bluuebunny/crossref_metadata_2025 huggingface dataset:
Tunable microwave characteristics of a superconducting planar transmission line by using a nonlinear dielectric thin film
Authors: Wu Chien-Jang
Published: July 2002

A field solution for a planar type-II superconducting transmission line made of two high-temperature superconducting films and a nonlinear dielectric thin film is derived. The combined effects of the nonlinear dielectric permittivity as well as of vortices inside the superconductors on the attenuation constant and phase velocity are numerically investigated. Variation in temperature-dependent phase velocity due to the dielectric nonlinearity is lowered pronouncedly in the presence of vortices. In addition, variation in phase velocity versus dc electric field is also reduced in the case of more vortices. The role played by the nonlinear dielectric as well as the vortices in such a tunable microwave component are thus demonstrated.
Electromigration-driven shape evolution of two-dimensional voids
Authors: Schimschak M. , Krug J.
Published: July 2002

We present a detailed numerical study of the electromigration-induced shape evolution of quasi-two-dimensional (cylindrical) voids in metallic thin films. The problem is treated within a continuum formulation which takes into account mass transport along surfaces, current crowding, and crystal anisotropy in the surface mobility. Finite strips with periodic boundary conditions in the current direction are treated as well as voids in infinite or semi-infinite films. For the strip geometry, it is shown that the linear instability of the strip edge can induce the release of voids into the interior of the film, while edge voids develop into fatal slits only in the presence of moderate (not too strong) crystalline anisotropy. Distorted voids in an infinite film typically disintegrate, but the breakup scenario is qualitatively different in isotropic and anisotropic media. A rigid boundary attracts voids and may also induce void breakup.
Nonlinear behavior of magnetostrictive particle actuated composite materials
Authors: Armstrong William D.
Published: July 2002

A new theory is presented for the nonlinear multiaxial magnetoelastic behavior of magnetostrictive particle actuated composite materials. The analysis assumes a uniform external magnetic field is operating on a large number of well-distributed, crystallographically and shape parallel ellipsoidal magnetostrictive particles encased in an elastic, nonmagnetic composite matrix. The aspect ratio of the particulates may vary between 1 and infinity and the volume fraction of the particulates may vary between zero and one. Comparisons between experimental and model magnetostriction results show that the model is able to provide a quantitatively correct dependence on particulate volume fraction and longitudinal stress and quantitatively accurate magnetostriction curves for both homogenous Terfenol-D rod and magnetically ordered Terfenol-D particulate actuated epoxy matrix composites over experimental applied field ranges. Model calculations clearly indicate that the particle actuated composites developed less longitudinal strain than would be expected from the behavior of the homogeneous material.
Magnetic properties of iron and iron platinum alloys synthesized via microemulsion techniques
Authors: Carpenter E. E. , Sims J. A. , Wienmann J. A. , Zhou W. L. , O’Connor C. J.
Published: July 2002

In this article, metallic iron, and iron/platinum alloys nanoparticles have been synthesized via chemical assembly and magnetically characterized. Fabrication of iron and iron/platinum particles was achieved by reducing 0.1 M aqueous metal salts confined in the polar portions of inverse micelles of cetyltrimethylammonium bromide with borohydride. The dc susceptibility of a sample of 8 nm iron nanoparticles exhibits a blocking temperature of 54 K and coercivity of 200 G at 10 K. The presence of the gold coatings prevented oxidation and allowed the samples to be manipulated without additional precautions to prevent oxidation. Two iron/platinum alloys have been synthesized and verified by x-ray powder diffraction and transmission electron microscopy. Magnetic characterization is performed using superconducting quantum interference device magnetometry.
Observation of magnetization reversal processes in Co–Cr and Co–Cr–Ta ultrathin films under the canted magnetic field using anomalous Hall effect
Authors: Nakagawa Shigeki , Sato Atsushi , Sasaki Ichiro , Naoe Masahiko
Published: July 2002

Normalized magnetization vector Me of ultrathin Co–Cr–Ta films under the canted magnetic field were derived from the results of anomalous Hall voltage and the magnetization measured by a vibrating sample magnetometer. The film deposited at high substrate temperature revealed a relatively large amount of an in-plane component because of the faint c-axis orientation in the perpendicular direction of the Co–Cr–Ta crystallites. The in-plane component at the remanent state seems to be larger for the film with worse c-axis orientation. The Pt underlayer was normalized to promote c-axis orientation in Co–Cr–Ta films deposited on it at a high substrate temperature above 200 °C. A 30 nm-thick Co77Cr20Ta3 film deposited on a 20-nm-thick Pt underlayer exhibited large perpendicular coercivity. The locus of normalized magnetization of the Co77Cr20Ta3(30 nm)/Pt(20 nm) implied that the film revealed a large perpendicular magnetization component even though the magnetic field was applied in the direction out of the normal line.
Magnetoresistance in electron doped Cr1−xMnxO2 double exchange ferromagnet
Authors: Martínez B. , Fontcuberta J. , Martínez-Lope M. J. , Alonso J. A.
Published: July 2002

