bluuebunny/crossref_metadata_2025 huggingface dataset:
Theory of Fluorescence Depolarization by Anisotropic Rotational Diffusion
Authors: Chuang T. J. , Eisenthal K. B.
Published: February 2004

The general expressions for the time-dependent fluorescence depolarization caused by anisotropic rotation diffusion have been obtained. It is shown that after an instantaneous exciting light pulse, the parallel and perpendicular components of fluorescence can have a maximum of six exponential decays and the difference of these two components a maximum of five decays. The present results differ from those of previous studies and the differences are discussed.
Determination of a Three Parameter Pair Potential from Second Virial Coefficients: Ar, Kr, and Xe
Authors: Davis Bruce W.
Published: February 2004

To prepare second virial coefficient data for use in determining the Ar, Kr, and Xe pair potentials, random errors in B(T) data are initially eliminated by least square fitting to a polynomial in T−1. After choosing an analytical form for the potential, optimum values for the potential parameters are obtained using a modified version of the method of selected points. This procedure permits rapid testing of three parameter model potentials without having extensive tables of reduced second virial coefficients. A piecewise potential (RMMV for rigid, Morse, Mie, and van der Waals) was selected and extensively compared with existing theoretical and experimental determinations of the pair potential for Ar, Kr, and Xe. The RMMV potential was found to be satisfactory, not only in the well region, but also in the short and long range limits.
Scattering of Diatomic and Polyatomic Molecules from the (100) Crystal Face of Platinum
Authors: West L. A. , Somorjai G. A.
Published: February 2004

The angular distributions of thermal energy molecular beams of diatomic (CO, N2, O2, NO, H2, D2) and polyatomic (CO2, N2O, C2H2, NO2, NH3, and methylene cyclobutane) molecules were monitored following scattering from the (100) crystal face of platinum. All of the gases studied (with the exception of ammonia) yielded directed scattering patterns with the maximum intensity peaked at or near the specular angle for scattering from a clean platinum surface or from a platinum surface covered by a layer of ordered graphite. Broad, cosinelike angular distributions which were independent of incident angle were observed, however, for the cases of C2H2 scattered from an adsorbed layer of C2H2 and CO scattered from adsorbed CO. These results seem to indicate that efficient energy transfer between the surface atoms and gas molecules, as indicated by angular distributions, occurs only in specific instances. Apparently, the incident particles are reflected whenever the nonlocalized vibrational energy modes of surface atoms and the translational energy of the incident molecules are of similar magnitude. The adsorption of gases may lead to the formation of additional low frequency localized surface modes that can be excited by the incident molecules. The efficient transfer of energy via localized surface modes would increase the residence time of the incident molecules and could thus account for the cosinelike angular distributions observed for C2H2 and CO.
Drift Velocities and Interactions of Cs+ Ions with Atmospheric Gases
Authors: McKnight L. G. , Sawina J. M.
Published: February 2004

The drift velocities and interactions of the Cs+ ion in atmospheric gases have been measured at 300°K using an ion drift apparatus. Cs+ was found not to form clusters with N2, O2, and Ar at 300°K, implying a reaction rate less than 10−24 cm6/sec or an equilibrium constant less than 10−2 torr−1. Low field mobilities (μN) for the ion were 6.0, 5.9, and 5.6 × 1019 (V·sec·cm)−1 in O2, N2, and Ar, respectively. Cs+ was found to form clusters with water by the three-body reaction Cs+ + H2O+N2→(Cs·H2O)++N2, with a forward rate constant 9× 10−30cm6/sec and a reverse rate constant of 1× 10−15cm3/sec at 306°K. Ion clusters as large as (Cs· 4H2O)+ were observed and, by measuring the equilibrium constants between 300 and 650°K, the entropy and enthalpy of formation of the first, second, and third water clusters were determined. With SO2, Cs+ was found to cluster by the reaction Cs++SO2+M↔ (Cs· SO2)++M, with ΔH°= − 11 kcal/mole and ΔS°= − 19 eu. The forward rate constant for the formation of (Cs·SO2)+ was 3× 10−20 cm6/sec and the reverse rate constant 1× 10−13cm3/sec. The rates were the same with either SO2 or N2 as the third body. In CO2 the equilibrium amount of the clustered ion was too small to enable the measurement of the rate of formation, but the equilibrium constant measured between 200 and 400°K allowed the ΔH° and ΔS° values to be determined as −6 kcal/mol and − 14 eu, respectively. The low field mobility of Cs+ in CO2 was found to be 3.1× 1019 (V·sec·cm)−1. The interactions of the Cs+ ion with its large radius, low ionization potential, and almost inert electronic structure should be the minimum ion-molecule interaction for an ion of this size. The interactions of smaller and more reactive ions should be at least as great as that of Cs+. Evidently the formation of ion-molecule clusters with polar and polarizable molecules is a nearly universal property of small ions.
Charge Transfer States of Molecular Crystals in Contact with a Metal
Authors: Pak Joong-Woong , Choi Sang-il
Published: February 2004

A quantum mechanical model study of electronic states of a molecular crystal in contact with a metal is made. A molecular crystal is represented by the parameters: intermolecular spacing, electron affinity of a constituent molecule, dielectric constant, charge transfer matrix, and polarization energy of the molecular crystal. A set of difference equations is established and solved for the energy eigenvalues and eigenfunctions under the assumption that the interaction between a transferred electron and a metal is that of electrostatic image potential. Appearance of lower energy bands corresponding to an electron localized in the x direction and one continuum energy spectrum representing the conducting state of an excess electron in the molecular crystal is noted. Also, the transferred electron density is calculated for each energy band.
Nuclear Magnetic Resonance Diffusion Studies of 23Na in Beta Alumina, Effect of Water on the 23Na Quadrupole Interaction
Authors: Kline D. , Story H. S. , Roth W. L.
Published: February 2004

