bluuebunny/crossref_metadata_2025 huggingface dataset:
Intramolecular rearrangements studied by two-dimensional nuclear magnetic resonance line shape analysis
Authors: Koenig Marianne , Jeener J.
Published: July 2002

The usual theory of nuclear magnetic resonance (NMR) line shapes in the presence of molecular rearrangements has been extended to two-dimensional (2D) NMR in liquids using an explicitly superoperator formalism. Advantages of the proposed 2D method include a clearer ‘‘signature’’ for the presence of a chemical reaction (even at a single temperature), peak shapes providing more information about the underlying NMR parameters, and (in favorable cases) the presence of off-diagonal peaks with characteristic shapes which can be analyzed even in cluttered spectra. Detailed calculations are shown for a single spin 1/2 and for a group of two strongly coupled spins 1/2, jumping between two different spin Hamiltonians. The agreement between the predicted peak shapes and the corresponding experimental results on simple molecules is excellent.
Resonant processes above the carbon 1s ionization threshold in benzene and ethylene
Authors: Piancastelli M. N. , Ferrett T. A. , Lindle D. W. , Medhurst L. J. , Heimann P. A. , Liu S. H. , Shirley D. A.
Published: July 2002

Resonant photoemission has been studied above the carbon 1s ionization thresholds in gas-phase benzene and ethylene. The experimental data for both molecules include relative partial cross section and asymmetry-parameter measurements for the C 1s main line and asymmetry-parameter measurements for one C 1s shake-up satellite in each system. Resonances above the C K edge have been analyzed on the basis of their decay to either the C 1s main line or valence-hole states, and have been tentatively assigned as either shape resonances or doubly excited states according to their observed one-electron or many-electron decay, respectively. The importance of determining the resonant behavior of all available photoemission channels in the proximity of a resonance is thus illustrated.
Vibrational autodetachment of NO−
Authors: Maricq M. Matti , Tanguay Normand A. , O’Brien Julie C. , Rodday Suzanne M. , Rinden Elizabeth
Published: July 2002

We report infrared cross sections for the photodetachment of the molecular anion NO− in the energy range of 1100–1500 cm−1. The measurements are made with a coaxial ion beam–laser beam aparatus. We observe a vibrational autodetachment resonance centered at 1284±10 cm−1. The resonance has a full width at half-maximum of 170 cm−1 corresponding to a lifetime of 0.35×10−12 s for NO−(v=1). The present value for the vibrational frequency of NO− is significantly lower than previous estimates obtained from photoelectron spectroscopy of NO− and from electron scattering resonances in NO. We discuss the implications of our results with regard to previous measurements of infrared photodetachment cross sections in the region 3000–4100 cm−1.
The Hubbard model for alternant and nonalternant systems
Authors: Lee Stephen
Published: July 2002

In this paper we consider the effects of two-electron, one-center interactions when added to the one-electron, two-center molecular orbital model. There are, therefore, two parameters considered: The standard Hückel β (two-center, one-electron) term and the Hubbard one-center, two-electron term U. It is shown how the change in the ground state as one changes the U/β ratio is highly dependent on the presence or absence of odd member rings.
Structure of hard sphere fluids in narrow cylindrical pores
Authors: Bratko D. , Blum L. , Wertheim M. S.
Published: July 2002

The structure of hard sphere fluid confined to cylindrical capillaries in equilibrium with the bulk fluid phase is considered. Simple analytical approaches are examined and compared with the results of simultaneous grand canonical ensemble Monte Carlo simulations. The validity of the limiting law according to which the fluid density in the capillary approaches its fugacity in vanishingly narrow pores is confirmed. The truncated graphical expansion around the exact narrow pore limit is found to represent a useful approximation for very narrow capillaries. In systems with the pore diameter exceeding a few diameters of the spheres and at the reduced bulk densities of the fluid ρbσ3≤0.6, the Percus–Yevick approximation provides a satisfactory description of the fluid distribution.
Mean-field theories for multidimensional diffusion
Authors: Kaufman A. D. , Whaley K. B.
Published: July 2002

Self-consistent-field (SCF) methods are developed for solution of multidimensional diffusion problems. Time-dependent self-consistent-field (TDSCF) equations are derived for the Smoluchowski diffusion equation, and are applied to a two-dimensional barrier crossing problem. This is compared to both time-dependent and time-independent SCF approximations derived for the Schrödinger equation in imaginary time, which is obtained by transformation of the diffusion equation. Results for the model problem show that the TDSCF approximation for the original diffusion equation is accurate, efficient, and readily implementable in higher dimensions. Applications to diffusion problems in condensed media are noted.
Emission spectra of SiF3
Authors: Suto Masako , Han J. C. , Lee L. C. , Chuang T. J.
Published: July 2002

Emission spectra of SiF3 radical were observed from photodissociative excitation of SiF4 at 99.1, 95.5, and 92.3 nm. The spectra show a broad visible band in the 350–800 nm region, a UV band in 290–340 nm, and a weak band in 240–280 nm. The visible band resembles the chemiluminescence spectra observed from etching of silicon by F or XeF2.
Recombination of electron–ion pairs for arbitrary mean free path
Authors: Sceats Mark G.
Published: July 2002