Electron doping in the half-metallic ferromagnet CrO2 oxide has been reached via partial Cr substitution by Mn. Synthesis of ceramic samples is accomplished under high temperature and high oxygen pressure. It is found that electron doping reduces the magnetization and the Curie temperature of the samples. Simultaneously, the low temperature and low field magnetoresistance of the samples increase. The results are discussed on the light of the current models for the electronic structure of this oxide and the possible role of segregated insulating impurity phases.
Precision cryogenic magnetostrictive actuator using a persistent high TC magnet
Authors: Teter J. P. , Horner Garnett C. , Bromberg Leslie
Published: July 2002

Cryogenic magnetostrictive materials, such as rare earth zinc crystals, offer high strains and high forces with minimally applied magnetic fields, making the material ideally suited for deformable optics applications. For cryogenic temperature applications, such as Next Generation Space Telescope, the use of superconducting magnets offer the possibility of a persistent mode of operation, i.e., the magnetostrictive material will maintain a strain field without power. High temperature superconductors (HTS) are attractive options if the temperature of operation is higher than 10° Kelvin (K) and below 77 K. However, HTS wires have constraints that limit the minimum radius of winding, and even if good wires can be produced, the technology for joining superconducting wires does not exist. In this article, the design and capabilities of a rare earth zinc magnetostrictive actuator using bulk HTS is described. Bulk superconductors can be fabricated in the sizes required with excellent superconducting properties. Equivalent permanent magnets, made with this inexpensive material, are persistent, do not require a persistent switch as in HTS wires, and can be made very small. These devices are charged using a technique which is similar to the one used for charging permanent magnets, e.g., by driving them into saturation. A small normal conducting coil can be used for charging or discharging. Very fast charging and discharging of HTS tubes, as short as 100 μs, has been demonstrated. Because of the magnetic field capability of the superconductor material, a very small amount of superconducting magnet material is needed to actuate the rare earth zinc. In this article, several designs of actuators using YBCO and BSCCO 2212 superconducting materials are presented. Designs that include magnetic shielding to prevent interaction between adjacent actuators will also be described. Preliminary experimental results and comparison with theory for BSSCO 2212 with a magnetostrictive element will be discussed.
Magnetic viscosity effects on the pinned layer loop of spin-valve materials
Authors: Goodman A. M. , Laidler H. , O’Grady K. , Owen N. W. , Petford-Long A. K.
Published: July 2002

In this work, we report on measurements of magnetization with time [M(t)] around the pinned layer loop in spin-valve materials. These time-dependent effects are manifest via changes in M(t) in constant field (H) and via variations in the apparent coercivity with the sweep-rate of the applied field. The changes in the apparent coercivity on the pinned layer loop differ for the magnetizing and demagnetizing branches as does the form of M(t) data.
Magnetic and optical studies of magnetic colloidal particles in water and oleic acid
Authors: Wu K. T. , Yao Y. D. , Huang H. K.
Published: July 2002

The macro-size magnetic colloidal particles in both distilled water and oleic acid were prepared by using Fe3O4 ferrofluids (SMG018), the sodium dodecyl sulfate (SDS), and distilled water or oleic acid. The optical transmission of these ferrofluid emulsions has been investigated as functions of concentration of SDS between 0.64 and 3.73 wt %, incident optical wavelengths between 450 and 750 nm, and applied magnetic fields up to 141 Oe. The optical transmission shows maximum with concentration of SDS near 3.13 and 1.90 wt % for samples in distilled water and oleic acid, respectively. In general, under an applied magnetic field, the size of the magnetic colloidal particles for samples in oleic acid is smaller than that of samples in distilled water; however, the concentration of the magnetic colloidal particles is the opposite. This can be explained due to the different aggregation ability of the magnetic colloidal particles in both distilled water and oleic acid. The optical transmission of the samples is observed to be reversed proportional to the area covered by the magnetic colloidal particles.
Thermally stimulated processes related to photochromism of scandium doped sillenites
Authors: Załȩski M.
Published: July 2002

The low temperature photochromism of the scandium doped sillenites was investigated. The time dependence of the light induced absorption was measured for different conditions of the stimulation process. The optical coloring spectrum and the optical bleaching spectrum have been established on the basis of the obtained kinetics. The distinction between short time illumination (<20 s) and long time illumination (>1000 s) in the coloring process has been noticed. The thermal bleaching curves obtained for the different conditions of illumination provided information about energy of the shallow trap levels responsible for the thermal stability of the photochromic effect. It has been shown that there are five energy levels involved in the thermal bleaching processes but their activity is strongly related to the conditions of illumination. Some arguments are presented that the investigation of thermal bleaching could be used as a good tool for the shallow trap spectroscopy as it is in the conventional thermoluminescence and measurements of thermally stimulated currents.
Comparative study of divacancy and E-center electronic levels in Si and strained Si0.87Ge0.13 layers
Authors: Monakhov E. V. , Kuznetsov A. Yu. , Svensson B. G.
Published: July 2002

The effect of strain and composition on deep electronic levels in the energy band gap of epitaxial Si0.87Ge0.13 layers grown by chemical vapor deposition has been investigated by deep level transient spectroscopy. Two major levels attributed to a vacancy–phosphorus (VP) pair and a singly negative divacancy [V2(−/0)] have been observed. It has been found that VP and V2(−/0) demonstrate opposite behavior on the Ge composition: the activation enthalpy of VP increases with respect to pure Si while that of V2(−/0) decreases. The apparent intensity of the VP level has been observed to decrease in the Si0.87Ge0.13 layers with respect to that in Si while the formation of V2 is enhanced during annealing above ∼100 °C.
Current perpendicular magnetoresistances of NiFeCo and NiFe “Permalloys”
Authors: Vila L. , Park W. , Caballero J. A. , Bozec D. , Loloee R. , Pratt W. P. , Bass J.
Published: July 2002

