bluuebunny/crossref_metadata_2025 huggingface dataset:
Isotopic vibration–vibration energy exchange in hydrogen chloride molecules at low temperatures
Authors: Shin H. K.
Published: July 2002

The temperature dependence of the isotopic VV energy exchange process H35Cl(1)+H37Cl(0)→H35Cl(0)+H37Cl(1) has been studied in the temperature range of 10–1000 K. As temperature increases the VV probability increases between 10–30 K, but above 50 K it decreases rapidly. The appearance of two regions of different temperature dependence has been discussed in terms of the local translational motion which causes the vibrational modes of two colliding molecules to couple efficiently in the presence of strong attractive interaction.
Static and dynamic light scattering studies on the melting behavior of crystalline latex
Authors: Sasaki Shigeo
Published: July 2002

The melting behavior of crystalline polystyrene latex was investigated using the static and dynamic light scattering techniques. The normalized time-correlation function of the electric field of the diffracted light was derived on the basis of the simplified theory for the randomized lattice vibration. The long time tail of gL(t) observed in a previous experiment [J. Phys. Soc. Jpn. 52, 2571 (1983)], which can be approximately expressed as (t/t0)−α, was confirmed experimentally and theoretically. The t0 and α values were found to be related to the interparticle forces and the size of microcrystal, respectively. Both the static and dynamic light scattering data indicated that the size of the microcrystal and the lattice constant decreased in the course of melting of the crystalline latex.
Interaction between dimethylsulfoxide and formamide in the liquid state
Authors: Nielsen O. Faurskov , Christensen D. H. , Praestgaard E.
Published: July 2002

Low frequency Raman spectra (20–400 cm−1) are presented of formamide dissolved in dimethylsulfoxide (DMSO). The concentration of formamide ranges from 2%–75% (v/v). The two formamide bands at 110 and 190 cm−1 in the neat liquid exhibit only smaller frequency shifts upon dilution. The intensities of both bands are proportional to the concentration of formamide. The conclusion is, that the linear chain structure, found in neat liquid formamide, is conserved in the DMSO solution. Raman spectra of the NH-stretching region (2950–3500 cm−1) confirm this hypothesis.
Structure and synthesis of the ternary alkali graphite intercalation compound KCsC16, an ideal layered heterostructure
Authors: Hark S. K. , York B. R. , Solin S. A.
Published: July 2002

We have prepared a stable two phase graphite intercalation compound (GIC) containing KC8 and KCsC16 by immersing CsC24 into liquid K at 70 °C. High resolution x-ray diffraction studies reveal that the KCsC16, which exhibits a stage one c-axis stacking sequence of ⋅⋅⋅ C K C Cs C K C Cs ⋅⋅⋅ is an ideal ternary heterostructure GIC with a c-axis repeat distance of dH=11.27 Å and correlation range of 350 Å. The intensities of the (00l) x-ray diffraction pattern calculated on the basis of the proposed c-axis repeat sequence are in excellent agreement with the experimental observations. The KCsC16 in plane structure is a (2×2)R0 ° superlattice with an in plane correlation range of 140 Å. The ordered intercalant layers stack along the c axis with an α,β,γ,δ site sequence, where, e.g., α,γ=K and β,δ=Cs, and stacking faults occur on average every 30 Å.
Normal vibrations in nickel, palladium, and platinum
Authors: Gupta O. P.
Published: July 2002

Calculations of the phonon frequencies, temperature variation of Debye temperature, and the Debye–Waller factor for nickel, palladium, and platinum have been made by employing a four parameter model. Expressions for electron pressure and equilibrium condition which preserves the crystal stability are derived using the Coulombian potential. The model satisfies the symmetry requirements of the lattice and the lattice is in equilibrium without recourse to external forces. A comparison between the theoretical results and the available experimental data exhibits good agreement.
Analysis and simulation of optical and magnetic properties of lanthanide aluminates LnMgAl11O19 (Ln=La/Nd,La/Eu,Pr) with magnetoplumbite-like structure
Authors: Saber D. , Dexpert-Ghys J. , Caro P. , Lejus A. M. , Vivien D.
Published: July 2002

Single crystals of LnMgAl11O19 aluminates with a magnetoplumbite-like structure, (Ln=La1−xNdx, La1−x Eux, Pr), are grown by the flame fusion (Verneuil) or floating zone methods. Optical absorption or fluorescence spectra of these crystals reveal that Ln3+ ions occupy at least two or three different sites, instead of only one as in the ideal magnetoplumbite structure. Eu3+ fluorescence under dye-laser excitation leads to the identification of two low symmetry (probably c2v) sites labeled A and B. Ab initio crystal field parameters for Eu3+ are calculated from the atomic coordinates deduced from the crystal stucture of LaMgAl11O19. These parameters and the experimental energy levels are used to derive an acceptable set of Bkq parameters for the A site. These Bkq corrected for the Nd3+/Eu3+ radial integrals ratio are used in turn to derive the Nd3+ Racah and spin-orbit coupling parameters which fit the Nd3+ absorption spectrum at 4 K. At least two sets of parameters ‘‘high 2P1/2’’ and ‘‘low 2P1/2’’ are required, confirming the multisite character of La1−xNdxMgAl11O19. For this compound, the ab initio crystal field parameters are used to calculate the magnetic susceptibility and Nd3+ ESR g values. The fairly good agreement between calculated and experimental magnetic parameters confirms that the real sites of the Lanthanide ion arise from minor perturbations of the normal magnetoplumbite one. These perturbations could arise from Al–Mg site disorder, and/or the presence of oxygen vacancies in the lattice.
Fluorescence spectra of matrix-isolated BiS, BiSe, and BiTe
Authors: Ahmed Fakhruddin
Published: July 2002