A theory is developed of the dependence of the steady-state electron–ion pair recombination rate constant on the electron mean free path. The problem, in classical mechanics, is reduced to the stochastic dynamics of the electron in the one-dimensional effective potential Ṽ(R)=−kTRc/R −2kT ln R. Rc is the Onsager length Ze2/4πεkT. For a large mean free path λ, the recombination rate is determined by energy relaxation of electrons which cross the transition state of Ṽ(R) at RT=Rc/2, whereas for small λ the Debye result for spatial diffusion-controlled recombination is obtained. The theory gives the dependence of the rate in the crossover regime where λ is comparable to Rc. The results are in good agreement with experiment and Monte Carlo simulations.
Sum rules and fugacity derivatives of classical fluids
Authors: Hernando J. A.
Published: July 2002

Equations relating integrals of distribution functions or correlation functions with fugacity derivatives of distribution functions are derived. The corresponding equations in the canonical ensemble are also derived and the system considered is a multicomponent fluid.
A reexamination of energy accommodation experiments using the vibrating surface technique
Authors: Stephens John R. , Rosenblatt Gerd M.
Published: July 2002

Measurements of gas/surface energy accommodation using the vibrating surface method have been augmented by experiments which use an infrared sensing technique, rather than a thermocouple, to measure surface temperature. In contrast to previous results no surface temperature rises were detected that can be attributed to gas/surface energy accomodation. A numerical model was developed to simulate the energy flow near the surface of a solid oscillating in a rarified gas. The numerical simulation includes energy exchange between the gas and surface, radiative exchange between the surface and the chamber, and conduction into the solid. Conduction of energy into the solid dominates the surface thermal balance and damps the surface temperature rise due to gas/surface energy exchange to microdegree levels, well below the sensitivity of conventional temperature sensing techniques. Differences between our data and previously reported results are discussed.
Fractal properties of polymer crystals
Authors: Ogawa Tetsuya , Miyashita Satoru , Miyaji Hideki , Suehiro Shoji , Hayashi Hisao
Published: July 2002

Small angle x-ray scattering is performed on the crystals of polyethylene and polytetrafluoroethylene up to Porod’s region. The scattering intensity I obeys a power law for the magnitude of the scattering vector q for large values of q: I∼q−α. The exponent α is smaller than 4 given by Porod’s law. If it is assumed that the folded chain crystals and the extended chain crystals have the fractal surface, the fractal dimension is from 2.2 to 2.8 depending on the crystallizing condition.
Sensitivity of unimolecular lifetime distributions and energy dependent rate constants to fluctuations in state specific rate constants
Authors: Lu Da-hong , Hase William L.
Published: July 2002

Different distribution functions are used to describe fluctuations in state-specific unimolecular rate constants, for states which lie within a narrow energy interval. The effect of these distributions on the reactant population vs time N(τ,E) and the time-dependent unimolecular rate constant k(τ,E) are considered. Comparisons are made with the exponential decay predicts by RRKM (Rice–Ramsperger–Kassel–Marcus) theory of unimolecular kinetics. The collision-averaged unimolecular rate constant k(ω,E) is also determined for each of the distributions of state-specific unimolecular rate constants. Overall, k(ω,E) is found to be relatively insensitive to fluctuations in state-specific unimolecular rate constants.
Photofragment spectroscopy of O2: Excitation of the Schumann–Runge band system
Authors: Cosby P. C. , Helm H.
Published: July 2002

Photodissociation of O2 is observed by direct detection of coincident neutral photofragments following laser excitation of a fast molecular beam. The O2 beam was prepared by charge-transfer neutralization of keV energy O+2 and irradiated by a linearly polarized, line selected Kr+ ion laser. Kinetic-energy resolved photofragments were observed at eight laser lines between 752.5 and 476.2 nm. Correlation of the observed fragment kinetic energies with laser wavelength shows that the observed photodissociations arise from O2 B 3σ−u(v′=1–18)←X 3σ−g (v″=22–37) Schumann–Runge transitions.
The radiation-induced oxidation and reduction of guanine: Electron spin resonance–electron nuclear double resonance studies of irradiated guanosine cyclic monophosphate
Authors: Kim Heasook , Budzinski Edwin E. , Box Harold C.
Published: July 2002

Two free radicals are identified by electron spin resonance–electron nuclear double resonance (ESR-ENDOR) spectroscopy in single crystals of guanosine 3′,5′-cyclic monophosphate x irradiated at 4.2 K. The two absorptions are attributed to the anion and cation formed on the guanine moiety. The characteristics of the cation absorption are consistent with those postulated previously for guanine cation presumed to form in irradiated DNA.
Contribution to the theory of diffusion-reaction controlled Liesegang patterns
Authors: Brechet Y. , Kirkaldy J. S.
Published: July 2002

A Turing-type reaction-diffusion model is explored which may be applicable to Liesegang bands, rings, and spirals evolving by precipitation in the environs of an equilibrium solubility product relation. Because of their incompletely specified initial and (or) boundary conditions the solutions exhibit a bivariate free boundary degeneracy. We find that one degree of freedom may be removed by the specification of a global rate constant and the other by the specification of a principle of optimal wave number selection within linear stability theory. Existence conditions for banding in one dimension are established and these agree with particular observations.
Nonequilibrium as a source of nonideality in chemical reacting systems
Authors: Li Ru-Sheng
Published: July 2002

