and yields a stochastic process which is nonstationary with a Gaussian conditional probability. The three assumptions on which the theory is based are predominately kinetic in nature and in order to apply the theory it is necessary to formulate rate equations in terms of elementary events. Examples of this are given for nonlinear chemical reactions and the complete nonlinear Boltzmann equation.
Evidence for the formation of CO2 in the photolyses of N2O and CO2 in the presence of CO
Authors: Loucks Leon F. , Michaelson Robert C.
Published: February 2003

The photolysis of CO2 at 1633 Å in the presence of 13CO has been found to give an appreciable yield of 13CO2. The photolysis of N2O at 1633 Å conducted in the presence of CO and a large excess of N2 has also been found to lead to CO2 formation. The experimental conditions for both photolyses are such that O 1D atoms generated in the photolysis would be efficiently deactivated to O 3P atoms and the product CO2 is believed to arise from reactions involving the latter. A radical-chain mechanism has been proposed for the formation of CO2, but the possibility of a surface reaction mechanism has not been ruled out.
Validity of the weak diffusion expansion for solutions to systems of reaction-diffusion equations
Authors: Rosen Gerald
Published: February 2003

The regime of applicability of the weak diffusion expansion (WDE) for solutions to a generic system of reaction-diffusion equations ∂ci/∂t = Di∇2ci + Qi(c) is delineated, where the enumerator index i runs 1 to n, ci = ci(x,t) denotes the concentration or density of the ith participating molecular or biological species, Di is the diffusivity constant for the ith species, and Qi(c) is an algebraic function of the n-tuple c= (c1,⋅⋅⋅, cn) that expresses the local rate of production of the ith species due to chemical reactions or biological interactions. Our results take the form of rigorous upper bounds on the absolute value of the difference between the exact solution and the leading terms in the WDE for an approximate solution. It is shown by example that the leading terms in the WDE provide an approximate solution which can be very accurate for an appreciable duration of time.
Linear response theory and molecular vibrations: The Thomas–Fermi model
Authors: Handler George S. , March Norman H.
Published: February 2003

Instead of treating the density change Δρ (r) associated with molecular vibrations via a many electron response function and the change ΔV (r) in the nuclear potential due to the displacements, single-particle potential theory is used to write Δρ (r) = ℱdr′ F (r,r′) ΔV (r′). The linear response function F may be constructed exactly from the orbitals and eigenvalues Ei of the (unique) single-particle potential that generates the exact single particle density V (r) in the equilibrium configuration. The argument that F is a functional of V implies F = F[ρ]. This in turn suggests extracting F from the Thomas–Fermi (TF) model and its refinements. The explicit form of F is given from (a) lowest order TF theory and (b) a theory that incorporates elements of higher order treatments. The linear response function found is formally similar to that derived from the free-particle density matrix with suitable redefinition of the Fermi energy.
A study of the isoenergetic reaction H+3+O2 ? O2H++H2
Authors: Fehsenfeld F. C. , Lindinger W. , Albritton D. L.
Published: February 2003

The isoenergetic reaction H+3+O2 ? O2H++H2 has been studied in a flowing afterglow and a flow-drift tube. In the former, the equilibrium constant was found to be 1.8±0.5. In the latter, the forward and reverse rate constants were measured separately and, at near-thermal energies, were 7×10−10 and 3×10−10 cm3/sec, respectively. These values are in good agreement with recent ion-cyclotron-resonance (ICR) studies of this reaction. The flow-drift tube study found the forward and reverse rate constants to be virtually energy independent, attesting to the isoenergeticity of this reaction. As a further comparison with the ICR measurements, the rate constant for the reaction H+3+N2 → N2H++H2 was measured as a function of relative kinetic energy. At near-thermal energies, k=2×10−9 cm3/sec, in excellent agreement with the ICR value.
The refractive index and Lorenz–Lorentz function of fluid methane
Authors: Olson James D.
Published: February 2003

The refractive index of gaseous and liquid methane was measured between 95 and 300 K and to pressures of 225 bar (1 bar = 105 Pa). The measurements were performed at the 198Hg vapor green line, λ=546.2 nm, with a Fabry–Perot interferometer referred to vacuum. The refractive index data were combined with the previously measured densities of methane to calculate the Lorenz–Lorentz (LL) function. Refractometric virial coefficients were obtained from analysis of the small (∼0.5%) maximum exhibited by the (LL) function with increasing density. BR, the second refractometric virial coefficient, is estimated to be ∼6.0 (cm3/mol)2 and is almost independent of temperature between 220 and 300 K. The critical point refractive index, nc=1.10333, was extrapolated from a rectilinear diameter treatment of the saturated liquid and vapor results. The critical point refractive index was combined with an estimate of the critical point (LL) function to yield a critical density of methane, ρc= 10.16±0.01 mol/l.
Energy absorption by N2O in the 4 to 14 eV region
Authors: Huebner Russell H. , Celotta R. J. , Mielczarek S. R. , Kuyatt C. E.
Published: February 2003

