bluuebunny/crossref_metadata_2025 huggingface dataset:
Multiphoton ultraviolet photodissociation of C2N2
Authors: Jackson William M. , Halpern Joshua B.
Published: February 2003

A detailed study of the multiphoton absorption of ArF laser photons in C2N2 has been done. Evidence is presented which shows that sequential two photon absorption occurs at threshold levels as low as 1024 photons/cm2 sec. A kinetic mechanism is proposed that agrees with both the observed pressure and intensity dependence of the fluorescence induced as a result of this sequential two photon absorption.
Absorption and emission spectra of K atoms trapped in rare-gas matrices
Authors: Balling L. C. , Havey M. D. , Wright J. J.
Published: February 2003

Pulsed dye-laser excitation has been used to investigate the structure of the optical absorption and emission spectra of K atoms trapped in Ar, Kr, and Xe matrices at 10 °K. The intensity of fluorescence produced by laser excitation in each absorption band has been measured as a function of emission wavelength. Observation of the laser induced fluorescence has permitted the unambiguous determination of the wavelengths of the peaks of overlapping absorption multiplets. The principal absorption bands have been found to have doublet or triplet structures, depending on the rare gas, and are clearly associated with the 4s→4p transition in K. Weaker absorption bands have been detected which are tentatively assigned to the 4s→5p transition in K. Optical pumping between levels of a bistable state of the K–rare gas system has been observed.
The spin-forbidden dissociation–recombination reaction SO3?SO2+O
Authors: Astholz D. C. , Glänzer K. , Troe J.
Published: February 2003

Rate constants for the spin-forbidden dissociation process SO3+Ar→SO2+O+Ar have been measured in shock waves between 1700 and 2500 K. The results are compared with data on the low temperature (200–400 K) recombination reaction. The analysis in terms of unimolecular reaction rate theory allows for a determination of the threshold energy of the reaction.
Temperature dependence of electron spin–lattice relaxation of presolvated and solvated electrons in methanol–water matrices
Authors: Michalik Jacek , Kevan Larry
Published: February 2003

In 1:1 volume ratio methanol–water matrices both solvated and presolvated electrons, with equilibrium and nonequilibrium solution shells, respectively, can be stabilized by radiolysis at 77 K. The temperature dependence of the electron spin–lattice relaxation of these two types of electrons has been studied by the saturation recovery method. The relaxation rate remains fast at low temperatures and shows a large component linear in temperature which dominates up to 30 K. This is interpreted in terms of the recently developed model of tunneling relaxation involving modulation of the electron nuclear dipolar interaction by tunneling of nuclei in the radical’s environment. [J. Phys. Chem. 81, 456 (1977)]. The tunneling relaxation coefficient for presolvated electrons is about 76% of that for solvated electrons. This is explained in terms of the average electron–proton distance changes that occur during electron solvation.
ESR and ENDOR study of x-irradiated single crystals of β-alanine at room temperature
Authors: Close David M. , Fouse George W. , Bernhard William A. , Andersen Roy S.
Published: February 2003

Three radicals have been identified in the room temperature ESR spectra of x-irradiated single crystals of β-alanine (N+H3CH2CH2CO−2). ENDOR spectra from one radical exhibit hyperfine coupling to 1 α-proton (Axx=−33.12, Ayy=—20.68, Azz=−10.50 G) and 2 β-protons [Aiso(Hβ1) =13.24 G, Aiso(Hβ2) =4.89 G]. From the anisotropic nature of the α-proton coupling it has been determined that these splittings arise from a N+H3CH2ĊHCO−2 radical. It has been shown that this radical is the decay product of the unstable low temperature oxidation product. A second room temperature radical, N+H3CH2CH2Ċ=0, has been shown to be a decay product of the primary reduction product. A minor room temperature product has been tentatively identified as a ĊH2–CH2–R radical.
A study of the thermal polymerization of styrene by depolarized Rayleigh light scattering spectroscopy
Authors: Alms G. R. , Patterson G. D. , Stevens J. R.
Published: February 2003

The technique of depolarized Rayleigh light scattering spectroscopy has been applied to follow the kinetics of the thermal polymerization of styrene. By measuring the spectrum of the depolarized scattered light we are able to separate the intensity of light scattered by the polymer being formed from the intensity of light scattered by the monomer. The spectrum consists of a wide Lorentzian due to the monomer and a central spike with instrumental width due to the polymer. This separation occurs because the polymer relaxation time which is determined by the longest Rouse–Zimm mode or by overall rotation is four orders of magnitude longer than the relaxation time of the monomer which is governed by overall rotation. Using the intensity data, the initial rate of the polymerization reaction is measured and is found to agree with the rate determined in previous experiments using classical techniques. After about one-third of the reaction is complete, the rate increases by 50%. This increase in rate is interpreted as resulting from the large increase in viscosity preventing the termination of the reaction by coupling of polymer radicals. Also the rotational relaxation time of the monomer is determined for the first 80% of the reaction and is found to increase linearly with time. However the value of the monomer rotational relaxation time at 80% of reaction is only 1.5 times the inital value. This indicates the monomer rotational motion is not determined by the large macroscopic viscosity, but by a local viscosity in the region of the monomer.
Analytic potential functions for weakly bound molecules: The X and A states of NaAr and the A state of NaNe
Authors: Goble James H. , Winna) John S.
Published: February 2003