Measurements of the 23Na nuclear magnetic resonance spectra in samples of sodium beta alumina are interpreted in terms of sodium diffusion and water absorption. Intense motional narrowing is observed below room temperature consistent with the low activation energy for diffusion. The 23Na spectra from finely powdered material show effects, similar to those observed in zeolites, due to absorbed water. The quadrupole interaction decreases markedly with increasing water content indicating the penetration of water into the beta alumina structure on a molecular scale.
Statistical Mechanical Study of Hydrophobic Interaction. IV. The Behavior of the Function y(R) at Short Distances
Authors: Ben-Naim A.
Published: February 2004

The function [A. Ben-Naim, J. Chem. Phys. 54, 1387, 3696 (1971)] y(R) = exp[−δAHI(R)], playing a central role in the theory of solute-solute interaction, is shown to be a monotonous decreasing function of R at short distances. A formal proof is given for two hard cube solutes approaching along a particular line. Further evidence, based on the Percus-Yevick equations for a two-dimensional system of spherical solutes, is provided.
Study of Excitation Transfer in a Flowing Helium Afterglow Pumped with a Tuneable Dye Laser. I. Measurement of the Rate Coefficient for Selected Quenching Reactions Involving He (53P)
Authors: Collins C. B. , Johnson B. W. , Shaw M. J.
Published: February 2004

A system is described for the measurement of excited state reaction times in the nanosecond range. A flowing afterglow produces large populations of chemically unstable species and a pulsed, tuneable dye laser is used to selectively pump these into the reacting excited state. The transient fluorescence from the populations of reactants and end products is used to determine reaction lifetimes and yields. This radiation is collected with a photon counting system which logs arrival times of spectrally dispersed photons with 10 nsec resolution. With this system the rate coefficient for the reaction He(53P)+He→He2++e has been measured to be 8× 10−11 cm3/sec. Upper limits on the reactions He(53P)+He→He(53D)+He and He(53P)+e→He(53D)+e were determined to be 8× 10−15 cm3/sec and 8× 10−9 cm3/sec, respectively.
Rotational Diffusion and Magnetic Relaxation of 119Sn in Liquid SnCl4 and SnI4
Authors: Sharp Robert R.
Published: February 2004

Longitudinal and transverse relaxation times of 119Sn have been measured as a function of temperature in liquid SnCl4 and SnI4. For SnCl4, T1 is a monotonically decreasing function of temperature and is dominated mechanistically by spin-rotation over the entire liquid range. In SnI4, T1 passes through a maximum near 190°C. Spin-rotation and scalar coupling to 127I, respectively govern the relaxation above and below this temperature. T2≪ T1 in both liquids; scalar coupling, modulated by relaxation of the halogen isotopes, dominates the transverse relaxation. Dipolar coupling does not contribute appreciably to relaxation in either compound. Knowledge of the scalar contributions to T1 and T2 in SnI4 permit calculation of the 127I relaxation time [τ127=1.5(10−7) sec at 150°C] and the angular correlation time [τθ=3.67(10−12) sec at 150°C]. These values, and the published τ35 for SnCl4, give the tin-halogen scalar coupling constants: J(119Sn–35Cl)=470 Hz and J(119Sn–127I)=940 Hz. Spin-rotation constants are obtained using Steele's rotational diffusion theory and are used to calculate an absolute shielding scale for 119Sn. From the shielding constants and the relative resonance frequencies of 119Sn and 1H, the 119Sn magnetic moment is calculated to be (−1.04347±0.00036μN). Rotational correlation times in SnCl4 and SnI4 have been compared with theoretical predictions of the J diffusion and damped diffusion models. SnCl4 shows significant deviations from Hubbard's relation although the motion is diffusive according to both theories. Inertial effects are important for reorientation in SnI4(τJ*∼ 2 at 220°C), and damped diffusion appears to describe reorientation more accurately at these temperatures than does J diffusion. The relative roles of spin-rotation, scalar coupling, and dipolar coupling as relaxation pathways in other tin-containing systems are considered. It is concluded that the first two interactions usually dominate dipolar coupling for tin and for other heavy metals.
Determination of D(AlO) from Crossed-Beam Chemiluminescence of Al + O3
Authors: Gole J. L. , Zare R. N.
Published: February 2004

In a molecular beam apparatus, a thermal beam of aluminum atoms (≈ 1700°K) intersects an uncollimated thermal beam of ozone molecules (300°K) and the resulting visible chemiluminescence is recorded with a 1 m scanning monochromator. The chemiluminescence spectrum consists of (1) the AlO B 2Σ+−X 2Σ+ blue-green system for which we have assigned bands to the strongly structured features in the region 4200–4900 Å, and (2) more intense weakly structured features in the region 4500–8500 Å, which appear to be emission from a polyatomic aluminum oxide on which there seems to be superimposed the AlO B 2Σ+−A 2Π band system. From the chemiluminescent spectrum a minimum value of 5.13±0.05 eV is deduced for the dissociation energy of the ground state of aluminum oxide. By accepting the upper limit of 5.20 eV deduced by MacDonald and Innes from Tyte's shock tube absorption data, we recommend the value D00(AlO)=5.15± 0.5 eV.
On the Possibility of Free Rotation in Crystalline Dimethylacetylene
Authors: Albert Shmuel , Ripmeester John A.
Published: February 2004