Apparent oscillator-strength values for transitions in the 4 to 14 eV region in nitrous oxide have been derived from electron energy-loss measurements. Detailed comparison with photoabsorption measurements in the ultraviolet region indicates a weak transition below the 1Δ←? 1Σ+ transition at 6.8 eV not observed optically. This analysis also provides oscillator-strength values in the region between 11.5 and 12.4 eV, where no quantitative photoabsorption data are available.
Rotational tunneling in solids
Authors: Hüller A. , Kroll D. M.
Published: February 2003

A variational method is developed to treat rotational excitations of molecules and polyatomic ions in crystals. The theory is applicable for all potential strengths and is exact in the limits of weak and strong potentials. Rotational motion with one, two, and three degrees of freedom are treated in a unified manner. Explicit calculations are performed for the one-dimensional rotation of a CH3 group in a C6 potential and the three-dimensional reorientational motion of a methane molecule in Td and D2d potentials. The results are compared with recent neutron scattering experiments.
The intrinsic viscosity of dilute solutions of stiff polymers
Authors: Titulaer U. M. , Deutch J. M.
Published: February 2003

The intrinsic viscosity of a dilute polymer solution is studied for a polymer model with rigid constraints on some quantities, such as bond lengths and bond angles. The constraints are introduced via a harmonic constraining potential; the strength of this potential is taken to infinity at the end of the calculation. Expressions for the frequency dependent intrinsic viscosity are obtained with the correlation function formalism. The limiting form for the case in which the constraints become rigid is obtained via a systematic expansion procedure. In the limit we obtain a contracted description in terms of the unconstrained variables only. We discuss the form of the polymer diffusion equation and various expressions for the stress tensor that may be used in the context of such a contracted description, as well as expressions for both the frequency dependent and the frequency independent part of the intrinsic viscosity. We compare our results with those of other authors. Complete agreement is found with the results of Fixman and Kovac, and with the corrected version of the theory of Erpenbeck and Kirkwood. Discrepancies are found with results of Doi, Nakajima, and Wada, and of Hassager. The origin of these discrepancies is explained.
The influence of symmetry on the conformational dependences of various molecular parameters
Authors: Maruani J. , Hernandez-Laguna A. , Smeyers Y. G.
Published: February 2003

It is shown how the symmetry properties of the linked groups in a molecule help to reduce the number of harmonics in the Fourier series expansions of aggregate, mononuclear, and binuclear parameters as a function of the dihedral angles. This provides a rationalization for some well-known conformational dependences of the torsional potentials, hyperfine couplings, and internuclear interactions and helps to predict how these simple formulas break down when the conformations become more complex.
Spectroscopic studies on naphthalene in the vapor phase. I. Fluorescence spectra from single vibronic levels
Authors: Stockburger M. , Gattermann H. , Klusmann W.
Published: February 2003

Fluorescence spectra originating from various single vibronic levels in the first excited singlet state of naphthalene-h8 and -d8 were studied under collision-free conditions. The interpretation of the vibrational structure and intensity of the spectra is given in terms of vibronic coupling theory.
Spectroscopic studies on napththalene in the vapor phase. III. Phosphorescence and intersystem crossing yields of single vibronic levels
Authors: Gattermann H. , Stockburger M.
Published: February 2003

Gas-phase phosphorescence spectra of naphthalene-h8 and -d8 are reported. A triplet lifetime of 4.2 msec was derived from the 000 band of the n-h8 phosphorescence. Intersystem crossing yields of single vibronic levels in S1 were determined from excitation spectra of biacetyl phosphorescence.
Collision-induced emission from O(1S) by He, Ar, N2, H2, Kr, and Xe
Authors: Black G. , Sharpless R. L. , Slanger T. G.
Published: February 2003

Collision-induced emission from O(1S) has been studied for collisions with He, Ar, N2, H2, Kr, and Xe. The O(1S) was made by CO2 photodissociation at 1120 Å and N2O photodissociation at 1290 Å. For all but Xe the emitted intensity (including both atomic line and associated molecular bands) increased linearly with the added gas pressure. This was not true at low pressures of Xe—the observed behavior in this case was used to deduce the rates for formation and collisional dissociation of XeO.
Extended Hückel calculation of repulsive interactions in noble gases
Authors: Hathaway Kristl B. , Krumhansl James A.
Published: February 2003