The interatomic potential functions for the ground and first excited electronic states of the weakly bound molecule NaAr and the first excited state of NaNe are derived by inverting spectral data to analytic potential functions. Using the Thakkar potential expansion, it is shown how one may deduce vibrational assignments, compute accurate dissociation energies, and combine two potentials with an atomic transition to advantage. The resulting potential functions are in excellent agreement not only with spectroscopic data, but also with potentials derived from scattering and atomic resonance line broadening experiments.
A high-pressure conductivity and laser Raman spectroscopic study of aqueous orthophosphate solutions at 25 °C
Authors: Adams W. A. , Preston Caroline M. , Chew H. A. M.
Published: February 2003

Conductivities of aqueous solutions of H3PO4, KH2PO4, and Na3PO4 (0.001–1 M), and Raman spectra of 0.1, 0.5, 10, and 15.5 M H3PO4, 1 M KH2PO4, and 0.1M Na3PO4, have been obtained at 25 °C, and pressures up to 200 MPa. Pressure enhanced the first dissociation of H3PO4 (κp/κ⊥, measured by conductivity vs [H3PO4] goes through a maximum), and reduced the extent of hydrolysis of Na3PO4. Volume changes for the first and third dissociations of H3PO4 were ΔV1=21±4 cm3 mol−1 (conductivity), −18±3 (Raman, 0.1 M H3PO4), −8±2 (Raman, 0.5 M H3PO4), and ΔV3=−36±3 (Raman, 0.1 M Na3PO4). Both Raman and conductivity studies of H2PO4− were consistent with the presence of hydrogen-bonded phosphate dimers, H4P2O82−, with a formation constant of 2–3 l mol−1 (conductivity), and ΔV?0 cm3 mol−1 (conductivity). This ΔV value agreed with the Raman study which indicated only a very small decrease in dimerization with increasing pressure.
Threshold photoelectron spectra of atmospheric molecules. I. Description of method and application to H2, D2, and N2
Authors: Stockbauer Roger
Published: February 2003

Threshold photoelectron spectra (TPES) are presented for H2, D2, and N2 with a resolution of 28 meV full width at half maximum. The results are compared with Franck–Condon transition probabilities, previous TPES and electron attachment threshold photoelectron spectra. Peaks in the TPES not predicted by Franck–Condon calculations are explained by autoionization processes. These processes in N2 make possible the observation of vibrational levels of the ions not visible spectroscopically or in photoelectron spectra. A shift of the TPES peaks in N2 toward lower energy is explained by conversion of rotational energy in the ionization transition. Peaks between the v=O and v=1 vibrational levels of the X 2Σg+ state of N2+ consist of near monoenergetic electrons implying little or no change in the rotational quantum number in the autoionization process.
Power law scaling for rotational energy transfer
Authors: Pritchard David E. , Smith Neil , Driver Richard D. , Brunner Timothy A.
Published: February 2003

We have applied a new scaling law to several sets of rotational energy transfer cross sections. The new law asserts that the square of the T-matrix depends on the amount of energy transferred as a power law. Two different kinds of angular momentum statistics are assumed, one corresponding to mj being conserved and the other corresponding to mj being completely randomized. Numerical fits are presented which demonstrate that the data follow the power law better than the widely used exponential gap law.
Entropy of a quantum square-well potential gas at low temperatures
Authors: Klemm Anthony D. , McGee Ian J.
Published: February 2003

We calculate the quantum second virial coefficients and their contributions to the canonical entropy for two- and three-dimensional systems interacting with a hard-core square-well potential. This provides three examples of quantum mechanical systems in which the canonical entropy becomes greater than the canonical entropy for the corresponding ideal (noninteracting) systems over a finite temperature interval when Boltzmann statistics is assumed, thus contradicting the conjecture of Baierlein. In addition, low temperature expansions of the second virial coefficient and its contributions to the canonical entropy are made for the general three-dimensional system in powers of the (reduced) temperature.
Analysis of interdiffusion in organic binary solutions with molecular association
Authors: Oishi Y. , Nanba Masao
Published: February 2003

Analysis of interdiffusion in the CH3OH–CCl4 system and C2H5OH–CCl4 system was carried out for a multicomponent diffusion model in which alcohol polymers of various degrees of association were regarded as separate diffusion units. The distribution of the degree of association necessary for the analysis was calculated from the infrared absorption spectrum data. Self-diffusion coefficients of alcohol polymers relative to that of the monomer were estimated by analogy with the self-diffusion coefficients of a series of alkanes in their CCl4 solutions. The theoretical interdiffusion coefficients calculated with these data by a multicomponent diffusion equation showed satisfactory agreement with the experimentally determined interdiffusion coefficients.
Collisional energy dependence of molecular ionization by metastable rare gas atoms
Authors: Martin R. M. , Parr T. P.
Published: February 2003

The collisional energy dependence of several molecular total ionization cross sections by metastable rare gas atoms was studied over the thermal energy region using the crossed molecular beam time-of-flight method. Results are reported for the collision systems He, Ne, and Ar ionizing the geometric isomers cis- and trans-dichloroethylene and ortho- and para-dichlorobenzene. The He ionization cross sections oscillate about an energy dependence of E−1/2 over the energy range 0.004–1.0 eV, and the Ar*+para-dichlorobenzene cross section oscillates about an energy dependence of E−2/5 over the energy range 0.011–0.64 eV. The remaining systems are characterized by ’’bent’’ E−m dependences with m values of 0.56–0.70 at low energies changing to 0.07–0.29 at higher energies. Comparison with the slopes of the He* systems and the Ar*+para-dichlorobenzene system shows that the ’’bent’’ and ’’oscillating’’ energy dependences are similar except for the form of the cross section functions at the lowest energies. No systematic differences are found between the cross section energy dependences for ionization of different geometric isomers or for ionization by the different metastable rare gas atoms.
Dissociative excitation of CO2 by electron impact: Translational spectroscopy of O fragments
Authors: Schiavone James A.
Published: February 2003

