bluuebunny/crossref_metadata_2025 huggingface dataset:
Study of the sensitivity of coupled reaction systems to uncertainties in rate coefficients. I Theory
Authors: Cukier R. I. , Fortuin C. M. , Shuler K. E. , Petschek A. G. , Schaibly J. H.
Published: February 2004

A method has been developed to investigate the sensitivity of the solutions of large sets of coupled nonlinear rate equations to uncertainties in the rate coefficients. This method is based on varying all the rate coefficients simultaneously through the introduction of a parameter in such a way that the output concentrations become periodic functions of this parameter at any given time t. The concentrations of the chemical species are then Fourier analyzed at time t. We show via an application of Weyl's ergodic theorem that a subset of the Fourier coefficients is related to 〈∂ci/∂kl〉, the rate of change of the concentration of species i with respect to the rate constant for reaction l averaged over the uncertainties of all the other rate coefficients. Thus a large Fourier coefficient corresponds to a large sensitivity, and a small Fourier coefficient corresponds to a small sensitivity. The amount of numerical integration required to calculate these Fourier coefficients is considerably less than that required in tests of sensitivity where one varies one rate coefficient at a time, while holding all others fixed. The Fourier method developed in this paper is not limited to chemical rate equations, but can be applied to the study of the sensitivity of any large system of coupled, nonlinear differential equations with respect to the uncertainties in the modeling parameters.
Study of the sensitivity of coupled reaction systems to uncertainties in rate coefficients. II Applications
Authors: Schaibly John H. , Shuler Kurt E.
Published: February 2004

The Fourier amplitude method developed in Paper I as a diagnostic tool for determining the sensitivity of the results of complex calculations to the parameters which enter these calculations has been applied to two chemical reaction systems involving sets of coupled, nonlinear rate equations. These were: (a) a five reaction set describing the high temperature (6000 °K) dissociation of air and (b) a nine reaction set describing the constant temperature (2000 °K) combustion of H2 and O2. We have evaluated the Fourier amplitudes for all the species at a number of different times for both reaction systems. The analysis of these results verifies the claims made in Paper I. The relative magnitudes of the Fourier amplitudes showed a several order of magnitude distribution which permitted a clear distinction of the relative sensitivity of the species concentration to uncertainties in the rate coefficients. The conclusions based on the Fourier amplitude method for these two reaction systems are in excellent agreement with sensitivity predictions which could be made on the basis of previous kinetic studies of these systems.
Molecular collisions. XX. First order generalized phase shift approximation for symmetric top molecules
Authors: Hunter L. W. , Curtiss C. F.
Published: February 2004

The development of a generalized phase shift approach to the theory of inelastic scattering of molecules of an arbitrary type is begun and carried out in detail for nonvibrating symmetric top molecules. The latter results are compared with the sudden approximation and the semiclassical limit of the restricted distorted wave approximation.
Hydrogen bond studies. 77. Electron density distribution in α-glycine: X-N difference Fourier synthesis vs ab initio calculations
Authors: Almlöf Jan , Kvick Åke , Thomas J. O.
Published: February 2004

Accurate x-ray and neutron diffraction data have been combined to study the electron density distribution in the simplest amino acid, α-glycine. Ab initio electron density calculations have also been made using an MO-LCAO SCF approach employing a Gaussian basis set of ``double-ζ'' type. Highly satisfactory qualitative agreement is found.
Simple bond-charge model for bending force constants of linear symmetric triatomic molecules
Authors: Ray N. K. , Parr Robert G.
Published: February 2004

A bond-charge model is used to derive a simple universal relation, Kθθ = 0.026K11, between the bond stretching force constant K11 and bond bending force constant Kθθ for linear symmetric triatomic molecules. The relation is shown to be reasonably accurate for 17 molecules.
Solvent effects on the coupling processes of polystyryl radicals
Authors: Yasukawa Tamio , Takahashi Tohru , Murakami Kenkichi
Published: February 2004

The molecular weight distributions of polystyrene prepared in various solvents at 60 °C showed broadening with increasing solvent viscosity, whereas the effects of solvent power were not conspicuous. Simulations of polymerization reactions with several models showed that the coupling probability of polystyryl radicals is not independent of chain length at 60 °C and that the chain length dependence becomes apparent with increasing solvent viscosity. These results were discussed in terms of the dynamical behavior of polymer radicals in solution and it was tentatively concluded that the chain length dependence of coupling probability of polystyryl radicals originates mainly from the hydrodynamic interactions between polymer segments.
Observation of strong nonlinearities in the high field Zeeman spectrum of NO at 1876 cm−1
Authors: Zeiger H. J. , Blum F. A. , Nill K. W.
Published: February 2004

Strong nonlinearities have been observed in the Zeeman effect in NO and quantitatively explained by taking account of off-diagonal Zeeman interaction terms in an accurate Hamiltonian diagonalization calculation. Zeeman spectra were obtained by tuning the Q(3/2)3/2 and Q(5/2)3/2 transitions of the fundamental band (1876 cm−1) through the P(15)9,8 laser line of CO.
Electron spin resonance of transition metal ions in calcium tartrate tetrahydrate host lattice I. Mn2+, Cu2+, and Ni2+ as dopants
Authors: Lau P. W. , Lin W. C.
Published: February 2004