Measurements are presented of the 4.2 K current perpendicular specific resistances (area times resistance) and magnetoresistances of a series of Ni66Fe13Co21=Py′-based symmetric exchange-biased spin valves and Py′–Co hybrid spin valves. The behaviors of both kinds of Py′-based spin valves are similar to those for comparable Ni84Fe16=Py-based spin valves. The low temperature giant magnetoresistive parameters of Py′ must, thus, be similar to those for Py, suggesting that Py′ should be a viable alternative to Py for technological uses.
Control of ion energy distribution at substrates during plasma processing
Authors: Wang S.-B. , Wendt A. E.
Published: July 2002

Control of ion energy distribution functions (IEDF) at the substrate during plasma processing is achieved using a specially tailored voltage waveform for substrate bias, consisting of a short voltage spike in combination with a slow ramp. A much narrower IEDF is possible compared to the conventional approach of applying a sinusoidal waveform to the substrate electrode. Measurements in a helicon plasma combined with a time-dependent spherical-shell plasma fluid model demonstrate the benefits of this method in producing a narrow IEDF of precisely controllable energy, independent of ion mass.
Spin density of radicals by finite field many-body methods
Authors: Sekino Hideo , Bartlett Rodney J.
Published: July 2002

The spin densities of several small radicals CH3, NH2,CH2CH, BeH, and H2CO+ are calculated by a finite field coupled-cluster method using a spin density operator as a finite perturbation on the systems. The calculated hyperfine coupling constants of the π radicals are in good agreement with experiment at a low level of correlation. The CH2CH radical required a higher level of correlation to obtain the experimental value. The calculations are also performed for the H2CO+ radical where theory has failed to predict the experimental splitting constants. The spin density on hydrogen calculated in the present study is lower than the result obtained by the low temperature gas ESR techniques, although the carbon spin density is well reproduced. An analysis of possible corrections for the H spin density is presented.
Direct observation of the fine structure transitions in the Ne+ and Ar+ ions with diode lasers
Authors: Yamada Chikashi , Kanamori Hideto , Hirota Eizi
Published: July 2002

The 2P1/2–2P3/2 fine structure transitions in the ground (np5) state of the neon (n=2) and argon (n=3) atomic ions have been observed in absorption in the positive column of a liquid–nitrogen cooled discharge cell, by employing tunable infrared diode lasers as sources. The transition frequencies were measured to be 780.4240±0.0011 and 1431.5831±0.0007 cm−1 for Ne+ and Ar+, respectively. A few transitions have also been observed for the neutral Ne and Ar atoms.
Theoretical determination of the indirect nuclear spin–spin coupling tensors, nuclear screening tensors, and magnetic susceptibilities of multiply bonded systems via the equations-of-motion method
Authors: Galasso V. , Fronzoni G.
Published: July 2002

In this paper we document the possible performances of the equations-of-motion method for predicting second-order magnetic properties (indirect nuclear spin–spin coupling tensors, nuclear screening tensors, and magnetic susceptibilities). Nonempirical calculations for a series of molecules containing conjugated or cumulated multiple bonds and most of them suffering from UHF triplet instability are reported. In spite of the limitation of the 631G** basis set used, the results fit reasonably well with the main features of the experimental data in all cases but some geminal J’s and the σ’s in diacetylene. Inclusion of the (2p-2h) interactions brings the theoretical results to a closer agreement with observation. Effects of electron correlation at (1p-1h) and (1p-1h) +(2p-2h) levels of approximation are analyzed by comparison with corresponding results obtained by standard CHF procedures. They are found to be of remarkable importance for the paramagnetic component of σ and χ and for the Fermi-contact contribution to the J’s, especially of geminal-type, but not for the noncontact terms of J.
Moment analysis in depolarized light scattering: Determination of a single-parameter empirical pair polarizability anisotropy for Ne, Ar, Kr, Xe, and CH4
Authors: Meinander N. , Tabisz G. C. , Zoppi M.
Published: July 2002

A method, based on classical physics, to utilize the first four even moments of the depolarized collision induced light scattering spectrum to derive an empirical model for the pair polarizability anisotropy of interacting molecules, with only one adjustable parameter, is described and applied to the spectra of Ne, Ar, Kr, Xe, and CH4. Good agreement with ab initio results in the literature is obtained and profiles calculated with these models are in excellent agreement with experiment.
Prominent, and restricted, vibrational state mixing in the fluorescence excitation spectrum of benzophenone
Authors: Holtzclaw Karl W. , Pratt David W.
Published: July 2002