Highly excited Rydberg (HR) oxygen atoms produced in electron impact dissociative excitation of CO2 are studied by time-of-flight (TOF) spectroscopy. The detector is highly discriminatory against non-HR metastable species. Fragment translational kinetic energy distributions, obtained from the TOF distributions, and excitation functions are used to investigate the dissociation channels between projectile energies of 19 and 56 eV. The dissociation processes can be divided into two groups: low energy processes having onset energies between 19 and 30 eV characterized by two-body dissociations from parent molecules with singly ionized cores and high energy processes having onset energies between 40 and 50 eV characterized by two- or three-body dissociations from parent molecules with singly or doubly ionized cores.
Comment on ’’Theory of collisions between an atom and a diatomic molecule in the body-fixed coordinate system
Authors: Schatz George C. , Kuppermann Aron
Published: February 2003

It is shown that the phase factor iJ+j+l omitted in a theory of atom-diatom monreactive scattering formulated by schatz and kupperman but included in the Choi, Poe, and Tang theory does not lead to errors in the analysis of te (H,H2) system.
Closed-form expressions for the correlated two-electron-core potentials and elastic form factors for 1⩽Z⩽4
Authors: Winkler P. , Porter R. N.
Published: February 2003

Precise calculations of the static potentials and the elastic form factors due to the two electrons in H−, He, Li+, and Be++ have been carried out. Analytical formulas for these quantities are derived from the generator coordinate representation of the ground-state wave functions described previously [J. Chem. Phys. 61, 2038 (1974)]. The core potential functions obtained in this way include dynamical electron correlation to all orders. These results are compared to those obtained from Hartree–Fock–Roothaan wave functions. Correlated wave functions for these systems are given in explicit form. In the case of He, the wave function reported here is an improvement over the one we reported previously in J. Chem. Phys. 62, 257 (1975).
Electronic spectroscopy of benzene and the fluorobenzenes by variable angle electron impact
Authors: Frueholz Robert P. , Flicker Wayne M. , Mosher Oren A. , Kuppermann Aron
Published: February 2003

Electron-impact spectra of benzene and 11 fluorine-substituted derivatives have been obtained at impact energies of 75, 50, and either 25 or 30 eV, and scattering angles from 5° to 80°. Each molecule shows an absorption maximum at about 3.9 eV corresponding to a singlet→triplet, π→π*, transition. In benzene, fluorobenzene, o- and m-difluorobenzene, and 1,3,5-trifluorobenzene, an additional singlet→triplet excitation was detected at about 5.7 eV. Three singlet→singlet transitions analogous to the 4.90, 6.20, and 6.95 eV benzene excitations are seen in each of the fluorine-substituted molecules. The more highly substituted compounds exhibit an additional singlet→singlet transition, which we designate as the C band system, that is most clearly observed in the hexafluorobenzene spectrum, where it has a peak at 5.32 eV. We briefly discuss the effects on relative transtion intensities due to the different molecular symmetries of the various fluorobenzenes. We also report numerous superexcited states for each molecule studied.
Quantum dynamics of a molecule (atom) in a coherent radiation field
Authors: Freed Karl F. , Villaeys A. A.
Published: February 2003

We consider the description of the quantum dynamics of a two-level system interacting with a single Glauber coherent mode of the radiation field. An exact solution (within the rotating wave and electric dipole approximations) is provided for both the time-independent and time-dependent Green’s functions for the coupled matter–radiation system. The atom (molecular) transition probabilities are shown to be Poisson averages of the corresponding semiclassical problem when the latter is likewise treated in the rotating wave approximation. At low radiation intensities, the quantum and semiclassical results differ, but at high intensities, they become the same when the average photon number n0 in the field satisfies the condition n01/2≫1. A similar behavior is displayed for the expectation value of the electric field of the coherent mode in the presence of the atom. The spectrum of the radiation, resonantly scattered by the atom, is shown to coincide with the results of Mollow.
Equilibrium properties of simple molecular fluids
Authors: Shukla K. P. , Singh S. , Singh Y.
Published: February 2003

The application of thermodynamic perturbation theory in which all tensor interactions are taken as perturbation of the pair central potential to the computation of the equilibrium properties of uniform molecular fluids is considered. Comparisons with experiment are made for nitrogen, oxygen, carbon monoxide, carbon dioxide, and methane. Theoretical expressions are given and calculations made for Helmholtz free energy, configurational energy, entropy, and pressure, taking into account the influence of permanent electric multipole moments, induced dipole moments, anisotropic dispersion, and overlap forces. The influence of three-body nonadditive interaction arising from dispersion and classical electric induction interactions between asymmetric molecules on the thermodynamic properties is also considered. Excellent agreement with experiment is obtained for all systems.
Quantum corrections to the second virial coefficient of a gas with a triangular-well potential
Authors: Sinha S. K.
Published: February 2003