The electron spin resonance of Mn2+, Cu2+, and x-irradiated Ni2+ doped calcium tartrate tetrahydrate single crystals was studied. This and earlier results were discussed together in the light of the known crystal structure of the host lattice. The nickel center was interpreted as the d7 Ni3+ ion. A possible doping mechanism for transition metal ions in calcium tartrate tetrahydrate was suggested.
Electron spin resonance of transition metal ions in calcium tartrate tetrahydrate. II. VO2+ as dopant
Authors: Lau P. W. , Lin W. C.
Published: February 2004

As a continuation of a previous work, the ESR of VO2+ doped calcium tartrate tetrahydrate was examined. Three vanadium centers were observed of which detailed analysis of two were carried out. It was concluded that, like Mn2+, Cu2+, and Ni2+, VO2+ entered the lattice in interstitial sites.
Investigations of a nonrandom numerical method for multidimensional integration
Authors: Cheng Vera B. , Suzukawa Henry H. , Wolfsberg Max
Published: February 2004

A numerical integration technique based upon the use of nonrandom number sequences is examined with test integrations of a simple, analytical function. A comparison of the nonrandom technique with the familiar Monte Carlo method shows that the error of the new method decreases faster as more points are used in the calculation. Moreover, the new method needs fewer points to calculate an integral to an accuracy of 10% than does the Monte Carlo method.
Empirical testing of the suitability of a nonrandom integration method for classical trajectory calculations: Comparisons with Monte Carlo techniques
Authors: Suzukawa Henry H. , Thompson Donald L. , Cheng Vera B. , Wolfsberg Max
Published: February 2004

A nonrandom method for approximating multidimensional integrations is compared to traditional ``random'' Monte Carlo techniques for determining reaction cross sections from quasiclassical trajectories. Reaction cross sections are calculated for the H + H2 collision system to determine the relative rates of convergence for each method as a function of the number of trajectories employed in the calculation. Estimates of the maximum probable error for the nonrandom integrations of a given number of trajectories compare favorably with the errors expected for Monte Carlo integrations and seem to imply that nonrandom integrations are more accurate than Monte Carlo calculations. However, the error of a Monte Carlo integration is easily estimated while that of a nonrandom integration is not. Thus the nonrandom method's advantage in accuracy may be overcome by other characteristics of the Monte Carlo method. For classical trajectory calculations, the nonrandom method should be considered as an alternative, but not a replacement, for the Monte Carlo method.
Indirect process in the dissociative attachment of low energy electrons to molecules
Authors: Nazaroff George V.
Published: February 2004

The dissociative attachment of low energy electrons to molecules is described in terms of two coupled processes-the ``direct'' process and the ``indirect'' process. In the ``direct'' process the incoming electron collides with the molecular target and attaches in one step, and fragmentation of the molecular negative ion follows. In the ``indirect'' process the target is first fragmented by the electron, and the electron is subsequently captured by one of the dissociating neutral fragments. The coupled electron-molecule scattering equations are formally integrated, and an expression for the T-matrix describing dissociative attachment is developed showing clearly the presence of the ``direct'' and the ``indirect'' contributions. An order-of-magnitude estimate for the dissociative attachment of 10 eV electrons to H2 indicates that the two processes are of comparable magnitude in this case. The ``indirect'' process is expected to contribute subsidiary structure to the dissociative attachment cross section in those cases in which the molecular negative ion potential surface lies above the parent-state potential surface in the initial state's Franck-Condon region. The subsidiary structure could range from a small bump in the case of weak coupling between the two processes to a series of oscillations in the case of strong coupling.
Normal modes and interaction energies for long chains
Authors: Wang S. Q. , Mahan G. D.
Published: February 2004

An elementary approach leads to solutions for (i) normal modes for single chains and (ii) normal modes and the interaction energy for double chains. Both conducting and nonconducting cases are studied. The retardation effect is unlikely to change the results significantly in actual cases of interest.
Near-molecular Hartree-Fock wavefunctions for CH3O−, CH3OH, and CH3OH2+
Authors: Tel Luis M. , Wolfe Saul , Csizmadia Imre G.
Published: February 2004

A total of nine molecular Hartree-Fock wavefunctions have been computed for CH3O− (I), CH3–OH (IIA–IId), and CH3–OH2+ (IIIa–IIId). The lowest energies obtained, in hartree atomic units, were: − 114.34285 (CH3O−), − 115.01162 (CH3OH), and − 115.32787 (CH3OH2+). The two proton affinity values for the successive protonations (CH3O−→ CH3OH→ CH3OH2+) were calculated to be − 419.4 and − 198.9 kcal/mole, respectively. For CH3–OH, the barriers to rotation and to in-plane inversion were computed to be 1.44 and 32.5 kcal/mole, respectively; CH3–OH2+ showed no barrier to either rotation or inversion. Some excitation energies, dipole moments, and charge distributions have also been computed.
Ion-molecule reactions in perdeuteriomethane
Authors: Futrell Jean H.
Published: February 2004

Ion cycoltron resonance techniques were used to measure absolute rate constants for the reactions (1) CD4+ + CD4 → CD5+ + CD5 and (2) CD3+ + CD4 → C2D5+ + D2. Rate coefficients deduced from the appearance of product ions and disappearance of reactant ions were identical within experimental precision, confirming the assumption that these are the only significant reactions of thermal energy CD4+ and CD3+, respectively. The magnitudes of the rate constants, k1 = 1.1 × 10−9 cm3 mol−1 · sec−1 and k2 = 1.2 × 10−9 cm3 mol−1 · sec−1 are consistent with the simple polarization theory of ion-molecule reactions and with previous measurements for ordinary and perdeuteriomethane.
Time-dependent concentration depolarization of fluorescence
Authors: Hemenger Richard P. , Pearlstein Robert M.
Published: February 2004

