bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic, temperature, and corrosion properties of the NiFe/IrMn exchange couple
Authors: Devasahayam A. J. , Sides P. J. , Kryder M. H.
Published: July 2002

Exchange biasing properties of the NiFe/IrMn exchange couple were investigated by varying the IrMn composition and sputtering conditions. At a composition of Ir20Mn80 an exchange field of ∼60 Oe and a coercivity of 8 Oe were obtained for the structure Si/Ta-75 Å/NiFe-250 Å/IrMn-500 Å. The maximum exchange field obtained was similar for rf diode, rf magnetron, and dc magnetron sputtering of the IrMn. X-ray diffraction measurements showed that the crystalline texture was (111) for both the NiFe and IrMn, but a strong crystalline texture did not necessarily correspond to a large exchange field. The interfacial exchange energy, Jk, was evaluated to be 0.145 erg/cm2 and the minimum thickness of IrMn needed to support an exchange field was 75 Å. The blocking temperature was measured to be a function of the IrMn thickness and was in the range of 220–250 °C for thicknesses >200 Å. Below this, the blocking temperature rapidly decreased to a value of 130 °C at 75 Å of IrMn. Corrosion testing was done in a Battelle Class II type corrosive environment. Using the exchange field as a figure of merit, it was found that the IrMn corrosion properties were only slightly better than FeMn, and significantly worse than NiMn and CoNiO. We were also able to successfully fabricate NiFe based spin-valves pinned with IrMn and they show good magnetic properties. Our results show than IrMn is a good alternative to FeMn.
Magnetism and Jahn-Teller effect in LaMnO3
Authors: Li M. Z. , Zou Liang-Jian , Zheng Q. Q.
Published: July 2002

Combining charge transfer with the Jahn-Teller electron-phonon coupling, the magnetic properties of LaMnO3 and the influence of the Jahn-Teller effect are studied. The interaction parameters of super exchange coupling between manganese spins are obtained. In the ground state, manganese spins are antiferromagnetically ordered but canted by a small angle. The spectrum of the low-energy spin excitation is very close to that observed experimentally. Behaviors of magnetization and spin correlation functions of LaMnO3 exhibit certain two-dimensional ferromagnetic characters, even though it is an A-type antiferromagnet with anisotropic super exchange coupling. These results agree with several experiments. Furthermore, it is expected that the super exchange interactions depend on the electron-phonon coupling strength exponentially, and the Néel temperature will exhibit isotope shift.
Nanometric cartography of tunnel current in metal–oxide junctions
Authors: Da Costa V. , Bardou F. , Béal C. , Henry Y. , Bucher J. P. , Ounadjela K.
Published: July 2002

Recently, ferromagnet/insulator/ferromagnet trilayer junctions were shown to exhibit large magnetoresistance effects. However, these effects proved to be poorly reproducible from sample to sample. To get a nanoscopic insight on the origin of these fluctuations, we have used a combined atomic force microscope/scanning tunneling microscope setup to map the tunnel current that flows through metal/oxide stacks. The current histogram, which extends over 1–2 orders of magnitude, is found to be well described by a simple model which takes into account tiny spatial fluctuations of tunnel barrier thickness (typically, 0.1 nm). Moreover, our analysis shows that the total conductance of imperfect metal/oxide junctions tends to be dominated by very few sites. This result allows us to relate the sample-to-sample conductance fluctuations to slight local variations of the tunnel barrier parameters.
Magnetic properties of MnZnTi and NiZn ferrite films deposited by laser ablation
Authors: Amado M. M. , Rogalski M. S. , Guimarães L. , Sousa J. B. , Bibicu I. , Welch R. G. , Palmer S. B.
Published: July 2002

The magnetic behavior of MnZnTi and NiZn ferrite films, deposited by laser ablation, is studied comparatively to that of the bulk material, using a vibrating-sample magnetometer (VSM), transmission, and conversion electron Mössbauer measurements. Both the VSM and Mössbauer analysis show that the films exhibit the single phase pattern of the target material. Mössbauer hyperfine field values for films are close to those found for the bulk, and this accounts for the same saturation magnetization values determined by VSM. Laser ablated films exhibit a higher coercive field, which is explained in terms of the crystallite size distribution, with average values of 300–600 nm, as estimated from the Mössbauer line broadening.
Universal magnetic fluctuations in the two-dimensional XY model
Authors: Archambault P. , Bramwell S. T. , Fortin J.-Y. , Holdsworth P. C. W. , Peysson S. , Pinton J.-F.
Published: July 2002