The quantum corrections to the second virial coefficient of a gas with a triangular-well potential are calculated using the modified Wigner–Kirkwood expansion method, developed by Derderian and Steele. The result is reported in an analytic form.
Design of basis sets for precise intermolecular force computation. Investigation of the He2 potential curve using CEPA-PNO correlated wavefunctions.
Authors: Burton Peter G.
Published: February 2003

Techniques for the systematic improvement of atomic (or molecular) basis sets for precise intermolecular force computations are used to refine the theoretical He2 ground state potential curve. Diagnostic parameters from the most recent experimental study of this curve (re=5.61a0, De=10.57 °K) are matched in the present work (re=5.63a0, De=10.55 °K). Specifications for the minimum basis capable of yielding a reliable He2 potential curve are elucidated, opening the way for a definitive determination of this curve from first principles.
Theoretical Compton profile anisotropies in molecules and solids. VI. Compton profile anisotropies and chemical binding
Authors: Matcha Robert L. , Pettitt Bernard M.
Published: February 2003

An interesting empirical relationship between zero point Compton profile anisotropies ΔJ (0) and nuclear charges is noted. It is shown that, for alkali halide molecules AB, to a good approximation ΔJ (0) =N ln(Zb/Za).
ESR studies on some five coordinate copper (II) complexes in solutions
Authors: Sastry B. A. , Asadullah S. Md. , Ponticelli G. , Massacesi M.
Published: February 2003

ESR and optical absorption studies have been made on four 5-coordinate copper complexes, namely, Cu (trien) Br2, Cu (trien) (ClO4)2, [Cu (trien) NCS]Bφ4, and Cu (Me6trien) Br2 (where trien and Me6trien stand for triethylylenetetramine and N,N,N′N″,N‴,N‴-hexamethlytrien, respectively) in solutions to study metal ligand bond nature and different contributions to line widths. The 4s character in the ground state is estimated and is found to influence spin-Hamiltonian constants, bond parameters, and hyperfine linewidth. The hyperfine linewidth at room temperature is explained using the theory of Wilson and Kivelson.
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o CI calculation of single vibronic level fluorescence emission spectra and absolute radiative lifetimes of H2CO (1A2)
Authors: Kemper M. J. H. , van Dijk J. M. F. , Buck H. M.
Published: February 2003

Overlap integrals and dipole transition moments which were obtained by an ab initio CI calculation are used for the calculation of fluorescence emission spectra and absolute radiative lifetimes of single vibronic levels of H2CO (1A2). The agreement betwen calculation and experiment is fairly good. The analysis of the results shows that a large fraction of the total emission intensity is due to low-intensity transitions and bands at wavelengths larger than 460 nm. The implications of this result for the determination of fluorescence quantum yields and radiative lifetimes are discussed.
Dielectric constant of dipolar fluid mixtures
Authors: Ho/ye J. S. , Stell G.
Published: February 2003

The development of the statistical mechanics of a polar fluid given by us earlier is extended to fluid mixtures. It is found that although the components of the correlation function hij(12) that contribute to the dielectric constant ε can no longer be directly expressed in terms of ε, as they can for the single-species fluid, ε can still be simply expressed as a functional of hiij(12).
Electrostatic contributions to the viscosities and diffusion coefficients of macroion solutions
Authors: Weissmana) M. B. , Pan R. C. , Wareb) B. R.
Published: February 2003

Electrostatic effects on the viscosity, the static structure factor, and the macroion diffusion coefficient are investigated in solutions of charged bovine serum albumin (BSA). We show that decreasing the ionic strength leads to a decrease in the static structure factor and an increase in the measured diffusion coefficient, but not by the same factor. We show further that the increase in the solution viscosity in the limit of low salt is due primarily to macroion–macroion interactions. The magnitude of the viscosity increase is not sufficient to explain the diffusion-structure factor data unless the long-range nature of the electrostatic interaction is taken into account.
A quantum-statistical Monte Carlo method; path integrals with boundary conditions
Authors: Barker J. A.
Published: February 2003

A new Monte Carlo method for problems in quantum-statistical mechanics is described. The method is based on the use of iterated short-time Green’s functions, for which ’’image’’ approximations are used. It is similar to the use of Feynman or Wiener path integrals but with a modification to take account of hard-core boundary conditions. It is applied to two one-dimensional test problems: that of a single particle in a hard-walled box and that of two hard particles in a hard-walled box. For these test problems, the results are in excellent agreement with exact quantum-mechanical results both at high temperatures (near the classical limit) and at very low temperatures such that essentially only the ground state is occupied. Generalizations to three-dimensional systems, to many-body systems, and to more realistic potentials are discussed briefly.
A model of solvent structure around ions
Authors: Chan Derek Y. C. , Mitchell D. John , Ninham Barry W.
Published: February 2003

The nature of solvent structure around ions is considered using a model of hard spheres with embedded point charges in a solvent of hard spheres with embedded point dipoles. The statistical mechanics of this model is treated in the mean spherical approximation which is a natural extension of the Debye–Hückel theory of electrolytes to include discrete charges and dipoles of finite size. Our results include (i) a modified expression for the Born energy which had been used empirically to fit solubility data, (ii) explicit forms for the polarization density about an ion from which we can deduce the orientation order of the dipolar solvents and the validity or otherwise of the concept of a ’’local’’ dielectric constant near charged bodies, and (iii) the form of the interaction free energy (potential of mean force) between ions at separations comparable to the solvent size. In presenting these results which are given in detail in Section IV only a familiarity with the general description of this model given in Section II is assumed; it will not be necessary to refer to the mathematical detail in Section III.
Monte Carlo trajectory study of Ar+H2: Vibrational selectivity of dissociative collisions at 4500°K and the characteristics of dissociation under equilibrium conditions
Authors: Blais Normand C. , Truhlar Donald G.
Published: February 2003