Crystalline dimethylacetylene (CH3–C≡C–CH3) was investigated by broad line and pulsed proton magnetic resonance in the temperature interval 217–77°K. The NMR second moment and line shape at 77°K along with the fact that we did not notice a change in the free induction decay following a 90° pulse in our experiments, agree with the presence of only methyl group rotation about the C–C axis in the entire temperature region of investigation. From the temperature dependence of the spin-lattice relaxation time (T1) we find that the CH3 group rotation in the low temperature phase is fast (ω0τc≪ 1) and its activation energy is 830±40 cal/mole. A discontinuity in the T1 curve was observed at the phase transition. In the high temperature phase the CH3 group rotation is enhanced and the possibility of the motion being a free rotation, or nearly so, is considered from the relatively long and temperature independent T1 behavior. We also discuss other possible relaxation mechanisms which could occur in the high temperature phase besides the dipolar one. The phase transition in DMA is discussed in view of available thermodynamic and x-ray as well as our NMR data.
Laser Flash Photolytic Study of Triplet of Fluorinated Benzenes in the Gas Phase
Authors: Stevens R. D. S. , Bonneau R. , Joussot-Dubien J.
Published: February 2004

Using laser flash photolysis, the lifetime of the triplet state of fluoro- and pentafluorobenzene in the gas phase, along with the energy transfer efficiencies to cis-2-butene and oxygen have been measured. The triplet transient absorption decay was found to be predominantly first order with a lifetime of 250 and 140 nsec, respectively, for fluoro- and pentafluorobenzene. The above results are compared with those of previous indirect measures and the apparent effect of fluorination on the excited state decay paths of benzene is briefly discussed.
Dipole Moment Studies. V. The Dipole Moments of the Methylphosphine Boranes
Authors: Morse Joseph G. , Parry R. W.
Published: February 2004

Dipole moments of methylphosphine borane, dimethylphosphine borane, and trimethylphosphine borane were determined in benzene solution. After correction for solvent effects the values obtained were: CH3PH2BH3, 4.58 D; (CH3)2PHBH3, 4.78 D; (CH3)3PBH3, 4.97 D. The variation in these moments is interpreted in terms of a polarization model.
Wavelength and Temperature Dependent Effects on Hydrated Electron Formation and Fluorescence of β-Naphtholate
Authors: Feitelson Jehuda , Stein Gabriel
Published: February 2004

The absorption spectrum of Na β-naphtholate shows an increase in optical density at its long wavelength edge as a function of temperature. However, fluorescence yield shows a red-edge effect: it decreases with temperature when excited anywhere in the last absorption band except at its long wavelength edge, where no dependence upon temperature is observed. When β-naphtholate is confined in a transparent ethylene-glycol water glass at low temperatures, the fluorescence peak is shifted towards the blue by ∼2000 cm−1. The formation of solvated electrons from the 1S excited state of β-naphtholate was also found to be dependent upon the excitation wavelength, no electrons being formed at λexc>365 nm. The various observations are interpreted in terms of a mechanism by which electrons are dissociated from the excited singlet state prior to solvent relaxation in competition with internal conversion to the fluorescent, solvent relaxed level.
Mean Spherical Model for the 6:12 Potential
Authors: Watts R. O. , Henderson D. , Barker J. A.
Published: February 2004

The mean spherical model (MSM) has been solved for the 6:12 potential. Comparison of the MSM results with the results of computer simulations and of the Percus-Yevick (PY) theory, shows the MSM thermodynamic properties to be inferior to those of the PY theory. On the other hand, the MSM radial distribution function (RDF) is somewhat better than that of the PY theory. In fact, for r>1.7σ, the MSM results are in excellent agreement with the simulation results.
Absolute Rate Constants for the Reactions of O(3P) Atoms with C2H4 and C2D4
Authors: Stuhl F. , Niki H.
Published: February 2004

Rate constants for the reactions of O(3P) with C2H4 and with C2D4 were determined at 298±2°K using pulsed vacuum-uv photolysis. Both NO2* and CO2* chemiluminescence were used to monitor decays of O atoms. The decay rates of O atoms in the presence of a large excess of C2H4 or C2D4 were independent of the initial concentration of O atoms in the range of approximately 109–1012 O atoms cm−3 and were linearly dependent on the reactant concentration. From these measurements, rate constants were determined to be 6.25 (± 0.63)× 10−13 cm3 molecule−1 · sec−1 for O+C2H4, and 5.6 (± 0.56)× 10−13 cm3 molecule−1· sec−1 for O+C2D4. The present value for O+C2H4 agrees well with that measured previously in this laboratory and confirms the validity of the pulsed vacuum-uv photolysis-chemiluminescence method.
Entire Phonon Spectrum of Molecular Crystals by the Localized Exciton Sideband Method: Naphthalene
Authors: Kopelman Raoul , Ochs Frederick W. , Prasad Paras N.
Published: February 2004

The complete one-phonon density-of-states of a molecular crystal can be mapped out by a carefully chosen exciton sideband involving a localized molecular internal excitation in a dilute isotopic mixed crystal. A theoretical derivation shows that the necessary criteria are: absence of localized in-band phonons; applicability of a phonon amalgamation limit for the mixed crystal; weak exciton-phonon, guest-lattice coupling and weak guest-host exciton interaction. Experimentally, at least two exciton-phonon sidebands should be investigated, so as to exclude trap and defect transitions, and at least one of the guest transitions should belong to the deep-trap limit and have sidebands weak enough to minimize multiphonon transitions. The above is demonstrated for the naphthalene crystal by high-resolution fluorescence and phosphorescence spectra of 0.25% C10H8 in C10D8 and by phosphorescence of 0.14% 2-DC10H7 in C10D8 at 2°K. The phosphorescence phonon sidebands correlate surprisingly well with Pawley's ``atom-atom'' calculated phonon density-of-states, and seems to give a much better phonon density map than the very recent high-resolution inelastic, incoherent neutron scattering data. New Raman data are also presented, showing defect (isotopic impurity) induced bands, which are interpreted in terms of the above phonon density-of-states peaks. Applications to reversible and irreversible thermodynamics are mentioned.
Entropy and Chemical Change. II. Analysis of Product Energy Distributions: Temperature and Entropy Deficiency
Authors: Ben-Shaul A. , Levine R. D. , Bernstein R. B.
Published: February 2004

