bluuebunny/crossref_metadata_2025 huggingface dataset:
ESR investigation of ScF2 isolated in rare gas matrices at 12 K
Authors: Knight Lon B. , Wise M. B.
Published: February 2003

The radical molecule ScF2 has been produced at high temperature, trapped in argon and xenon matrices at 12 K and studied via electron spin resonance (ESR). Attempts to study the radical in neon matrices at 4 K and nitrogen at 12 K were unsuccessful. The observed 45Sc and 19F hyperfine splittings in an argon matrix were 220 and 28 MHz, respectively. The g tensor was not fully resolved; however, the most intense component had a g value of 1.995 (1) in argon. The magnetic parameters and electronic structure of ScF2 are compared to ScO, ScS, and TiF2+. A nearly tenfold decrease in metal hfs is observed for ScF2 relative to ScO.
An experimental study of multiple peak periodic and nonperiodic oscillations in the Belousov–Zhabotinskii reaction
Authors: Hudson J. L. , Hart M. , Marinko D.
Published: February 2003

Experiments have been carried out on the Belousov–Zhabotinskii reaction in an isothermal continuous stirred tank reactor. The flow rate was varied from low values where simple single peak oscillations occur to large values where the reactor is in steady state. Several types of periodic multipeak oscillations were observed. Three regions of nonperiodic behavior were found, each of which occurred in a well defined range of flow rates bracketed by periodic oscillations.
Polarizability calculations with the SCF method. I. Linear and dynamic polarizabilities of conjugated hydrocarbons and aromatics
Authors: Zamani-Khamiri O. , Hameka H. F.
Published: February 2003

We calculate the static and dynamic linear electric polarizabilities of a group of aromatic and conjugated hydrocarbon molecules by means of a modified Pariser–Parr–Pople method. One purpose of the calculation is a comparison between various PPP results and previously obtained corresponding Hückel results. We calculate linear static polarizabilities and a contribution, the C term, to the third-order nonlinear susceptibilities. The PPP values and Hückel values are not too different from each other except for those molecules that have unusually large susceptibilities. For the latter molecules the PPP results are significantly smaller than the Hückel results.
Statistical mechanics of helical wormlike chains. IX. Anisotropic light scattering
Authors: Yamakawa Hiromi , Fujii Motoharu , Shimada Jiro
Published: February 2003

The anisotropic light scattering by polymer molecules in dilute solution is studied on the basis of the helical wormlike chain on which optical polarizability tensors are arrayed with respect to its localized coordinate systems. The four independent components of the scattered intensity are evaluated as functions of scattering angle. It is facilitated by the use of irreducible (spherical) tensors with the expansion of the Green’s function in terms of the normalized Wigner functions. Rather detailed numerical results are presented. Evaluation is also carried out for the rigid rod, regular helix, random coil, and wormlike chain, which are the extreme cases of the helical wormlike chain. It is then noted that there are three possible types of anisotropic rods, and also of anisotropic wormlike chains, one of them being already well known as the one having cylindrically symmetric local polarizability tensors. A procedure for determining accurately the isotropic scattering function from observed scattered components is proposed on the basis of the numerical results. By a computer simulation, it is shown that the procedure does not involve an amplification of experimental errors in the individual components, except near the backward scattering angle. The mean-square optical anisotropy determined from the depolarized component is also evaluated as a function of chain length. The ratio of it to chain length is shown to exhibit a maximum for some helical wormlike chains, and damped oscillation for one of the three types of rods with certain polarizabilities. An analysis of experimental data is made for polymethylene as an example.
Molecular dynamics of surface diffusion. I. The motion of adatoms and clusters
Authors: Tully John C. , Gilmer George H. , Shugard Mary
Published: February 2003

The motion of isolated adatoms and small clusters on a crystal surface is investigated by a novel and efficient simulation technique. The trajectory of each atom is calculated by molecular dynamics, but the exchange of kinetic energy with the crystal lattice is included through interactions with a ’’ghost’’ atom. This atom represents surface atoms of the lattice and is subjected to random and dissipative forces that are related by the fluctuation–dissipation theorem. The diffusion process is characterized by measurements of the velocity autocorrelation function, mean square displacement, directional correlations between hops, and the mean displacement per hop. In addition, the rate of evaporation of single adatoms and the rate of dissociation of clusters are discussed. The diffusion of an isolated adatom is found to be somewhat faster than that predicted by the classical rate theory for an activated process. This effect is a result of diffusion jumps of several atomic diameters that occur preferentially at high temperatures. But Arrhenius behavior is observed over the entire range of temperatures below the melting point. Dimers and larger clusters are found to diffuse more slowly than individual atoms, but with a smaller apparent activation energy. These results do not exhibit the high-temperature anomalies that have been inferred from some experimental data on surface mass transport. In a subsequent paper the method is extended to treat mass transport in the layer of adatoms and clusters that results from a dynamic equilibrium with the vapor phase.
Dynamics and ensemble averages for the polarization models of molecular interactions
Authors: Stillinger F. H.
Published: February 2003