We have used the quasiclassical trajectory method and a realistic potential energy surface to calculate rate constants and Arrhenius activation energies for dissociation of p-H2 in Ar from each of H2′s fifteen different vibrational levels at a rotational–vibrational temperature of 4500°K. We have also calculated the equilibrium rate constant and energy of activation and many other attributes of the equilibrium reaction at 4500°K. The effect of considering the seven quasibound states with longest unimolecular lifetimes as reactant states is also studied in detail. Reaction is favored by high internal energy—either high rotational quantum number at low vibrational quantum number or vice versa. In particular, at equilibrium the groups of vibrational levels with vibrational quantum numbers v equal to 0–6, 7–11, and 12–14 contribute 26%, 48%, and 26% to the reaction rate. Dissociation from low v levels proceeds primarily from the topmost j state for a given v level; as a consequence neither the assumption of vibrational equilibrium nor the assumption of rotational equilibrium is valid for treating nonequilibrium effects.
Crossed molecular beam studies on the interaction potentials for F(2P) + Ne,Ar,Kr(1S)
Authors: Becker C. H. , Casavecchia P. , Lee Y. T.
Published: February 2003

Angular distributions are presented of F(2P3/2,1/2) scattered off Ne,Ar, and Kr in the thermal energy range measured in crossed molecular beams experiments. The data are analyzed as previously done for the F–Xe system to obtain the interaction potential curves for the three relevant states (X 1/2, I 3/2 II 1/2)governing the scattering. The resulting X 1/2 curves for the fluorine– rare gas systems show no simple trend and the origin of these interactions is discussed. The I 3/2 and II 1/2 states resemble those of the ground state Ne–Ne,Ar,Kr systems.
Role of pseudomolecules in vibrational relaxation in solidsa)
Authors: Ladouceur H. Douglas , Diestler D. J.
Published: February 2003

A quantum-mechanical theory of the participation of pseudolocal modes in vibrational energy relaxation (VER) of molecules in solids is developed. A simple closed expression for the VER rate constant is derived in terms of the microscopic properties of the system. This expression is used to explore the role of local translational modes in a one-dimensional model. The results of model calculations are consistent with experimental findings for the system Cl2 isolated in rare-gas matrices.
Two classification systems for smectic phases, based on symmetry and order
Authors: de Vries Adriaan
Published: February 2003

On the basis of evidence in the literature, it is concluded that the basic molecular packing underlying all smectic structures is a herringbone arrangement of the molecular planes with an orthogonal lattice of the molecular centers. Starting from this basic packing, two sets of five orthorhombic and three monoclinic smectic layer structures are derived which can all be classified with crystallographic space-group symbols. One set is for centrosymmetric ’’molecules,’’ the other for noncentrosymmetric ’’molecules.’’ A second classification of the same set of structures is developed on the basis of the symmetry of the molecular positions. This classification is equally specific but more easily visualized, and it leads to simpler classification symbols. With an additional symbol to indicate order or disorder in the stacking of the smectic layers, a set of 14 possible smectic structures is obtained (each structure allowing centrosymmetric as well as noncentrosymmetric ’’molecules’’), and all known layered smectic phase types are classified within this system, each phase type assigned to a different structure. The structure of the smectic B phase appears to be different than usually assumed, and the so far not understood smectic F phase has been assigned a specific structure.
High temperature thermodynamics of the solutions of hydrogen in palladium-silver alloys
Authors: Picarda) C. , Kleppa O. J. , Boureaub) G.
Published: February 2003

The thermodynamic properties of solutions of hydrogen in palladium-silver alloys with silver contents ranging from 25 to 50% have been determined by a calorimetric-equilibrium method at 555 and 700 K. The results are compared with corresponding data recently reported for hydrogen in Pd and in Pd0.9Ag0.1. (1) For the alloy Pd0.75Ag0.25 the thermodynamic measurements give no evidence for an order–disorder transition in the considered temperature range. (2) Comparisons between the solutions of hydrogen and deuterium in the same alloy and at the same temperature allow calculations to be made of the vibrational frequencies of hydrogen. The calculated values of ?H show a very significant increase with increasing silver content. (3) The partial excess entropies of hydrogen in dilute solutions in palladium-silver alloys are reduced significantly compared to the values in pure palladium. It is probable that these changes, in large measure, are caused by a nonrandom distribution of the hydrogen atoms among the available interstitial sites. However, other possible interpretations also are discussed.
Neutron optical activity
Authors: Harrisa) R. A. , Stodolsky L.
Published: February 2003

It is shown that there is a nonzero ’’optical activity’’ of a beam of polarized neutrons due to its magnetic interaction with the electrons of a closed shell chiral molecule. The effect is entirely general. Estimates of the magnitude of the effect are given in general, and for a polymeric system in particular.
The coordination (hydration) of rare earth ions in aqueous chloride solutions from x ray diffraction. I.TbCl3,DyCl3, ErCl3,TmCl3,and LuCl3
Authors: Habenschuss Anton , Spedding Frank H.
Published: February 2003