Laser-induced fluorescence spectra are reported for BiS, BiSe, and BiTe for the first time in argon matrices. A total of nine band systems have been observed, out of which eight are believed to be new low energy electronic states of these molecules. Two of these belong to BiSe, and three each to BiS and BiTe.
On definitions of L convergence of atomic correlation energies
Authors: Jankowski Karol , Zaharevitz Daniel W. , Silverstone Harris J.
Published: July 2002

The two usual definitions of energy increments that characterize convergence of electronic energy calculations are shown to be numerically significantly different. In two special cases, helium and neon, their ratios are approximately 1.4. Care must be exercised when comparing calculations from separate sources lest differences of definition be interpreted physically.
A quasiclassical trajectory study of vibrational predissociation and collisional relaxation in Ar–OCS
Authors: Gibson Lester L. , Schatz George C.
Published: July 2002

This paper describes the results of two closely related trajectory studies of the ArOCS system simulating (a) deactivation of OCS(0110) in thermal collisions with Ar, and (b) dissociation and energy transfer in the ArOCS van der Waals complex. Both studies used a potential surface which sums together an accurate OCS potential with an empirically determined Ar+OCS interaction potential. Two parametrizations of the surface are studied, and one of them (surface II) is found to match all the known properties of ArOCS complex as well as the results of ab initio calculations quite well. Collisional deactivation of OCS(0110) by Ar is studied using the quasiclassical trajectory method. A recently developed fast Fourier transform (FFT) method for determining the vibration/rotation good action variables in OCS is used to determine the deactivation transition probability in these collisions, and the resulting value on our better surface (0.5×10−4) is quite close to the measured value (0.96±0.3)×10−4. Semiclassical eigenvalues for OCS are also calculated using the FFT method, and the results are within 0–8 cm−1 of accurate quantal values for states within 2500 cm−1 of the ground state. The ArOCS van der Waals cluster simulation is also done using quasiclassical trajectories, with OCS excited to either the 0200 or 0220 state and the Ar–OCS stretch and bend states varied over a wide range of energies from zero point to 90% of dissociation. In none of these simulations was either dissociation or intramolecular energy transfer important on a time scale of at least 15 ps and very likely 100 ps. This indicates that the 5.4 ps lifetime which appears to govern the absorption linewidth of ArOCS does not arise from either vibrational predissociation or intramolecular energy transfer.
Radical cations of sulfides and disulfides: An ESR study
Authors: Bonazzola L. , Michaut J. P. , Roncin J.
Published: July 2002

Exposure of dilute solutions of dimethylsulfide, methanethiol, tetrahydrothiophene, terbutyl and diterbutyl-sulfides, dimethyl-disulfide, and diterbutyldisulfide, in freon at 77 K to 60Co γ rays gave the corresponding cations. From the reported ESR spectra, g tensors were obtained. It was found that both sulfide and disulfide cations exhibit the same g tensor: (gmax=2.034±0.002, gint=2.017±0.001, gmin=2.001±0.005). From this result it has been shown that the disulfide cation is planar. This finding was supported by fully optimized geometry ab initio calculations.
Dependence on vibrational excitation of energy transfer processes for HF(v, j)+HF(v=0)
Authors: Bollati L. A. , Argüello G. A. , Staricco E. H.
Published: July 2002

Calculations of kR–R,T rate constants using the power scaling law and accounting for vibrational excitation dependence have been carried out. Considerable improvements in the reproduction of fluorescence signals derived from double resonance experiments are achieved.
Periodic structures induced by director reorientation in the lyotropic nematic phase of disodium cromoglycate–water
Authors: Hui Y. W. , Kuzma M. R. , San Miguel M. , Labes M. M.
Published: July 2002

A nonequilibrium periodic structure is induced by a magnetic field H applied to an aligned lyotropic uniaxial nematic phase of disodium cromoglycate–water. A series of parallel lines perpendicular to H represents boundaries between 180° out-of-phase regions of director reorientation. The distance between the lines decreases with increasing H. The line spacing is also directly proportional to thickness of the sample (in a limited range of thickness), and a secondary periodicity, consisting of nodes in these lines, is observed in thicker samples. An extension of a theoretical model by Guyon et al. is used to qualitatively interpret the abovementioned dependencies.
1
7O and 39K quadrupole resonance study of the ferroelastic phase transition in KH3(SeO3)2
Authors: Seliger J. , Z̆agar V. , Blinc R. , Novak A.
Published: July 2002

The 17O-proton nuclear double-resonance spectra of KH3(SeO3)2 have been measured above and below the ferroelastic transition and the quadrupole coupling has been determined for all three chemically nonequivalent oxygen sites in the unit cell. The 17O-proton magnetic dipolar coupling as well as the 17O quadrupole coupling data clearly show the presence of proton motion between two equilibrium sites in the O(2)–H- - -O(2) bond which freezes out below Tc. The temperature dependence of 30K quadrupole frequency has been as well determined.
New equation for the internal field correction on the infrared spectra of condensed phases
Authors: Akiyama Minoru
Published: July 2002