The statistical theory of solutions which provides a relation between chemical potentials and the composition fluctuations is extended to the nonequilibrium chemical reacting systems. The chemical potentials in nonequilibrium reacting systems are shown to be dependent not only on the concentrations, but possibly also explicitly on the nonequilibrium constraints acting on the system. Such dependence of chemical potentials on the nonequilibrium constraints may give the system a nonideal behavior, even though it was ideal at equilibrium. To characterize the dependence of nonidealities on the nonequilibrium extent, a nonequilibrium activity coefficient is formally defined and the quantitative dependences of nonequilibrium chemical potential and activity coefficient on the nonequilibrium extent are given for a simple reaction scheme. Some implications of such dependence to the chemical reaction and diffusion processes are discussed.
Electron spin resonance investigations of 11B12C, 11B13C, and 1B12C in neon, argon, and krypton matrices at 4 K:  Comparison with theoretical results
Authors: Knight Lon B. , Cobranchi S. T. , Petty J. T. , Earl E. , Feller David , Davidson E. R.
Published: July 2002

The first spectroscopic study of the diatomic radical BC is reported which confirms previous theoretical predictions of a 4∑− electronic ground state. The nuclear hyperfine interactions (A tensors) obtained for 11B, 10B, and 13C from the electron spin resonance (ESR) measurements are compared with extensive ab initio CI calculations. The BC molecule is one of the first examples of a small high spin radical for such an in-depth experimental–theoretical comparison. The electronic structure of BC obtained from an analysis of the nuclear hyperfine interaction (hfi) is compared to that obtained from a Mulliken-type population analysis conducted on a CI wave function which yields Aiso and Adip results in good agreement with the observed values. The BC radical was generated by the laser vaporization of a boron–carbon mixture and trapped in neon, argon, and krypton matrices at 4 K for a complete ESR characterization. The magnetic parameters (MHz) obtained for 11B13C in solid neon are: g∥ =2.0015(3); g⊥ =2.0020(3); D(zfs)=1701(2); 11B: ‖A∥‖ =100(1); ‖A⊥‖ =79(1); 13C: ‖A∥‖ =5(2) and ‖A⊥‖ =15(1). Based on comparison with the theoretical results, the most likely choice of signs is that all A values are positive.
Macroscopic anisotropy of the molecular reorientational dynamics in nematic liquid crystals
Authors: Dozov I. , Kirov N.
Published: July 2002

The reorientational diffusion equation is solved for the case of rotational diffusion tensor D̂ depending on the instantaneous molecular orientation. New equations for the rotational contribution to the IR bands of aligned nematic mesophase taking into account also the anisotropy of the rotational viscosity are proposed and an attempt to explain the temperature dependence of the rotational diffusion coefficients D∥ and D⊥ is reported.
Application of Onsager’s reciprocity relations to interface motion during phase transformations
Authors: Kaplan Theodore , Aziz M. J. , Gray L. J.
Published: July 2002

A number of theories have been developed for the kinetics of steady-state interface motion during a phase transformation. One requirement of such theories is that they satisfy Onsager’s reciprocity relations for coupled irreversible processes. We show how to apply Onsager’s relations to a phase transformation at a moving planar interface in a two-component system. The appropriate pairs of thermodynamic forces and conjugate fluxes are determined and used to test two proposed theories for interface motion during solidification of binary alloys. It is shown that the continuous growth model ‘‘with solute drag’’ of Aziz and Kaplan is inconsistent with Onsager’s relations, but the continuous growth model ‘‘without solute drag’’ is consistent with Onsager’s relations.
Local mode of motions in amorphous solid. I. o-Terphenyl and triphenylchloromethane
Authors: Naoki Motosuke , Ueda Masaharu
Published: July 2002

Dielectric constants have been obtained for the dispersion process in the glassy states of o-terphenyl and triphenylchloromethane as a function of temperature and pressure. The magnitude of the relaxation of triphenylchloromethane with a large dipole moment is smaller than that of slightly polar o-terphenyl. Simple treatments of the activation process and the static dielectric constants are given. The intermolecular configurational contributions are extremely small in the activation process, while those compose about 20% of the energy disparity which determines the relaxation magnitude. Hindered revolving vibrations of the disk shape molecules are presumed as the main mode of motions of the present system.
Microscopic model for microemulsions. II. Behavior at low temperatures and critical point
Authors: Ciach A. , Ho/ye J. S.
Published: July 2002

Low temperature properties and critical behavior for the more simple versions of the microemulsion model introduced in Ref. 1 are investigated. For the lattice case with nearest-neighbor interactions an analytic asymptotic expression for the surface tension at the oil–microemulsions–water coexistence is found for low T. For both lattice and continuum cases the critical point is determined, and we show how an oscillating phase (microemulsion) may be formed below the critical temperature.
The quantum Henon–Heiles problem with Coriolis coupling: A comparison of algebraic and exact results
Authors: Sage Martin L. , Child Mark S.
Published: July 2002

The results of an algebraically computed double Van Vleck perturbation theory are reported for combined anharmonic and Coriolis perturbations to a degenerate harmonic oscillator. The results to sixth order in the anharmonic coupling and comparable Coriolis coupling are in excellent agreement with exact calculations for systems with anharmonic splittings of up to 5% to 10% of the vibrational spacing. Particular care is required in handling Fermi resonance interactions in the algebraic computations.
Transient photophysical hole-burning spectroscopy of the hydrated electron: A quantum dynamical simulation
Authors: Motakabbir Kazi A. , Schnitker Jürgen , Rossky Peter J.
Published: July 2002

