bluuebunny/crossref_metadata_2025 huggingface dataset:
Application of the finite-difference boundary value method to the calculation of Born–Oppenheimer vibrational eigenenergies for the double-minimum E,F 1Σ+g state of the hydrogen molecule
Authors: Truhlar Donald G. , Tarara William Daniel
Published: February 2003

The finite-difference boundary value method is applied to the calculation of Born–Oppenheimer vibrational energies and expectation values of R−2 for an excited state of H2. We estimate the accuracy attainable by this method, point out a systematic error in the previous calculations of Tobin and Hinze, and correct several unjustified statements in the literature. Finally we point out that there is a large uncertainty in the final results due to choice of interpolation scheme.
Difficulties with the Maier–Saupe theory of liquid crystals
Authors: Wulf A.
Published: February 2003

The Maier–Saupe anisotropic dispersion energy is estimated and found to be an order of magnitude smaller than the value usually assumed in the liquid crystal theory. The idea behind the estimate is to compare the anisotropic part of the dispersion energy to the average dispersion energy. This is done with the help of the relation R∼ (Δα/3α)2, where R is the ratio of the perturbation theory sums involved in the anisotropic and average dispersion energies and Δα, α are the polarizability anisotropy and average polarizability, respectively. It is suggested that the total attractive force contributes to the stability of nematic liquid crystals through both a small change in the radial correlations and any density change at the mesomorphic transition (at constant volume the latter is zero). In the resulting picture of liquid crystals the repulsive forces play the primary role.
Electron spin relaxation of di-tertiary-butyl nitroxide in supercooled water
Authors: Ahn Myong-Ku
Published: February 2003

The linewidths and line shapes of electron spin resonance spectra of dilute solutions of di-t-butyl nitroxide in supercooled water were analyzed at temperatures ranging from 15 to −33 °C. The electron spin relaxation is mainly due to the motional effect of anisotropic magnetic interactions. The rapidly increasing linewidths at temperatures below 0 °C reflect a large temperature dependency of the viscosity of supercooled water.
High-temperature thermodynamics of the Ti–H2 and Ti–D2 systems
Authors: Dantzer P. , Kleppa O. J. , Melnichak M. E.
Published: February 2003

The high-temperature thermodynamic properties of the Ti+H2 and Ti+D2 solid systems have been studied by a combined calorimetric and equilibrium method at 706–721 K (both systems) and 971 K (Ti+H2 only). The limiting enthalpies of solution of hydrogen in close-packed hexagonal α-Ti is −10.6 kcal mole−1(H) at the lower temperature, and about −10.9 kcal mole−1(H) at the higher temperature. The corresponding value of ΔH̄D at 707 K is −10.1 kcal mole−1(D). From the hydrogen and deuterium data at 707–721 K we estimate ν̃H in α–Ti to be about 800 cm−1 and ν̃D about 565 cm−1. The equilibrium pressures and the partial enthalpies of hydrogen and deuterium allow an evaluation of the partial entropies and excess entropies, S̄EH and S̄ED. The limiting value of S̄EH at NH≈0 and 706–721 K is 6.5 cal K−1⋅mole−1(H), that of S̄ED at the same temperature is 8.9 cal K−1⋅mole−1(D). These values are larger than corresponding values calculated from ν̃H and ν̃D. This discrepancy suggests either much lower vibrational frequencies (than calculated from ΔH̄H and ΔH̄D), or perhaps a very significant communal entropy term.
An effective Schrödinger equation for the rovibronic energies of H2 and D2
Authors: Bishop David M. , Shih Shing-kuo
Published: February 2003

A new effective Schrödinger equation for the calculation of the rovibronic energies of H2 and D2 is proposed. The equation takes into account nonadiabatic effects and it is used to calculate the nonadiabatic corrections to the adiabatic vibronic energies. The root-mean-square deviation of the corrections from the experimentally derived ones is less than the accuracy of the experimental vibronic energies and smaller than the deviation of the corrections calculated by alternative methods.
Fluids of spheres containing quadrupoles and dipoles: A study using perturbation theory and Monte Carlo computations
Authors: Patey G. N. , Valleau J. P.
Published: February 2003

Thermodynamic perturbation theory is applied to fluids of hard spheres containing quadrupole moments, and the first two nonvanishing terms are calculated. Calculations are carried out to the same order for fluids containing both dipoles and parallel quadrupoles. Monte Carlo computations are performed for a range of quadrupole moments, both for the purely quadrupolar case and for the dipole–quadrupole case with fixed dipole (μ*=1.0). As in the purely dipolar case, convergence of the perturbation series is poor and two terms are inadequate. The Padé approximation to the series is again found to give a remarkably successful representation of the Monte Carlo results, although it is inexact. There is evidence that the perturbation series converges more rapidly than one would infer from the Padé formula. Quadrupoles appear to have much larger thermodynamic effects than comparable dipoles, and some interesting contrasts in their structural behaviors are discussed.
The vibrational spectrum of liquid chromium pentafluoride
Authors: Brown Steven D. , Loehr Thomas M. , Gard Gary L.
Published: February 2003

The infrared and Raman spectra of liquid chromium pentafluoride have been recorded. Based on the observation of strong fluorine bridging, characterized by the 475 cm−1 infrared absorption, and upon the number, type, and position of the chromium–fluorine stretches, the compound is assigned to a cis-fluorine bridged, polymeric structure (of C2v microsymmetry) in the liquid state. No evidence for monomer was observed near room temperature.
Rotational correlation in chloroform
Authors: Rosenthal Lois C. , Strauss Herbert L.
Published: February 2003