The Lorentz internal field model has been widely used in order to correct the observed infrared spectra for the effect of the internal electric field. In all previous papers, the total polarization required in the Lorentz model has been considered to have only one component. In this paper, however, another component was introduced, and the total polarization was given by the sum of the two components. Such a change in the Lorentz model led to a new equation for the absolute band intensity corrected for the internal field effect.
Collisional deactivation of Xe(5p56p) states in Xe and Ar
Authors: Ku J. K. , Setser D. W.
Published: July 2002

One-photon excitation in the afterglow of a pulsed discharge and two-photon excitation in a static cell have been used to generate the six Xe(5p56p) states in variable pressures of Xe. The decay times of the initially excited states and their products have been analyzed to obtain state-to-state rate constants at 300 K for collisional transfer among the Xe(5p56p) levels and the Xe(5p56s′) levels. The depolarization rate constants for the Xe(5p[5/2]2) and Xe(5p[3/2]2) states prepared by two-photon excitation were measured to be ∼6×10−10 cm3 molecule−1 s−1. The collisional deactivation rate constants of the two-photon prepared states, Xe(6p[1/2]0), Xe(6p[3/2]2), and Xe(6p[5/2]2), in Ar also are reported.
Derivation of the conformational density of states of a normal hydrocarbon
Authors: Tevlin Patrick , Jones Francis P. , Lafleur Sean , Trainor L. E. H.
Published: July 2002

We consider conformational states of a saturated linear hydrocarbon, within the rotational isomeric approximation. The principal nonbonded interaction within the chain, the ‘‘pentane effect,’’ is assigned a finite energy; other nonbonded interactions are ignored. Within these approximations, we derive an exact closed expression for the conformational density of states. This result is compared to previous work. Some consequences of this result are examined.
Kinetics of near-critical quenches in homogeneous binary polymer mixtures
Authors: Fredrickson Glenn H.
Published: July 2002

The dynamical response of a binary mixture of homopolymers in the vicinity of its critical point is investigated. We consider the situation in which the mixture is subjected to a rapid quench, with both initial and final equilibrium states in the homogeneous one-phase region, but near Tc. The theory of Kawasaki and Ohta for mixtures of small molecules is extended to the present case of high molecular weight polymer mixtures. The resulting equation of motion for the structure factor is expected to accurately describe the results of neutron and light scattering experiments subsequent to a rapid quench of a two-component polymer melt. Mode coupling terms in the kinetic equations that were neglected in previous treatments of critical dynamics in polymer mixtures are shown to be important for scattering wavelengths larger than the size of a coil and for temperatures and compositions sufficiently close to the critical point. In a narrow region surrounding the critical point we find that the mode coupling corrections lead to several new predictions for the linear dynamical response of polymer mixtures. One notable prediction is that the mutual diffusion coefficient is expected to scale like D∼N2e N−7/2‖1−χ/χs‖0.53, where Ne, N, χ, and χs are, respectively, the entanglement length, the chain length, the Flory interaction parameter, and the interaction parameter on the spinodal. The experimental consequences of the present results are discussed in some detail.
On the weaknesses of the valence shell electron pair repulsion (VSEPR) model
Authors: Ro/eggen Inge
Published: July 2002

The validity of the valence shell electron pair repulsion model (VSEPR) is discussed within the framework of an antisymmetric product of strongly orthogonal geminals (APSG). It is shown that when a molecule is partitioned onto fragments consisting of a central fragment, lone pairs, bond pairs, and ligands, the total APSG energy including the nuclear repulsion terms, can be written as a sum of intra- and interfragment energies. The VSEPR terms can be identified as three out of 13 different energy components. The analysis is applied to the water molecule. Six of the neglected energy components in the VSEPR model have a larger variation with the bond angle than the terms which are included in the model. According to this analysis it is difficult to consider the VSEPR model as a valid framework for discussing molecular equilibrium geometries. It is suggested that energy fragment analysis might represent an alternative model.
An integral equation approach to structure and dynamics of ionic colloidal solutions
Authors: Bratko Dušan , Friedman Harold L. , Zhong En Ci
Published: July 2002

The Ornstein–Zernike equation with either the hypernetted chain (HNC) closure or a composite HNC/Percus–Yevick (PY) closure approximation is applied to the primitive model of highly asymmetric electrolytes that mimic ionic micellar solutions. There is substantial agreement of the calculated partial structure factor with the small angle neutral scattering data for a lithium dodecylsulfate solution. New theoretical results are applied to calculate the ionic self-diffusion coefficients for Smoluchowski models with equilibrium structures obtained from the HNC approximation. Fair agreement with experimental data is found for the small ions whereas the theory predicts too fast diffusion for the colloidal particles.
Theory of resonant inelastic one-phonon scattering of He atoms from a LiF(001) single crystal surface
Authors: Eichenauer Dieter , Toennies J. Peter
Published: July 2002

For the He–LiF(001) system, molecular beam measurements of the inelastically scattered intensity have revealed a large number of resonance structures. In this paper the theoretical description of these resonant inelastic one-phonon scattering processes is provided in the framework of the distorted wave Born approximation. In the first step the elastic diffractive scattering problem is solved exactly using close coupling calculations for a recently developed pairwise additive semi ab initio potential and a rigid lattice. As the potential contains both the attractive well and the corrugation in a realistic manner, bound state resonances are fully taken into account. In the next step the inelastic coupling due to one-phonon processes is treated as a perturbation of the elastic wave functions obtained from the close coupling solutions. The inelastic coupling potential is the same semi ab initio two-body potential used to describe the atom–static surface potential, and the LiF–surface lattice dynamics are described by realistic Green’s function calculations. The theoretical results provide a good description of most of the structures seen in experimental angular distributions and time of flight spectra. The resonant features can be interpreted in terms of one-phonon assisted adsorption into and desorption out of specified bound states of the atom–surface potential. In addition to the contributions of Rayleigh phonons the bulk phonons contribute about 40% to both the creation and annihilation inelastic scattering processes.
Direct measurement of intermolecular forces between a polymer layer and mica
Authors: Granick Steve , Patel Sanjay , Tirrell Matthew
Published: July 2002