A family of ’’polarization models’’ has been generated for description of polarizable and deformable molecules in condensed phases. Within these models the intermolecular forces are not pairwise additive, but have a many-body component that generalizes the polarization interactions present in conventional electrostatics. It is shown that the classical dynamical equations have a rather compact form, in spite of the many-body interactions. Novel molecular distribution functions are introduced in terms of which the usual formulas of statistical thermodynamics can be expressed. Finally, the static dielectric constant is discussed for the polarization models, and it is related to fluctuating local moments in the system.
Variationally deorthogonalized localized molecular orbitals
Authors: Sundberg Kenneth R. , Bicerano Jozef , Lipscomb William N.
Published: February 2003

The Edmiston–Ruedenberg localized orbitals are shown to be solutions to the Hartree product of orthogonal orbital equations on the space of the occupied Hartree–Fock orbitals. The nonorthogonal Hartree orbitals on this space are thus a possible deorthogonalization of the localized orbitals. From the relationships of the Pauli principle to the orthogonality of the orbitals in the Hartree product wave function and to the full antisymmetry of the Hartree–Fock wave function, we propose an energy functional which imposes the Pauli principle on the Hartree product wave function without forcing the orbitals to be orthogonal. Minimization of this functional leads to the Pauli-constrained Hartree equations. An algorithm is developed for their solution on the space of the Hartree–Fock orbitals. The results are called the variationally deorthogonalized Hartree product orbitals. This algorithm is then extended to apply to other localization functionals. Variationally deorthogonalized Edmiston–Ruedenberg orbitals are obtained by maximizing a function of the sum of the orbital self-repulsions, and variationally deorthogonalized Boys localized orbitals are obtained by maximizing a function of the sum of the squares of the distances between orbital centroids. All three types of variationally deorthogonalized orbitals are obtained for H2O, cis- and trans-N2H2, C2H2, C2H4, eclipsed and staggered C2H6, BH3, and B2H6. Comparisons are made in terms of the population distributions and the magnitudes and phases of the overlap integrals.
Carbon-13 NMR of carbon monoxide. II. Molecular diffusion and spin–rotation interaction in liquid CO
Authors: Fukushima Eiichi , Gibson A. A. V. , Scott T. A.
Published: February 2003

Carbon-13 NMR was used to measure the molecular diffusion coefficient D and the spin-rotation correlation time τsr in liquid CO from its freezing point to about 110 K at several pressures up to 1.73 kbar. The behavior of D and τsr is similar for liquid CO and N2. Diffusion in CO at equilibrium vapor pressure takes place with an activation enthalpy of 2.9 kJ/mole and its pressure dependence leads to an activation volume which is a factor of 5 smaller than in the solid phase just below freezing. τsr is nearly equal for CO and N2 at T?80 K and its variation with pressure for CO is smaller than that of D by almost a factor of 2. We also present a method for determining the magnetic field gradient used in the measurement of D which is free from many of the usual problems.
The reaction of ethanol with an aluminum oxide surface studied by inelastic electron tunneling spectroscopy
Authors: Evans H. E. , Weinberg W. H.
Published: February 2003

Inelastic electron tunneling spectroscopy (IETS) has been employed to study the vibrational structure of ethanol reacting with a clean alumina surface as a function of temperature from 295 to 575 K. The spectra for the surface species up to approximately 450 K correspond to infrared spectra of aluminum ethoxide, Al(OC2H5)3. Between 450 and 475 K the structure changes from an ethoxide to an acetate, the most obvious spectral change being the appearance of a new peak at approximately 1585 cm−1 (197 meV) which is characteristic of the asymmetric OCO stretching mode of various inorganic acetates. No further changes are observed above 475 K. Above 370 K, there is also a significant increase in the total concentration of adsorbed species. This is due to a partial dehydration or dehydroxylation of the surface, thus freeing active sites which had previously been blocked by water or hydroxyl groups formed during the initial stages of ethanol adsorption. This dehydration or dehydroxylation of the surface is simultaneously accompanied by a transformation of the bulk aluminum oxide to aluminum hydroxide. While IETS has been applied successfully in the past to study a wide variety of adsorbate–adsorbent systems, here tunneling spectroscopy is demonstrated explicitly to be effective in monitoring quantitatively the structural changes occurring in a reacting system at low pressures as a function of temperature.
Quantum-mechanical calculation of three-dimensional atom–diatom collisions in the presence of intense laser radiation
Authors: DeVries Paul L. , George Thomas F.
Published: February 2003

A formalism is presented for describing the collision of fluorine with the hydrogen molecule in the presence of intense radiation. For a laser frequency on the order of the spin–orbit splitting of fluorine, the interaction of the molecular system with the radiation occurs at relatively long range where, for this system, the electric dipole is vanishingly small. Hence the interaction occurs due to the magnetic dipole coupling. Even so, at low collision energies a substantial enhancement of the quenching cross section is found for a radiation intensity of 1011 W/cm2.
The effects of strong excitation-phonon coupling on mixed crystal spectra: Diphenylmethylene in benzophenone
Authors: Anderson Richard J. M. , Kohler Bryan E. , Stevenson James M.
Published: February 2003

We present low temperature absorption and emission spectra of diphenylmethylene in benzophenone. Although the spectra are broad at temperatures greater than ∼20 K, considerable structure appears at lower temperatures. The spectra and their temperature dependence are readily explained by a large excitation-phonon coupling which is expected for this type of mixed-crystal system.
Radiative decay and radiationless deactivation in selectively excited CN
Authors: Katayama D. H. , Miller Terry A. , Bondybey V. E.
Published: February 2003