We report the first successful observation of the fluorescence excitation spectrum of benzophenone in the collision-free environment of a supersonic jet. A comparison of this spectrum with an earlier prediction of Heller et al. [J. Chem. Phys. 73, 4720 (1980)], together with other experimental and theoretical data, reveals the existence of prominent vibrational state mixing of the totally (A) and nontotally (B) symmetric ring torsional modes in the S1 state, via a cubic anharmonicity term of the form λAB2. Fully 64 of the 66 vibrational degrees of freedom of this large molecule do not participate in this mixing process, suggesting that the phase space accessible to benzophenone following optical excitation to its S1 state is extremely restricted. The implications of these findings for intramolecular vibrational relaxation in the electronically excited states of this and other large molecules are discussed.
NMR spectra of dilute spins under slow sample-spinning and homonuclear decoupling
Authors: Miura H. , Terao T. , Saika A.
Published: July 2002

Dilute-spin spectra under decoupling between abundant spins and slow sample spinning at general angles are discussed, and experimentally observed with an example of calcium formate. Spectra obtained at off-magic angles break up into a train of characteristic patterns different in shape from each other. The center pattern was found to be especially sensitive to the mutual orientation between the chemical shift and dipolar coupling tensors. Each sideband observed at the magic angle shows splitting due to the 13C–1H indirect coupling. The absolute sign of the coupling constant is determined to be positive from the J-split sideband pattern.
Consistently averaged hydrodynamic interaction for dumbbell models in elongational flow
Authors: Biller Peter , Öttinger Hans Christian , Petruccione Francesco
Published: July 2002

We apply the recently proposed consistent averaging approximation for the hydrodynamic interaction to elongational flow. This flow situation can be treated to a great extent analytically for Rouse and FENE-P dumbbells. In both cases expansions for the elongational viscosity are presented for low and high elongational rates.
Kinetic study of the reaction CH(X 2Π)+H2⇄CH2(X 3B1)+H in the temperature range 372 to 675 K
Authors: Zabarnick S. , Fleming J. W. , Lin M. C.
Published: July 2002

The reaction CH(X 2Π)+H2⇄CH2(X 3B1)+H was studied over the temperature range 372 to 675 K. Laser-induced fluorescence detection of CH radicals allowed direct determination of absolute rate constants for the forward reaction k1. The data are well fit by the Arrhenius expression k1=(2.38±0.31)×10−10 exp[−(1760±60)/T] cm3/s over the temperature range studied. A transition state theory (RRKM) calculation yields the following form for k1, k1=(5.5±1.5)×10−16 T1.79±0.04 exp[−(840±30)/T] cm3/s for the temperature range 300 to 2500 K, thus allowing cautious extrapolation to combustion temperatures. The rate constants for the reverse reaction are evaluated by utilization of the equilibrium and the forward rate constants. The data for k−1 are well fit by k−1=(4.7±0.6) ×10−10 exp[−(370±60)/T] cm3/s over the temperature range 372 to 675 K. A transition state theory calculation yields the following form for k−1, k−1=(6.4±1.1) ×10−15 T1.54±0.02 exp[(430±20)/T] cm3/s for the temperature range 300 to 2500 K. The heat of formation of CH2 at 0 K was determined to be ΔHfo {CH2}=92.6±0.5 kcal/mol, assuming that the CH2+H radical recombination reaction has no activation energy.
High pressure isotropic bandwidths and frequency shifts of the C–H and C–O modes of liquid methanol
Authors: Zerda T. W. , Thomas H. D. , Bradley M. , Jonas J.
Published: July 2002

The Raman bands of the C–H ν3 and C–O ν8 stretching modes of liquid methanol have been measured at temperatures ranging from 273 to 363 K and pressures from 10 bar to 4 kbar. The effects of density and temperature on the isotropic linewidth, peak frequency of the isotropic band, ν0 (ISO), and the difference δν between anisotropic ν0(VH) and ν0(ISO) band frequencies are reported and discussed qualitatively in terms of available theoretical models. It appears that repulsive interactions are responsible for the observed C–H line changes, and the Schweizer–Chandler (SC) model is used to evaluate frequency shift and bandwidth of the ν3 C–H mode after the effect of Fermi resonance coupling to the 2ν4 overtone was removed. In particular, the anomalous temperature and density dependence of the Raman band of the C–O stretching mode is noted and compared to the relatively typical behavior observed for the Raman line shape of the C–H mode.
Phase space bottlenecks: A comparison of quantum and classical intramolecular dynamics for collinear OCS
Authors: Gibson Lester L. , Schatz George C. , Ratner Mark A. , Davis Michael J.
Published: July 2002

We compare quantum and classical mechanics for a collinear model of OCS at an energy (20 000 cm−1) where Davis [J. Chem. Phys. 83, 1016 (1985)] had previously found that phase space bottlenecks associated with golden mean tori inhibit classical flow between different chaotic regions in phase space. Accurate quantum eigenfunctions for this two mode system are found by diagonalizing a large basis of complex Gaussian functions, and these are then used to study the evolution of wave packets which have 20 000 cm−1 average energies. By examining phase space (Husimi) distributions associated with the wave functions, we conclude that these golden mean tori do indeed act as bottlenecks which constrain the wave packets to evolve within one (or a combination of) regions. The golden mean tori do not completely determine the boundaries between regions, however. Bottlenecks associated with resonance trapping and with separatrix formation are also involved. The analysis of the Husimi distributions also indicates that each exact eigenstate is nearly always associated with just one region, and because of this, superpositions of eigenstates that are localized within a region remain localized in that region at all times. This last result differs from the classical picture at this energy where flow across the bottlenecks occurs with a 2–4 ps lifetime. Since the classical phase space area through which flux must pass to cross the bottlenecks is small compared to ℏ for OCS, the observed difference between quantum and classical dynamics is not surprising. Examination of the time development of normal mode energies indicates little or no energy flow quantum mechanically for wave packet initial conditions. Classical trajectory bundles constructed from the wave packet phase space distributions also show little or no energy flow even though noticeable flow is observed for more localized bundles chosen from the turnstile associated with flow through the bottleneck.
On the relative stabilities of H- and D-bonded water dimers
Authors: Engdahl Anders , Nelander Bengt
Published: July 2002