We discuss the probability distribution function for the magnetic order parameter M, in the low temperature phase of the two-dimensional XY model. In this phase the system is critical over the whole range of temperature. The thermally averaged value of the order parameter 〈M〉, which is zero in the thermodynamic limit, has abnormally large finite size corrections. An exact result, within a spin wave calculation gives 〈M〉=(1/2N)T/8πJ, where J is the magnetic exchange constant and N the number of spins. We show, using Monte Carlo simulation, that the distribution function, Q(y−〈y〉), y=T−1LT/4πJM, is an asymmetric universal function. Using a diagramatic technique, we show that the asymmetry comes from three-spin and higher correlations. If only two-spin correlations are considered, the distribution is Gaussian. However, as there are contributions from two-spin terms separated by all distances, the distribution remains broad and is consistent with a divergent susceptibility.
Observation of dipole complexes in PbWO4:La3+ single crystals
Authors: Han Baoguo , Feng Xiqi , Hu Guanqin , Wang Pingchu , Yin Zhiwen
Published: July 2002

The frequency dependence of dielectric loss factor (tan δ) in undoped and La-doped PbWO4 crystals has been investigated over a frequency range from 10 Hz to 10 MHz and a temperature range from 40 to 370 °C. A typical dielectric relaxation phenomenon in PbWO4:La3+ has been observed. Experimental results indicate that there exist intrinsic mobile defects in pure PbWO4 crystals and lead vacancies are the predominant mobile defects. In La-doped PbWO4 crystals, La3+ ions may be located at the Pb2+ sites and combine with lead vacancies to form the dipole complexes [2(LaPb3+)•−VPb″], which may be the origin of the dielectric relaxation phenomenon in PbWO4:La3+ crystals.
Reciprocal space maps of PbTe/SnTe superlattices
Authors: Ferreira S. O. , Abramof E. , Rappl P. H. O. , Ueta A. Y. , Closs H. , Boschetti C. , Motisuke P. , Bandeira I. N.
Published: July 2002

PbTe/SnTe superlattices were grown on (111) BaF2 substrates by molecular beam epitaxy using PbTe as buffer layers. The individual layer thickness and number of repetitions were chosen in order to change the strain profile in the superlattices from completely pseudomorphic to partially relaxed. The superlattices structural properties were investigated by making reciprocal space maps around the asymmetric (224) Bragg diffraction points and ω/2Θ scans for the (222) diffraction with a high resolution diffractometer in the triple axis configuration. With the strain information obtained from the maps, the (222) ω/2Θ scan was simulated by dynamical diffraction theory. The simulated spectra of the pseudomorphic superlattices, in which the in-plane lattice constant is assumed to be the same as the PbTe buffer throughout the superlattice, fitted in a remarkably good agreement with the measured data, indicating that almost structurally perfect samples were obtained. For the thicker superlattices, the (224) reciprocal space maps revealed a complex strain profile. Our results show the importance of detailed structural characterization on the interpretation of the electrical properties.
Single-electron-parametron-based logic devices
Authors: Korotkov Alexander N. , Likharev Konstantin K.
Published: July 2002

We analyze the operation of the wireless single-electron logic family based on single-electron-parametron cells. Parameter margins, energy dissipation, and the error probability are calculated using the orthodox theory of single-electron tunneling. Circuits of this family enable quasireversible computation with energy dissipation per bit much lower than the thermal energy, and hence may circumvent one of the main obstacles faced by ultradense three-dimensional integrated digital circuits.
Improved analytical model for threshold behavior of sidegating effect in GaAs metal–semiconductor field-effect transistors induced by impact ionization of deep traps
Authors: Zhao Fuchuan , Xia Guanqun , Du Lixin , Tan Huizu
Published: July 2002