Detailed experimental and theoretical information on the distribution of product energy states resulting from reactive molecular collisions are characterized by their entropy deficiency and temperature. Explicit algorithms are developed both for the case of ultimate resolution (both angular and internal state distribution) which provides the intrinsic (i.e., maximal) entropy deficiency and for the more realistic situations (e.g., chemiluminescence, molecular beam velocity analysis) where only averaged distributions are available and the entropy deficiency is therefore smaller. Twelve ``known'' product distributions are analyzed. The largest values of the entropy deficiency are found for reactions where there is significant deviation from a simple equilibrium distribution of products. A temperature parameter is introduced as a measure of the deviation from equilibrium. Inverted populations are characterized by a negative value of this temperature. Consideration of a number of isotopic reactions indicate that this temperature is essentially invariant under isotopic substitution. The new temperature parameter introduced in this work is the one appropriate for a finite system and differs from the more familiar (but special) form appropriate for a system coupled to an infinite heat bath. Two new tools are thus proposed for characterizing the deviation of an observed product state distribution (or a computational simulation thereof) from an equilibrium, microcanonical one. These are the temperature parameter (a differential measure) and the entropy deficiency (an integral one). They measure, respectively, the local and the average deviation between observed and equilibrium distributions.
Ionization of the Noble Gases by Protons: Jesse Effects as a Function of Pressure
Authors: Parks J. E. , Hurst G. S. , Stewart T. E. , Weidner H. L.
Published: February 2004

A new method has been developed to measure W, the ratio of the energy lost by a proton to the number of ion pairs produced when these particles interact with a gas. In this method, protons are Rutherford scattered from a beam by a thin gold foil into a W cell where total gas ionization is measured. The number of protons scattered into the W cell is measured with a silicon surface barrier detector, and the energy lost to the gas is calculated from stopping power data. Most of the protons pass through the thin gold foil and enter an emission cell where emission spectra are studied with a vacuum ultraviolet scanning monochromator. At 400 torr for pure gases the following values of W (eV per ion pair) were found for 3.6-MeV protons: He, 45.2±0.9; Ne, 39.3±0.8; Ar, 26.6±0.5; Kr, 23.0±0.5; Xe, 20.5±1.2; N2, 36.6±0.7. No appreciable pressure dependence was observed for the pure gases. The Jesse effect, which is the increase in ionization observed when impurities are added to certain gases, was studied as a function of concentration and pressure for mixtures of C2H4, C2H2, and CO2 with Ar. At small concentrations of C2H4 or C2H2 the Jesse effect decreases as the total gas pressure increases. These data, along with other facts cited in this paper, tend to confirm an energy pathways model for argon. Based on a comparison of our data with this model, we deduce the values 6.5×10−10 and 1.1×10−9 cm3 sec−1 for the rate constants for producing the Jesse effect from the 1P1 (1048 Å) resonance state of argon by collisions with C2H4 and C2H2, respectively. W values were also studied as a function of pressure and concentration for mixtures of Ne, Ar, Kr, and Xe with He. The dependence of W on pressure and concentration was similar to that of argon.
Computer Simulation of Some Reactions of Energetic Hydrogen Atoms
Authors: Malcolme-Lawes D. J.
Published: February 2004

A simple hard sphere model of chemical reaction is used to study the reactions of hot hydrogen atoms with H2, D2, HD, RH, and RD. The fate of excited products in the presence of rare gases is determined and it is suggested that discrepancies between more exact theoretical treatments and experimental results may be caused partly by the collisional dissociation of excited molecular hydrogen formed at high reaction energies.
Thermodynamics of Lithium-Isotope-Exchange Reactions. III. Electrochemical Studies of Exchange between Isotopic Metals and Aqueous Ions
Authors: Singh Gulzar , Rock Peter A.
Published: February 2004

This paper reports our results for the direct experimental determination of the equilibrium constant for the lithium-isotope-exchange reactionLi(s)7+6LiCl(aq)=6Li(s)+7LiCl(aq).This reaction was studied in an electrochemical quadruple cell without liquid junction of the type Li(s)7|7LiBr(PC)| 7Li(Hg)|7LiCl(aq)| Hg2Cl2 (s)| Hg(l)| Hg2Cl2 (s)|6LiCl(aq)|6Li(Hg)|6LiBr(PC)|6Li(s),where PC denotes the solvent propylene carbonate. The experimental value of the equilibrium constant at 296.6°K for this reaction is K = 1.046±0.013. The experimental value of K is compared with values for K calculated from statistical thermodynamic theory for various model reactions. The results of these calculations are consistent with a tetrahedrally coordinated structure for the aqueous lithium ions.
Effects of Long-Lived Collisions in the Boltzmann Equation
Authors: Smith Felix T.
Published: February 2004

The general formulation of transport theory in gases does not take into account long-lived collisions or other properties of collision duration and molecular size that become especially important at higher densities. All these properties can be included in the theory in a uniform way by introducing the concept of the collision lifetime in addition to the collision cross section in the derivation of the equations of transport theory. A formulation of the classical Boltzmann equation is given in which the two-body collision term containing the collision lifetime explictly appears. In addition, two-body correction terms reflecting the spatial extension of the collision are derived.
Anisotropic Self-Diffusion in Erbium Single Crystals
Authors: Spedding F. H. , Shiba Koreyuki
Published: February 2004