We report here the first direct measurement of intermolecular forces between a polymer layer and a solid surface. When solid surfaces bearing adsorbed polymer approach one another, interactions develop that may be categorized as polymer–polymer and polymer–solid (and a negligible contribution of solid–solid interactions at the large solid–solid separations imposed by adsorbed polymer). Direct measurements of the forces between polymer layers adsorbed on mica have been made recently with apparatus of the type developed by Israelachvili. Attractive forces are attributed to a combination of osmotic (polymer–polymer) and bridging (polymer–solid) interactions. Bridging occurs if macromolecules adsorbed one one surface can reach a second surface. In the work presented here, poly(α-methylstyrene) (PαMS) adsorbed on one mica sheet was brought into contact in cyclohexane with a bare mica sheet. Adhesion was measured as a function of separation and contact time and found to be more than 20 times greater than between two polymer–coated surfaces under otherwise identical conditions. This direct measurement of molecular forces between dissimilar surfaces enables estimation of the PαMS segmental sticking energy on mica in cyclohexane as (1)/(3) kT.
Polyelectrolyte solutions with ionic mixtures
Authors: Ramanathan G. V.
Published: July 2002

From the Poisson–Boltzmann (PB) equation for polyelectrolyte solutions with arbitrarily many species of counterions and coions, valence selectivity properties and exact expressions for the osmotic coefficient are derived in the limit of infinite dilution, generalizing Manning’s results for two species. Expressions are also obtained for the distribution function for the condensate.
Iterative maps with multiple fixed points for excitation of two level systems
Authors: Cho H. , Baum J. , Pines A.
Published: July 2002

Iterative schemes have been used in NMR to generate pulse sequences which excite spin systems over narrow or broad ranges of transition frequencies and radio frequency amplitudes. Mathematical methods employing iterative maps and related concepts from nonlinear dynamics have been applied in the analysis of these schemes. The effect of transforming a pulse sequence by an iterative procedure can be represented as an iterative map on a quantum statistical propagator space, with fixed points in this space corresponding to certain desired responses of the spin system. The stability of these points with respect to variations of parameters, such as amplitudes or energies, determines the bandwidth characteristics of the corresponding sequence; broadband behavior results from stable fixed points, and narrowband behavior from unstable fixed points. This paper examines schemes which produce maps with more than one stable fixed point. Such schemes are shown to generate sequences which exhibit bistable or selective, bandpass behavior. Spatially selective NMR, spin decoupling, nk-quantum selective multiple-quantum NMR, isotope selective zero-field NMR, and optical information storage are some of the applications which can benefit from bandpass selective excitation sequences.
Diffusion and thermal diffusion in binary mixtures of hydrogen with noble gases
Authors: Dunlop Peter J. , Robjohns H. L. , Bignell C. M.
Published: July 2002

Diffusion coefficients and thermal diffusion factors are reported for binary mixtures of hydrogen with neon, argon, krypton, and xenon: the temperature range for the former measurements is 200–340 and 255–350 K for the latter. The results are used to test excellent potential functions which have recently been reported for hydrogen–noble gas interactions.
Fourier transform infrared spectroscopy of molecular clusters: The structure and internal mobility of clustered carbon dioxide
Authors: Barnes J. A. , Gough T. E.
Published: July 2002

Infrared spectra of supersonic jets of carbon dioxide seeded in helium are reported: Features assignable to clusters were observed for the ν2, ν3, ν1+ν3, and 2ν2+ν3 bands. A detailed study was made of the ν3 band, from which it was concluded that the clusters do not adopt the face-centered cubic crystal structure of solid carbon dioxide. The observed spectra indicate that the cluster geometry is largely determined by pairwise interactions between adjacent molecules. Furthermore, expansions of pure carbon dioxide produced clusters whose spectra indicate motional averaging: such clusters seem to be fluid on a picosecond time scale.
Mixed Cu–simple metal dimers and trimers: CuLi, CuLi2, CuNa, CuK, CuBe, CuBe2, Cu2Be, CuAl, and CuAl2
Authors: Bauschlicher Charles W. , Langhoff Stephen R. , Partridge Harry , Walch Stephen P.
Published: July 2002

Theoretical studies of selected diatomic and triatomic molecules containing copper and the simple metals Li, Na, K, Be, and Al are presented, with emphasis on elucidating the nature of the bonding in mixed transition metal–simple metal systems. Large Gaussian basis sets are used in the diatomic calculations, and are used to calibrate the triatomic calculations, in which somewhat smaller Gaussian basis are employed. Electron correlation is incorporated using both the single-reference singles plus doubles configuration interaction and coupled pair functional methods. We find that alkali atoms form very polar σ bonds with copper, and that the ionicity increases with the inclusion of higher excitations, because they improve the electron affinity of copper, which in turn allows a larger negative charge on copper. Aluminum is found to form stronger bonds than beryllium, since it does not have to undergo sp hybridization. Some of the trimers bond by forming three-center three-electron bonds. These multicenter bonds are quite strong even when compared to the two-electron bonds in the dimers or to other bonding mechanisms in the trimers.
Rotational spectra of s-t
r
a
n
s and s-c
i
s glyoxal-d1 (CHO–CDO) observed by microwave Fourier transform spectroscopy
Authors: Rodler M. , Oldani M. , Grassi G. , Bauder A.
Published: July 2002