A theory of the time course of fluorescence anisotropy (polarization) after impulsive excitation is presented for viscous solutions of identical molecules. In a point-dipole model of the molecular oscillators, it is shown that the relative anisotropy is a universal function A of the quantity T = c2t/τ, where c is solute concentration (in units of the usual critical concentration), t is time, and τ is actual fluorescence lifetime. The function A(T) is expressed as a contribution A0 from the initially excited dipole plus one from all other dipoles, with the latter shown to be quite small in the region of interest. It is also shown that the representation, A0=Σk=0∞αk Tk/2, is useful for calculations except when T ≫ 1. The kth term in the series corresponds to energy transfer pathways involving k + 1 dipoles. The αk alternate in sign, with α0 = 1 and α1 = − 1.06004 derived analytically; numerically derived values of α2 through α6 are also given. We show that A(T) is the Laplace transform of c2 Ã(c), where Ã(c) is the steady-state anisotropy, and we use that relation to obtain an expansion of Ã(c) in powers of c. The resultant steady-state curve compares favorably with the best previous theoretical curves. The results of the point-dipole model are corrected for the effects of finite molecular volume. Specifically, it is shown that, for an excluded spherical volume v of twice the molecular ``radius,'' the behavior of A(T) for t/τ ≪(v/V0)2 is simply 1 − c(V0/v)(t/τ), which gives a finite decay slope at t = 0 in contrast to the point-dipole case. (V0 is the volume of the sphere of radius R̄0.) In addition to the A(T) theory, a simple derivation is given for the fluorescence-intensity formulas for anisotropy in linearly polarized and unpolarized exciting light. Finally, potential applications of the A(T) theory, particularly to testing the validity of the Förster mechanism in multiple homotransfer, are discussed.
Fine structure of ortho-and para-D2 d(3p) 3Πu via microwave optical magnetic resonance induced by electrons
Authors: Freund Robert S. , Miller Terry A.
Published: February 2004

The MOMRIE (microwave optical magnetic resonance induced by electrons) spectrum has been measured for ortho-D2 d(3p) 3Πu in vibrational levels v = 0−4 and for para-D2 in vibrational levels v = 0−5. The theory used to analyze these spectra is identical to that used previously to analyze the MOMRIE spectrum of para-H2. Least squares fits to the data provide values for the so-called spin-orbit and spin-spin coupling constants, the orbital g factor, and the magnetic and electric susceptibilities. Differences between the constants for ortho- and para-D2 demonstrate significant breakdown of the Born-Oppenheimer approximation. Zero field fine structure separations have been calculated from the molecular parameters. Hyperfine structure is smaller than the natural linewidth and so is unresolved. It does broaden the lines, however, by an amount which is consistent with expectations.
Born-Oppenheimer breakdown and isotope effects in 3Π electronic states
Authors: Miller Terry A.
Published: February 2004

Recent MOMRIE (microwave optical magnetic resonance induced by electrons) experiments on the d (3p) 3Πu state of ortho- and para-H2 and D2 have revealed discrepancies in measured fine structure parameters (spin-orbit and spin-spin coupling constants, etc.) which are inexplicable in terms of the Born-Oppenheimer approximation. A general theory is developed to account for the effect of homogeneous and heterogeneous perturbations, both regular and irregular, upon the measured fine structure constants of a 3Π electronic state. In particular the various perturbations' mass and symmetry dependences are determined. To make the theory applicable to an analysis of the experimental results for the d(3p) 3Πu states of H2 and D2, other mass dependent effects-adiabatic, Born-Oppenheimer isotope, and vibrational-which alter fine structure are also considered.
Fine structure and perturbations in the d (3p) 3Πu states of H2 and D2
Authors: Miller Terry A. , Freund Robert S.
Published: February 2004

Previous measurements of the so-called spin-orbit and spin-spin coupling constants, orbital angular momentum g factor, and the anisotropy of the magnetic susceptibility of H2 and D2 in the d (3p) 3Πu state are analyzed according to the theory of the preceding paper [T. A. Miller, J. Chem. Phys. 59, 4078 (1973)]. This analysis yields fine structure parameters which are free of the effects of perturbation or Born-Oppenheimer breakdown. These parameters are compared to recent theoretical calculations, and quite good agreement is found except for the spin-orbit coupling constant. However, the discrepancy between theory and experiment is much larger than the experimental error for all the parameters except the least accurately measured hyperfine coupling constants. The analysis also determines values for regular and irregular heterogeneous perturbations of the d (3p) 3Πu state, as well as showing that homogeneous perturbations are not significantly greater than the experimental error of the parameters. The heterogeneous perturbations are used to obtain approximate values of matrix elements between the d (3p) 3Πu state and 3Σu+ states. These matrix elements test the hypothesis of pure precession, the variability of perturbations with internuclear distance, and the number of perturbing states.
Theoretical studies of hot-atom reactions. III. Solution of the integral reaction probability equation for quantum-mechanical nonreactive scattering
Authors: Adams John T. , Porter Richard N.
Published: February 2004