We have measured the band shapes of the vibrational and low frequency features in the infrared and Raman spectra of liquid chloroform. The various measurements are analyzed to yield the appropriate orientational correlation functions. The dielectric corrections proposed by Klug et al. [J. Chem. Phys. 50, 3904 (1969)] provide the most consistent analysis of the far infrared band. Intensity comparisons for the depolarized Rayleigh wing show the need for ’’cavity’’ corrections to the polarizability anisotropy. The distinct correlation functions [such as Σii≠j〈μi(o) ⋅μj(t) 〉] decay much more slowly than the total of self-correlation functions in agreement with the theory of Keyes and Kivelson [J. Chem. Phys. 56, 1057 (1972)]. We compare our results with previous measurements and discuss a number of the difficulties involved in abstracting the desired correlation functions. Some results for chlorobenzene are also presented and for this molecule ’’cavity’’ corrections seem to be required even for explanation of the intensity of the far infrared band.
Statistical theory of entanglement density in linear polymers and fiber systems. II. Effect of orientation, configurations, and motions on the effectivity of two-dimensional entanglement
Authors: Ziabicki Andrzej
Published: February 2003

Based on the general equations derived in the preceding paper a special case of two-dimensional entanglement has been discussed. It has been shown that the entanglement coefficient ε depends on the geometry of structural elements and their orientations as well as orientation of local motions experienced by the elements.
NMR study of sodium ion motion and distribution in beta-alumina
Authors: Bailey W. , Glowinkowski S. , Story H. , Roth W. L.
Published: February 2003

NMR studies of 23Na in single crystal beta-alumina have been made which include (1) investigation of the quadrupole induced shifts of the 1/2↔−1/2 magnetic transition at 77 and 103 K, and (2) measurement of the width of the 23Na-NMR line as a function of temperature for several crystal orientations. The low temperature rotation patterns show that sodium ions occupy several independent sites in the lattice. At temperatures above about 110 K, the jumping of sodium ions among these several sites is manifested by motional narrowing of the quadrupolar spectrum. At these higher temperatures, a single, symmetric resonance line is observed. Analysis of the narrowing of this resonance line with increasing temperature yields an activation energy of 0.1 eV.
Phase transition in the dioxygenyl salt O+2AsF−6
Authors: Naulin C. , Bougon R.
Published: February 2003

The phase transition previously observed by 19F broad-line NMR spectroscopy has been confirmed by calorimetry, x-ray diffraction, and vibrational spectroscopy. A hysteresis effect has been detected between the transition temperature through cooling (∼268 K) and through heating (289.8±0.2 K). In both cases, entropy and enthalpy variations have been evaluated to be 4.85±0.02 cal  mol−1⋅K−1 and 1.405±0.005 kcal mol−1, respectively. The low temperature x-ray diagram has not yet been indexed but seems to belong to a crystalline system of a lower symmetry than orthorhombic. Vibrational spectroscopy has shown that passing from the cubic to the low symmetry form, the AsF−6 site symmetry group is lowered from Th to C2h or Ci. The attribution of the phase transition to a dioxygenyl motion freezing is confirmed by this study.
High field level crossing measurements of the A 2Σ+ state of OD
Authors: German K. R.
Published: February 2003

High field level crossing measurements have been performed on the v′=0 and the v′=1 levels of the A 2Σ+ state of OD using a tunable laser excitation source. The hyperfine constants were found to be b=109.73±0.10 MHz, c=25.73±0.25 MHz, and eqQ=0.22±0.03 MHz for v′=0 and b=111.15±0.10 MHz, c=24.40±0.25 MHz, and eqQ=0.05±0.04 MHz for v′=1. The measured values of the magnetic hyperfine constants are found to be within a few percent of the values obtained from an ab initio theoretical calculation.
Intensity dependence in laser flash photolysis experiments: Hydrated electron formation from ferrocyanide, tyrosine, and tryptophan
Authors: Lachish Uri , Shafferman Avigdor , Stein Gabriel
Published: February 2003

The light intensity dependence in monophotonic and consecutive biphotonic processes under laser flash photolysis conditions is derived. In a monophotonic process the relation between photoproduct yield and exciting light intensity is linear but there is saturation at high intensity. In a biphotonic process there are three different regions. The relation is quadratic at low intensity, linear at medium intensity, and there is saturation at high intensity. The difference between the two linear relations is discussed. These results are applied for analyzing the process of hydrated electron formation from excited states of various substances. The process is found to be monophotonic for ferrocyanide. For tyrosine and tryptophan in aqueous neutral solutions, under the conditions of the laser experiments, a biphotonic process is observed. For the tyrosinate ion (alkaline solution pH 12) the findings are not conclusive. Other work on this topic is discussed with reference to the analysis.
Calculation of the contact value of the first- and second-order terms in the perturbation expansion of the radial distribution function for the square-well potential
Authors: Henderson D. , Barker J. A. , Smith W. R.
Published: February 2003

More accurate values of the first-order perturbation term g1(r) of the square-well fluid RDF are given. These values should be used in place of the earlier values of Smith, Henderson, and Barker [J. Chem. Phys. 55, 4027 (1971)].
Theoretical thermodynamic functions for argon gas
Authors: Carley David D.
Published: February 2003