Rotational spectra of both conformers of glyoxal-d1 have been investigated in the 7.8–18 GHz region. The asymmetric isotopic labeling induces in the s-trans conformer a small permanent electric dipole moment. Exploiting the unique properties of a pulsed Fourier transform spectrometer 20 of the extremely weak rotational transitions of s-trans glyoxal-d1 have been observed and assigned. Three rotational constants and four quartic centrifugal distortion constants have been determined from the frequencies of transitions with J≤22. Nuclear quadrupole hyperfine splittings have been resolved for two low J transitions. Approximate values for the quadrupole coupling constants have been obtained therefrom. In addition, 16 transitions of s-cis glyoxal-d1 have been observed and assigned. From the transition frequencies with J≤22 improved rotational constants have been derived along with all quartic centrifugal distortion constants.
Direct detection of very slow two-jump processes by saturation recovery electron paramagnetic resonance spectroscopy
Authors: Sugano Tetsukuni , Mailer Colin , Robinson Bruce H.
Published: July 2002

A theory of saturation recovery EPR has been developed to explore the very slow motional regime using the two-jump model. The EPR signal is predicted to be a biexponential curve for this motional model. From the two exponential decay constants λ1 and λ2 the exchange rate constant k can be calculated by the simple formula: k= 1/2 (λ2−λ1). Experimental results obtained from slowly tumbling 15N-TEMPOL in sec-butylbenzene have been fitted to the two-jump model. Even though this is a crude attempt, good agreement has been observed between the two-jump rate constant (k=0.043 μs−1) and the isotropic Brownian diffusion constant calculated from the hydrodynamic Debye expression (D=0.051 μs−1).
The direct observation of hindered rotation of a chemisorbed molecule: PF3 on Ni(111)
Authors: Alvey Mark D. , Yates John T. , Uram Kevin J.
Published: July 2002

By using the bond direction imaging capabilities of the electron stimulated desorption ion angular distribution (ESDIAD) technique, we have observed a thermally induced azimuthal disorder effect due to the thermal population of unbound hindered rotor states in chemisorbed PF3 on Ni(111). The six beam F+ ESDIAD patterns observed for PF3 on Ni(111) are interpreted as evidence for a weak barrier that hinders the rotation of isolated PF3 molecules on the Ni(111) surface. At a coverage of ∼0.04 PF3/Ni, a barrier to rotation of ∼80±20 cm−1 is estimated from the observed temperature dependence of the F+ ESDIAD patterns using a two-dimensional hindered rotor model. The PF3 coverage dependence of the thermally induced azimuthal disorder effect indicates that intermolecular forces are responsible for an increase in the hindering potential at high PF3 coverages.
The rotational hindrance potential of NH3 groups in Ni(NH3)6I2
Authors: Blank Herma , Kearley Gordon J.
Published: July 2002

The INS librational spectra of Ni(NH3)6I2 and Ni(ND3)6I2 are shown to be consistent with the motions of a single-type ammine rotor in a hindrance potential of the form cos(3φ). A barrier height of 18.6 meV is derived. The three peaks which arise in the spectrum of the tunnel-split ground state are attributed to ammine:ammine interactions and do not simply reflect the local symmetry at the nickel atom. A qualitative study of the differing behavior of these three tunneling peaks on changes in temperature, partial deuteration, and pressure shows that the NH3:NH3 coupling is sensitive to the rotational states of neighboring groups and changes to the order parameter as the II–I phase transition is approached. Direct interaction of the NH3 groups with the anion seems to be very slight.
Phase transitions of lipid bilayers. I. Density of states calculation
Authors: Tevlin Patrick , Jones Francis P. , Trainor L. E. H.
Published: July 2002

We consider the problem of modeling the thermodynamic behavior of a lipid bilayer using statistical mechanics. In this paper, we present Monte Carlo calculations of the single chain density of states appropriate to the mean field model of Pink et al., under a variety of assumptions on the time scales of various lipid motions. We find that Pink et al.’s density of states agrees qualitatively with our calculation. Our results also provide justification for assumptions in the density of states calculation of Jacobs et al.
Polymerization of 5,6-indolequinone: A view into the band structure of melanins
Authors: Galvão D. S. , Caldas M. J.
Published: July 2002

We present for the first time a study of finite and infinite polymers of 5,6-indolequinone. We show that the band structure of the infinite polymer presents semiconductor characteristics, and that the intrinsic paramagnetism of eumelanin can be modeled through electron trapping at deep ‘‘end-effect’’ defects.
Thermal roughening on stepped tungsten surfaces. I. The zone (011)–(112)
Authors: Gong Y. M. , Gomer R.
Published: July 2002