Individual vibrational levels (v=3–9) of the A 2Π state of the CN radical are excited by a tunable dye laser. The time and wavelength resolved fluorescence of the selectively excited levels is then recorded as a function of the Ar carrier gas pressure. It is found that the decay of many levels is, particularly at lower pressures, strongly double exponential, with the longer component time constant considerably in excess of the CN A 2Π radiative lifetime. The short time constant portion of this exponential is interpreted in terms of a model which includes fast collisional equilibration between the excited v′A 2Π level and a nearby v″, X 2Σ level. The slower part of the decay consists of quenching and radiative decay from the coupled levels. Approximate values for the rate constants governing these processes are derived.
LiH state-to-state rotationally inelastic cross sections in collisions with HCl and DCl
Authors: Dagdigian Paul J. , Wilcomb Bruce E. , Alexander Millard H.
Published: February 2003

A new technique is presented for the determination of state-to-state rotationally inelastic cross sections, which employs electric quadrupole state selection and laser fluorescence detection. Results for the scattering of 7LiH j=1 molecules by HCl and DCl scattering gas (?rel= 0.74 eV) are reported. With knowledge of the number density and scattering path length l and the observed invariance of the experimental cross sections with decreased l, absolute integral state-to-state cross sections σj=1→j′ have been obtained. For both 7LiH–HCl and 7LiH–DCl, the σj=1→j′ values are large (10–200 Å2), the j′=2 level being most probable; the cross sections fall monotonically with increasing j′ out to j′=6, the highest level probed. An unsuspected isotopic enhancement has been observed for the DCl system: All the σj=1→j′ values are ∼25% larger for 7LiH–DCl than for the corresponding transitions in the 7LiH–HCl system. Because both scattering partners have relatively large dipole moments, these systems are paradigms for rotational energy transfer induced by a dipole–dipole interaction. Several theoretical models, which have been widely used to interpret energy transfer in similar systems, are reviewed and compared to these detailed experimental results. It is found that the Born approximation gives cross sections which are far too large and predicts insufficient flux into the higher j′ states, even when higher-order electrostatic terms are included in the potential. The sudden approximation and the recently introduced adiabatically corrected sudden (ACS) approximation reproduce the experimental cross sections much better both in magnitude and in dependence on j′. The ACS method does significantly better and, in particular, successfully predicts the isotopic enhancement observed in the 7LiH–DCl system. The origin of this effect is shown to be due to energetic resonances: For dipole–dipole transitions of the type ja=1, jb→ja±1, jb∓1, the translational energy defect is less in DCl than HCl for those values of jb which made the largest contributions to the 298 °K Boltzmann rotational distribution of the hydrogen halides.
Sudden theories of rotationally inelastic LiH–HCl and LiH–DCl collisions
Authors: Alexander Millard H.
Published: February 2003

The impact parameter sudden approximation is applied to rotationally inelastic collisions between two polar molecules. The transition probabilities can be factored into a sum of squares of angular momentum coupling coefficients multiplied by dynamical factors which are related to coefficients in the expansion of the sudden scattering operator. The evaluation of these dynamical factors is discussed for the case of a potential which consists of the dipole–dipole term as well as both dipole–quadrupole terms in the standard multipole expansion. Even at relatively high collision velocities these long-range potentials will necessitate significant adabatic corrections to the pure sudden approximation, which can be determined by the introduction into the sudden action integral of a ’’dephasing frequency’’ proportional to the average rotational energy transfer per single quantum transition. The resulting adiabatically corrected sudden (ACS) approximation [M. H. Alexander and A. E. DePristo, J. Chem. Phys. 83, 1499 (1979)] yields a factorization similar to that obtained in the pure SA. The appropriate dynamical factors can be evaluated by a two-dimensional quadrature. ACS and SA calculations are reported for the collision of a LiH molecule with both HCl and DCl at a collision energy of 0.78 eV. The presence of the dipole–quadrupole terms results in an interesting alternance in some of the jajb→ja′jb′ cross sections, but leads to little change in the total cross section obtained by summing over the final states of the hydrogen halide partner. In a strong resonance effect the magnitude of these summed cross sections for directly coupled dipole transitions (Δja=±1) varies substantially with the initial rotational state of the partner.
Photoionization of carbon disulfide monomers and dimers in a supersonic molecular beam
Authors: Trott Wayne M. , Blais Normand C. , Walters Edward A.
Published: February 2003

Photoionization efficiency curves have been obtained for CS2+ and (CS2)2+ using molecular beam sampling. The monomer was studied between 1005–1240 Å using an optical resolution of about 1.5 Å (12 meV at 1200 Å). The observed ionization potential of CS2(2π3/2 ground state) is 10.070±0.006 eV. A small number of steplike fine structure features are seen in the vicinity of threshold. This structure is identified with transitions to the 2π1/2 spin state (10.125±0.006 eV) and a few low energy vibrational levels of the ion. These features and the intense autoionization structure exhibited by this species are discussed. The photoion yield curve of (CS2)2+ was measured over the wavelength range 1000–1295 Å at an energy resolution of about 30 meV. Ionization is first observed at approximately 9.63 eV. The onset is very weak and the photoionization efficiency rises gradually with increasing photon energy. From the measured monomer and dimer ionization thresholds, a lower limit to the dimer ion binding energy is calculated to be 11.3 kcal/mole. In comparing monomer and dimer curves, a very close correspondence of autoionization features in the region 1000–1060 Å is observed. In contrast, autoionization structure which occurs in the photoion yield curve of CS2+ between 1100–1125 Å is either markedly shifted in energy and broadly distributed or entirely absent in the (CS2)2+ curve. These changes are interpreted in terms of the geometry of the CS2 dimer.
On Raffenetti-type atomic basis set
Authors: Huzinaga S.
Published: February 2003