Results for the time-dependent adiabatic eigenspectrum of an electron in water evolving in dynamic equilibrium have been obtained via quantum molecular dynamics simulation and used to evaluate the results expected from time-resolved transient optical hole-burning experiments. The dependence on excitation frequency and pulse length have been explored. The calculated results indicate that a relatively broad hole is created, but that, for ultrashort pump–probe time delays (≤100 fs) and comparably short pulses, the shape is distinctly different from the equilibrium spectrum. A slower component in the spectral evolution is also present, but appears likely to be difficult to distinguish experimentally. The shape of the absorption deficit is characteristic of the inhomogeneously broadened 1s, 2p-type electronic state structure found previously to underlie the equilibrium spectrum, and distinguishes between this description and a number of proposed alternatives. With pulse durations comparable to the best now available, the phenomenon appears experimentally accessible.
Dynamics of ferroelectric phase transition in vinylidene fluoride/trifluoroethylene (VF2/F3E) copolymers. II. Proton nuclear magnetic resonance study
Authors: Tanaka Hajime , Yukawa Hideyuki , Nishi Toshio
Published: July 2002

Here we study the ferroelectric phase transition of a random copolymer of vinylidene fluoride (VF2) and trifluoroethylene (F3E), VF2/F3E(52/48), by 1H-pulsed nuclear magnetic resonance (NMR). Spin–spin relaxation time T2, spin–lattice relaxation time T1, and T1 in the rotating frame T1 ρ show the anomaly reflecting the phase transition. We demonstrate that the motional state in the crystalline and amorphous region is not so different. From the direct fitting of the Kubo–Tomita relation to a free induction decay, we have succeeded in obtaining the correlation time of the fluctuating local field and the second moment of the rigid lattice separately. The critical slowing down of the order-parameter fluctuation is observed through the temperature dependence of the correlation time. The anomaly of T1 near the Curie point has been found to be weak. This weak divergence of T−11 is consistent with our results on acoustic measurements. The weak anomaly can be ascribed to (1) the long-range nature of the bare interaction between dipoles which may come from the connectivity of a polymer chain (a cooperative conformational change over at least three bonds) or the dipolar long-range interaction, (2) the randomness due to random copolymerization, and/or (3) the dimensionality of the order parameter.
Semiclassical quantization and the Langer modification
Authors: Watson James K. G.
Published: July 2002

A recent proposal by Collins of a method for obtaining the classical-limit quantization of momenta conjugate to angles is examined. Among other results, this method gives half-integral quantization for the angular momentum pφ in circular cylinder or spherical polar coordinates, in contradistinction to the integral quantization given by quantum mechanics. Collins’ method is shown to give incorrect results because of an incorrect use of the stationary-phase approximation. However, departures from integral quantization are not generalized Langer corrections, because the Langer modification from l(l+1) to (l+1/2)2 in the expression for the square of the angular momentum in the radial quantization condition does not correspond to a change of angular-momentum quantization but rather to the inclusion of a higher-order correction which improves the quality of the zero-order energies and wave functions for certain classes of potentials. The question of whether the Langer modification should be used in higher-order RKR calculations for diatomic molecules is discussed, and it is suggested that no advantage is achieved in calculations of this type.
The electric dipole moment of ArH+. Disagreement between theory and experiment
Authors: Geertsen Jan , Scuseria Gustavo E.
Published: July 2002

The experimentally determined dipole moment of the ArH+ molecular ion (1.4 D, 1.59 D) is in considerable disagreement with previous ab initio calculations (2.2 D). In this work we present further theoretical evidence strongly supporting a dipole moment of 2.1±0.1 D. We have carried out an extensive basis set study and calculated the dipole moment using the coupled cluster analytical energy gradient and polarization propagator techniques. Based on a theoretical determination of the equilibrium rotational g factors for ArH+ and ArD+ we conclude that the extrapolation of the experimentally determined g factors to their equilibrium values is the main source of the discrepancy between theory and experiment.
The statistical theory of electrolyte melts
Authors: Livshits A. I. , Martynov G. A.
Published: July 2002

The exact system of equations for the two-particle distribution function of the system of particles with the Coulomb interaction potential is transformed into the set of equations with the first equation describing the purely Coulomb interaction, the second—the short-range interaction, and the third—the mixed interactions. For each of these equations we choose its own approximation of the bridge functional. In the short-range interaction it is the Martynov–Sarkisov approximation, which gives the best results for systems with the Lenard-Johns interaction potential; in the ‘‘mixed’’ equation it is the hypernetted-chain approximation, which ensures the highest accuracy in systems with the electrostatic potential; the third equation, which does not contain the bridge functional at all, is retained in its original exact form. The system of three approximate equations obtained in this way proves to be more exact than any of the presently known approximations. At the density close to the melt crystallization density and at the corresponding ‘‘melting’’ temperatures the thermodynamical inconsistency in pressure is calculated to be several percent and the accuracy in determination of the internal energy is still more high (deviations from the Monte Carlo data do not exceed fractions of percent).
An experimental and theoretical study of shape resonances in CH+
Authors: Sarre P. J. , Whitham C. J. , Graff M. M.
Published: July 2002