Theoretical thermodynamic functions are computed for argon gas assuming a pair-potential function of the Lennard-Jones 6-12 form. A parametric integral equation is used to obtain radial distribution functions which are then used to obtain the pressure and internal energy. The entropy, enthalpy, heat capacity at constant volume, Helmholtz function, and Gibbs function are then obtained as functions of temperature and density. The parameter in the integral equation is obtained by requiring agreement in the theoretical and experimental pressures at high density. The theoretical computations are compared with experimental results for a range of temperatures from 0 to 150 °C and for densities up to 640 amagat (pressures to 2900 atm). The agreement between experiment and theory is reasonably good; however, some differences indicate that improvement might be obtained using a different pair-potential function.
Anticrossings and microwave transitions between triplet states of D2
Authors: Freund Robert S. , Miller Terry A. , Zegarski Bernard R.
Published: February 2003

Electric field induced anticrossings and X-band microwave transitions have been observed between the magnetically tuned Zeeman levels of the d (3p) 3Πu, v=3, N=1 and the i (3d) 3Πg, v=3, N=1 levels of para D2. This experiment provides the second, and most precise, interconnection between the two sets of D2 triplets which are not connected by visible spectra. The separation between the above named states is 0.8960±0.0003 cm−1. Values for the spin–orbit coupling constant, the spin–spin coupling constant, and the orbital angular momentum g factor in the 3d 3Πg state have been determined. These values show strong L uncoupling effets and indicate that the D2 i (3d) 3Πg state is intermediate between Hund’s case b and d coupling.
Effect of angular momentum on the relaxation time in a multicomponent gas mixture
Authors: Biolsi Louis
Published: February 2003

The effects of molecular angular momentum (spin polarization) on the bulk viscosity and relaxation time in a multicomponent gas mixture are considered. Formal theoretical results are obtained, using the Wang Chang–Uhlenbeck approach to the kinetic theory of gases with internal states. The results are given in terms of integrals over the weighted quantum mechanical degeneracy averaged cross section.
Magnetic effects on delayed fluorescence in doped naphthalene and anthracene crystals
Authors: Chabr M. , Zschokke-Gränacher I.
Published: February 2003

We have solved the density matrix equation for mutual triplet annihilation in some special cases. The solution allows a simple calculation of the magnetic field dependence of the annihilation rate γs for homofusion at high and intermediate magnetic fields and for heterofusion in the high field limit. In our experiments we have measured the magnetic field anisotropy of the guest delayed fluorescence in doped anthracene and naphthalene crystals. By using the resonance condition for heterofusion, the positions of the resonance peaks have been calculated. A comparison of the measured and calculated resonance directions shows that tetracene enters the anthracene lattice substitutionally oriented, whereas the orientation of pyrene molecules in naphthalene differs slightly from the substitutional one. Furthermore, we have shown that in the latter case the host–guest annihilation gives rise almost exclusively to guest delayed fluorescence, although the excitation of the host singlet state is energetically possible.
Ethylene hydrogenation on evaporated iridium films
Authors: Mahaffy Paul , Masterson Paul B. , Hansen Robert S.
Published: February 2003

The reaction of ethylene with hydrogen to form ethane and methane is studied over evaporated iridium thin film catalysts. The rate law obtained at total pressures up to 1000 μ and temperatures between 110 and 200°K is of the form R=KP0C2H4P1/2H2 exp(−3.3 kcal/mole/RT), where 0 and 1/2 are the reaction orders in ethylene and hydrogen, respectively. Over a wider temperature range (up to 100 °C) the reaction is characterized by the use of 13C labeled ethylene or deuterium in the place of hydrogen. The kinetic results taken in conjunction with the isotope studies are consistent with a Langmuir–Hinshelwood hydrogenation mechanism involving the half-hydrogenated ethyl species C2H5 (a) first postulated by Polanyi. At temperatures greater than ∼150°K the rate of a surface dehydrogenation reaction becomes significant. The extent of this surface reaction can be determined by monitoring the amount of ethane produced when only ethylene is dosed on a clean Ir film or by observing nonlinearities in the Arrhenius plots when both hydrogen and ethylene are dosed. Production of methane from ethane decomposition at 373°K is poisoned by ethylene adsorption. Film area as measured by both hydrogen adsorption and catalytic activity is proportional to film thickness for average thicknesses of 30 to 200 Å.
Generalized Nernst–Planck and Stefan–Maxwell equations for membrane transport
Authors: Mehta G. D. , Morse T. F. , Mason E. A. , Daneshpajooh M. H.
Published: February 2003

A generalized treatment of fluid transport in a porous membrane is developed on the basis of the ’’dusty-gas’’ model, which is extended to include electrical forces due to charges on the solutes and the membrane. The Stefan–Maxwell diffusion equations are augmented to include viscous flow, and then phenomenologically generalized for the case of any fluid mixture. The resulting generalized transport equations are cast back into the original Stefan–Maxwell form. From these a set of generalized Nernst–Planck equations is obtained that includes convective flow and solute–solute interactions. It is demonstrated that viscous flow effects can be properly incorporated into the Stefan–Maxwell equations by augmenting the diffusion coefficients with viscosity terms. It is also shown that the main source of error in the usual simplified form of the Nernst–Planck equations lies in the treatment of convective flow terms. The generalized Nernst–Planck equations approach the proper limit for gases in both the Knudsen and continuum regimes, and can be easily reduced for liquid solutions to the simple form proposed by Schlögl and others.
Systematics of the Landau–Zener rate constant
Authors: Faist M. B. , Bernstein R. B.
Published: February 2003