The surface self-diffusion behavior of tungsten along the zone (011)–(112) was measured on the orientations corresponding to (011), (257), (123), (235), and (112) directions by the field emission current fluctuation method. These regions correspond to steps and terraces of (011) orientation, with terrace widths shrinking as one goes from (011) to (112), where the ‘‘width’’ is only one atomic spacing. On (011) no signal was seen. On (112) a single regime corresponding to two-dimensional diffusion was seen, as indicated by the t−1 dependence of the correlation function at long time. On the intermediate regions two-dimensional diffusion attributed to W atom diffusion on the terraces, and one–dimensional diffusion identified by t−1/2 behavior at long times was seen. This is attributed to kink motion along the steps. For two-dimensional diffusion E=16 kcal, D0≂10−5 cm2 s−1 with some variation in D0 depending on orientation. For one-dimensional diffusion E=13 kcal, D0≂10−11 cm2 s−1 with some variation in D0 with orientation. The temperature dependence of the mean square fluctuations is used to estimate an enthalpy of formation of single atoms on terraces of ∼7 kcal, and of the diffusing kink entities of ∼19 kcal/mol.At 875 K D, for one-dimensional diffusion decreases sharply, reaching a minimum at 925 K, and then increasing again. For T≥950 K this diffusion becomes two dimensional. The two-dimensional diffusion increases normally with T to 890 K, then decreases sharply. Above 1000 K only a single two-dimensional diffusion regime can be observed. These observations are interpreted as corresponding to increasing step disorder, which initially leads to a decrease in kink diffusion, then global disorder which makes this diffusion two dimensional. Concomitantly single atom diffusion on terraces decreases and eventually disappears. Thus disorder occurs at first gradually, and between 950 and 1000 K becomes complete. A discussion of the effect of free atom creation and annihilation, as well as, of temporary adsorption at steps is given. Some prediffusive fluctuation results from 80–300 K are also presented.
Helium emission spectra from doped samples of solid hydrogen and deuterium
Authors: Brooks R. L. , Hunt J. L.
Published: July 2002

Using proton-beam irradiation at 15 MeV, the emission spectra from 3He and 4He doped samples of solid hydrogen and deuterium have been observed from 350–750 nm at 4.2 K. Such samples simulate the conditions of solid tritium or tritiated hydrogens after about six days of helium accretion. The spectra are very similar to pure helium gas spectra acquired at 4.2 K and closer still to spectra acquired using helium gas in the upper portion of a sample cell partially filled with solid hydrogen. The helium collects as macroscopically large bubbles whose pressure has been determined. The pure 4He gas spectrum at 4.2 K contains a band near 460 nm previously assigned to an unspecified excimer–dimer radiative transition. The pressure and isotope dependence of this band is presented which lends support to that interpretation. A mechanism is proposed for the transition.
A comparison of rotational energy accommodation in catalytically produced OD and OH radicals desorbing from a smooth Pt(111) single crystal
Authors: Hsu David S. Y. , Lin M. C.
Published: July 2002

Rotational energy distributions of OD and OH radical reaction products desorbing from a smooth Pt(111) single crystal surface have been measured under closely similar experimental conditions by using the laser-induced fluorescence technique in conjunction with an UHV apparatus. Over the temperature ranges studied, nearly full rotational energy accommodation was observed for OD with a rotational to surface temperature ratio, Tr/Ts =0.96±0.04, and a somewhat lower ratio of 0.86±0.05 was obtained for OH. For both OD and OH the spin–orbit temperatures were the same as the rotational temperatures and no preference for any lambda-doublet state was observed.
Theoretical study of the force fields of the three lowest singlet electronic states of linear polyenes
Authors: Zerbetto Francesco , Zgierski Marek Z. , Negri Fabrizia , Orlandi Giorgio
Published: July 2002

The potential energy surfaces of all trans hexatriene and octatetraene are investigated within the harmonic approximation in the diabatic and adiabatic representations for the 1A−g, 2A−g, and 1B+u electronic states by an extended Pople–Pariser–Parr (PPP/CI) model. The effect of excitation and of vibronic coupling on the molecular force fields of the three states is examined. While electronic excitation affects only diagonal force constants of local oscillators, vibronic coupling changes drastically the couplings between local oscillators. The calculations reproduce well the observed increase of the frequency of the in-phase ag C=C stretch upon excitation to the 2A−g state.
High resolution laser spectroscopy of NO: The A, v=1 state and a series of n
f, v=1 Rydberg states
Authors: Biernacki D. Therese , Colson Steven D. , Eyler E. E.
Published: July 2002

A high resolution pulse-amplified cw laser with a bandwidth of 0.002 cm−1 has been used to measure transition energies from the ground state to the A 2Σ+(3sσ), v=1 state to an accuracy of about 0.01 cm−1. Transitions to the 7f, 12f, and 15f, v=1 states from the A state have been measured to an accuracy better than 0.02 cm−1 using optical double resonance. The long-range interaction model accurately describes the nf term energies. Improved values for the ionization potential of NO and for the isotropic polarizability and rotational constant of the NO+ ion core have been obtained from the analysis of these states. The lifetimes of the 7f, 12f, and 15f, v=1 states have been determined by measuring their natural linewidths.
Dynamic elements of chaos in the Willamowski–Rössler network
Authors: Aguda Baltazar D. , Clarke Bruce L.
Published: July 2002