The rate of self-diffusion in single crystals of erbium has been studied over the temperature range from 1202 to 1412°C using a radioactive tracer (169Er)-sectioning (grinding) technique. The diffusion coefficients along the a axis (Da) and along the c axis (Dc) of the close packed hexagonal structure are: Da=(4.51+0.55, 4.51–0.49) exp[−(72.27± 0.36)× 103/RT] cm2/sec,Dc=(3.71+0.87, 3.71–0.71) exp[−(72.05± 0.65)× 103/RT] cm2/sec.By making use of Mullen's table for the diffusion of hcp metals by the vacancy mechanism, the ratio of jump frequencies is determined to be ωc/ωa=0.85 exp(+270/RT) where ωc and ωa are frequency out of the basal plane and frequency in the basal plane, respectively.
Calculated a4Σ−, A2Δ, B2Σ− States of CH
Authors: Lie George C. , Hinze Juergen , Liu Bowen
Published: February 2004

Ab initio CI calculations have been performed over a wide range of internuclear distances to obtain the potential curves for three low-lying excited electronic states, a4Σ−, A2Δ, B2Σ−, of CH. With the computed potential curves, vibration-rotational levels are obtained by numerical integration of the radial Schrödinger equations for the motion of the nuclei. The term values are analyzed to yield the conventional spectroscopic constants. Results, with known experimental values in parentheses, are Re(A 2Δ)=2.074(2.082) a.u., Re(B 2Σ−)=2.208(2.200) a.u., Re(a 4Σ−)=2.047 a.u.; De0(A 2Δ)=1.89(2.01) eV, De0(B 2Σ−)=0.17(∼ 0.40) eV, and De0(a 4Σ−)=2.88 eV. The computed spectroscopic constants are found to be within 4% of known experimental values. A potential maximum of height 1600 cm−1 occurs in the computed potential curve of the B2Σ− state. The a4Σ− state, not known experimentally, is estimated to lie between 0.52 eV and 0.75 eV above the X2II ground state.
Diagrammatical Method for Geminals. II. Applications
Authors: Paldus J. , Sengupta S. , Čížek J.
Published: February 2004

The diagrammatical method for the calculation of the matrix elements of an arbitrary spin-independent operator in the basis of single antisymmetrized geminal products, developed in Part I, is applied to derive the overlap and energy mean value expressions for various types of geminal wavefunctions, namely for strongly and weakly orthogonal, nonorthogonal and identical geminals. The applications to other problems and the use of molecular symmetry in this formalism are also briefly discussed.
Formation of NO+ by the Reaction of O+ and Vibrationally Excited N2 in Crossed Molecular Beams
Authors: Cohen Ronald Bruce
Published: February 2004

The cross sections for the reaction of vibrationally excited N2 with O+ (4S) to form NO+ plus N over the O+ ion energy range 4–100 eV have been determined in modulated crossed molecular beams. The total effective cross section of N2 did not change by more than 15% in the temperature range 300–3000°K. The reaction cross section for N2 (v =1, 2, 3) did not vary by much more than a factor of 2 from the cross section for N2 (v =0) in this collision energy range.
Many-Body Effects and the Depolarization of Light by Simple Gases
Authors: Gelbart William M.
Published: February 2004

We present a statistical mechanical description of the depolarized light scattering by simple gases which contains as a special case the well-known binary collision result. For pressures greater than 50 atm, three-and four-particle correlations are shown to make important negative contributions to the experimental measurements.
Electric Resonance Spectrum of NaLi
Authors: Graff J. , Dagdigian P. J. , Wharton L.
Published: February 2004

Δ M J =± 1 transitions from the J =1, MJ =0 and the J =2, MJ =0 molecular rotational states of 23Na7Li have been observed by the molecular beam electric resonance method at 1–15 MHz. With an experimental linewidth of 7.5 kHz, the nuclear hyperfine pattern consisted of six unresolved doublets. In the beam, originating from a supersonic source, only one vibrational state was observed, which was shown to be the ground vibrational state by measurement of a 23Na6Li spectrum. The ground vibronic Stark coefficient μ02/B0 and the molecular electric dipole moment μ0, the equilibrium dipole moment μe, the molecular electric polarizabilities αs and αa, and the two nuclear electric quadrupole coupling constants eqQ were determined in 23Na7Li (using the reported rotational constant B0=0.394 cm−1) to be: μ02/B0=2740± 5 Å3#α3=40± 5 Å3μ0=0.463± 0.002 Dαa=24± 2 Å3μe=0.46 ± 0.01 D(eqQ)Na=−749± 4 kHz|(eqQ)Li|=28± 4 kHz.
Self-Consistent Procedures for Generalized Valence Bond Wavefunctions. Applications H3, BH, H2O, C2H6, and O2
Authors: Hunt W. J. , Hay P. J. , Goddard W. A.
Published: February 2004

Methods of efficiently optimizing the orbitals of generalized valence bond (GVB) wavefunctions are discussed and applied to LiH, BH, H3, H2O, C6H6, and O2. The strong orthogonality and perfect pairing restrictions are tested for the X 1Σ+ state of LiH, the X 1Σ+, a 3π, and A 1π states of BH, and the H2+D⇄H+HD exchange reaction. The orbitals of H2O and C2H6 naturally localize into OH, CH, and CC bonding pairs. The nonbonding orbitals of H2O are approximately tetrahedral but this description is only 2 kcal lower than the optimum description in terms of σ and π lone-pair functions. The calculated rotational barrier for C2H6 is 3.1 kcal, in good agreement with the experimental value (2.9 kcal). The description of the O2 molecule in the GVB approach is presented and the results of carrying out CI calculations using the GVB orbitals are discussed. The GVB orbitals are found to be a good basis set for configuration interaction calculations. The general features of GVB orbitals in other molecules are summarized.
Electron Temperature and Relaxation Phenomena behind Shock Waves
Authors: Carlson Leland A. , Rieper Robert G.
Published: February 2004