The binary rate coefficient for atomic collision processes governed by a potential curve-crossing mechanism is obtained from the closed-form Landau–Zener (LZ) cross section approximation. The results are presented in the form of a table (and graphs) of reduced LZ rate constants vs reduced temperature T* as a function of a reduced ’’system-parameter’’ ζ*. The dependence of the rate coefficient upon the curve-crossing characteristics of the system and the temperature is readily understood in terms of the structure of the parameters ζ* and T* and the scaling of the reduced rate constant.
Photoemission from hydrogen-bonded solids: Quasiliquid layer effect
Authors: Nason D.
Published: February 2003

Photoemission studies have been conducted for several hydrogen-bonded and non-hydrogen-bonded substances using uv radiation from a mercury arc. Only the hydrogen-bonded substances showed measurable photoemission. The photoemission current was generally similar for the liquid and solid phases near the melting point, decreasing with decreasing temperature and vanishing at a temperature well below the melting point. The photoactivity threshold lies between 4.9 and 6.7 eV for the photoactive substances studied. The temperature dependence of the photoactivity supports the case for the existence of a quasiliquid layer on the surface of hydrogen-bonded solids, the layer being stable to temperatures well below the bulk melting temperature.
Ion identity and transport properties in CO2 over a wide pressure range
Authors: Ellis H. W. , Pai R. Y. , Gatland I. R. , McDaniel E. W. , Wernlund Roger , Cohen M. J.
Published: February 2003

We have investigated in drift tube mass spectrometers the identity and the transport properties of ions formed in CO2 gas at pressures ranging from 10−4 to 762 torr. Under bombardment by low energy (20–100 eV) electrons in the ion source, the primary positive ion is predominantly CO+2, with traces of C+, O+, and CO+. The predominant ion becomes O+2 at pressures above 100 μ (0.1 torr), and clustering of CO2 molecules to the O2+ occurs even at pressures below 1 torr. Break-up of the clusters also occurs, the ion identity changing many times in the drift region. The zero-field reduced mobility of the O+2⋅ (CO2)n charge carrier is a function of pressure, and varies from (1.30±0.03) cm2/V⋅sec at 0.2 torr to (1.18±0.03) cm2/V⋅sec at 1 torr. The sole negative ion produced directly by the electron bombardment is O−, which clusters to form the stable ion CO−3, whose reduced mobility is (1.27±0.06) cm2/V⋅sec for E/N ?60 Td at all pressures below 1 torr. At much higher pressures and under somewhat different conditions (above 30 torr and using beta source ionization), ions in CO2 are observed to form multiple clusters, the population distribution among the clusters being strongly dependent on gas temperature. The zero-field reduced mobility of the charge carrier is largely independent of the identity of the core ion, and varies with pressure from roughly 1.2 cm2 /V⋅sec at 35 torr to about 1.0 cm2/V⋅sec at 762 torr.
Electron paramagnetic resonance of palladium complexes in ammonium chloride single crystals
Authors: Sastry M. D.
Published: February 2003

Electron paramagnetic resonance (EPR) study of γ-irradiated ammonium chloride single crystals doped with Pd(II) revealed the formation of paramagnetic Pd(I) and Pd(III) centers at room temperature. Pd(I) has been found to be in a square planar coordination; its g values and chlorine superhyperfine constants suggest a possible formation of (NH4)2 PdCl4 in NH4Cl lattice. Pd(III) with low spin configuration has been found to be in a compressed octahedral coordination. Pd(III) in such a coordination presumably forms owing to the hole trapping of Pd(II) ions situated at the interstitial positions in the ammonium chloride lattice.
Intermolecular forces involving the water molecules in lithium sulfate monohydrate
Authors: Hayward H. Preston , Schiffer Jerome
Published: February 2003

A study of the low-temperature infrared spectra of varyingly deuterated mulls of lithium sulfate monohydrate has afforded information as to the nature of vibrations of water molecules causing infrared absorptions. Using intra- and intermolecular force constants, obtained from the data of doublet spectra, spectra of intermolecularly coupled species were predicted and compared with experiment. The agreement between calculated and observed spectra is good, but not perfect. This indicates that nonneighbor interactions are weak but significant in determining the nature of the stretching modes involving water molecules in Li2SO4⋅H2O. Furthermore, it is shown that the intermolecular interactions involving water molecules are mostly dipolar in origin.
Search for low activation energy abstraction of H from C–H bonds by D atoms in hydrocarbons at 77 K
Authors: Wilkey D. D. , Willard J. E.
Published: February 2003

Experiments have been done to determine whether thermal D atoms produced at 77 K in 3-methylpentane-d14 containing ∼1% C–H bonds as an isotopic impurity are able to abstract H by a low activation energy process, as CH3 radicals are known to do. The D atoms have been produced by 254 nm photolysis of DI. The trends in HD/D2 ratio with changing ratio of C–H bonds to [DI] are consistent with the conclusion that the D+C6H13H→ HD+C6H13 abstraction occurs at 77 K with low activation energy requiring either a tunneling mechanism or unusual molecular distortion in the glass.
Fluorescence of ice by low energy electrons
Authors: Prince R. H. , Sears G. N. , Morgan F. J.
Published: February 2003