This article presents an improved analytical model for the threshold behavior of the sidegating effect in GaAs metal-semiconductor field-effect transistors. The model takes into account impact ionization of deep trap EL2 and the charge neutrality condition in the undoped semi-insulating GaAs substrate. Based on the model, we provide a new simple analytical expression for the threshold voltage of the sidegating effect (Vth). The new expression of Vth indicates that Vth is proportional to not only the distance of sidegate from the channel but to the substrate impurity compensation ratio ξ also. The model predicts that closely compensated substrates will minimize the sidegating effect in agreement with earlier experimental results.
Infrared attenuated total reflection spectroscopy of 6H–SiC(0001) and (0001̄) surfaces
Authors: Tsuchida H. , Kamata I. , Izumi K.
Published: July 2002

Fourier-transformed infrared attenuated total reflection (FTIR–ATR) spectroscopy was used to study the adsorbates on 6H–SiC(0001) and (0001̄) surfaces after chemical treatments and after heat treatments in hydrogen. We obtained clear absorption bands attributable to hydrides and oxides on the SiC surfaces. The ATR spectroscopy revealed polarity dependencies of Si–H and C–H stretch modes between the 6H–SiC(0001) and (0001̄). The surface Si–H bonds on 6H–SiC(0001) formed by the heat treatment in hydrogen were found to have a quite long life time against air exposure, and the heat treatment in hydrogen also produced a flat (0001̄) surface with ordered surface C–H bonds. The oxidation characteristics of 6H–SiC(0001) and (0001̄) surfaces were also studied, and we discussed the roles of surface treatments using H2O2 solution and H2SO4 solution at elevated temperature.
Magnetoimpedance effect in nanocrystalline Fe90−xBxZr7Cu1Al2 (x=2,4,6,8) alloys
Authors: Lee Heebok , Kim Yong-Kook , Kim Taik-Kee , Song Yoon-Ho , Yu Seong-Cho
Published: July 2002

The magnetoimpedance of Fe90−xBxZr7Cu1Al2 (x=2,4,6,8) alloys has been measured to investigate the influence of the structural changes in the crystallization process as well as the changes of magnetic properties such as permeability, coercivity, magnetic anisotropy, etc. after thermal treatment. The frequency of magnetoimpedance measurement ranged from 100 kHz to 10 MHz, and the current was fixed at 10 mA for all measurements. Annealing was performed at temperatures of 350, 450, and 550 °C for 1 h in a vacuum. Ultrasoft magnetic behavior has been observed in the samples annealed at 450 °C. The magnetoimpedance ratio coincides with the softness of magnetic properties of thermally treated samples. A giant change of the longitudinal permeability as a function of external field is also observed.
Thin films formation of poly(N-vinylcarbazole) by laser ablation deposition
Authors: Tsuboi Yasuyuki , Goto Masaharu , Itaya Akira
Published: July 2002

The laser-ablation deposition technique was examined for poly(N-vinylcarbazole), PVCz, which is a representative photoconductive aromatic vinylpolymer. Thin films were deposited under various irradiation conditions (laser wavelengths were 351, 308, and 248 nm and their fluences were 70, 300, and 450 mJ/cm2), and their chemical structures and surface morphology were revealed by means of infrared-absorption, fluorescence spectroscopy, and atomic force microscopy, respectively. They were quite sensitive to the laser fluence, as well as wavelength. A thin film of PVCz was formed only under an optimum irradiation condition where the laser fluence and wavelength were 300 mJ/cm2 and 351 nm, respectively. When the irradiation condition deviated from the optimum one, thin films contained carbazolyl derivatives such as N-alkylcarbazole and N-vinylcarbazole oligomers. It was revealed that the thin PVCz film was formed by a repolymerization due to radical mechanism. In addition, it was suggested that cross-linking reactions occurred in the films deposited at 248 and 308 nm. All the films were amorphous, and particle-like aggregates, with sizes varying with the irradiation conditions, were observed on their surface. It was demonstrated that the ablation-deposition technique is applicable to the formation of thin PVCz films.
High-temperature reliability of GaN metal semiconductor field-effect transistor and bipolar junction transistor
Authors: Yoshida Seikoh , Suzuki Joe
Published: July 2002