A mathematical technique by which the previously derived IRP equation for a multicomponent mixture can be solved accurately for the integral reaction probability, when quantum-mechanical oscillations are included in the model for nonreactive scattering, is described. The kernel corresponding to a quantum-mechanical hard-sphere model for nonreactive scattering is developed. The known functions required for the calculation of the kernel are analyzed for the case of hot tritrium reactions with isotopic hydrogen molecules in the presence of rare-gas moderators. The algebraic method of solution of the IRP equation is general and can be applied to any inhomogeneous Volterra equation of the second kind. It is particularly recommended when the kernel is oscillatory and/or asymmetric.
Molecular electron affinities from collisional ionization of cesium. I. NO, NO2, and N2O
Authors: Nalley S. J. , Compton R. N. , Schweinler H. C. , Anderson V. E.
Published: February 2004

The relative cross sections for the production of parent negative ions and O− fragment ions resulting from collisions of fast cesium atoms with Maxwellian target gases of NO, NO2, and N2O have been studied as a function of the incident cesium beam energy from 0 to ≈40 eV. A charge exchange source is used to produce the atomic cesium beam, and the energy distribution of the cesium beam is determined by a time-of-flight analysis. A time-of-flight mass spectrometer employing ion counting techniques is used to identify the masses of the ions. Measurements of the thresholds for the charge exchange reactions yield accurate lower limits to the electron affinities of NO, NO2, and N2O of 0.1 ± 0.1, 2.5 ± 0.1, and − 0.15 ± 0.1 eV, respectively. The tailing of the cross section at threshold due to Doppler motion of the target gas is accounted for by a mathematical unfolding procedure.
Termolecular and saturated termolecular kinetics for Li+ and F−
Authors: Spears Kenneth G. , Ferguson E. E.
Published: February 2004

The termolecular association of Li+ with nineteen molecules was observed in helium at 0.3–1.0 torr. The molecules included N2, CO2, SO2, NH3, substituted methanes, and substituted ethylenes. The rates ranged from 8(−31) to 5(−27) cm6 molecule−2 sec−1. Six molecules were observed to have a transition from termolecular to saturated termolecular kinetics in the 0.3 to 1.0 torr pressure range and C4F8, C2Cl2F4, and C2F6 were saturated termolecular at 0.2 torr in both helium and argon buffer and their rate constants were independent of buffer. Some qualitative comparisons are made on the Li+ association data. The F− associations with NH3, CO2, and SO2 were measured and the large rate for CO2 and SO2 indicates covalent bonding in these compounds. The over-all importance of such measurements as a ``tunable'' probe of kinetics is emphasized.
Oxidation of carbon on (100)W and (100)Mo
Authors: Viswanath Y. , Schmidt L. D.
Published: February 2004

The interaction of carbon and oxygen on the (100) planes of W and Mo has been examined by Auger electron spectroscopy and flash desorption mass spectrometry. When surfaces containing up to one monolayer of carbon are exposed to oxygen at ∼ 10−8 torr at substrate temperatures of 1000 to 1300 °K, rapid removal of carbon is observed. This is described well by assuming that every adsorbed oxygen atom desorbs as a CO molecule as long as the temperature is high enough for evaporation of CO. Binding states of CO on clean and carbon covered surfaces and the diffusion of carbon to the surfaces are also examined. It is shown that the desorption properties of adsorbed oxygen and carbon are essentially identical to those of adsorbed carbon monoxide, and it is suggested that CO in the tightly bound states on these metals may be dissociatively adsorbed. Desorption as CO will occur if both bulk solution and desorption of one of the species are slow at temperatures up to the desorption temperature. This is found to be true on W but less so on Mo.
Multiplet splitting in 1s hole states of molecules
Authors: Davis D. W. , Martin R. L. , Banna M. S. , Shirley D. A.
Published: February 2004

The binding energies of selected C, N, O, and F 1s electrons in six paramagnetic molecules were measured by x-ray photoemission. A splitting of 1.934(41) eV was observed in the N(1s) line of NF2, and several other splittings were remeasured or obtained by fitting asymmetric but unresolved lines. Use of the Mg Kα12 doublet profile in fitting improved the fits markedly. A multiplet hole theory was developed to predict the final-state multiplet splitting. It uses atomic exchange integrals, INDO calculations on an ``equivalent-core'' final state to obtain spin densities, and Van Vleck's Theorem to account correctly for multiplicity. It gives results in very good agreement with experiment, and it can be used for larger molecules. During photoemission spin density migrates away from the 1s hole in most cases, and electronic charge flows toward this hole, affecting both the 1s splitting and the 1s binding energy. The lower N(1s) binding energy in di-t -butylnitroxide than in NO arises from electron flow to nitrogen from the t -butyl group during photoemission. This inductive effect is closely related to the ease of substitution of nucleophilic groups in unimolecular reactions with tertiary alkyl halides, a phenomenon that must also be understood in terms of final- (or transition-) state properties, rather than simply in terms of the initial state. Inequivalent fluorines in N2F4 were identified by an unresolved doublet structure in the F(1s) peak.
Photoionization of carbon dioxide
Authors: McCulloh K. E.
Published: February 2004