It is shown that Raffenetti-type STO basis sets are capable of producing total energy values which surpass the best values so far obtained by the analytical expansion method. (AIP).
Asymptotic form of quantum momentum distributions
Authors: Berman D. H. , Snider R. F.
Published: February 2003

The behavior at large momentum, of the first density correction to the momentum distribution of a gas of interacting particles, is investigated for a wide variety of model potentials. The treatment involves neither an expansion in powers of the potential strength VO nor of Planck’s constant h/. As well, the results are valid for all temperatures and include exchange effects. It is shown that slow algebraic decay of the momentum distribution is not peculiar to hard sphere interactions, but also occurs for such smooth interactions as the Yukawa and exponential potential, whose momentum distributions decay as p−8 and p−12, respectively. The pseudopotential gives rise to a p−4 decay, in contrast to the p−6 decay for the hard sphere interaction which it is designed to model. For singular potentials of the form VO(a/r)n, a lower bound is obtained which has (almost) exponential decay.
Generalized oscillator strengths for beryllium atom in the random-phase approximation with exchange
Authors: Amusia M. Ya. , Cherepkov N. A. , Z̆ivanović Dj. , Radojević V.
Published: February 2003

The generalized oscillator strengths for the transitions from the ground state to the excited discrete and continuous states of the beryllium atom are calculated in the framework of the random-phase approximation with exchange for a range of momentum transfer values from 0 to 3 a.u. The results for the 2s→2p transition are compared with calculations of Sinanoglu and Davis and good agreement is obtained. Also the influence of electron correlation is examined for the transitions to the lowest excited states in the discrete and continuous spectrum, as for these transitions the influence is strongest.
A
b i
n
i
t
i
o studies of the electronic structrue of UF6, UF6+, and UF−6 using relativistic effective core potentials
Authors: Hay P. Jeffrey , Wadt Willard R. , Kahn Luis R. , Raffenetti Richard C. , Phillips Donald H.
Published: February 2003

A b initio calculations are performed on the electronic states of UF6, UF6+, and UF−6 using a relativistic effective core potential (ECP) for uranium and a nonrelativistic ECP for fluorine. In most of the calculations 56 valence electrons are treated explicitly using a contracted [3s3p2d2f/2s2p] Gaussian basis. Various ECP’s were explored, but all yield an overall charge density of U+2.4 (F−0.4)6. The bonding in the ground state of UF6 is discussed. SCF and CI calculations on UF6+ are compared with the experimental photoelectron spectrum and with previous scattered-wave calculations. The role of spin–orbit coupling in the states of UF6+ and UF6− is discussed. The calculated electron affinity of UF6 (7.1 eV) is considerably larger than the current experimental estimates, but the relative energies of the states of UF6− are in excellent agreement (0.1–0.2 eV) with experiment.
Emission spectrum of rare gas dimers in the vacuum UV region. II. Rotational analysis of band system I of Ar2
Authors: Freeman D. E. , Yoshino K. , Tanaka Y.
Published: February 2003

The emission spectrum of Ar2 excited by a Tesla discharge has been photographed at high resolution in the region 1073.5–1081.5 Å by 6.65 m spectrograph. Experimental conditions were chosen to produce only the band system emitted in the transition from the lowest excited state to the ground state. Rotational analyses of several bands indicate that the coupling scheme in the lowest excited state is closer to Hund–Mulliken case b than to case c, so that the excited state symmetry may be assigned approximately as 3Σ+u rather than 1u, 0−u. Rotational constants obtained for seven high-lying emitting levels with consecutively decreasing vibrational quantum numbers range from 0.073 to 0.105 cm−1. An attempt has been made to use spectroscopic results to depict the shapes and positions of the long range portions of the potential curves of the first two excited states (3Σ+u and 1Σ+u) of Ar2 relative to each other and to that of the ground state X 1Σ+g.
Physical properties of the nonionic surfactants surrounding gas cavitation nuclei
Authors: D’Arrigo Joseph S.
Published: February 2003