The infrared spectra of water dimers formed from H2O, D2O, and HDO in krypton matrices have been recorded. Thermal equilibria between H- and D-bonded dimers have been studied. D bonding is preferred, and H-bonded dimers are approximately 60 cm−1 less stable than D-bonded dimers. The energy difference seems to be due to the higher value of the intermolecular out-of-plane H-bond shear vibration compared to the corresponding D-bond vibration.
Photodissociation processes in the CH molecule
Authors: van Dishoeck Ewine F.
Published: July 2002

The photodissociation processes in the CH molecule have been investigated using ab initio self-consistent-field with configuration-interaction (CI) methods. Potential energy curves of all states which dissociate into the lowest four atomic limits have been calculated, as well as those of several higher-lying states with Rydberg character. Transition dipole moments connecting the excited states with the lowest states have been obtained. Direct photodissociation of CH may occur by absorption into the continua of the B 2∑− and 2 2∑+ states, and cross sections for absorption from the X 2Π v″=0 state into these states are reported. Indirect photodissociation of CH may take place by absorption into bound states, which are subsequently dissociated through interactions with continuum states. The A 2Δ vibrational levels couple with the continuum of the X 2Π state through the nuclear rotational operator. The nuclear rotational coupling elements have been obtained from the CI wave functions, and predissociation rates are presented. The C 2∑+ v′=0 state is shown to be predissociated efficiently by spin-orbit coupling with the B 2∑− state. The 2, 3, and 4 2Π states of CH interact strongly through the radial nuclear kinetic energy operator. The nuclear radial coupling elements between these states have been computed by numerical differentiation of the CI wave functions. The coupled equations for the nuclear wave functions have been solved in a diabatic formulation. The calculated cross section for

absorption into the coupled states is similar to that found recently for absorption into the 2 2Π and 3 2Π states of the OH molecule: it consists of a series of resonances with asymmetric Beutler–Fano profiles superimposed on a strong continuous background. The 3(F)2∑+ state, as well as the higher-lying (Rydberg) states, may interact with the 2Π states through rotational coupling or with the 2 4∑− state through spin-orbit coupling. Due to uncertainties in the coupling elements, the efficiencies with which these states are dissociated are not well determined, but they are probably small for most states. The photodissociation rate of CH by the unattenuated interstellar radiation field has been computed. The total rate is 9.5×10−10 s−1. The 2 2∑+ and coupled 2Π channels are most effective in the photodissociation of interstellar CH.
High-pressure calorimetric study on the ice XI–Ih transition
Authors: Yamamuro Osamu , Oguni Masaharu , Matsuo Takasuke , Suga Hiroshi
Published: July 2002

A newly developed high-pressure calorimeter was used to measure the XI–Ih phase transition of ice doped with KOH (mole fraction 1.3×10−3) at two pressures: 0 and 158.9 MPa. The transition temperature was found to be (71.6±0.1) and (74.0±0.1) K at the respective pressures, resulting in its mean pressure dependence of (0.015±0.001) K MPa−1. With this dependence and the theoretical entropy of the transition for the complete transformation of the XI phase, 3.4 J K−1 mol−1, the application of the Clausius–Clapeyron’s equation yields (0.051±0.003) cm3 mol−1 for the volume change associated with the transition. From these results in conjunction with other data, negative volume expansivity, as observed in the proton disordered phase Ih at low temperatures, was also suggested for the proton ordered phase XI.
On the structure of the water trimer. A matrix isolation study
Authors: Engdahl Anders , Nelander Bengt
Published: July 2002

The infrared spectra of several isotopomers of the water trimer have been studied in argon and krypton matrices. The results show that the trimer is cyclic, with three equivalent water molecules.
Semiclassical treatment of nonadiabatic transitions: Multilevel curve crossing and nonadiabatic tunneling problems
Authors: Nakamura Hiroki
Published: July 2002

Nonadiabatic transition in a multilevel curve crossing system and the one accompanying quantum mechanical tunneling are investigated theoretically and numerically for the one-dimensional case. The first problem is analyzed using the semiclassical formulation based on the sophisticated two-state theory for nonadiabatic transition. This formulation is applied to three- and four-level model systems and is found to work surprisingly well even when the avoided crossings (or the transition zones) cannot be regarded to be well separated. The significance of the Stokes phase is noticed. As for the second problem, analysis is made not only for the simple tunneling but also for the elastic scattering accompanied by the nonadiabatic tunneling. A combination of the following two formulas is recommended for practical use: (1) the formula essentially based on the one proposed by Coveney et al., and (2) the formula of Ovchinnikova with additional Stokes phase and tunneling corrections.
IOS and ECS line coupling calculation for the CO–He system: Influence on the vibration–rotation band shapes
Authors: Boissoles J. , Boulet C. , Robert D. , Green S.
Published: July 2002