Repulsive potential energies for all of the possible pairs of atoms of the noble gases helium, neon, and argon are calculated by the semiempirical extended Hückel molecular orbital method. The agreement of the calculated energies with other theoretical results is significantly improved by computing overlaps using analytic approximations to the atomic Hartree–Fock atomic orbitals instead of the more commonly used Slater functions.
Potential energy and force constants of a potassium chloride molecule from extended Hückel calculations
Authors: Hathaway Kristl B. , Krumhansl James A.
Published: February 2003

The potential energy and vibrational force constants of a potassium chloride molecule are calculated by the extended Hückel molecular orbital method using analytic approximations to the Hartree–Fock atomic orbitals in the computation of overlaps. The addition of a simple Coulomb attractive energy to the repulsive extended Hückel energy yields total potential energies in reasonable agreement with the experimental energy curve.
The acetyl cation and its geometrical isomers
Authors: Yarkony David R. , Schaefer Henry F.
Published: February 2003

A b initio self-consistent-field (SCF) calculations are reported on the acetyl cation (CH3CO+) and three of its possible geometrical isomers. The wavefunctions are discussed in terms of Mulliken populations and simple valence bond arguments. The energies of the low-lying electronic states of CH3CO+ are estimated and compared with those of CO. The similarities and differences are explained in terms of simple chemical arguments. Finally an accurate two configuration wavefunction for the CH3CO+ fragmentation is presented, showing unambiguously the dissciation products to be the expected ones, CH3+ and CO.
Fourier transform NMR in the rotating frame
Authors: Krishna N. R.
Published: February 2003

A density matrix description of the Fourier transform (FT) NMR experiment on a coupled spin system interacting with a strong rf field (maintained throughout the experiment) is presented. The strong irradiation causes a mixing of the nuclear spin states giving rise to additional transitions, as well as polulation redistribution among the various energy levels. Both these features manifest themselves in the FT NMR spectrum in the form of intensity and linewidth changes that are dependent upon the details of the nuclear spin relaxation as well as the parameters of the irradiating rf field. Thus this experiment provides an interesting alternative to the study of the details of nuclear spin relaxation in coupled spin systems using the FT NMR technique. The problem is solved in a frame rotating at the frequency of irradiation. The resulting expressions indicate that the FT NMR spectrum is dependent upon the flip angle as well as the relative phase angle ψ (at the time of pulse) between the irradiating rf field and the pulse rf field. The conditions under which this experiment can be analyzed by the much simpler theory of the slow passage continuous wave (cw) Nuclear Magnetic Double Resonance (NMDR) experiment are discussed. General expressions for the FT NMR line shapes are derived for the case of a single nucleus of spin 1/2 and the theory is tested on the single spin 1/2 system in a sample of neat undegassed CHCl3. The experiment is in good agreement with theory.
n,π* fluorescence from selected vibronic levels of pyrimidine vapor: Franck–Condon factors and excited state anharmonic coupling
Authors: Knight A. E. W. , Lawburgh C. M. , Parmenter C. S.
Published: February 2003

An analysis is presented of fluorescence from various selected vibrational levels in the 1B1(S1) state of pyrimidine vapor. The intensity distribution in fluorescence from the zero point level establishes with security the general pattern of vibrational activity in the 1B1–1A1 transition, and the Franck–Condon intensities in this fluorescence set the molecular parameters required for calculation of Franck–Condon intensities in fluorescence from other levels. The fluorescence from every higher level so far reached shows marked deviations from the predicted Franck–Condon intensities. These deviations can be attributed to strong (ca., 30 cm−1) anharmonic coupling in the excited state. Every observed totally symmetric fundamental in the 1B1 state is perturbed by this mixing. Calculations which include the coupling provide a successful account of the perturbed Franck–Condon intensities. The fluorescence analyses secure the assignment of a number of absorption bands as well as several excited state fundamentals. Specifically, ν6a′, ν9a′, and ν16a′ are confirmed and the fundamentals ν1′=941 cm−1, ν6b′=335 cm−1, ν12′=1012 cm−1, and ν16b′=366 cm−1 are newly established. Fluorescence studies at various pressures show that vibrational relaxation is a poor competitor to a very efficient collision-induced electronic relaxation of the 1B1 state. Vapor phosphorescence cannot be detected under any conditions.