Two dynamic elements of the Willamowski–Rössler network are identified: one of which is a Lotka–Volterra oscillator involving two autocatalytic species X and Y, while the other is a switch between X and a third autocatalytic species Z. These two dynamic elements are coupled via X. Nonperiodic oscillations arise only if X autocatalyzes faster than Z. The chaotic nature of the oscillations is confirmed using the Shil’nikov theorem which requires the existence of a homoclinic orbit doubly asymptotic to a steady state of the saddle-focus type. Under chaotic conditions, two steady states coexist inside the positive orthant of concentration space and both satisfy the conditions of the Shil’nikov theorem. Chaos is further shown by the existence of several unstable period-3 fixed points of first-return Poincaré maps. A chaotic attractor is found and its changing structure under various sets of parameters is established.
Intermultiplet transfers of excited sodium atoms induced by nitrogen molecules
Authors: Mestdagh J. M. , Paillard D. , Berlande J. , Cuvellier J. , de Pujo P.
Published: July 2002

The predictions of a multiple curve crossing model (MCC) were compared to experimental observations of various intermultiplet transfers in thermal energy Na/N2 collisions. This includes comparisons to the energy dependence and the absolute value of the Na(4D→5S) cross section that was measured in the experimental section of the present work using a crossed beam apparatus. This also includes comparisons with beam data available in the literature. These last experimental results are not always directly comparable to the calculated cross sections. Deconvolution or simulation procedures are then needed. The general agreement between the MCC calculations and the experimental results is good. In many cases it is much better than a factor 2. The cases or disagreement were discussed carefully, and each of them can be attributable to uncertainties in the experiment or in the procedures of deconvolutions and simulations.
Vibrational energy transfer in solutions: From diffusive to impulsive binary collisions
Authors: Granek Rony , Nitzan Abraham , Weitz Eric
Published: July 2002

The effect of diffusion on energy transfer from excited donor to acceptor molecules in liquid solutions is studied with particular attention focused on vibrational energy transfer between solute molecules in dilute solutions. Such processes are often discussed in the independent binary collision (IBC) framework and diffusion effects are assumed to be negligible. We introduce the concept of diffusive collisions (encounters between acceptor and donor molecule within an effective energy transfer range) and investigate the conditions under which the cross section for the energy transfer process may be affected by the cross section for the diffusive collision as opposed to the more common fast diffusion limit where the energy transfer is dominated by direct binary collisions. We conclude that while in most common situations vibrational energy transfer is indeed dominated by binary collision events, pronounced diffusion effects should exist at moderately high pressures. Explicit estimates are provided for the HCl/Xe system.
Theoretical study of the NO γ system
Authors: Langhoff Stephen R. , Bauschlicher Charles W. , Partridge Harry
Published: July 2002

The potential curves for the X 2Π and A 2Σ+ states of NO have been determined using large Gaussian basis sets and accounting for electron correlation with the MCPF and CASSCF/multireference CI methods. The A 2Σ–X2Π electronic transition moment (γ system) is found to increase monotonically with decreasing internuclear distance. It differs significantly from the functional form deduced empirically from either branching ratio or lifetime measurements. The increase in the moment as r decreases is correlated with the increasing degree of diffuse character in the X 2Π state. Inclusion of 2s correlation is found to have a relatively small effect on the functional form of the moment once the valence correlation is accurately determined. However, the NO γ system transition moment is found to be sensitive to the choice of the molecular orbital basis. The X 2Π and A 2Σ+ dipole moment functions are studied to provide an additional assessment of the quality of the wave functions. The X 2Π vibrationally averaged dipole moments and the (1–0) and (2–0) vibration–rotation band intensities are in excellent agreement with the experimental values.
Ultraviolet photodissociation dynamics of H2S and D2S
Authors: Weiner Brad R. , Levene Harold B. , Valentini James J. , Baronavski A. P.
Published: July 2002

Nascent SH(X 2Πi, v″=0,1) and SD(X 2Πi, v″=0,1) rotational state population distributions, spin–orbit state population ratios, and Λ-doublet state population ratios have been measured following the UV excimer laser photodissociation of H2S (λ=193, 222, and 248 nm) and D2S (λ=193 and 222 nm), respectively. Nascent SH(X 2Πi, v″=0) rotational state distributions following 193 nm photodissociation of cold H2S in a free jet expansion vs 300 K H2S in a flowing gas cell were essentially the same, indicating that photofragment angular momentum must be originating predominantly in the dissociation event, and not from rotational energy contained in the parent triatom. Laser excitation spectra of SH(X 2Πi, v″=1) and SD(X 2Πi, v″=1) have been recorded for the first time. Rotational state distributions for SH(X 2Πi, v″) and SD(X 2Πi, v″) are independent of v″. Λ-doublet population ratios of the nascent photofragments are essentially unity for all the cases measured. The nascent rotational state distributions are consistent with an impact parameter model for the dissociating triatomic molecule.
An electron energy loss study of the surface formate species chemisorbed on Ni(110): Dipole, impact, and resonance scattering for adsorbate covered surfaces
Authors: Jones T. S. , Ashton M. R. , Richardson N. V.
Published: July 2002