Low energy electron-induced fluorescence at 77 °K under conditions of improved signal-to-noise ratio and wavelength resolution is reported, which exhibits differences with respect to high energy radiolysis and previous published work. Three distinct visible emissions are now evident, corresponding to the ∼380 nm emission in bulk irradiated samples, and each is assigned to electron–ion recombination. An intensity increase following deuterium substitution is attributed to predissociation involving states active in the known 124 nm diffuse ultraviolet absorption bands of H2O. Ultraviolet emission at 306 nm is assigned to the hydroxyl (?2Σ+→?2Π) system, and while confirmed by deuterium substitution, this observation is in disagreement with previous low energy radiolysis results which report on substantial blue shift for this spectral feature to ∼280 nm. Finally, alternative radiative schemes are proposed to attempt to reconcile conflicting published data from diverse experimental methods.
Two-mode vibronic interaction between neighboring 1 2A2 and 2 2B2 excited electronic states of the benzyl radical
Authors: Cossart-Magos Claudina , Leach Sydney
Published: February 2003

The 2 2B2–1 2B2 transition of the benzyl radical occurs in the same frequency region as the 1 2A2–1 2B2 transition. Vibronic coupling between the 2 2B2 and 1 2A2 excited electronic states via 6b and 18b vibrational modes is shown to be responsible for the unusual structure of the electronic spectrum of benzyl observed in the visible region. Calculations of vibronic interaction were carried out using a model constructed with crude adiabatic, harmonic oscillator basis functions. The model was expressed in terms of four dimensionless parameters: D, the energy separation between the deperturbed 2 2B2 and 1 2A2 states; Cα and Cβ, which are interaction constants for the α≡18b and β≡6b modes, respectively; the ratio ωα/ωβ of these zero-order mode frequencies. The possible range of these constants is discussed in detail. The model reproduces well the vibronic energies and relative transition intensities of bands observed within 700 cm−1 of the 1 2A2–1 2B2 transition origin for isotopic benzyl radicals. The deperturbed 2 2B2 state origin is found to lie between 430 and 485 cm−1 above the 1 2A2 state in gas phase benzyl-h7 and between 355 and 370 cm−1 in benzyl-d7.
Thermodynamic investigation of the lead molecules Pb2, Pb3, and Pb4 by mass spectrometry
Authors: Gingerich K. A. , Cocke D. L. , Miller F.
Published: February 2003

The high-temperature Knudsen effusion mass spectrometric technique has been used to determine the thermodynamic properties of the molecules Pb2, Pb3, and Pb4. The enthalpies of the following reactions were determined: nPb(s,l) =Pbn(g), Pb(s,l)+Pbn−1(g) = Pbn(g), and Pbn(g) =nPb(g). From the values obtained and appropriate literature data the following atomization energies D°298 and standard heats of formation ΔH°f,298, in kJ per mole, were obtained: Pb2, 81±6 and 310±6; Pb3, 224±16 and 360±16; and Pb4, 408±16 and 372±16.
Endoergic ion–molecule-collision processes of negative ions. V. Collision of I− on HNO3. The electron affinity of NO3
Authors: Refaey Kamel M. A. , Franklin J. L.
Published: February 2003

Endoergic collisions of I− on HNO3 are studied and the cross sections for formation of NO3− for different incident ion I− energies is reported. (AIP)
The multiphoton ionization spectrum of t
r
a
n
s-1,3-butadiene
Authors: Johnson Philip M.
Published: February 2003

The multiphoton ionization spectrum of trans-1,3-butadiene has been measured from dye laser wavelengths of 365 to 468 nm using an intensity-corrected system. In the four-photon ionization region to lower energy than 405 nm, many three-photon resonances with Rydberg states are seen and a new series with a quantum defect of 0.04 is identified. The symmetries of the observed Rydberg series are discussed. Above 405 nm in energy, a resonance occurs with the ? state seen in one-photon absorption spectra, only the structure in the multiphoton ionization spectrum is characteristic of an allowed two-photon resonance. From the vibronic structure of this state, it is argued that it has symmetry 1Bg. In the region covered by this study (42 700 to 54 800 cm−1 in two-photon energy) no state was found to which a 1Ag symmetry designation could be applied.
Fluctuations in spatially homogeneous chemical steady states
Authors: Jähnig Fritz , Richter Peter H.
Published: February 2003

The investigation of the properties of small fluctuations serves as a basis for the generalization of equilibrium and irreversible thermodynamics, to encompass all spatially homogeneous situations of stable chemical steady states. In terms of a Gibbs ensemble picture, the reactants are coupled to particle reservoirs, often in a more intriguing way than in usual grand canonical statistics. It is shown how these couplings can be represented as generalized forces, by postulating an equipartition theorem. Response functions connected with the action of external forces are introduced, and the fluctuation–dissipation theorem is derived as a consequence of the proper definition of forces. The symmetry properties of the systems, with respect to time reversal, provide a classification scheme for the large body of possible steady states.
Oscillator strengths for transitions involving excited states not lowest of their symmetry: Carbon I and fluorine II transitions
Authors: Luken W. L. , Sinanoğlu O.
Published: February 2003