The rare earth complex,[RE(H3O)8]3+,has been identified in concentrated (3.2−3.6 m) aqueous TbCl3,DyCl3,ErCl3,TmCl3, and LuCl3 solutions from x ray diffraction measurements. The inner sphere water coordination of rare earth ion was obtained from quantitative resolution of the radial distribution functions. In each solution the rare earth ion has eight water nearest neighbors with the average RE3−H2O distances being 2.409, 2.396, 2.369, 2.358, and 2.338Å for TbCl3,DyCl3, ErCl3, TmCl3, and LuCl3,respectively. The average RE3+. . . Cl− ion pair distances are near 4.8Å.
Interactions of O2 (b 1Σg+) with O(3P) and O3
Authors: Slanger T. G , Black G.
Published: February 2003

Rate coefficients at 300°K have been measured for the reactions of O2(b 1Σg+) with O(3P) and with O3. Quenching of O2(b 1Σg+) by O(3P) proceeds with a rate coefficient of (8.0±2.0) ×10−14 cm3 molecule−1 sec−1. This means that O(3P) is probably of only marginal importance in quenching O2(b 1Σg+) in the thermosphere, although this conclusion depends on assumptions about the activation energies of the relevant reactions. A value of (2.2±0.2) ×10−11 cm3 molecule−1 sec−1 was found for O2(b 1Σg+) quenching by O3, in excellent agreement with two previous determinations. The product of the O(3P) yield in this reaction and the O2(b lΣg+) yield from O(1D) quenching by O2 was found to be 0.48±0.04. This leads to the conclusion that approximately 2/3 of O2(b 1Σg+)−O3 reactions lead to O3 dissociation. The quenching of O2(b 1Σg+) by O3 in the stratosphere may be a significant additional source of oxygen atoms.
A tunable diode laser study of the reactions of nitric and nitrous acids: HNO3+NO and HNO2+O3
Authors: Streita) G. E. , Wells J. S. , Fehsenfeld F. C. , Howard Carleton J.
Published: February 2003

This study of the reactions of nitrous and nitric acids demonstrates a new application of tunable diode laser technology. The diode laser is used for the direct detection of HNO2 and HNO3 in a chemical kinetic system. We have established an upper limit for the rate constant for HNO3+NO→HNO2+NO2 [k1? (3.4±2) ×10−22 cm3/molecule⋅s] and have confirmed that nitrous acid is a product of this reaction. We have also established an upper limit for the rate constant for [HNO2+O3→HNO3+O2[k4? (4.5±3) ×10−19 cm3/molecule⋅s.]
Influence of inelastic collision between excited states on the electron energy distribution in argon
Authors: Vervisch P. , Terrier M.
Published: February 2003

The influence of inelastic collisions between excited states on the electron energy distribution have been investigated for a low pressure argon plasma. We take into account the inelastic collision between 3p54s and 3p54p levels. For that the Chapman–Engskog procedure has been used. This method seems satisfactory converge for such collisions.
Wave functions and effective potentials of alkalilike ions. I. Lithiumlike ions
Authors: Daniele Rosalba
Published: February 2003

Energy values, approximate wave functions, and effective potentials are determined for several states of the valence electron of the lithium atom and of a group of lithiumlike ions. ns, np and nd states with n=2,...,8 are considered for Li, Be1+, B2+, C3+, N4+, O5+, F6+, Na8+, Mg9+, Al10+, Si11+, and P12+. Though the adopted calculation procedure is quite simple, the results are in very good agreement with experimental values and more sophisticated calculations. The present calculations may be of use in the physics of highly stripped ions. Moreover, the reported effective potentials may be used for physical processes, where the pseudo or model potentials are out of the question.
A hydrodynamic theory for homogeneous vapor nucleation in a carrier gas
Authors: Mou Chung Yuan , Lovett Ronald
Published: February 2003

A dynamical theory is constructed for the spontaneous development of a liquid drop out of an homogenous supersaturated vapor in a dense carrier gas. The work required to create intermediate state is estimated macroscopically, as in the classical theory of nucleation, but the dynamical equations are based upon hydrodynamic fluctuation theory. For the classical drop growth model the resulting nucleation rate is very similar to that traditionally assigned. The characterization of the mechanism is a little different from the traditional one, however, and nonequilibrium features of the process are described in greater detail. The vapor condensation process is also contrasted with the liquid– liquid separation process which occurs in binary mixtures.
Laser spectroscopy of matrix-isolated UF6 at 12 K
Authors: Miller John C. , Allison Stephen W. , Andrews Lester
Published: February 2003

Fluorescence excitation spectra of the lowest charge transfer state of UF6 isolated in solid argon and krypton at 12 K have been obtained using a pulsed, N2-laser-pumped dye laser. The complex, multiline spectrum from 360 to 406 nm is much better resolved than previous absorption spectra and is assigned in terms of the ν1, ν3, ν4, ν5, and ν6 normal modes and their overtones and combinations. The role of Jahn–Teller distortion in the upper state is discussed, and the matrix, neat crystal, and gas spectra are compared. The lifetime of the electric dipole forbidden emission is measured at 600 μs in solid argon.
Measurement of the A 3π1u←X 1Σ+g continuum absorptivity in Br2
Authors: Hemenway C. P. , Lindeman T. G. , Wiesenfeld J. R.
Published: February 2003