A comprehensive energy and angular dependent high resolution electron energy loss study of the surface formate species (HCOO), adsorbed on Ni(110) at room temperature, has been carried out. By varying both the primary electron beam energy Ei and the scattering geometry, dipole, impact, and resonance scattering processes have been identified and exploited, to gain information regarding the different vibrational excitations of the HCOO/Ni(110) system. Application of the appropriate dipole and impact scattering selection rules, yields information concerning the HCOO orientation at the surface. It is found that the HCOO bonds to the surface, via the two oxygen atoms, with the C2 axis normal to the surface and with the plane of the HCOO aligned along the close-packed 〈110〉 rows. A dipole active Ni phonon, at 29 meV, observed in specular scattering geometry, is assigned to an S̄ phonon of the clean surface Brillouin zone and clearly indicates that the HCOO is adsorbed with the C–H bond projecting onto a short-bridge site, with the two oxygen atoms occupying effectively on-top sites. Finally, enhancement of the symmetric O–C–O stretch is attributed to a resonant scattering process, centered at an incident electron beam energy, Ei=14 eV, resulting in the formation of a temporary negative ion. On the basis of the energy and angular dependence of the enhancement, the resonant state is related to the so-called σ-shape resonances recently observed in near-edge x-ray absorption spectroscopy studies of HCOO adsorbed on copper surfaces. Overtone and combination bands, some of which are also enhanced by the resonant excitation, are also assigned.
Hybrid mechanics. II
Authors: Huber Daniel , Ling Song , Imre Dan G. , Heller Eric J.
Published: July 2002

We recently published a new method for the calculation of the time evolution of a wave function. We used an accurate approximate method to calculate the time propagator for a finite time Δt. Numerical calculations showed that this scheme works quite accurately, but that it is not more efficient than conventional methods. In this paper we propose to use a very fast and simple, but less accurate semiclassical method for the calculation of the time propagator. The approximation consists in the replacement of the Hamiltonian by a quadratic approximation around the center of the evolving wave packet called thawed Gaussian dynamics. We show by numerical examples in one and two dimensions that, despite this crude approximation, we achieve nearly the same accuracy as in the foregoing paper, but with an efficiency that is typically more than an order of magnitude better. We further show that the method is able to describe tunneling and long time dynamics (e.g., 1000 vibrational periods).
An electron spin resonance study of the structure of CCl+4 radical cation in carbon tetrachloride γ-irradiated at low temperatures by powder and single crystal analyses
Authors: Muto Hachizo , Nunome Keichi , Iwasaki Machio
Published: July 2002

The CCl+4 radical cation produced in CCl4 by γ irradiation at low temperatures was studied by electron spin resonance (ESR) spectroscopy to clarify the electronic structure. By combining an analysis of the angular dependence of ESR spectra in a single crystal plane with a spectral simulation of the powder pattern including the isotropic combinations of 35Cl and 37Cl atoms, it was found that two chlorine atoms are concerned in the radical, having different hyperfine coupling tensors of A(35Cl1)=11.2, 0.5, 1.3 mT and A(35Cl2)=6.2, 0.8, 1.8 mT. The g tensor is approximately axially symmetric and shows a large positive g⊥ shift (g=1.999, 2.10, 2.116), different from the rhombic g tensor of σ* dimer cations of alkyl halides and freons (gmax=2.04). The directions of the maximum hyperfine coupling of the two chlorine atoms Cl1 and Cl2 are close to each other and close to the gmin direction, though having a small deviation from the gmin direction by about 3°–10°. From a consideration on the g anisotropy combined with the optical absorption spectrum, the radical was suggested to be a Cl atom-like species, in which one of the C–Cl bonds in the parent CCl+4 is released and the atom-like chlorine nuclei formed makes a three electron bond [(σCl⋅⋅⋅Cl)2 (σ*Cl⋅⋅⋅Cl)1] with a Cl atom in the released CCl+3 group. A discussion is given for the difference in the formation of the cationic species in CCl4 and the σ* dimer radical cation in the other alkyl halides.
Gaussian approximation for Rouse chains with hydrodynamic interaction
Authors: Öttinger Hans Christian
Published: July 2002

A new approximate method for treating hydrodynamic interactions in a bead–spring model for dilute polymer solutions is developed. This method, which is based on the assumption that the configurational distribution function is Gaussian, accounts for fluctuations in the hydrodynamic interaction. In this Gaussian approximation, we construct a rheological equation of state and a codeformational memory-integral expansion for chains of arbitrary length. As a straightforward application of these general results, we discuss small-amplitude oscillatory and steady shear flows. For dumbbells, the rheological equation of state in the Gaussian approximation is obtained by a slight modification of the corresponding equation for the consistent averaging method.
A method to constrain vibrational energy in quasiclassical trajectory calculations
Authors: Bowman Joel M. , Gazdy Bela , Sun Qiyan
Published: July 2002

In this paper, we present a general method to constrain the classical energy of a vibrational mode to be greater than a specifled amount. In particular, zero-point energy constraints can be applied with this method to (zero-order) vibrational modes of a polyatomic system or complex. A demonstration of the method is made for a model two-mode Henon–Heiles Hamiltonian.
Line-shape analysis of extra resonance signal in coherent Stokes Raman scattering of acridine in the T1 state
Authors: Kamisuki Toshio , Suzuki Kazuhiro , Adachi Yukio , Maeda Shiro
Published: July 2002

The coherent anti-Stokes Raman scattering (CARS) and coherent Stokes Raman scattering (CSRS) line shapes near the 1350 cm−1 region of acridine in the T1 state were recorded in the various resonance (ω1 frequency) conditions over the Tn←T1 absorption band in the n-heptane solution at room temperature. The ω1 frequency dependencies of CARS and CSRS line shapes of the T1 signal at 1368 cm−1 were simulated well on the basis of the theoretical χ(3) expression. On the other hand, the ω1 frequency dependence of the line shape of the extra resonance (ER) signal observed at 1335 cm−1 in CSRS, showing no obvious change of the line shape by changing the ω1 frequencies, could not be simulated at all on the basis of the similar expression. The discrepancy of the ER line-shape simulation was discussed.