The effects of a wide variety of electrolytes (each at 0.4 M) on bubble production in agarose gels has been studied. The relative effectiveness of the different ions tested in decreasing the degree of bubble formation in the aqueous gels was as follows: As sodium salts, citrate 3−≳SO42−, tartrate2−≳F−≳ acetate−≳SCN−≳Br−, NO3−, I−≳Cl−; as potassium salts, citrate 3−≳SO42−≳F−, tartrate 2−≳acetate−, SCN−≳Br−≳I−, NO3−≳Cl−; as chloride salts, Cd2+≳Mg2+≳Li+, Na+, Ca2+?NH4+, K+≳Ba2+≳Ni2+≳Sr2+≳Co2+; as nitrate salts, Mg2+, Sr2+≳Na+, K+, Li+≳Ag+, NH4+, Ca2+≳Cd2+≳Zn2+≳Ni2+. In view of many similarities with published data in the physicochemical literature for salting out of identified nonionic surfactants, the above anion and cation sequences probably reflect a decreasing tendency of the ions toward salting out of predominantly nonionic surfactant(s) stabilizing the gas cavitation nuclei present in agarose gels. Moreover, the precise pattern of electrolyte effects on bubble formation carries certain implications as to the structural characteristics of these nonionic surfactants. Specifically, the pronounced and very similar anion sequences, combined with earlier data, suggest that the polar portions of these nonionic surfactants represent either weak bases and/or amide groups. This view is in accordance with the relative position of Mg2+ in the two cation sequences, indicating strong salting out in both cases, and hence rendering it quite unlikely that ether linkages contribute to the hydrophilicity of the nonionic surfactants stabilizing gas nuclei. Finally, the relative position of SCN− within each anion sequence, corresponding to appreciable salting out rather than salting in, indicates that large portions of these nonionic surfactant molecules are composed of hydrocarbon moieties, specifically methyl and methylene groups.
Mössbauer effect study of the magnetic properties of the intermediate-spin complex perchlorato (m
e
s
o-tetraphenylporphinato ) iron (III)
Authors: Spartalian K. , Lang G. , Reed Christopher A.
Published: February 2003

Mössbauer spectra of the polycrystalline form of the intermediate-spin complex perchlorato (meso-tetraphenylporphinato) iron (III) 0.5 m-xylene have been observed at a variety of temperatures in high external fields. Analysis of the resulting spectra yields a positive electric field gradient interaction with quadrupole splitting ΔE=3.5 mm/s (4.2 K) and 2.79 mm/s (300 K). At low temperature an external magnetic field induces negligible internal field along the symmetry axis. In the transverse direction it gives rise to a temperature-dependent negative internal field of about 23 T (4.2 K). The data have been analyzed in terms of a S=3/2 spin-Hamiltonian and the five spin-Hamiltonian parameters required to characterize the spectra at all temperatures and fields were D=8.0 cm−1, λ=0.15, Ax=1.273, Ay=1.119, Az=−0.164 mm/s (excited state).
Formation of vibrationally excited diatomic molecules by stimulated radiative association: Theoretical calculations in H+2
Authors: Ramaker David E. , Peek James M.
Published: February 2003

Calculations are performed to determine the degree of formation of vibrationally excited H+2 by stimulated radiative association. Low energy thermal collisions between the H and H+ are assumed to take place in the presence of an intense radiation field. The parameters in the system include the temperature characterizing the thermal collisions, the width, intensity, and frequency of the stimulating radiation, and the time of flight of the colliding partners in the radiation field. The effect of each parameter on the initial production rate and the radiative equilibrium populations for each vibrational state are discussed. Possible experimental procedures are also considered. The results indicate a rather surprising degree of vibrational selectivity, particularly for the early time populations of the higher states. Relative ’’initial’’ and radiative equilibrium populations and the rate coefficients for stimulated and spontaneous emission and absorption are tabulated for individual vibrational states for a select set of calculations. Absolute populations are not tabulated but can be easily obtained from the data given.
Ethane hydrogenolysis on evaporated iridium films
Authors: Mahaffy Paul , Hansen Robert S.
Published: February 2003

The reaction of ethane with hydrogen to form methane is studied over iridium films prepared by evaporation under high vacuum. Kinetic studies in combination with the results of isotope labeling experiments support in a self-consistent way the following mechanism of hydrogenolysis. Dissociative adsorption of ethane produces CH2–CH3(a) and H(a). The final kinetically significant elementary step on the surface is the reaction of an adsorbed hydrogen atom with CH2–CH3(a) which is accompanied by the breaking of the carbon–carbon bond. Other processes which are also kinetically significant include slow (sticking coefficient ∼10−5) ethane adsorption, slow ethane desorption [by reaction of C2H5(a) with H(a)], the reversible dehydrogenation of CH2–CH3(a) to produce CH–CH3(a) and competition of hydrogen atoms for the sites on which the hydrocarbon species are adsorbed. A Langmuir-type approach is used to derive a rate law from this mechanism which fits the experimental data over the following range of reaction conditions: a∼3 order of magnitude variation in the partial pressure of each reactant (∼1–1000μ) and a catalyst temperature in the range 80–205°C.
Time-independent methods in classical mechanics: Calculation of invariant tori and semiclassical energy levels via classical Van Vleck transformations
Authors: Jaffé Charles , Reinhardt William P.
Published: February 2003

Recently introduced methods for semiclassical quantization of nonseparable systems implicitly or explicitly rely on the existence of the invariant tori of time-independent classical mechanics. We present an accelerated convergence scheme for calculation of such tori based on the classical limit of the Van Vleck transformation, and give theoretical and computational comparisons with the methods of Percival and Pomphrey, and Chapman, Garrett, and Miller.
Temperature dependence of the electron attachment coefficient in iodine
Authors: Brooks Howard L. , Hunter Scott R. , Nygaard Kaare J.
Published: February 2003

The attachment coefficient for iodine in a (1% I2+99% N2) mixture, 50 Torr total pressure, has been measured in an electron swarm experiment from 1 to 50 Townsends (1 Townsend=1Td=10−17 V cm2). As the temperature was increased from 35 to 110 °C, the attachment coefficient increased for any E/N (electric field intensity/gas number density) values greater than 7 Td. These results are compared to other experimental data and an explanation for the temperature dependence, based on the population of upper vibrational states, is presented.
Study of the 2Ar+Ar+2=Ar+Ar+3 reaction
Authors: Turner D. L. , Conway D. C.
Published: February 2003