The yields of photoions from CO2 cooled to 150 °K have been measured at a resolution of 0.22 Å for CO2+ and 0.4 Å for the O+ and CO+ fragments, in the photon energy region extending from onset for each species to approximately 20 eV. Most of the observed structure of the molecular ion yield curve recapitulates the well known features of the absorption spectrum, but a number of anomalies are reported. Autoionization peaks at photon energies just above the first molecular ionization limit of 13.773 ± 0.002 eV do not fit into a pattern characteristic of Rydberg series converging to excited vibrational levels of the ion. Although the Tanaka-Ogawa series and Henning's sharp series can be assigned as ns Rydberg series on the basis of quantum defects, the expected 3s members could not be observed in the present study. The most prominent feature of the O+ yield curve is a step at 19.39 eV, suggesting that the principal mechanism for production of this fragment is predissociation of CO2+ (C 2 Σg+) in its ground vibrational state. Completeness of this predissociation is inferred, although the proposed explanation involves doublet-quartet mixing at large bending angles. The structure of the O+ yield curve between 19.07 and 19.39 eV suggests that Rydberg states converging to CO2+ (C) also undergo predissociation, with spontaneous ionization, to produce this fragment ion. Evidence pertaining to production of CO+ fragments by predissociation of excited vibrational states of CO2+(C) is also presented.
Ionic collision processes in mixtures of hydrogen and rare gases
Authors: Ryan K. R. , Graham I. G.
Published: February 2004

Bimolecular reactions which occur in weakly ionized mixtures of (H2 + He), (H2 + Ne), (H2 + Ar), and (H2 + Kr) have been studied while the ions are contained in the space charge trap generated by the passage of a low energy electron beam through the ion source of a mass spectrometer. For the mixtures (H2 + He) and (H2 + Ne) the results observed for the primary ions are in agreement with the results of earlier studies. However the hydride ions, produced by reaction of H2+ with He or Ne, have been found to react with rate coefficients which are about 50 times higher than those reported previously. In (H2 + Ar) and (H2 + Kr) mixtures the H2+ ions have been found to react with rate coefficients which are in good agreement with the polarization theory. Ar+ ions on collision with H2 react with only about half the predicted value, and approximately one reactive collision in four leads to the formation of H2+. Both the 2P(3/2) and the 2P(1/2) states of Kr+ appear to react with a rate coefficient which is only 10% of the value predicted by the polarization theory. A process has been observed in (Kr + H2) mixtures which leads to the production of H2+ ions. Evidence is presented to support the contention that this process is the collisional deactivation of a krypton ion in a metastable state.
Linewidths and transition probabilities for the carbon monoxide laser lines
Authors: Weisbach Michael F. , Chackerian Charles
Published: February 2004

The pressure broadening at high temperatures and the radiative transition probabilities for some of the carbon monoxide vibration-rotation transitions, Δν = 1, have been measured by the absorption of laser light in shock heated CO. The results are compared with other experimental data, and formulas for pressure broadening and the dipole moment function of CO are deduced.
Positron lifetimes in alkali borate glasses
Authors: Paul A. , Singru R. M. , Singh K. P.
Published: February 2004

Positron lifetimes have been studied in alkali borate glasses of types x Na2O, (1 − x) B2O3 and 0.17 Na2O, 0.83 B2O3 + m Al2O3 for various values of x and m, respectively. It is known that the coordination and free volume in these glasses show a marked variation with the molar fractions x and m. Present measurements show that the orthopositronium lifetimes τ2 and their intensities I2 are significantly affected by the changes in the coordination and the free volume in these glasses. Although the behavior of I2 is in qualitative agreement with the trends predicted by the free volume model, the lifetime τ2 of the orthopositronium shows an anomalous behavior. Four-coordinated aluminum has been found to have more influence in determining τ2 and I2 than four-coordinated boron in these glasses.
Liquid crystal phase transitions in mixtures of rodlike and platelike molecules
Authors: Alben Richard
Published: February 2004

Model calculations are presented which indicate that the character of the nematic-isotropic phase transition can be continuously changed from first to second order and that a new biaxial liquid crystal phase can be obtained by mixing suitable platelike and rodlike molecules. Precursors of the predicted behavior should be observable from trends in the concentration dependence of the transition temperature and the discontinuity in the order parameter.
NMR relaxation of adsorbed gases: Hydrogen on graphite at low coverages
Authors: Riehl J. W. , Fisher C. J.
Published: February 2004

Spin-lattice (T1) and spin-spin (T2) relaxation times have been measured for hydrogen (H2) adsorbed on a graphitized carbon black, using pulse techniques at 30 MHz. Temperatures ranged from 12–28 °K, fractional coverages from 0.03 to 0.33 of a statistical monolayer. An interpretation based on a hindered translation-rotation model is presented.
Photoelectron spectra of intramolecularly hydrogen bonded compounds
Authors: Leavell Sharron , Steichen John , Franklin J. L.
Published: February 2004

The photoelectron spectra of a series of intramolecularly hydrogen bonded compounds have been studied at several temperatures along with the spectra of their nonhydrogen bonded analogs. The hydrogen bonded compounds studied were 2-aminoethanol, 3-amino-1-propanol, N, N-dimethyl-2-aminoethanol, N,N-diethyl-2-aminoethanol, N,N-dimethyl-3-amino-1-propanol, N,N-diethyl-3-amino-1-propanol, and 2-iodoethanol. The nonhydrogen bonded analogs include 2-methoxyethylamine, 3-methoxypropylamine, and 2-methoxyethyl iodide. The spectra were studied at 23 and at 200 °C with a few also examined at intermediate temperatures. It was observed in all the hydrogen bonded compounds that the ionization potential of the electron donor, i.e., N or I was temperature dependent, and decreased with increasing temperature. The ionization potentials of these compounds were markedly greater than the values for the nonbonded analogs. This difference is interpreted to be due to the stabilization energy of the lone pair involved in hydrogen bonding. In two of the systems, N,N-dimethylaminopropanol and N,N-diethylamino-propanol, the oxygen band also appeared temperature dependent. In these more strongly hydrogen bonded systems, hydrogen bond formation was interpreted to affect the electronic charge density on the oxygen with consequent effects on the oxygen ionization potential.
Ab initio dynamics: HeH+ + H2 → He + H3+ (C 2ν) classical trajectories using a quantum mechanical potential-energy surface
Authors: McLaughlin Donald R. , Thompson Donald L.
Published: February 2004