Theoretical f values are reported for the 1657 and 1329 Å transitions of carbon I and the 485, 549, 457, and 513 Å transitions of fluorine II. These involve excited states not lowest of their symmetry. We calculate these using the nonclosed shell many electron theory (NCMET) of Sinanoğlu and proper application of the variational theory required for such nonlowest of symmetry states. The results of this work differ from Hartree–Fock and other values in previous literature by factors of 2–5. Experimental values, where available, are in good agreement with the results of this work. New experimental measurements by methods such as beam foil spectroscopy are recommended for several transitions.
The optical properties of crystalline 1,1′-diethyl-2,2′-cyanine iodide
Authors: Marchetti A. P. , Salzberg C. D. , Walker E. I. P.
Published: February 2003

Optical properties of oriented single crystals of 1,1′-diethyl-2,2′-cyanine iodide (DCI) have been determined by Kramers–Kronig transformation of the reflectance in the visible region. The gross features of these spectra are understood in terms of simple exciton theory when account is taken of directional dispersion. Transmittance and reflectance measurements were also made on thin crystals. These spectra indicated that the thin crystals have a structure different from that of the large opaque crystals. Comparison of all of the crystal spectra with the so-called ’’J’’ and ’’H’’ aggregate bands of photographic importance suggests that these aggregate bands may be due to crystal transitions.
Calculation of the pressure dissociation of H2 by the van der Waals one-fluid theory
Authors: Aviram I. , Goshen S. , Rosenfeld Y. , Thieberger R.
Published: February 2003

A semiclassical model has been proposed earlier to describe the dissociation of molecular hydrogen as a function of temperature and density. The model system consists of free atoms and molecules allowed to interact through repulsive forces only, while the essentially quantum mechanical effect of binding is replaced by artificially assigning each molecule an intrinsic energy −B, where B is the experimental binding energy. In this work the equations are solved in Percus–Yevick (PY) and van der Waals (vdW) one-fluid approximations, and compared with previously published Monte Carlo results. The vdW theory reproduces very well the Monte Carlo calculations, while PY is found to be inadequate in this case.
Generalized valence bond calculations on the ground state (X 1Σ+g) of nitrogen
Authors: Dunning Thom H. , Cartwright David C. , Hunt William J. , Hay P. Jeffrey , Bobrowicz Frank W.
Published: February 2003

Accurate generalized valence bond calculations (GVB) have been carried out on the ground state (X 1Σ+g) of the nitrogen molecule for internuclear distances from 0.80 to 5.00 Å. For comparative purposes, corresponding Hartree–Fock (HF) and valence bond (VB) calculations are also reported. While accounting for only ∼25% of the correlation energy of N2 at R=Re, the GVB calculations account for ∼80% of the molecular extra correlation energy, and yield a dissociation energy of 8.58 eV (compared to 5.08 eV from the HF corresponding calculations). In addition to considerably improving on the HF and VB descriptions of N2, the GVB wavefunction retains a simple orbital form which is susceptible to analysis in terms of nonclassical, as well as classical, chemical concepts.
Electron-impact excitation of UF6 at an electron energy of 20 eV in the energy-loss range of 0–10 eV
Authors: Chutjian A. , Srivastava S. K. , Trajmar S. , Williams W. , Cartwright D. C.
Published: February 2003

Electron-impact excitation of UF6 at low incident electron energies is reported. (AIP)
Dynamical features of the high energy isotope effect in chlorine atom reactions with hydrogen and deuterium
Authors: Stevens Don J. , Spicer Leonard D.
Published: February 2003

An experimental study of recoil chorine atom reactions with H2 and D2 to yield HCl so a function of average relative translational energy is reported. (AIP)
A helium Hartree–Fock orbital suitable for reduced Green’s function calculations
Authors: McDowell H. Keith , McCollum W. N.
Published: February 2003

The occupied radial Hartree-Fock orbital for the ground state of helium atom was determined using many-body perturbation theory. (AIP)
Radiation-induced oxidation and reduction of chloropropionamide
Authors: Box Harold C. , Budzinski Edwin E. , Lilga Kenneth T.
Published: February 2003

The primary oxidation and reduction products were identified using ESR and ENDOR spectroscopy in single crystals of chloropropionamide X irradiated at 4.2 °K. The oxidation product is the radical produced by removal of hydrogen from the amide group. The reduction product results from a dissociative electron attachment process which also produces Cl−.
Inelastic contributions to ion–molecule diffusion cross sections: Li+–H2
Authors: Alexander Millard H.
Published: February 2003

We examine the role played by inelastic collisions in the diffusion of Li+ ions in H2. Explicit expressions are derived for partial diffusion cross sections corresponding to j=0→j′=0,2 transitions. These are used, along with the results of close-coupling calculations, to demonstrate that virtual rotational coupling results in a significant enhancement of the 0→0 diffusion cross section at low energy. The total diffusion cross section and the corresponding collision integral are larger than predicted by a purely elastic calculation based on the spherically symmetric component in the intermolecular potential. This discrepancy might be significant enough to be detected in drift tube experiments.
Interpretation of the low temperature phase transitions in ammonium and potassium chromic alums in terms of vibrational and static crystal distortion contributions to the spin Hamiltonian zero-field splitting parameter D. III
Authors: Manoogian A. , Leclerc A.
Published: February 2003