A study of shape resonance energies and widths in the A 1Π state of 12CH+ and 13CH+ is reported. The experimental data were obtained by high-resolution laser photofragment spectroscopy of CH+ in a fast ion beam. Spectroscopic transitions were recorded by tunable laser excitation from levels of the X 1Σ+ state to shape resonances (quasibound rotational levels) of the A 1Π state and detection of photoproduct C+ ions. Some of the dissociation lifetimes are sufficiently short to cause broadening of the spectral lines. The linewidths are interpreted in terms of tunnelling through the centrifugal barrier and the effects of rotational-electronic and radial coupling. The e lambda-doublet component in two of the resonances is found to have a narrower linewidth than the corresponding f component. This is shown to be due to the effect of the rotational-electronic (Coriolis) interaction on the shapes of the rotationally adiabatic potential-energy curves which determine the tunnelling probability. The contributions to the predissociation rates are calculated and are in good agreement with the experimental results.
Close-coupled calculations of resonance widths observed in photodissociation spectra of CH+
Authors: Freed Karl F. , Sarre P. J. , Whitham C. J. , Williams Carl J.
Published: July 2002

The widths of near-threshold resonances observed in photodissociation spectra of CH+ are calculated by a close-coupled method. Potentials are derived from a combination of experimental data and ab initio computations. The results are in good agreement with experiment. Comparison is made with Fermi golden rule perturbative calculations of the resonance widths from the preceding paper (paper I). Calculations are presented for the branching ratio between the spin–orbit states of the C+ fragment that are produced by laser excitation to these resonances and that are yet to be determined experimentally.
Effects of periodic variations of reactant influxes on the combustion of methane in power production
Authors: Hjelmfelt Allen , Ross John
Published: July 2002

Periodic variations are applied to the influxes of oxygen and methane entering a reaction vessel in which takes place a combustion reaction. We measure the temperature and chemical responses of the system as we change the forcing amplitudes, periods, and equivalence ratios. Using a simple model of a Carnot engine we calculate efficiency changes in an externally varied flux mode (VFM) of operation relative to the constant flux mode (CFM) of operation. We find increases and decreases in the average temperature, efficiency, and unburnt fuel concentrations in the VFM relative to the CFM. For certain constraints we find regions where the average temperature in the VFM is less than that of the CFM and there is an efficiency increase. We find other regions where the entire temperature response in the VFM is greater than that of the CFM and this also can lead to an efficiency increase which is due to changes in extent of combustion and heat losses. The effects of forcing amplitudes, periods, and equivalence ratios on the system are explored, and predictions of numerical calculations agree with much of the data. A simple model of the reaction limited by one reagent, and the absorption of heat by the products and the other reagent predicts for variations of one reagent the number of maxima in the response, and phase relations of external variations and the response.
Square-well gas collision integrals and diffusion in a square-well Lorentz gas
Authors: Korlipara Ravi K. , Stell George , Karkheck John
Published: July 2002

A representation for collision cross sections of a square-well dilute gas mixture is developed that reduces their computation to the evaluation of one-dimensional integrals with integrands of elementary closed form. Consequently, the computation of collision integrals and Chapman–Enskog and Kihara transport-coefficient approximations, which depend on the collision cross sections, is analytically and numerically simplified. These results are then applied to the limiting case of a Lorentz gas, i.e., a dilute gas of mobile particles diffusing through a bed of scatterers that can be regarded as fixed. In particular, our results are used to evaluate the exact diffusion coefficient DL of a Lorentz gas with square-well potential interactions as a function of both square-well width and temperature, i.e., square-well depth. (We treat here only the case in which the scatterers are dilute enough for the problem to be accurately described by a Boltzmann equation.) The exact DL is compared with its first and second Chapman–Enskog approximations, D1 and DCE2, as well as its second Kihara approximation, DK2. (The first Kihara approximation coincides with the first Chapman–Enskog approximation so that it is unnecessary to attach a superscript to D1 to distinguish between the two approximation schemes.) The DK2 is found to be of high accuracy over the whole range of parameters studied, suggesting that it represents the most accurate of these three approximations available for the binary diffusion coefficient of a dilute square-well gas. Finally, a simple approximation for the collision integrals linear in well depth (i.e., inverse temperature) as well as one that adds to the linear term all contributions from ‘‘soft’’ scattering are used to evaluate D1. For wide wells the latter yields an excellent approximation (which, in turn, is a good approximation to DL for such wells). This approximation is no longer useful for narrow wells. As the temperature goes to zero, DL approaches the diffusion coefficient of a hard-sphere Lorentz gas with interaction diameter equal to the hard-core diameter plus the square-well width. This represents a

special case of the general limiting coincidence of square-well and square-mound scattering in the infinite-strength limit.
Electron and ion mobility in carbon disulfide liquid from 163 to 501 K
Authors: Gee Norman , Freeman Gordon R.
Published: July 2002