Tabular values of near-Hartree-Fock ab initio energies for the ground electronic state of HeH3+ were expressed in analytical form by fitting with spline interpolation functions. The interpolation functions were then used to provide the potential-energy gradients necessary for dynamical calculations. General features of this method for representing potential-energy surfaces are discussed. Classical trajectories have been computed for the ion-molecule reaction HeH++H2 → He+H3++2.6 eV, constrained to follow C2ν symmetry reaction paths for which there is no energy barrier. Trajectories were run under the conditions: relative translational energies 0.001 and 0.1298 eV and internal vibrational states of reactants with quantum numbers 0 and 2; the initial vibrational phases of each trajectory were selected randomly. Analysis of the results revealed that most of the energy available to the products (including the exothermicity of the reaction) ends up as H3+ vibrational energy; more than half of the collisions produced greater than 90% vibrational energy conversion independent of temperature but decreasing slightly for higher initial vibrational states.
Exciton transitions in crystalline anthracene for k perpendicular to the b axis
Authors: Philpott Michael R.
Published: February 2004

The energy and oscillator strength of exciton transitions with wave vector k perpendicular to the b crystal axis of anthracene are calculated using the second quantized boson theory and compared with the results of reflection spectroscopy. The lattice sums of intermolecular interactions used in the calculations have a dipole component, computed using Ewald's method, and a nondipolar higher multipole part. The latter was obtained by rescaling the lattice sums of Silbey, Rice, and Jortner who calculated the exciton interactions using Pariser wavefunctions. The calculations are compared with the reflection spectra of faces (001) and (201̄) obtained by Clark. Inclusion of the nondipolar interaction leads to substantial improvement in the agreement of theory with experiment. Predictions are made for wave vectors with directions k perpendicular and parallel to the long (L) axis of the molecule as well as for another direction intermediate between the normals to the (001) and (201̄) planes.
ESR studies of electron irradiated K3IrIII(CN)6 in KCl single crystals. II. Strong quadrupole effects on the hyperfine structure in IrII(CN)5 species
Authors: Vugman N. V. , Caride A. O. , Danon J.
Published: February 2004

The effects of a large quadrupolar interaction in the IrII(CN)5 molecule in a KCl lattice are analysed using a MAGNSPEC computer program. Some empirical rules are given to help in the interpretation of this kind of spectra. g and A formulas deduced in a ligand field approximation for a d z2 ground state are used to calculate the unpaired electron density on the metal. The hyperfine constant are determined to be positive leading to a positive value for the core polarization constant χ, indicating a contribution of 6s wave function to the unpaired electron molecular orbital. The analysis of the ESR data indicate the presence of two nonequivalent sites for the IrII(CN)5 molecule in KCl, differing only by the orientation of the principal axes of the quadrupolar interaction. A possible influence of the vacancies created by charge compensation on the existence of these two sites is discussed. The ratio between the nuclear quadrupole moments for the iridium isotopes is determined to be 193Q: 191Q = 0.91 ± 0.03.
Vibrational levels near dissociation in Mg2 and long-range forces
Authors: Li Kwong C. , Stwalley William C.
Published: February 2004

The vibrational levels v = 0 – 12 of the (ground state) van der Waals molecule, Mg2, were observed and analyzed by Balfour and Douglas [Can. J. Phys. 48, 901 (1970)]. It was subsequently shown that the outer turning points of the higher observed levels were sensitive to the r−6 and r−8 terms of the long-range potential. We have reexamined a plate of Mg2 spectrum generously made available to us by Balfour and Douglas and obtained analyses of two bands involving v = 13. We have constructed new RKR potentials up to v = 13 for various values of J(14, 20, 32) which have turning points at distances as large as 8.28 Å. The analysis of these data to obtain more reliable values of the dissociation limit [D0 = 404.1 (±0.5) cm−1] and of the C8 coefficient [C8 = 0.51(±0.09) × 108 cm−1 Å8] is given.
Toluene: Phosphorescence spectrum and distortion in the triplet state
Authors: Haaland David M. , Nieman G. C.
Published: February 2004

Relatively sharp phosphorescence spectra have been obtained for toluene and a few of its deuterated analogs in a crystalline benzene matrix at 4°K. The vibronic fundamentals observed in the phosphorescence are reported for toluene-h8(C6H5CH3), toluene-αd3(C6H5CD3), toluene-d5(C6D5CH3), and toluene-d8(C6D5CD3). The entire phosphorescence spectra obtained for toluene-h8 and toluene-d8 are recorded and assigned. The relative intensities of some important vibronic progressions in all four toluenes are shown to indicate both planar and nonplanar distortions in the lowest triplet state of this molecule. Making use of the results of a normal coordinate analysis, quantitative calculations show that the lowest triplet of toluene has an expanded ring which is quinoidally distorted (two short, four long C–C bonds) with the methyl group lying at the apex of two long bonds and out of the plane of the ring. The side aryl hydrogens appear to be bent in the plane of the molecule. Although some of the intensity of the 0,0 transition is shown to be vibronically induced by the distortion, some of its intensity is derived from the purely electronic transition of the lowest triplet to the ground state.
Mössbauer spectroscopy of 121Sb in adduct complexes of antimony pentachloride
Authors: Friedt J. M. , Shenoy G. K. , Burgard M.
Published: February 2004