The spin Hamiltonian zero-field splitting parameter D obtained in ammonium and potassium chromic alums and their isomorphs is analyzed in terms of the temperature dependence of vibrational and static crystal distortion contributions. The analysis shows that the low temperature phase transitions existing in the chromic alums are due to a change in sign of the static trigonal distortion at the chromium sites. For NH4Al and KAl sulfate alums dilutely doped with Cr3+ it is found that the distortions at the Cr3+ sites change sign at temperatures higher than the known transition points in the undoped crystals. Dilutely doped NH4In sulfate alum represents a special case in which the crystal changes phase but the static distortion at the Cr3+ site does not change sign.
Microwave spectrum of formyl chloride
Authors: Takeo Harutoshi , Matsumura Chi
Published: February 2003

The unstable product found in the chlorination of formic acid has been identified as formyl chloride by microwave spectroscopy. The lifetime of this molecule was about 3 min in the waveguide cell at dry ice temperature. The rotational constants of seven isotopic species have been measured and analyzed, yielding moments of inertia from which a molecular structure was calculated. The bond lengths found are (in Å)C–Cl=1.760, C–O=1.188, and C–H= 1.096. The bond angles are HCCl=109°58′ and HCO=126°29′. Planarity was established by the analysis of the inertia defects. The nuclear quadrupole coupling constants in the C–Cl bond-axis system are χzz= −59.8 MHz and η=−0.30. From the analysis of the Stark effect under a weak electric field condition, the dipole moment has been determined as ‖μa‖=0.3±0.2 D, ‖μb‖=1.6±0.2 D, and ‖μtotal‖ = 1.6±0.2 D.
A calculation of the electron affinity of the lithium molecule
Authors: Andersen Earl , Simons Jack
Published: February 2003

Using the equation-of-motion method, an electron affinity of 0.90 eV was computed for the Li2 molecule. This value is larger than the results of other calculations and is also larger than the experimental electron affinity of the lithium atom. A prediction of the stable ground state for Li−2 is a result of our calculation. Using some experimental data and the calculated Li2 electron affinity within a Born–Haber cycle, an approximate dissociation energy of Li−2 can be obtained. SCF-level potential energy curves have been calculated for Li2 and Li−2 as well as spectroscopic constants which give qualitatively good agreement with available experiment results. A comparison between properties of Li−2 and Li+2 is also discussed.
Concentration dependence of the rate of diffusion-controlled reactions
Authors: Felderhof B. U. , Deutch J. M.
Published: February 2003

A theory for the concentration dependence of the rate of diffusion-controlled reactions is formulated. One of the reacting partners is taken to be a collection of static sinks. The steady state situation for a random distribution of these sinks is studied. The rate coefficient is predicted to increase with concentration of sinks and the dependence on concentration is shown to be nonanalytic.
Competitive effects in diffusion-controlled reactions
Authors: Deutch J. M. , Felderhof B. U. , Saxton Michael J.
Published: February 2003

We study diffusion-controlled reactions in a system of static sinks reacting with diffusing molecules and investigate the competitive effects due to the global distribution of sinks. We also study the effect of competition on growth or shrinkage of droplets in coagulation or burning.
Diatomic molecules as perturbed Morse oscillators. II. Extension to higher-order parameters
Authors: Huffaker J. N.
Published: February 2003

Energy levels are calculated for a rotating, vibrating diatomic molecule with perturbed-Morse-oscillator potential energy, V (r) =Ve [y2+b4y4+b5y5+⋅⋅⋅], where y=1−exp [−a (r−re)]. Formulas are presented which permit the determination of model parameters up through b12 from spectral data. Formulas are applied to analyses of electronic ground states of CO, HF, and HCl, and to the B (3Π0u+) state of I2. Results for CO and HF are compared with RKR calculations. While the analyses are mathematically precise for all cases, physical accuracy is greatest for states with many bound vibrational levels.
Many-body perturbation theory applied to electron pair correlation energies. II. Closed-shell second-row diatomic hydrides
Authors: Bartlett Rodney J. , Silver David M.
Published: February 2003

Diagrammatic many-body perturbation theory (MBPT) has been applied to the correlation energy of NaH, AlH, and HCl, within a basis of 47 Slater-type functions located on both centers in the molecule. By summing all second and third order two-body diagrams plus a selection of higher order diagrams via a denominator shift, about 80% of the total correlation energy could be obtained in each case. The individual pair correlation contributions are analyzed and grouped into the shell structure of these molecules, showing that the principal deficiency lies in the inadequacy of the basis sets to describe the inner-shell correlation to extremely high accuracy. Using experimental values for the correlation energy of the Ne-like inner cores of these molecules, together with the calculated MBPT valence shell values, gives an improved estimate of the total correlation energy that is within ∼5% of the experimental result for each of the three molecules.
Determination of the argon intermolecular pair potential by x-ray diffraction from the dense gas
Authors: Karnicky Joseph F. , Reamer H. Hollis , Pings Cornelius J.
Published: February 2003

The intensity distributions of x rays scattered by fluid argon were meausred at −100 °C and densities of 0.0824, 0.1331, 0.2087, and 0.3111 g/cm3. The experiment at 0.2087 g/cm3 was repeated to establish reproducibility. The structure factors measured at the three highest densities were Fourier transformed to obtain the direct correlation functions and the radial distribution functions. These functions were used along with the Percus–Yevick equation and a correction for three-body effects by Rowlinson to obtain four separate experimental estimates of the (state-independent) pair potential of argon. These four estimates were weighted by their precision and averaged to produce an optimal estimate of the pair potential, which has the characteristics ε=146.3±4.9 °K, σ=3.389 ±0.015 Å, and r0=3.86 ±0.05 Å. Quantities calculated from this potential are in reasonable agreement with the reported values for the second virial coefficient of argon and the transition energies of the argon dimer.
Soft mode behavior and anharmonicity of some two-dimensional layer compounds
Authors: Stoelinga J. H. M. , Wyder P.
Published: February 2003