The variation of the bound electron temperature behind air normal shock waves has been investigated using a combined set of numerical and shock-tube experiments. It is concluded that for medium speed (5–7 km/sec) shock waves the magnitude of bound electron temperature is independent of the band considered, that the postshock N2 (1+) emission, while initially excited by atom-molecule collisions, is primarily controlled by vibration-electronic coupling, and that the corresponding radiative intensity profiles are not indicative of chemical relaxation but only of radiative relaxation. A method of predicting the associated bound electron temperature is presented and compared with experimental results. Finally, it is demonstrated that nonequilibrium chemistry calculations using realistic chemistry and vibrational coupling models do yield results for chemical relaxation in accordance with experimental measurements.
Theory of Relative Reorientational Correlation Times for First and Second Rank Spherical Harmonics
Authors: Keyes T.
Published: February 2004

A theory is developed which relates the ratio of first to second rank orientational correlation times, τ1/τ2, to a single dimensionless parameter characteristic of the system of interest. The theory is based upon the Zwanzig-Mori formalism for time correlation functions and the Gaussian memory function approximation of Harp and Berne. The theory yields the exact overdamped (rotational diffusion) rotor result, and comes very close to the exact free rotor result, in the appropriate limits. The expected temperature dependence of the ratio, τ1/τ2, is calculated. The range of validity of the theory is discussed.
Boundary Free Energy in the Lattice Model. I. General Formulation
Authors: Kikuchi Ryoichi
Published: February 2004

In order to provide the basis for solving the paradox in the theory of the boundary structure, the general expression for the boundary free energy between two phases is derived by applying the cluster variation method rigorously. The surface free energy nσ for the phase boundary is expressed as exp(−nσ/kT)=h(II)·g(I), where h and g are the row and column vectors used in the eigenvalue formulation of the cooperative problem, and (II) and (I) signify the two phases meeting at the boundary. This expression is the same as the one previously derived by Clayton and Woodbury. In the process of the derivation, the local free energy density is identified which will play the key role in solving the paradox in a subsequent paper. The symmetric boundary, the asymmetric boundary, and the case of long-range interaction are discussed.
Boundary Free Energy in the Lattice Model. II. Applications of the General Formula
Authors: Kikuchi Ryoichi
Published: February 2004

The general expression for the boundary free energy σ derived in Paper I is calculated for the square-lattice Ising model using the pair and the square-angle approximations of the cluster variation method for both the 〈 10 〉 boundary and the 〈 11 〉 boundary. As the approximation is improved, the σ vs T curves show the tendency of approaching Onsager's exact result, although further examinations using better approximations are desirable. It is shown that even in the approximate calculations, the critical point exponent μ in the expression σ ∼(Tc–T)μ is unity, which is the same as the exact value.
Boundary Free Energy in the Lattice Model. III. Solution of the Paradox
Authors: Kikuchi Ryoichi
Published: February 2004

A formulation of the boundary profile using the square approximation of the cluster variation method is given in such a way that the local free energy density can be indentified clearly and comparison with Paper I can be made easily. It is pointed out that the formulation in Paper II brings in an approximation at the last stage of the method in Paper I, while the formulation in the present Paper does so at an earlier stage. Comparison of the local free energy density in this paper and that in Paper I leads to the solution of the paradox by concluding that the hump in the free energy curve is not objectionable but has a physical significance in the approximate treatment of the boundary profile.
Comprehensive Urey-Bradley Force Field for Molecules with Geminal Methyl Groups. I. Acetone
Authors: Mann Richard H. , Dixon William B.
Published: February 2004

The coupling of motion between methyl groups in gem-dimethyl molecules is studied by performing a normal coordinate analysis of acetone and acetone-d6. A Urey-Bradley force field (UBFF) is employed, and the usefulness of four-atom (cis) and five-atom (supercis) configurations is investigated. Improvement over previous analyses of acetone is found when the in-plane C–H bending and nonbonded force constants are adjusted separately from the other C–H terms, and when certain cis configurations are included. Possible physical significance is discussed for the negative value of the cis H–O nonbonded force constant obtained; attraction between the in-plane hydrogens and the carbonyl oxygen is indicated.
Gas Phase Homogeneous Catalysis in Shock Waves. II. The Oxidation of Carbon Monoxide by Oxygen in the Presence of Iron Pentacarbonyl
Authors: Matsuda Shimpei
Published: February 2004

The catalytic effect of iron pentacarbonyl on the oxidation of carbon monoxide was investigated in shock waves. Reaction mixtures, typically containing 200 ppm Fe(CO)5, 4% CO, 2% O2, and 94% Ar, were shock heated to between 1000 and 2400°K in incident shock waves. The rate of CO2 formation was followed by monitoring infrared emission at 4.20 μ. It was found that the rate of CO2 formation was greatly accelerated in the presence of small amounts of Fe(CO)5. The observation with a time-of-flight mass spectrometer coupled to a shock tube, to study the formation of intermediate species, suggested that the larger portion of Fe existed as polymeric iron oxides, although small mass peaks due to Fe+ and FeO+ were detected. A mechanism of the catalytic oxidation of CO by Fe(CO)5 in the homogeneous gas phase is discussed. The catalytic effect of Fe(CO)5 disappeared below about 1600°K where the Fe vapor pressure becomes supersaturated under the present conditions. This indicates the removal of Fe and Fe containing species from the gas phase by a condensation process. At temperatures below 1400°K evidence for the direct oxidation of CO in Fe(CO)n (n=1–5) was obtained.
Ligand Contribution to the Spin-Spin Anisotropic Hyperfine Interaction in the Tetragonal Cu2+ Complex Ion
Authors: Lupei A. , McMillan J. A.
Published: February 2004