Equilibrium constants for the reaction 2Ar+Ar+2=Ar+3+Ar have been determined mass spectrometrically from 144 to 217 °K. Assuming Ar+3 to be linear, ΔH °200=−5.06±0.08 kcal/mole, ΔS °200=−20.3±0.4 cal/mole deg, and D0(Ar+2−Ar) =5.05±0.11 kcal/mole. The ΔS° is too negative for the ’’loose cluster’’ model in which it is assumed that the Ar+2 is freely rotating in the Ar+3 cluster. It is concluded that Ar+3 is probably linear. The rate constant for the formation of Ar+3 was computed and compared to experimental results at 77 and 298°K.
Phase transitions in lattice gases with linear clusters. I. Singularities in activity and low temperature series; interacting dimers
Authors: Poland Douglas , Swaminathan P. K.
Published: February 2003

The phase transition behavior of a lattice gas where the particles interact so as to give linear clusters is studied. High density/low temperature series show that there is an order–disorder line in the density–temperature plane. A similar model, that of interacting dimers is also studied and the temperature at which long range order sets in at close packing is estimated. Using low density activity series, the behavior of the Lee–Yang fugacity roots for these models is obtained and we conjecture on the relation of the behavior of the roots to the presence or absence of cluster surface energy.
Phase transitions in lattice gases with linear clusters. II. Behavior on the Bethe lattice
Authors: Poland Douglas
Published: February 2003

A lattice gas model with particles that interact to give linear clusters is treated exactly on the Bethe lattice. Unlike the behavior of the same model on the quadratic lattice, on the Bethe lattice the model exhibits a first order phase transition when the density approaches close packing.
The analog of surface molybdenyl ion in Mo/SiO2 supported catalysts: The isopolyanion Mo6O193− studied by EPR and UV-visible spectroscopy. Comparison with other molybdenyl compounds
Authors: Che M. , Fournier M. , Launay J. P.
Published: February 2003

Electrochemical reduction of the isopolyanion Mo6O192− in solution leads to x-band EPR spectra at 77 K characterized by g⊥=1.930, g∥=1.919, A⊥=34.5 and A∥=80.5 G. The magnetic parameters were confirmed using a Q-band spectrometer. The EPR spectra are attributed to localized molybdenyl (Mo=0)3+ species surrounded by oxide ions in C4v symmetry with one short Mo–O bond. The magnitude of the g components g⊥≳g∥ confirms the earlier assignment made for reduced Mo/SiO2 supported catalysts where a similar type of molybdenyl Mo(V) species was found to be present on the surface. The magnetic parameters are discussed and compared with those obtained for other oxomolybdenum ions in the frame of the LCAO–MO theory.
On the theory of H+OH (2Π) collisions and interstellar OH maser action
Authors: Shapiro M. , Kaplan H.
Published: February 2003

The role of H atom collisions as a pump for the 18 cm OH maser lines in interstellar sources is considered. Theory of 2Π molecules collision with a doublet-state atom is formulated. Explicit expressions for the interaction matrix between the sublevels of the H(2S)+OH(2Π) system are derived, and correlated to the H2O Born–Oppenheimer states. The interaction matrix thus derived is used to obtain cross-sections and rate constants between (and within) the j=3/2 and J=5/2 rotational manifolds, using the exponential Born method. The H+OH collision is shown to selectively excite the upper, (ε=+1), Λ-doubled state of the j=5/2 manifold. This selectivity is shown to result from the attractive nature of the X 1A′ component, which is also helpful in bringing about rotational excitation. The repulsive (3A″, 3A′ and B1A′) components are shown to have smaller propensities for rotational excitation and selectivity. The collisional rate constants are used in a simple cloud model, in which radiative decay and effects of background radiation are also incorporated. The model is solved for a wide range of H atom densities. Nonthermal, and often inverted, Λ level populations are shown to exist for a large variety of kinetic temperatures and densities, thus suggesting that collisions with H serve as a major pump source of all four 18 cm emission lines.
A phase transition of the adsorbed layer: High pressure effect on fatty alcohol adsorption at an oil–water interface
Authors: Lin Michel , Firpo Jean-Luc , Mansoura Pierre , Baret J. François
Published: February 2003

Measurement of the interfacial tension of fatty alcohol solutions permits determination of the amount of amphiphile adsorbed. This amount varies with both pressure and concentration. At some critical value, the interfacial solution splits into two phases. In the dilute phase, the adsorbed molecules are solvated by the oil whereas in the condensed phase there is no solvent interspersed between the aliphatic chains. A thermodynamical analysis of this two-dimensional phase transition is given assuming the interfacial solution to be regular.
Effects of off-diagonal disorder on localization of electronic excitations in mixed molecular solids
Authors: Klafter Joseph , Jortner Joshua
Published: February 2003