The Mössbauer spectra of Sb121 in a variety of oxygen and nitrogen adduct complexes of antimony pentachloride (SbCl5L where L = NCCH3, NCC(CH3)3, NCCl, NCCCl3, OPCl3, OP(Ph)3, DMF, DMSO, NO2CH3, ON(CH3)3, Cl−, Br−) are reported. The experimental data are analyzed using the transmission integral. This technique is shown to be essential in order to get reliable hyperfine interaction parameters. Under these conditions the quadrupole interactions deduced from the Mössbauer spectra are in perfect agreement with those measured by NQR spectroscopy. The dependence of the quadrupole interaction and isomer shift on the donor power of the adduct ligand is explained in terms of the variation of the number of electrons transferred between the antimony atom and the six surrounding ligands and is supported by the NQR data available on the chlorine ions.
Magnetic and structural properties of manganese pyridine linear chain salts
Authors: Richards Peter M. , Quinn Rod K. , Morosin B.
Published: February 2004

We report on the structure and magnetic susceptibility of the pyridine complexes of manganese chloride PyHMnCl3 · H2O (PMC) and MnCl2 · 2Py (DCPM) (Py = NC5H5, pyridine) and on the ESR of PMC. The structures suggest that the Mn++ ions form magnetic linear chains similar to those in MCl2 · 2Py (M = Cu or Co). The exchange constants from the susceptibility are J/kB = −0.69°K±0.04°K and −0.59°K±0.04°K for PMC and DCPM, respectively. The ESR shows the angular dependence and non-Lorentzian line shape characteristic of one-dimensional systems.
Visible and near ultraviolet light produced by the radiative decay of long-lived states in a nitrogen ion beam
Authors: Maier William B. , Holland Redus F.
Published: February 2004

Optical emissions from the decay of long-lived, excited states of N2+28 and N2+30 in ion beams have been studied. Spectra are obtained for wavelengths between 3200 and 6000 Å. Most (∼ 80%−90%) of the emission is consistent with light emitted in A 2Πu → X 2Σg+ transitions, for A2Πu vibrational levels with ν′ as high as 30. For an electron energy Ee of 63 eV, about 25% of the N2+28 produced is initially in the A2Πu, ν′ = 2–9 levels; 0.7% is in the ν′ = 10–19 levels; and 0.3% is in the ν′ = 20–30 levels. Energies of N2+ (A 2Πu, v′) states for ν′≤ 30 are found to be close to the energies calculated from formulas that are known to be valid when ν′ ≤ 9. The electronic transition moment R̄e is found to vary rather slowly for internuclear distances between 0.92 and 1.1 Å. Apparent lifetimes of 6–7 μsec have been measured for emission in selected spectral ranges; these apparent lifetimes are consistent with the observed R̄e and with previously measured lifetimes of the A2Πu vibrational states. The electron energy dependences measured for light output at selected wavelengths rise from threshold to a maximum around Ee = 32 eV and then decrease at higher Ee. The electron impact ionization process produces rotational populations of N2+ (A 2Πu) which correspond to an effective temperature higher than the temperature of the target N2. We suggest that the high A2Πu vibrational levels, rather than the N2+ quartet states, may be involved in the production of N3+ by electron impact on room-temperature N2.
Temperature and density dependence of 129Xe chemical shift in xenon gas
Authors: Jameson Cynthia J. , Jameson A. Keith , Cohen Sheila M.
Published: February 2004

Studies of density dependence of 129Xe chemical shift in xenon gas at room temperature have shown that while the chemical shielding does have quadratic and cubic dependence on density over densities up to 250 amagat, σ(ρ, T) = σ0 + σ1(T)ρ + σ2(T)ρ2 + σ3(T)ρ3, the curve is essentially linear up to about 100 amagat. We have now obtained σ1(T), the linear density coefficient of chemical shielding, for pure xenon over the temperature range 240–440 °K. The experimental values of σ1(T) can be fitted by a fourth degree polynomial: σ1(τ) = 0.536 − 0.135 × 10−2τ + 0.132 × 10−4 τ2 − 0.598 × 10−7τ3 + 0.663 × 10−10τ4 (ppm/amagat), where τ = T − 300 °K. Comparison is made with σ1(T) for other nuclei and with σ1(T) predicted by various theoretical models.
Circular dichroism of an optically active benzene chromophore-1-methylindan
Authors: Allen Susan D. , Schnepp O.
Published: February 2004

The gas phase circular dichroism and absorption spectra of a conformationally stable, optically active benzene chromophore, S-(+)-1-methylindan, has been measured from 280 to 170 nm. The structure of the CD spectrum differs from that of the absorption in the B1u region and this observation is interpreted as evidence for the presence of a σ−π* or π−σ* E1g state in addition to the π−π* B1u state. Also, the CD spectrum near 190 nm requires the conclusion that an additional electronic state is located between the analogs of the B1u and E1u states. This state is assigned as E2g, in agreement with consistent theoretical predictions. The observed CD spectra can be accounted for in a consistent manner on the basis of a scheme which uses the results of parametrized calculations of coupled-oscillator contributions and one-electron term calculation results due to Caldwell and Kauzmann for the molecule studied.
Photoionization yields in N2 in the band series from 734 to 796 Å
Authors: Carter Virginia L. , Berkowitz Joseph
Published: February 2004