Line coupling coefficients resulting from rotational excitation of CO perturbed by He are computed within the infinite order sudden approximation (IOSA) and within the energy corrected sudden approximation (ECSA). The influence of this line coupling on the 1–0 CO–He vibration–rotation band shape is then computed for the case of weakly overlapping lines in the 292–78 K temperature range. The IOS and ECS results differ only at 78 K by a weak amount at high frequencies. Comparison with an additive superposition of lorentzian lines shows strong modifications in the troughs between the lines. These calculated modifications are in excellent quantitative agreement with recent experimental data for all the temperatures considered. The applicability of previous approaches to CO–He system, based on either the strong collision model or exponential energy gap law, is also discussed.
The effect of resonances on collisional energy transfer
Authors: Sumpter Bobby G. , Thompson Donald L. , Noid D. W.
Published: July 2002

The effect of resonances on the collinear inelastic scattering of CO2 with He, Ne, and Ar has been studied. The initial conditions for the CO2 molecule were chosen by using Poincaré surfaces of section to identify trajectories which lie on resonant tori. Near-resonant and nonresonant trajectories have also been examined. The dynamics of the CO2 molecule undergoes a dramatic change as a rare gas atom approaches. Resonances are created and destroyed and, in some cases, a transition from quasiperiodic to chaotic motion occurs. The energy transfer is enhanced for trajectories involving resonant or near-resonant CO2 states.
Rotational spectra and structures of small clusters: The Ar4–H/DF pentamers
Authors: Gutowsky H. S. , Chuang Carl , Klots T. D. , Emilsson Tryggvi , Ruoff R. S. , Krause Karl R.
Published: July 2002

The 40Ar4–HF and –DF clusters have been identified and characterized by their microwave rotational spectra using a Flygare–Balle FT spectrometer with a pulsed supersonic nozzle to generate and detect the clusters. The observed J=2→3 to 6→7 transitions have fine structure limited to K=0, ±3 and ±6, indicative of symmetric tops with a threefold axis of symmetry produced by I=0 nuclei. For Ar4–HF the rotational constants B0, DJ, and DJK are 623.4539(1) MHz, 1.062(1) kHz, and 0.611(31) kHz, respectively; and for Ar4–DF, 618.5846(1) MHz, 1.030(1) kHz, and 0.665(4) kHz. The results show that the clusters consist of the trigonal Ar3–H/DF tetramer reported earlier, with a fourth argon on the back side of the Ar3 group to form a tetrahedral or near tetrahedral Ar4. In both clusters the H/DF lies along the threefold axis of the Ar3 group, with the H/D end pointed at its face. If one assumes an Ar–Ar distance of 3.85 Å for both clusters, the Ar3 plane to HF c.m. distance for Ar4–HF with a tetrahedral Ar4 is 2.713 Å compared to 2.735 Å for Ar3–HF. The nuclear hyperfine structure of the rotational transitions shows that the H/DF experiences large amplitude bending vibrations with respect to the C3 symmetry axis. The average amplitude for HF (40.4°) is comparable with that reported for the smaller Arm–HF complexes (m=1, 2, 3). However, for DF the apparent 25.1 (1.6)° amplitude found is 10° less than that in the smaller complexes. The difference is attributed to an increased electric field gradient at the D in the pentamer. A possibly related feature is an Ar4 c.m. to F distance which is 0.013 Å longer for Ar4–DF than for Ar4–HF.
Inelastic helium scattering studies of ordered Ar, Kr, and Xe monolayers physisorbed on Ag(111): Dispersion curves, scattering cross sections, and excitation line shapes
Authors: Gibson K. D. , Sibener S. J.
Published: July 2002

This paper is the first in a series covering our experiments examining the physical properties of ordered overlayers of Ar, Kr, and Xe physisorbed on Ag(111). In this paper, we examine the desorption kinetics of the Xe monolayer/Ag(111) system. Desorption is zeroth order until ∼90% of the monolayer has desorbed, then becomes first order. We also measured the inelastic scattering of an 18 meV He beam from unconstrained monolayers of (111) oriented Ar, Kr, and Xe. The transitions are mapped across the entire surface Brillouin zone from Γ̄ to M̄. The data are dispersionless, indicating that for the measured mode the adatoms are behaving as independent Einstein oscillators. Parametrized physisorption potentials for RG–Ag(111) [RG=Ar, Kr, Xe] are constructed using these results. Inelastic scattering probabilities and linewidths are also presented. The inelastic scattering probabilities vary by at most a factor of 3 across the entire surface Brillouin zone, and are reported as a function of incident angle, final wave vector, and surface temperature. Variations in the inelastic scattering probabilities are indicative of dynamical adatom–substrate coupling. Experimental techniques which turn these dynamical couplings on or off for the same phonon energy are discussed. Limited results for clean Ag(111) are also presented. It is hoped that these measurements, on such ideal systems as ordered rare gas monolayers, will provide further impetus for developing improved theoretical treatments of inelastic single phonon scattering.
Liquid potassium–antimony alloys: Investigation of some thermodynamic properties
Authors: Saboungi Marie-Louise , Ellefson Julie , Johnson Gerald K. , Freyland Werner
Published: July 2002