The nondiagonal, first-order contributions to the hyperfine-structure anisotropy of EPR spectra of the Cu2+(3d9) ion in tetragonal fields of O, N, S, F−, and Cl− have been calculated. It is shown that such effects are comparable in order of magnitude with some of the effects due to orbital admixture. The ligand s and pz contributions are computed separately and equations for the case of hybrid s–pz orbitals are derived. Tables of values of the nondiagonal term as a function of the metal-ligand distance are presented. Consideration of the nondiagonal contribution leads to larger values of the electron localization, as exemplified by five cases discussed in this paper.
High Resolution Measurements of Hyperfine Structure in the Rotational Spectrum of CH3NC
Authors: Kukolich Stephen G.
Published: February 2004

A molecular beam maser spectrometer with separated oscillating fields was used to make very high resolution measurements of hyperfine structure on the J=1→ 0 rotational transition in CH3NC. Electric and magnetic interaction strengths obtained from analysis of the spectrum are: the nitrogen quadrupole coupling eqQ=489.4± 0.4 kHz, the nitrogen spin-rotation CN=1.73± 0.08 kHz, the hydrogen spin-rotation CH=−0.24± 0.08 kHz, and the hydrogen-hydrogen spin-spin DHH=19.5± 0.4 kHz.
The Sulfur K and L and Fluorine K X-Ray Emission and Absorption Spectra of Gaseous SF6
Authors: LaVilla Robert E.
Published: February 2004

With the exception of the sulfur L-absorption spectrum, measurements of all the soft x-ray spectra from gaseous SF6 in their respective threshold regions are reported. The valence emission x-ray spectra are interpreted in terms of a molecular orbital model of SF6 with the inclusion of sulfur d orbitals. The experimental emission profiles are in fair agreement with a calculated profile based on the assigned orbital ionization energies and molecular orbital theory. The sharp resonance structures in the absorption spectra are found to result from the potential barrier formed by the surrounding fluorine atoms and are consistent with the molecular orbital model. The identification of the absorption resonance structure in terms of transitions to ``virtual'' unoccupied electronic levels is substantiated by the observation of ``resonance radiation,'' i.e., x-ray emission in coincidence with the peak positions in the absorption region. The sulfur Kα spectrum is also presented and discussed. A notable feature in this spectrum is a weak peak on the low energy side of the Kα1,2 line, which is interpreted as a semi-Auger process.
Distribution Function for Self-Avoiding Walks. II. Numerical Part
Authors: Chay Teresa Ree
Published: February 2004

By using the exact enumeration data of self-avoiding walks on the triangular and face-centered cubic lattices, we determine the asymptotic behavior of the generating function Gn(θ). With this Gn(θ) we find that δ=52 and ν=35 for the face-centered cubic lattice and δ=4 and ν=34 for the triangular lattice. Here, δ and ν are defined, respectively, by Fn(x)∼exp[−(|x|/xn)δ] and xn∼nν, where Fn(x) is a one-dimensional distribution function of the end point lying distance x away from the origin in n steps, and xn behaves as the mean square end-to-end distance.
Water Cluster Ions: Formation and Decomposition of Cluster Ions in the Oxygen-Water System
Authors: Young C. E. , Falconer W. E.
Published: February 2004

Drift-tube techniques have been employed to determine rate constants in the reaction sequence leading to formation of the hydronium ion hydrates H3O+(H2O)n starting from O2+ ions in O2–H2O gas mixtures at 310°K. Total pressures used ranged from 0.5 to 2 torr with water partial pressures from 0.15 to 1.2%. Measured three-body clustering rate constants declined in all cases as E/P0 increased in the range 5–30 V cm−1· torr−1. Thermal rate constants were deduced from the low E/Po data. Mobilities for O2+ and H3O+(H2O)n in oxygen are given as a function of E/Po in the range 5–60 V cm−1· torr−1 and for O2+ and H3O+ in argon from 4 to 20 V cm−1· torr−1. In oxygen, quasiequilibrium studies were conducted in which a cluster ion H3O+(H2O)n loses one or more water molecules during drift, successive ions from n=3 to 0 becoming dominant as E/Po increased from 5 to 60 V cm−1· torr−1. A simple analytical model for treating sequential reactions in drift experiments is presented.
Rydberg States of CH
Authors: Walker T. E. H. , Kelly H. P.
Published: February 2004

A basis set of atomic orbitals that is very close to atomic Rydberg orbitals is used to calculate the Rydberg levels in diatomic CH. Good agreement is found with the experimental assignments, and bands at 81 006, 81 545, and 82 788 cm−1 are attributed to an nf series. An explanation is suggested for only two members of the np series being observed.
On the Law of the Rectilinear Diameter
Authors: Zollweg John A. , Mulholland George W.
Published: February 2004