In this paper we explore the effects of off-diagonal disorder on electronic energy transfer (EET) in an impurity band of an isotopically-mixed, organic solid at low temperatures. We have considered the localization of an elementary excitation in a system characterized by both diagonal disorder, originating from inhomogeneous broadening W of the site-excitation energies, and of off-diagonal disorder arising from the energetic spread σ of the transfer integrals. We have utilized an exact expression for the self-energy of a disordered system where both the site-excitation energies and the transfer integrals are characterized by a Lorentzian distribution, together with the localization function method of Liciardello and Economou to establish the localization condition in the center of the impurity band. Model calculations were performed for a Bethe lattice and for the Hubbard density of states, demonstrating the enhancement of delocalization due to off-diagonal disorder, whereupon the Anderson transition (AT) will be exhibited at higher values of W than in the original Anderson model (OAM), when σ=0. For large values of the ratio W/σ≳12 the effects of off-diagonal disorder are negligible. Numerical calculations of σ were performed for a random distribution of impurities, while W was roughly estimated for recent spectroscopic measurements. These data, together with the results of the model calculations for a Bethe lattice, established the existence of the critical impurity concentration ? for EET in the impurity band. Off-diagonal disorder results in the lowering of ? relative to the OAM; however, the effect of diagonal disorder is dominant in determining the termination of EET in the impurity band.
Reactive scattering of B+  (3P
u) by molecular deuterium
Authors: Sondergaard Neal A. , Sauers Isidor , Jones Andrew C. , Kaufman Joyce J. , Koski Walter S.
Published: February 2003

The angular and energy distribution of the ionic products from the reaction of B+ in its first excited state, 3Pu, with molecular deuterium was studied over a projectile energy range of 1 to 40 eV in the laboratory system. The product states as determined from the limiting values of the translational exoergicity were BD+  (2Σ+) and BD+  (2Π). The experimental velocity contour maps indicated that BD+(2Σ+) was arising through complex formation whereas BD+  (2Π) was proceeding by a direct mechanism.
Electron transfer in fixed-nuclei systems: A comparison of propagator descriptions
Authors: Ondrechen Mary Jo , Ratner Mark A. , Sabin John R.
Published: February 2003

Site-to-site electron transfer rates in a fixed-nucleus system are described using the polarization propagator, the time-dependent number operator, and the electron propagator. We show that given a proper choice of the initial state, the first two agree with each other. The number-operator expression forms an upper bound to the transfer rate given by the electron propagator. Numerical studies on two-site and three-site Hubbard models indicate that the electron propagator in the Hartree–Fock approximation provides a good approximation to the initial transfer rate, for a wide choice of electron repulsion strengths.
Liquid state rotational dynamics of nonrigid molecules. III. Four, five, and six bond chains
Authors: Evans G. T. , Knauss D. C.
Published: February 2003

Single particle orientation correlation times are calculated for liquid state alkane chain molecules using a Zwanzig–Mori formulation of Fizman’s equations of motion for stiff chains. The correlation times associated with first and second rank functions of the bond vectors sample overall tumbling of the molecule as well as the internal torsional dynamics. Torsional averaging is accomplished by means of the rotational isomeric model using a few different torsional energies. The results of this study are combined with our earlier work to analyze the chain length dependence of correlation times for two to six bond chains.
A test of the quantum mechanical sudden vibrational approximation for collinear inelastic collisions
Authors: Bowman Joel M. , Drolshagen Gerhard , Toennies J. Peter
Published: February 2003

Numerical results for collinear vibrationally inelastic transition probabilities based on a quantum mechanical sudden vibrational approximation are presented. The results are compared with those obtained by replacing the vibrational wave functions by a semiclassical formula. For the exponentially repulsive potential employed, the quantal and semiclassical transition probabilities are given analytically. To test both theories transition probabilities are compared with exact results for three collision systems with different mass ratios as a function of energy. As the relative mass of the atom decreases the quantal approximation becomes quantitatively accurate whereas the semiclassical does not, independent of the energy.
The absorbing boundary method. II. Generalization of the Golden Rule
Authors: Nordholm Sture
Published: February 2003

The recently developed absorbing boundary method is implemented by the use of a weak coupling approximation. The derivation then results in a generalized Golden Rule which in the limit of vanishing coupling reproduces the usual simple exponential decay for elastic processes. The same arguments are then applied to inelastic decay processes driven by a monochromatic external perturbation. It is shown that the usual single step Golden Rule mechanism can be decomposed into a two-step mechanism with one vertical (inelastic) step followed by a horizontal (elastic) step. This form of the absorbing boundary method applies, e.g., to photoionization and photodissociation and allows the calculation of cross sections and decay rates without the use of continuum energy eigenstates.
Unrestricted Hartree–Fock (UHF) calculations of singlet and triplet diradicals: Nitrene peroxide (HNOO)
Authors: Yamaguchi Kizashi , Yabushita Satoshi , Fueno Takayuki
Published: February 2003

It is shown that the eight different diradical states of nitrene peroxide (HNOO) are well represented by the spin density wave (SWD) solutions which are equivalent to the unrestricted Hartree–Fock (UHF) solutions for this radical. (AIP)
Photodissociation spectroscopy of O−3 and O−3⋅H2O. 4170–4700 Å
Authors: Smith G. P. , Lee L. C.
Published: February 2003

The photodissociation and photodetachment cross sections for O3− are reported to 4100 Å. A drift tube mass spectrometer and tunable dye laser are used in the experiments.(AIP)
On the dissociation products of the C 1Πu state of Na2 and K2 molecules
Authors: Allegrini M. , Kopystynska A. , Moi L.
Published: February 2003

Laser-induced fluroescence experiments have been conducted to used to excite the C band of Na2.(AIP)
Ground state dipole moment of NaH
Authors: Dagdigian Paul J.
Published: February 2003