High-temperature emf measurements of the activity of potassium in liquid K–Sb alloys were carried out at T=921 K for compositions covering the range XK=0 to 0.65. A solid electrolyte of potassium-substituted beta alumina was used in a coulometric titration technique to generate in situ potassium. The limiting slope of ln γK vs XK (γK being the activity coefficient of K) was negative, which indicates that the alkali atoms tend to form clusters, such as dimers and higher order species. An inflection point in ln γK was found at the equiatomic composition, leading to a maximum in the Darken excess stability functions. This feature, which was recently observed in equiatomic alloys formed between Na or K and Bi, Pb, or Te, can be interpreted in terms of the formation of stable species. An investigation of the enthalpies of KSb as a function of temperature showed a relatively small excess heat capacity in the temperature range T=878 to 1100 K.
Calculations of rate constants for the three-body recombination of H2 in the presence of H2
Authors: Schwenke David W.
Published: July 2002

We construct a new global potential energy hypersurface for H2+H2 and perform quasiclassical trajectory calculations using the resonance complex theory and energy transfer mechanism to estimate the rate of three-body recombination over the temperature range 100–5000 K. The new potential is a faithful representation of ab initio electronic structure calculations, is unchanged under the operation of exchanging H atoms, and reproduces the accurate H3 potential as one H atom is pulled away. Included in the fitting procedure are geometries expected to be important when one H2 is near or above the dissociation limit. The dynamics calculations explicitly include the motion of all four atoms and are performed efficiently using a vectorized variable-stepsize integrator. The predicted rate constants are approximately a factor of 2 smaller than experimental estimates over a broad temperature range.
The importance of vibrational motion and solvent diffusional motion in excited state intramolecular electron transfer reactions
Authors: Su Shyh-Gang , Simon John D.
Published: July 2002

Time resolved emission spectroscopy has been used to examine the dynamics of intramolecular charge transfer in dimethylaminobenzonitrile (DMABN) and diethylaminobenzonitrile (DEABN) in linear alcohol solutions as a function of temperature. For both DMABN and DEABN in methanol and DMABN in ethanol solutions, the population decay of the local excited (LE) state can be fit by a single exponential function. However, over the temperature range examined, 0 to −50 °C, the population decay of the local excited state in longer chain alcohol solutions (ethanol, propanol, butanol, pentanol, and hexanol) cannot be fit by a single exponential. The average survival probability of the LE state Q(t) is obtained by fitting the population decay to a multiexponential function. In all of the alcohol solvents studied, the average lifetime of Q(t) is faster than the solvent fluctuation rate gauged by the longitudinal relaxation time of the solvent τL(τDε∞/εs) corresponding to the slow collective hydrogen bonding dynamics. Comparison with recent dynamical solvation studies suggest that the multiexponential electron transfer kinetics reflected by Q(t) do not result from contributions of higher frequency responses of ε(ω). The experimentally observed dynamics of electron transfer are compared to a recent theoretical model of Marcus and co-workers which address the importance of contributions from both solvent fluctuations and intramolecular vibrational motions to the electron transfer rate. From this comparison it is concluded that fluctuations in the intramolecular coordinates for this reaction make a greater contribution to the rate of reaction in alcohol solutions than solvent diffusion.
Nonequilibrium molecular dynamics calculation of the shear viscosity of liquid water
Authors: Cummings P. T. , Varner T. L.
Published: July 2002

The shear viscosity, pressure, and configurational (SPC) internal energy of liquid water at four densities along the 303.15 K isotherm are calculated using nonequilibrium molecular dynamics. The interaction between the water molecules is modeled by the SPC pair potential of Berendsen and co-workers. The simulation results are compared with experimental data at the same temperatures and densities. The shear viscosity is found to be approximately 50% lower than the experimental results but has a similar slope as a function of density. The results for the full SPC potential are compared to those of a model fluid whose pair potential is obtained by setting the electrostatic part of the SPC interaction to zero. The results for the shear viscosity are remarkably similar to those of SPC water, suggesting that the electrostatic interactions make a very small contribution to the viscosity for this fluid.
Formation and stabilities of cluster ions Ar+n
Authors: Hiraoka Kenzo , Mori Toshiharu
Published: July 2002

Temperature dependence of the rate constants for the clustering reaction, Ar+(2P3/2)+2Ar=Ar+2(2Σ+u)+Ar, was measured in the temperature range 300–55 K using a pulsed electron-beam mass spectrometer. The rate constant shows a steady increase with decrease of temperature, from 2.0×10−31 cm6/s at 300 K to 7×10−31 cm6/s at 55 K. The metastable atomic ion Ar+(2P1/2) was found to start to form the cluster ion Ar+2 below 130 K. The thermochemical stabilities of the cluster ions Ar+n were also determined with n=3–11. A sudden drop in the −ΔH0n−1,n values was observed between n=3 and 4, indicating that the Ar+3 ion is the core in the cluster Ar+n.
Charging of the liquid metal surface and the capacitance of the metal–electrolyte interface
Authors: Goodisman Jerry
Published: July 2002