Electron mobility μe and cation mobility μ+ were measured in liquid carbon disulfide at 163 ≤ T/K ≤ 501. The cations diffuse about half as fast as neutral molecules. Values of μ+ were correlated using a free volume model. The electron mobility increased with increasing T up to ∼460 K and then tended to level off. Unlike in ethers or hydrocarbons, μe /μ+ =6–10 over a very large temperature range, ΔT=338 K. Electron migration by hopping from one group of molecules to the next, as in hexafluorobenzene, is suggested. Empirical correlations of the yields and lifetimes of ortho-positronium (o-Ps) with the values of μe in liquids were tested. Values of the static dielectric constant of CS2 were measured at 163–501 K: ε=3.4166−1.9826×10−3 T−6.5630×10−6 T 2 +2.2367×10−8 T 3 −2.4997 ×10−11 T 4 .
Light scattering studies on solutions of charged rod-like fd-virus at very low ionic strength
Authors: Schulz Susanne F. , Maier Erich E. , Weber R.
Published: July 2002

Light scattering experiments are reported on semidilute, aqueous solutions of rod-like fd-virus (length L=880 nm, molecular weight 16.4×106 dalton) near the overlap concentration c*=1 particle/length3. In solutions of very low ionic strength, a liquid-like structure with a significant intensity maximum of the elastically scattered light is observed. The structure is caused by the electrostatic interaction of the charged rods. It vanishes, when enough salt is added so that the interaction potential is screened on the interparticle distance. The scattering vector qmax of the maximum scales with the fd concentration as c1/2. The experimental values for qmaxL fit very well to Monto Carlo simulations if the concentration is scaled to c*. Dynamic light scattering of the fd solutions reflects the influence of the static structure factor in the same way as observed for interacting spherical macromolecules: The first cumulant of the field correlation function divided by the square of the scattering vector shows a behavior reciprocal to that of the static structure factor.
Temperature dependence of termolecular association of diatomic ions with diatomic molecules
Authors: Bates D. R.
Published: July 2002

The dependence of the rate coefficient k for termolecular association between diatomic ions A+ and diatomic molecules B on the temperature T of the ambient gas M is considered. There is experimental evidence that k decreases rapidly as T is increased if the association energy is small. A proposal that this behavior may be explained by the introduction of a super-complex AB+⋅M is rejected. It is shown that required T variation could ensue if the reactants in the energized AB+* complex repel one another at some relative orientations.
Nonstatistical unimolecular decay in quasiperiodic systems
Authors: Dumont Randall S. , Brumer Paul
Published: July 2002

We examine the nonstatistical character of the unimolecular decay associated with regular dynamical systems. In doing so, a longstanding problem due to Slater is solved in a proof that the lifetime for decay from a metastable torus is bounded from above. The random gap assumption is thus invalidated for isolated torus decay. In addition, the microcanonical unimolecular decay of the regular open circle billiard system is treated in detail. Nonstatisticality is observed in both product and lifetime distributions. In particular, the lifetime distribution exhibits an O(t−2) long time tail which is linked, analytically, to the existence of resonant tori in the circle billiard phase space.
Cu overlayers on oxygen and on carbon monoxide adsorbed on tungsten (110)
Authors: Shamir N. , Lin J. C. , Gomer R.
Published: July 2002

The existence of Cu overlayers on O/W(110) and CO/W(110) was investigated using thermal desorption, work function, UPS, XPS, and energy loss measurements. It was shown that these layers exist and have very different properties from O/Cu/W(110) and CO/Cu/W(110), respectively. The most striking fact is that the work function at Cu monolayer coverage (slightly higher in the case of CO/W(110), probably because of Cu second layer formation and gaps in the first Cu layer) is almost that of Cu1/W(110) regardless of the underlying adsorbate. HeI UPS spectra show a Cu d-band structure even at Cu submonolayer coverages for Cu/O/W and for Cu1/CO/W(110). A loss peak at 4.64 eV was found for both systems [and for Cu8/W(110)] at θCu≥0.2 for O/W(110), and at θCu≥0.6 for CO/W(110). This is tentatively interpreted as a Cu interband transition. Unexpectedly small shifts in Cu2p3/2 and O1s binding energies were found under all conditions; the reasons for the virtual absence of shifts are not understood. The main conclusion of this work is that overlayers of Cu on top of other adsorbates show metallic properties even at submonolayer Cu coverages.
Flame diagnostics and molecular constants of CaO by tunable diode laser spectroscopy
Authors: Hedderich Hartmut G. , Blom Cornelis E.
Published: July 2002

The infrared absorption spectrum of the CaO molecule has been recorded with a tunable diode laser. Transitions with J″=3 to J″=54 of the v=1←0, v=2←1, and v=3←2 bands have been measured. The new data have been combined with previous millimeter wave measurements to yield a set of Dunham rovibrational constants. CaO monomers were produced by reacting hot calcium vapor with nitrous oxide. The distribution of CaO over the rotational and vibrational states has been determined by comparing the relative intensities of the rovibrational transitions. The vibrational temperature increased from 500 to about 1500 K with increasing N2O pressure.
Kinetics of a structural phase transition in Langmuir monolayers studied using x-ray diffraction
Authors: Lin B. , Peng J. B. , Ketterson J. B. , Dutta P. , Thomas B. N. , Buontempo J. , Rice Stuart A.
Published: July 2002