The far infrared reflection spectra of the layer structure compounds of the type (CnH2n+1NH3)2MCL4, n=1,2,..., (M=Cu,Cd) have been measured in the region 10–200 cm−1 as function of temperature between 20 and 300 K. The change of the number of modes in the spectra at ∼120 K is in agreement with a structural phase transition where the layer structure changes from not entirely square to square with increasing temperature. The presence of two-phonon transitions in the spectra is an indication for anharmonicity of the potential energy. The observed strong increase of the damping of several modes with increasing temperature is explained by interaction with a (infrared inactive) soft mode of the two-dimensional layer. The critical temperature of this soft mode has been determined as 180 K for (CH3NH3)2CuCl4 and 160 K for (CH3NH3)2CdCl4.
Degenerate autoionization processes in the photoionization of molecular hydrogen
Authors: Peatman Wm. B.
Published: February 2003

The contribution of both autoionization and direct ionization processes to the photoionization continuum of hydrogen has been examined experimentally in order to ascertain the relative importance of the above two processes, to determine the final state to which a particular autoionizing Rydberg state decays, and to see if there are any preferred routes for the two types of processes. Autoionization processes which produce electrons with energies in the range 0 to 0.003 eV, so-called degenerate autoionization processes, have been studied here by means of a new type of threshold electron analyzer which has an identically zero transmission probability for energetic electrons. It was found that degenerate autoionization processes are not uncommon and that there is a preference in such autoionization processes for J=K between the ground state hydrogen molecule and the final state of the molecular ion. Direct ionization also appears to be favored for J=K. The detailed routes of several degenerate autoionization processes are examined and other inferences made.
Momentum eigenfunctions in the complex momentum plane. Local potential functions
Authors: Lassettre Edwin N.
Published: February 2003

Singular points for one-electron momentum functions in the complex momentum plane are located. The momentum functions are obtained from molecular orbitals which satisfy one-electron Schrödinger equations with local potential functions. If the molecular orbitals are expressed as linear combinations of atomic orbitals which satisfy Schrödinger equations with single-center local potential functions, then there are severe restrictions on the type of single-center potential functions which are acceptable. The problem of obtaining single-center potentials is discussed.
Kinetic energy distributions from unimolecular decay: Predictions of the Langevin model
Authors: Klots Cornelius E.
Published: February 2003

The kinetic energy released in a unimolecular decomposition is examined within the framework of quasiequilibrium theory. It is assumed that the motion is governed by the long-range forces between the separating moieties. Explicit formulas are obtained for cases where the total angular momentum is either very low or very high. Comparison with experiment and with other formulations is made.
Excitation spectra of atoms and small molecules using effective valence shell Hamiltonians generated by canonical transformations
Authors: Bradford E. G. , Westhaus Paul
Published: February 2003

The canonical transformation–cluster expansion formalism is used to generate the effective valence shell Hamiltonian for carbon. Hydrogenlike orbitals defined by an effective nuclear charge parameter 𝒵 are used to span the core (K shell), valence (L shell), and excited (3⩽n⩽9) spaces. The effective Hamiltonian containing one- and two-body interactions is diagonalized on the Nv-particle valence space to yield the low-lying excitation spectrum. Considering alternative approximations to carry out the calculations, we indicate the importance of including the two-body pair potential as well as the single particle operators in the generator of the canonical transformation. Upon doing this, good agreement with experiment is obtained for the lowest valence shell transitions over a wide range of 𝒵. For certain physically reasonable 𝒵 the entire valence shell experimental excitation spectrum can be accurately reproduced. In contrast, a ’’zeroth order’’ effective Hamiltonian using only the ’’charge cloud’’ of the core to modify the one-body potential and using e2/r12 for the two-body potential fails to reproduce the spectrum for any choice of 𝒵. We compare our effective Hamiltonian with those currently used in semiempirical calculations. We find the splitting in the 2s–2p orbital energies as well as the ’’strength’’ of the two-body interaction to be substantially reduced from those corresponding quantities occurring in the zeroth order effective Hamiltonian. These results generally fulfill the semiempirical expectations. We thus consider the procedure as a method for obtaining the valence shell Hamiltonian for molecules. Preliminary results for ethylene are presented and discussed.
Rate constants for the reactions of OH with ethane and some halogen substituted ethanes at 296 K
Authors: Howard Carleton J. , Evenson K. M.
Published: February 2003

Absolute rate constants for the reactions of OH radicals with C2H6 and twelve fluorine, chlorine, and bromine substituted ethane compounds are reported. The measurements are made at 296 K and pressures ranging from 100 to 1000 Pa (0.7–7 torr) using a discharge-flow system and laser magnetic resonance detection of OH. The results are similar to those of an earlier work on a series of methane compounds and indicate that the reaction mechanism is the abstraction of an H atom. Thus, completely halogenated molecules are relatively inert. The hydrogen containing molecules react with rate constants ranging from about 3 to 400×10−15 cm3 molecule−1⋅sec−1.