Density profiles for the conduction electrons of a simple liquid metal are calculated for a series of surface charge densities, using the self-consistent Kohn–Sham approach with an oscillatory density profile for the distribution of positive ions. The effect of charging on the electronic density profile is discussed. Considering an interface between the metal and an electrolyte phase such that the two phases have no common charged components (polarizable electrode), we derive an expression for the capacitance in terms of the centroids of the induced charge densities in the two phases, which are themselves functions of surface charge density. The calculated electron density profiles are used to calculate these centroids and to estimate the position of adsorbed water of the electrolyte phase relative to the position of the metal positive-ion profile. From these one obtains the capacitance of the interface; the contribution of nonideality of the metal is shown to be important.
Coriolis induced vibration and rotation mixing in formaldehyde
Authors: Gray Stephen K. , Davis Michael J.
Published: July 2002

The effect of Coriolis interaction on the intramolecular dynamics of formaldehyde is investigated theoretically. Classical dynamics calculations are presented that include all seven degrees of freedom, i.e., the six vibrational modes and the rotational mode associated with K, the projection of total angular momentum on a body-fixed axis. These calculations show that vibrational modes 4 (out of plane bend) and 6 (HCO bend) can be significantly coupled due to Coriolis interaction. The qualitative features of such coupling is further understood via study of a reduced dimension model that includes just modes 4, 6, and the rotational degree of freedom. Two interesting classical consequences of Coriolis interaction are noted. First, for large K (e.g., for ‖K‖∼J) we find vibrational mixing can occur without significant deterioration of K. We find that this mixing is not due to the usual ‘‘Chirikov’’ or pendulum picture of nonlinear resonance. Second, we find that both vibrational and rotational mixing can occur when the rotational frequency is in resonance with the difference in vibrational frequencies. In this situation, the resonances lead to a partial K mixing. Chaos about the resonances can lead to a more extensive K mixing. Quantum calculations are also performed for the reduced dimension model and the nature of the quantum eigenstates is discussed in relation to the corresponding classical dynamics.
The fractal structure and the dynamics of aggregation of synthetic melanin in low pH aqueous solutions
Authors: Huang J. S. , Sung J. , Eisner M. , Moss S. C. , Gallas J.
Published: July 2002

We have used static and dynamic light scattering to study the dynamics of aggregation of synthetic melanin, an amorphous biopolymeric substance, in low pH aqueous solution. We have found that, depending on the final pH value of the solutions, there existed two regimes of the aggregation kinetics, one corresponding to diffusion limited aggregation (DLA), and the other corresponding to reaction limited aggregation (RLA). The precipitates formed in these two regimes can be characterized by fractal structures. We have found fractal dimensions of df =1.8 for the DLA clusters and df =2.2 for the RLA clusters. These results agree well with the proposed limits of the fractal dimensions of the gold aggregates formed in aqueous solutions by Weitz et al.
Rotational relaxation of OCS by spherical and nearly spherical perturbers
Authors: Odashima Hitoshi , Kajita Masatoshi , Matsuo Yukari , Minowa Tatsuya , Shimizu Tadao
Published: July 2002

Collision cross sections for the transverse relaxation of OCS by spherical and nearly spherical perturbers have been measured. The observed cross sections vary linearly with β=[I22/(I1+I2)2α22M]1/5, where I1 and I2 are the ionization energies of OCS and the perturber. α2 is the polarizability of the perturber, and M is the reduced mass of the colliding molecules. Calculations based on the Anderson–Tsao–Curnutte theory using a simple dispersion force model for the OCS–perturber interaction are in qualitative agreement with the experimental results. By doubling the strength of the dispersion forces used to model the OCS–perturber interactions, the calculated cross sections are brought into agreement with the measured ones. The observed linear relation between the cross section and β can be used to predict cross sections for other (polar molecule)–(nonpolar nearly spherical perturber) collisions.
Comparison of complete model space quasidegenerate many-body perturbation theory for LiH with multireference coupled cluster method
Authors: Wang Xiao-Chuan , Freed Karl F.
Published: July 2002

The relative efficacy of using low order trucations with large reference space vs high order methods with small reference space is tested by comparing quasidegenerate many-body perturbation theory (QDMBPT) calculations of potential curves for the five lowest electronic states of LiH with the multireference coupled cluster calculations of Ben-Shlomo and Kaldor [J. Chem. Phys. 89, 956 (1988)]. The infinite order coupled cluster calculations use two configurational reference spaces involving the 2σ, 3σ, and 1π orbitals, while the QDMBPT computations are truncated at either second or third orders and employ the full active reference space formed either from the 2σ, 3σ, and 1π or from the 2σ, 3σ, 4σ, and 1π orbitals. This gives us the opportunity of testing the dependence of QDMBPT computations on the size of reference space, the available freedom in choosing valence orbitals and orbital energies, and the order of truncation. Second order, four valence orbital space QDMBPT calculations provide good agreement with the repulsive portion of the coupled cluster potentials, but yield a separated atom limit that is too high and that therefore distorts the remainder of the potential. Third order improves the separated atom limit considerably, providing good agreement with the coupled cluster calculations. The ‘‘full chemical’’ five orbital reference space, on the other hand, yields very good agreement with coupled cluster potentials when using only the simpler second order QDMBPT calculations, and third order corrections in this case are very small but generally improve agreement with coupled cluster potentials. The five orbital reference space calculations are quite insensitive to a wide range of different choices of valence orbitals and orbital energies, demonstrating a robustness to the QDMBPT formalism used.