Measurements and analysis of the electric deflection of a sodium hydride molecular beam is presented. The electric dipole moment of ground state NaH is calculated from measurement of beam deflection. (AIP)
Classical transition state theory is exact if the transition state is unique
Authors: Pechukas Philip , Pollak Eli
Published: February 2003

Under mild conditions on the long-range behavior of the potential, we show that classical transition state theory is exact at energy E for a collinear atom–diatom reaction if there is only one candidate for transition state at energy E—that is, only one periodic vibration of energy E across the interaction region.
X-ray diffraction study of liquid tertiary butyl alcohol at 26 °C
Authors: Narten A. H. , Sandler S. I.
Published: February 2003

The x-ray diffraction pattern of liquid tertiary butyl alcohol (CMe3OH) near the melting point has been measured. The data are analyzed to yield the molecular structure. The distinct structure function Hd(k) derived from the data is compared with that obtained previously for liquid neopentane (CMe4). The replacement of one methyl group in CMe4 by a hydroxyl group to produce CMe3OH results in significant changes in Hd(k). The data show clearly that hydrogen-bonded hydroxyl groups occur in liquid CMe3OH with an O⋅⋅⋅O distance of 2.74 Å, and that each hydroxyl group has two nearest neighbors at this distance.
A
b i
n
i
t
i
o study for the structure of propane and the n-propyl radical
Authors: Pacansky J. , Dupuis M.
Published: February 2003

A b initio calculations are presented for three possible conformations of the n-propyl radical. The completely optimized geometry and total energy for each conformation is found by using the gradient method. The theoretical results show that the conformations are energetically very close to each other. This agrees with experimental studies on the n-propyl radical in rare gas matrices but disagrees with experiments performed in solutions.
The kinetics of free radicals generated by IR laser photolysis. I. Reactions of C2(a 3Πu) with NO, vinyl cyanide, and ethylene
Authors: Reisler H. , Mangir M. , Wittig C.
Published: February 2003

C2(a 3Πu) molecules are produced by multiple photon dissociation of either vinyl cyanide or ethylene with the focused output from a CO2 TEA laser. Their reaction with NO is reported in this paper. The total quenching rate coefficient of C2(a 3Πu) by NO is determined both from laser induced fluorescence of C2(a 3Πu) and from the time resolved chemiluminescence from CN(B 2Σ+) and CN(A 2Π) which are formed in the reaction, and is (7.5±0.3)10−11 cm3 molecule−1 sec−1. The vibrational energy disposal within the B 2Σ+ and A 2Π states of CN is estimated from the resolved bands of the CN(B 2Σ+→X 2Σ+) and CN(A 2Π→X 2Σ+) emission systems. Vibrational levels of CN(B 2Σ+) up to at least v′=5 but lower than v′=10 are excited, accompanied by high rotational excitation. CN in the A 2Π state is excited to at least the 16th vibrational level. The reaction populates the A 2Π state about 7 times more efficiently than it does the B 2Σ+ state. The reaction mechanism is discussed, and it is concluded that most of the electronically excited molecules are produced via the single step reaction C2(a 3Πu)+NO→CN(B 2Σ+ or A 2Π)+CO(X 1Σ+). Quenching rate coefficients of C2(a 3Πu) by vinyl cyanide and ethylene are also reported.
High resolution laser spectroscopy of Cs2. I. Ground state constants and potential curve
Authors: Höning G. , Czajkowski M. , Stock M. , Demtröder W.
Published: February 2003

Excitation and fluorescence spectra of the Cs2 molecule were measured with high resolution allowing resolution of the rotational structure. These spectra were studied under excitation by different lines of a single mode argon laser which could be continuously tuned across spectral intervals of about 10 GHz. For excitation in a cesium vapor cell the spectral resolution was only limited by the Doppler width of the absorption lines while in a collimated cesium beam a resolution between 20 and 60 MHz could be achieved. Accurate molecular constants and the RKR potential of the X 1Σ+g ground state are derived from more than 900 fluorescence lines, most of which were precisely measured with a Fabry–Perot interferometer crossed with a monochromator. The dissociation energy of the ground state is deduced from an extrapolation beyond the highest measured level with v″=72, and also from a second laser-excited fluorescence spectrum that appears at the red end of the singlet spectrum and consists of a continuum and a few discrete lines. This spectrum is assigned to transitions terminating in the X 3Σ+u state, which is mainly repulsive. Like the X 1Σ+g state, it too dissociates into two Cs atoms in their 6 2S1/2 ground states.
Absolute rate parameters for the reactions of formaldehyde with O atoms and H atoms over the temperature range 250–500 K
Authors: Klemm R. Bruce
Published: February 2003

Absolute rate coefficients for the reaction of H atoms and O atoms with formaldehyde were determined over the temperature range of 250 to 500 K. Linear Arrhenius behavior was observed in log(ki) vs 1/T plots for both reactions and the following rate parameters were obtained: k1(T) = (3.27±1.61) ×10−11 exp (−3670±365/RT) cm3 molec−1 s−1, k2(T) = (2.78±0.32) ×10−11 exp (−3030±80/RT) cm3 molec−1 s−1. Indicated error limits are two standard deviations. These results are compared with those of previous studies and are further discussed in terms of extrapolation to higher temperatures.