Of the numerous attempts to decompose the visible absorption continuum of Br2 into its three components,1π1u,B3π1u →X 1𝒥+g, most have neglected the A←X continuum. Although the intensity of the absorption continuum underlying the B←X lines can in principle be measured, extreme spectral resolution is required in order to separate the bound–bound spectrum from the bound free. For the present experiment, a simpler approach was taken using a tunable dye laser, the output of which was 3.5 W at 514 nm.
Photodissociation and photodetachment of Cl2−,ClO−, Cl3− and BrCl2−
Authors: Lee L. C. , Smith G. P. , Moseley J. T. , Cosby P. C. , Guest J. A.
Published: February 2003

Absolute cross sections for the photodestruction of Cl2−, ClO−, Cl3−, and BrCl2− were measured over the wavelength range of 3500–7600 Å using a drift tube mass spectrometer–laser apparatus. The photodissociation cross section for Cl2− has two bands, as has been observed for the isoelectronic Ar2+ ion. The wavelength dependence of these bands is used to adjust the calculated potential curves of the ion in the Franck–Condon region. The photodestruction cross section for ClO− has a narrow band peaked at 4300 Å with a width of 400 Å, superimposed on a continuum that slowly increases with photon energy. The narrow band is attributed to photodissociation and the continuum to photodetachment. Cl3− and BrCl2− have no significiant photodestruction cross sections for wavelengths longer than 4700 Å. At shorter wavelengths, the cross sections increase with increasing photon energy. The photodestruction of these ions is attributed to photodissociation. The present gas phase measurements are compared with optical spectra for the ions obtained in different environments.
A Mössbauer study of xenon compounds
Authors: de Waard Hendrik , Bukshpan Shmuel , Schrobilgen Gary J. , Holloway John H. , Martin Dominique
Published: February 2003

A large number of xenon compounds have been synthesized and studied by nuclear gamma resonance of the 39.6 keV transition in 129Xe. The quadrupole interaction strengths (Q.S.) of all divalent xenon compounds with linear F–Xe–F groups lie close together, but a small increase of the Q.S. with the acceptor strength of adduct groups is observed. For compounds with F–Xe–O– and –O–Xe–O– groups a reduction of the Q.S. of up to 10% is found. The tetravalent compounds exhibit a Q.S. with absolute magnitude very close to that of the divalent compounds, consistent with a square planar configuration and nearly equal contributions to the Q. S. for each Xe–F bond. Hexavalent xenon in XeF6 also exhibits an appreciable Q.S., indicative of distortion of the octahedral fluorine configuration around the xenon atom in the polymeric solid. An increase of the Q.S. relative to XeF6 is observed in the adducts and in hexavalent compounds with mixed oxygen/fluorine bonding. This is interpreted as due to increased distortion around the central xenon atom.
Classical model for electronic degrees of freedom in nonadiabatic collision processes: Pseudopotential analysis and calculations for F(2P1/2)+H+,Xe→F(2P3/2)+H+,Xe
Authors: McCurdy C. W. , Meyer H. D. , Miller W. H.
Published: February 2003

It is shown how the classical version of a pseudopotential analysis can be used to obtain classical models for the electronic degrees of freedom in a molecular collision system. This allows one to construct a completely classical model for electronically nonadiabatic collision processes, which has the virtue that electronic and heavy particle degrees of freedom are described dynamically consistently (i.e., by classical trajectories). Application of this approach to fine-structure changing collisions of F by collision with H+ and Xe gives encouraging agreement with quantum mechanical coupled-channel calculations, suggesting that this model may in general be of useful accuracy for describing electronically nonadiabatic processes.
An algorithm to solve open and closed-shell and restricted MC–SCF equations
Authors: Hinze Juergen , Yurtsever Ersin
Published: February 2003

An algorithm, similar to the Jacobi matrix diagonalization procedure, is presented to obtain eigenvalues and eigenfunctions for the closed- and general open-shell Hartree–Fock equations. A specific, restricted form of the MCSCF orbital equations, similar to the general open-shell HF equations, is dealt with as well.
Theory of photogeneration and fluorescence quenching
Authors: Noolandi J. , Hong K. M.
Published: February 2003

We give the exact solution of the geminate recombination probability of a pair of oppositely charged particles, corresponding to the boundary condition of a partly absorbing sphere of finite radius at the origin. In the limit of an infinite recombination velocity (κ→∞) and a vanishing radius (a→0) we recover the well-known result of Onsager. We use the solution in the formulation of a model of photogeneration and fluorescence quenching in organic solids, with thermalization lengths which are comparable to the lattice spacing. As an illustration we analyze fluorescence quenching and quantum efficiency data for x-metal-free phthalocyanine, assuming the extreme case of complete internal conversion and no thermalization length. We discuss the form of the slope-to-intercept ratio for small applied fields determined from the solution for the generalized escape probability.
Molecular theory of lipid membrane ordera)
Authors: Jähnigb) Fritz
Published: February 2003

Starting from the inter- and intramolecular interactions of the hydrocarbon chains the orientational long-range order in lipid membranes is calculated to study the ordered-fluid phase transition. The positional order is described by the lateral packing density and treated as an external parameter, in addition to temperature. The results for the orientational order parameter, the phase transition temperature, and the latent heat are analyzed to distinguish between the effects of the different chain interactions, the van der Waals interaction, steric hindrance, and flexibility. The dependence of the results on chain length is compared with existing experimental data.
Infrared laser single photon absorption reaction chemistry in the solid state. I. The system SiH4–UF6 a)
Authors: Catalano Edward , Barlettab) Robert E. , Pearson Richard K.
Published: February 2003