Frequently, time-dependent effects are seen in monolayers of amphiphilic molecules (Langmuir films) when they are compressed, so that the pressure after some time is different from that recorded immediately after compression. We have identified for the first time a microscopic relaxation mechanism in monolayers of heneicosanol (C21H43OH): namely, a transition from a uniaxially distorted (‘‘pseudohexagonal’’) structural, formed upon compression, to an undistorted hexagonal structure. For T>20 °C we observe only an apparently hexagonal phase, while at T=5 °C we observe only an apparently stable pseudohexagonal phase. When 10≤T≤20 °C, the monolayer structure changes with time from pseudohexagonal to hexagonal. The rate at which this transformation occurs is strongly temperature dependent. We propose that the observed temperature dependence is determined by the rate of nucleation of a hexagonal phase from a metastable shear-induced structure.
State-to-state dynamics of H+HX collisions. II. The H+HX→HX°+H (X=Cl,Br,I) reactive exchange and inelastic collisions at 1.6 eV collision energy
Authors: Aker Pamela M. , Germann Geoffrey J. , Tabor Kevin D. , Valentini James J.
Published: July 2002

We report measurement of product state distributions for the rotationally and/or vibrationally excited HX formed in collisions of translationally hot H atoms with HX (X=Cl, Br, and I) at 1.6 eV collision energy. The product state distributions are probed after only one collision of the fast H atom, using coherent anti-Stokes Raman scattering spectroscopy. Whether proceeding by inelastic collisions or reactive exchange, the transfer of translational energy to vibrational and rotational energy is quite inefficient in H+HX collisions at 1.6 eV. For all three hydrogen halides only 2–3% of the initial translational energy appears as HX vibration. For H+HCl only 6% of the initial energy is converted to HCl rotational energy, while for H+HBr and H+HI, this percentage is twice as large, 11–12%, but still small. The indistinguishability of the two H atoms involved makes it impossible to distinguish reactive exchange from inelastic energy transfer in these H+HX collisions. However, the difference in rotational energy partitioning for H+HBr and H+HI as compared with H+HCl, suggests that reactive exchange is dominant in the former and inelastic energy transfer dominates in the latter. The total cross sections for the combined energy transfer/reactive exchange do not change much with the identity of X, being 13±3, 11±2, and 11±2 Å2, for H+HCl, H+HBr, and H+HI, respectively.
Phase stability of multicomponent highly asymmetric electrolytes: A charged hard sphere model study
Authors: Caccamo C.
Published: July 2002

The phase diagrams and the spinodal lines of different types of charged hard sphere fluid mixtures (CHSM) are determined through the use of the mean spherical approximation (MSA). The attention in the paper is particularly addressed to the low density regime of these systems, where the physical parameters are chosen in such a way so to mimic polyelectrolyte solutions with an added salt, or dilute electrolyte solution mixtures of simple salts. The phase diagrams at densities corresponding to the molten salt regime, obtained in a previous paper, are also reported, in order to get a complete picture of the phase stability behavior of CHSM. In all cases investigated the MSA predicts the existence of a closed solubility loop in the low density domain of the phase diagram. The location and the extension of this feature turns out to be crucially affected by the pressure, by the diameter ratios of the ionic components, and by the asymmetry of the ionic charges. A comparison of the MSA predictions in the low density regime with more refined theoretical approaches, or with computer simulation data, has not been possible for reasons which are explained in the text. However, the theory is expected to work at the same level of accuracy as in other physical contexts, where its predictions for the phase stability conditions of various systems have been found to be qualitatively reliable; moreover, for the case in which the model mimics a polyelectrolyte solution with an added salt, the form of the theoretical spinodal closely resembles the cloud points curve of an ionic micellar solution experimentally investigated by other authors.
Dissociation energy of the molecule AlBr from equilibrium measurements
Authors: Hildenbrand D. L. , Lau K. H.
Published: July 2002

The dissociation equilibrium AlBr=Al+Br was studied by effusion beam mass spectrometry over the range 1970 to 2260 K and the dissociation energy D00(AlBr) was derived as 4.41±0.06 eV. This value is in general agreement with other fragmentary thermochemical results, but it is lower than a value derived from a short extrapolation of vibrational levels in the excited 1π state, doubtless because of a potential maximum of about 0.22 eV in that state. A Birge–Sponer extrapolation of the ground state vibrational levels, when corrected for degree of ionicity, yields a D00 value in close accord with the experimental result, but an electrostatic model calculation falls short by 0.45 eV.
Detection of the silylene ν2 band by infrared diode laser kinetic spectroscopy
Authors: Yamada Chikashi , Kanamori Hideto , Hirota Eizi , Nishiwaki Nobuki , Itabashi Naoshi , Kato Kozo , Goto Toshio
Published: July 2002

The ν2 band of the silylene SiH2 molecule in X̃ 1 A1 was observed for the first time in the gas phase by using infrared diode laser kinetic spectroscopy. Silylene molecules were generated by the photolysis of phenylsilane at 193 nm. The observed spectrum was analyzed to determine the rotational and centrifugal distortion constants in the ground and v2 =1 states and the band origin ν0 =998.6241(3) cm−1 with one standard deviation in parentheses. The significance of the derived parameters is discussed in detail.
Relativistic well-tempered Gaussian basis sets for helium through mercury
Authors: Okada Satosi , Matsuoka Osamu
Published: July 2002