The diameter of the coexistence curve, 12(ρl+ρg), is calculated numerically for a model that is known to have an asymptotic singularity comparable with that in Cv near the critical point. The model is an extension of Mermin's decorated lattice gas to simple cubic, body centered cubic, and face centered cubic lattices. The model diameter has a gradual curvature at all temperatures instead of a sudden kink near the critical point. In the asymptotic critical region, the experimental data are not sufficiently precise to distinguish between a diameter predicted by the decorated lattice gas and a linear diameter, which is predicted by the ``law of rectilinear diameters.'' Away from the critical point, the model diameter gives good qualitative agreement with experimental data if the proper choice of one parameter is made.
Trapped Electrons Produced in Ethanol Glass at 4°K
Authors: Hase Hirotomo , Warashina Tetsuo , Noda Masato , Namiki Akira , Higashimura Takenobu
Published: February 2004

Optical absorption and ESR measurements were carried out on et− produced in ethanol at 4°K. The same et− yield for γ radiolysis at 4 and 77°K indicates that electrons are stabilized in pre-existing traps at 4°K where molecular dipoles remain unrelaxed. et− prior to solvation can be classified into two groups. One with λmax = 1500 nm, W1/2= 4 × 103 cm−1 and Δ Hpp = 5.5 ± 0.5 G is easily photobleached by the infrared light. The other with broad absorption band in the visible and Δ Hpp = 13.5 ± 1.5 G is not photobleached by the infrared light. The successive shift of the absorption spectrum to the higher energy side on warming is interpreted by the molecular reorientation mechanism. et− decay is observed during the solvation process, depending on time required for the solvation. The blue shift of the absorption spectrum on reducing the temperature is attributed to contraction of electron traps.
Microwave Spectrum, Structure, and Dipole Moment of Ethylene Sulfone
Authors: Kim Hyunyong
Published: February 2004

The microwave rotational spectra of the 32S and 34S isotopic species of ethylene sulfone have been observed. The rotational constants A, B, and C in megahertz are: 6676.06, 4924.01 and 3759.97 for the 32S species; and 6679.20, 4917.07, and 3757.64 for the 34S species. The structural parameters obtained are r(S–O) = 1.42 ± 0.02 Å, r(C–C) = 1.586 ± 0.01 Å, r (C–S) = 1.76 ± 0.02 Å, and ∠OSO = 124 ± 2o, with the assumption that the C–H distance and ∠HCH and ∠H2CC angles are the same as those of ethylene sulfide. From the measurements of Stark shifts, the dipole moment has been determined to be 4.47 ± 0.02 D.
Electron Spin Resonance of Single Crystals of Cystine Dihydrochloride Irradiated with Monochromatic uv Radiation at Various Wavelengths
Authors: Thomsen E. Lund , Nielsen S. O.
Published: February 2004

Single crystals of cystine dihydrochloride were irradiated at room temperature with monochromatic uv radiation. The optical bandwidth was about 20 Å for each wavelength used. Essentially two ESR centers were observed, the relative yield being approximately 1. One center is identified as the RS radical also detected after γ irradiation at room temperature, the second center is tentatively identified as a RS radical stabilized in an environment different from that of the first mentioned RS radical or alternatively as the RSS+R radical ion.
Empirical Equations to Calculate 16 of the Transport Collision Integrals Ω(l, s)* for the Lennard-Jones (12–6) Potential
Authors: Neufeld Philip D. , Janzen A. R. , Aziz R. A.
Published: February 2004

We have calculated 16 of the reduced transport collision integrals Ω(l, s)* as a function of reduced temperature T* for the Lennard-Jones (12–6) potential. These calculations are more accurate than those of Hirschfelder, Curtiss, and Bird, which are frequently used. Empirical equations are presented which allow the calculation of the collision integrals for any reduced temperature in the range 0.3≤ T*≤ 100 without interpolation from tables. The error in the values so obtained is probably less than 0.1%.
Millimeter Wave Rotational Spectrum and Molecular Constants of 31P14N
Authors: Wyse F. C. , Manson E. L. , Gordy W.
Published: February 2004

The rotational spectrum of diatomic phosphorus nitride has been measured in the millimeter and sub-millimeter wave regions by use of a high temperature, microwave spectrometer. Transitions have been observed in five different vibrational states. From analysis of the data the following Dunham coefficients are obtained: Y01=23578.240(11) MHz, Y11=−165.976(18) MHz, Y21=−0.192(9) MHz, Y31=−7.6(13) kHz, and Y02=−32.70(8) kHz. The Dunham potential constants are found to be: a0=5.670(11)× 105 cm−1, a1=−2.992(2), a2=5.7(4), and a3=−10(3). The equilibrium internuclear distance is re=1.49086(2) Å.
Accurate Potential Curves and Properties for the X 2π and A 2Σ+ States of LiO
Authors: Yoshimine Megumu
Published: February 2004

Ab initio calculations have been performed to determine potential curves and molecular properties for the X 2π and A 2Σ+ states of the LiO molecule. The calculations use a conventional configuration interaction (CI) method in which the Hartree-Fock configuration is taken as reference configuration and only valence shells are correlated. The molecular orbital (MO) basis set used in the CI calculations is composed of the Hartree-Fock orbitals and additional MO's. These additional MO's are formed by truncating a set of pseudonatural orbitals (PSNO's) obtained as the natural orbitals of a CI calculation on a single pair of valence electrons. The main results are Re=1.695 Å, De0=3.37 eV, ωe=851.5 cm−1 (7Li16O), μ=6.76 D for the X 2π state; and Re=1.599 Å, De0=4.90 eV, ωe=866.8 cm−1 (7Li16O), μ=5.96 D for the A 2Σ+ state. The computed De0(X 2Π)=3.37 eV is in good agreement with the observed value of 3.39± 0.26 eV. The other results are also believed to be accurate to within a few percent. The computed term energy Te(X 2Π → A 2Σ+) is 2330 cm−1 with the CI wavefunctions in surprising agreement with the Hartree-Fock value of 2342 cm−1.