The reaction between SiH4 and UF6 under thermal gas phase and photon initiated conditions in cryogenic matrices has been investigated. The gas phase thermal reaction begins at 130–140° C producing HF, SiH3F, and a solid uranium fluoride product. When the UF6 is matrix isolated within SiH4 at 12 K and exposed to low power infrared radiation of 25 mW cm−2 using laser emissions resonant with the ν3 band of UF6, a reaction also occurs. This reaction produces SiH3F, UF5, and UF4 as products. The same reaction is also catalyzed using a broad band incoherent source with a photon flux density of 10 μW cm−2. The activation energy for the photoreaction (1.8 kcal mol−1) is considerably lower than the thermal activation barrier for the gas phase reaction. These experiments are part of the bases for uncovering a process of photochemistry of reactants in fixed relative configurations–single photon absorption reaction chemistry in the solid state (SPARCSS). This process is a manifestation of a previously unrecognized, general matrix phenomenon in which spatial configurations dramatically affect potential energy surfaces for reaction.
NMR in rotating solids
Authors: Maricq M.Matti , Waugh J. S.
Published: February 2003

The NMR free induction decay from a spinning sample having inhomogeneous anisotropic interactions (chemical shifts, first order quadrupole couplings) takes the form of a train of rotational spin echoes. The Fourier transform of the echo envelope is a sharp spectrum from which the effects of anisotropy have been removed. The Fourier transform of the echo shape contains information concerning the anisotropies: This information can be extracted by a moment analysis. The effects of localized homonuclear spin–spin interactions are to convert the ’’isotropic’’ spectrum into a characteristic powder pattern. Second order quadrupole coupling produces a similar effect. It is shown in this case that the usual second-order level shifts cannot be used to calculated this pattern, which must be described by a proper average Hamiltonian theory. Finally it is shown that rotational spin echoes provide a convenient means of studying very slow random molecular rotations (τc≲1 sec).
Theoretical optical spectra for large aggregates of chromophores
Authors: Hemenger R. P. , Kaplan Theodore , Gray L. J.
Published: February 2003

The problem of calculating optical absorption and circular dichroism spectra for large aggregates of chromophores interacting through electronic transition dipoles is studied. The emphasis throughout is on relating band shapes of such aggregate spectra to band shapes of the consituent chromophores for all interchromophore coupling strengths. We argue that because of its close connections to an exact formulation, an approximation developed earlier (DGS model) predicts spectral band shapes much more accurately than other commonly used methods of calculating aggregate spectra. This is particularly true for intermediate or strong coupling, i.e., for interchromophore coupling strengths comparable to or greater than the bandwidths of the individual chromophores. A number of calculations of optical absorption and circular dichroism spectra for simple helical polymers have been carried out using the DGS model. These calculations exploit the formal identity of the DGS model to the ’’cellular disorder’’ problem of solid state physics and the existence of well established methods for solving this problem. The theoretical spectra found in this way differ considerably from those found using other methods, especially in intermediate and strong coupling. Consequences of these results for several polymers of biological interest are discussed.
Microwave modulated saturation spectroscopy
Authors: Kasper J. V. V. , Lowe R. S. , Curl R. F.
Published: February 2003

By combining intermodulated fluorescence saturation spectroscopy with microwave optical double resonance, a new experimental laser spectroscopy technique, microwave modulated saturation (MMS) spectroscopy, has been developed. This technique has been used to simplify the complex 14N and proton hyperfine structure observed by saturation spectroscopy of NH2[110, J=3/2←220, J=5/2, ?2A1π (0,10,0) ←?2B1(0,0,0)]. This simplification made possible a complete assignment of the hyperfine energy levels. A population model of these experiments has been developed.
Multiphoton ionization spectra of polycyclic alkanes
Authors: Heath B. A. , Kuebler N. A. , Robin M. B.
Published: February 2003

Three-photon ionization spectra, resonant at the second photon, have been obtained for cyclohexane and the polycyclic systems norbornane, trans-decalin, adamantane, hexamethylene tetramine, and bicyclo[2.2.2]octane in the 3580–5000 Å one-photon region. In each of the alkanes, a well-structured excitation to the 3s Rydberg orbital was observed, with term values following the convergent pattern established for other highly alkylated chromophores. The prominent excitation of t2 and e vibrations in the lowest Rydberg band of adamantane is suggestive of Jahn–Teller distortion in the upper state. Nontotally symmetric vibrations were observed with less certainty in the two-photon excitations to 3s in cyclohexane and bicyclo[2.2.2]octane.
Energy transfer of argon excited diatomic molecules
Authors: Oka Takefumi , Kogoma Masuhiro , Imamura Masashi , Arai Shigeyoshi , Watanabe Tsutomu
Published: February 2003

Argon excited diatomic molecules Ar*2(3𝒥+u)were produced by irradiating argon gas with short electron beam pulses. The kinetic behavior was studied by monitoring the time dependence of the 987.6 nm absorption band due to Ar*2 under various conditions.The method is largely different from the vacuum UV emission spectroscopy used previously in such kinetic studies. Ar*2 was found to be produced by a three-body reaction with a rate constant of (1.0±0.3) ×10−32 cm 6 sec−1. Then, the rate constants and cross sections of energy transfer were determined for 12 fundamental acceptor molecules. The theoretical formula proposed previously for Penning ionization was applied to energy transfer between Ar*2 cross sections given by the formula have the values comparable to the observed ones.