Exponent parameters of the nonrelativistically optimized well-tempered Gaussian basis sets of Huzinaga and Klobukowski have been employed for Dirac–Fock–Roothaan calculations without their reoptimization. For light atoms He (atomic number Z=2)–Rh (Z=45), the number of exponent parameters used has been the same as the nonrelativistic basis sets and for heavier atoms Pd (Z=46)–Hg(Z=80), two 2p (and three 3d) Gaussian basis functions have been augmented. The scheme of kinetic energy balance and the uniformly charged sphere model of atomic nuclei have been adopted. The qualities of the calculated basis sets are close to the Dirac–Fock limit.
On the coupled-channel calculation of bound states for trimeric systems using hyperspherical coordinates
Authors: Hutson Jeremy M. , Jain S.
Published: July 2002

We discuss the bound states of weakly bound van der Waals trimers within the framework of hyperspherical coordinates. The wave function is expanded in terms of hyperspherical harmonics, which form a complete basis set in the angular variables. The resulting set of coupled second-order differential equations in the hyperradius is solved exactly. Our method gives a value for the zero-point energy of H+3 which is in excellent agreement with previous calculations. For (H2)3 and Ne3, however, our results show some discrepancy with earlier work.
Brownian dynamics study of the end-to-end distribution function of star and linear polymers in different regimes
Authors: Bishop Marvin , Clarke Julian H. R.
Published: July 2002

Brownian dynamics computer simulations are used to investigate the shape of the mean-squared end-to-end distance distribution function in the three regimes: (1) excluded volume; (2) θ; (3) collapsed. It is found that Mazur’s function fits regime (1), that the Gaussian function fits regime (2), and that neither of these appear to describe the collapsed state. The implications of these results to theories of ring formation during polymerization is pointed out.
A stability condition for the Hartree–Fock solution of the infinite one-dimensional system
Authors: Tanaka Kazuyoshi , Kobayashi Hiromi , Yamanaka Shozo , Yoshizawa Kazunari , Yamabe Tokio
Published: July 2002

A simplified stability condition for the Hartree–Fock (HF) solution giving the self-consistent field crystal orbitals (SCF-CO) of the infinite one-dimensional system is derived. Since the present formulation, particularly for the systems having nearly or entirely degenerated highest occupied and the lowest unoccupied COs, contains only two physical parameters, that is, the density of states and the Coulomb repulsion integrals both at the Fermi level, it is tractable to examine the stability of the HF solutions of such polymers as well as the ordinary molecular systems. An example of its application to metallic trans-type polyacetylene is also shown.
Distributed electronic relaxation and nonexponential fluorescence in polymers: Reversibility in donor–excimer pairs—A perturbation theory treatment
Authors: Mollay Bernhard , Landl Gerhard , Kauffmann Harald F.
Published: July 2002

An ensemble of distributed donor molecules that undergoes rotational transitions into a discrete excimer state has been analyzed, in an attempt to model distributed electronic relaxation and nonexponential fluorescence of aromatic polymers in presence of rotational sampling processes. In case of irreversible trapping, the donor survival function has been formulated in terms of the one-sided Laplace transform and specified for a modified Gaussian distribution to yield a closed-form expression for the donor decay. The formalism permits a time-dependent rate function to be derived that makes possible the construction of the excimer excitation function by means of the convolution theorem. In case of reversible constraints, a generalized treatment based upon time-dependent transition and transform matrices has been given which applies a perturbation technique for approximately solving the system of nonautonomous differential equations in the time domain. In the limit of weak coupling, the method develops approximate Mth order expressions (M=2,4,6, and 8) to the fluorescence response functions of donor and excimer. The perturbational solutions are well behaved up to relatively long time scales and they prove useful for providing the typical nonexponential time behavior of such a system affected by dispersion and dissociation. The physical restriction of this mathematical analysis (weak reversibility) has been addressed and the implications of distributed event times in future analyses of polymer fluorescence have been discussed.
Pressure tuning of Fermi resonance in crystal CO2
Authors: Cardini Gianni , Remigio Salvi Pier , Schettino Vincenzo , Jodl Hans J.
Published: July 2002

A solid state theory on pressure tuning of Fermi resonance in crystals is presented and applied to the CO2 case. The theory relies on consideration of delocalized ω2+ω2 two-phonon states anharmonically coupled to ω1 and it is developed along the formalism of the Green function technique. This gives a straightforward method to split bound states (or biphonons) out of the continuum. Explicit expressions for their energy separation and intensity are obtained. Calculations are performed on the pressure dependence of the main parameters governing the Fermi resonance and discussed in terms of the crystal approach. In contrast with the more limited molecular treatment, W is seen to decrease with pressure. The effect is specifically related to the spread of the two-phonon continuum over a finite energy interval. Other quantities, for instance the intensity ratio between bound states, do not suffer such a big discrepancy between the two models. Limits of applicability of our approach are also sketched.
Infrared spectra of diatomic polar molecules in rare-gas liquids. II. Application to the HCl in Ar, Kr, and Xe solutions
Authors: Pérez J. , Luis D. , Hernández A. Calvo , Velasco S.
Published: July 2002

In paper I (the preceding paper), a spectral theory describing the near infrared fundamental band spectra of diatomic polar molecules impurities in nonpolar solvents has been developed in terms of a reduced set of parameters. In this paper, this spectral theory is applied to HCl in Ar, Kr, and Xe liquid solutions. The parameters obtained by fitting the experimental and calculated profiles are in good agreement with those calculated using several microscopic theories.