Photoionization yields in the band series in N2 from 734 to 796 Å are computed using the narrow bandwidth (Δλ = 0.04 Å) photoabsorption cross sections of Carter and the relative photoionization cross sections of Berkowitz and Chupka (Δλ = 0.12 Å). The relative data are normalized to photoionization cross section data of Samson and Cairns. The results presented for the Ogawa-Tanaka Rydberg series and Worley's third Rydberg series are in substantial agreement with the 0.2 Å bandwidth work of Cook and Ogawa although new data at higher principal quantum numbers (m = 7, 8, 9) are presented. Photoionization yields in the four Ogawa progressions are also reported. Even with less peak overlapping at higher resolution the underlying continuum appears to have an ionization yield less than unity. This result is in accord with findings in other simple diatomic molecules.
On the problem of the vibrational spectrum and structure of ice Ih: Lattice dynamical calculations
Authors: Bosi Paola , Tubino Riccardo , Zerbi Giuseppe
Published: February 2004

It is experimentally known that ice Ih is orientationally disordered. The vibrational spectrum has been previously interpreted by other authors in terms of a simplified point mass model. On the basis of this model long-range forces, spectral activation by the disorder, fluctuating ordered polar domains, etc., were proposed. We present in this paper the results of a lattice dynamical treatment on a complete ordered model of ice Ih which includes the hydrogen atoms. A valence force field has been derived from optical and neutron spectra of H2O and D2O. The introduction of all the vibrational degrees of freedom and their possible interactions does affect the interpretation of the spectrum and the derived spectral conclusions. The interpretations of the spectral evidences on which the previous works were based are discussed.
Sequential adsorption of D2 and C2H4 on single-crystal planes of tungsten
Authors: Cartier P. G. , Rye R. R.
Published: February 2004

The sequential adsorption of deuterium and ethylene has been studied on the (110), (100), (112), and (111) planes of tungsten at [inverted lazy s] 135°K using thermal desorption mass spectroscopy. Adsorption of D2 followed by C2H4 on both the (110) and (112) planes, respectively, leads to 0.24 and 0.37 monolayers of ethylene adsorbed with no displacement of deuterium for an ethylene exposure which would just be sufficient to saturate a bare surface. Since the resulting spectra are apparently superpositions of ethylene decomposition and deuterium desorption, it appears that ethylene and deuterium in part occupy separate sites. On both the (100) and (111) planes adsorption of ethylene occurs through displacement of 1.3 molecules of deuterium for each molecule of ethylene adsorbed. This displacement is more extensive on the (111) plane: θ C2H4=0.86 and θ D2=0.36 on the (111) plane vs θC2H4=0.52 and θD2=0.67 on the (100) plane. Displacement on the (100) plane occurs through adsorption of ethylene on sites separate from deuterium with the ethylene perturbing deuterium sufficiently to lead to desorption. Arguments are given for this interaction being relatively short range. On the (111) plane hydrogen displacement is a thermal process with both D2 displaced by C2H4 and H2 by D2. The D2 is able to displace an amount of H2 corresponding to all the β1 and β2 states and [inverted lazy s] 3/4 of the β3 state. The extent of this displacement indicates that there is extensive interchange between the β states on W(111). Previous data for the sequential adsorption of D2 and C2H4 on polycrystalline tungsten were interpreted as a composite of contributions from individual planes with specifically the (100) plane contributing a high C2H4:D2 ratio and the (110) plane a low C2H4:D2 ratio. The single-crystal results are shown to be in agreement with this. If we assume the polycrystalline surface was partially carbon contaminated, both the spectra and the coverages resulting from sequential adsorption of D2 and C2H4 and the ethylene decomposition spectrum, can be reconstructed using a reasonable linear combination of the results from these four planes.
Rotational motion of molecules and neutron scattering
Authors: Larsson K. E.
Published: February 2004

The differential neutron scattering cross section for scattering from a rigid rotating molecule in a general isotropic medium (condensed or gas state of matter) is presented. It is based on a model, which assumes the complete rotational motion to consist of a damped form of free rotations and of damped librations, respectively. The two phases of rotation are assumed to be coupled to microscopic density fluctuations in the medium in such a way that densities larger than the average allow only damped librations, whereas densities lower than the average allow only damped rotations. The cross section is derived with the aid of a step function formalism first used by Singwi and Sjölander. Further, use is made of Sears' earlier work on rotational scattering cross sections. The resulting cross section describes the molecular motions in a range of conditions from free rotations to undamped libration including all possible intermediate damped motions. The model differs from those created earlier insofar as the rotational diffusion is not necessarily described as a motion consisting of free rotations over smaller or larger angles interrupted by brief collisions. The collisions may in the present model be replaced by shorter or longer periods of libration. Numerical calculations of the Fourier transform, S1(ω), of the first rotational relaxation function, F1(t), is performed using explicit models for the librational and rotational relaxation functions and for such a choice of numerical constants, that the results should describe various hypothetical rotational motions of the methane molecule.