High-quality GaN was grown using gas-source molecular beam epitaxy (GSMBE). We fabricated a GaN metal semiconductor field-effect transistor (MESFET) and an n–p–n bipolar junction transistor. The high-temperature reliability of the GaN MESFET and bipolar junction transistor was investigated. That is, the life performance of the FET at 400 °C was examined during continuous current injection at 400 °C. We confirmed that the FET performance did not change at 400 °C for 300 h. No degradation of the metal–semiconductor interface was observed by secondary ion-mass spectrometry and transmission electron microscopy. Furthermore, an n–p–n bipolar junction transistor using GaN grown by GSMBE was demonstrated. The bipolar junction transistor was operated at 300 °C. The reliability of a GaN MESFET and the bipolar junction transistor at high temperature was thus confirmed.
Wigner function formulation in nonparabolic semiconductors using power series dispersion relation
Authors: Kim Kyoung-Youm , Lee Byoungho
Published: July 2002

A Wigner transport equation taking account nonparabolic energy band structures of electrons is formulated using the expanded power series dispersion relation in the kinetic energy term in the Hamiltonian. Numerical simulations for GaAs/AlGaAs resonant tunneling diodes are performed based on this model. In the analysis of steady-state current–voltage characteristics, the introduction of nonparabolicity gives overall reduced current densities. However, as in the case of mass correlation terms, the tunneling current when we include the correlation of spatially varying nonparabolicity parameter is bigger than that with constant nonparabolicity parameter. In the transient response analysis, it gives a damping effect which reduces the oscillatory behavior of current and electron densities.
Temperature dependence of Young’s modulus and degradation of chemical vapor deposited diamond
Authors: Szuecs F. , Werner M. , Sussmann R. S. , Pickles C. S. J. , Fecht H. J.
Published: July 2002

Temperature dependent measurements of Young’s modulus were performed for the first time on black and transparent bulk material of chemical vapor deposited (CVD) diamond by a dynamic three point bending method in a temperature range from −150 to 850 °C. The CVD specimens correspond to a room-temperature Young’s modulus of single crystal diamond (1143 GPa). A lower Young’s modulus of polycrystalline diamond is caused by crystal imperfections and impurities. At temperatures between −150 and 600 °C (black type) or −150 and 700 °C (transparent type) the Young’s modulus is only slightly temperature dependent and decreases monotonically with an average temperature coefficient of −1.027×10−4 K−1, which is much higher than theoretically expected. At higher temperatures the bending stiffness and apparent Young’s modulus of the diamond beams are drastically reduced to one third of the initial value before fracture occurs due to oxygen etching effects in air. The onset temperature of this degradation phenomenon and the rate of decline are dependent on grain size, texture and the crystal lattice imperfections of the CVD diamond material.
Photonic crystal-based resonant antenna with a very high directivity
Authors: Temelkuran B. , Bayindir Mehmet , Ozbay E. , Biswas R. , Sigalas M. M. , Tuttle G. , Ho K. M.
Published: July 2002

We investigate the radiation properties of an antenna that was formed by a hybrid combination of a monopole radiation source and a cavity built around a dielectric layer-by-layer three-dimensional photonic crystal. We measured a maximum directivity of 310, and a power enhancement of 180 at the resonant frequency of the cavity. We observed that the antenna has a narrow bandwidth determined by the cavity, where the resonant frequency can be tuned within the band gap of the photonic crystal. The measured radiation patterns agree well with our theoretical results.
Polarization beam smoothing for inertial confinement fusion
Authors: Rothenberg Joshua E.
Published: July 2002

For both direct and indirect drive approaches to inertial confinement fusion (ICF) it is imperative to obtain the best possible drive beam uniformity. The approach chosen for the National Ignition Facility uses a random-phase plate to generate a speckle pattern with a precisely controlled envelope on target. A number of temporal smoothing techniques can then be employed to utilize bandwidth to rapidly change the speckle pattern, and thus average out the small-scale speckle structure. One technique which generally can supplement other smoothing methods is polarization smoothing (PS): the illumination of the target with two distinct and orthogonally polarized speckle patterns. Since these two polarizations do not interfere, the intensity patterns add incoherently, and the rms nonuniformity can be reduced by a factor of √. A number of PS schemes are described and compared on the basis of the aggregate rms and the spatial spectrum of the focused illumination distribution. The √ rms nonuniformity reduction of PS is present on an instantaneous basis and is, therefore, of particular interest for the suppression of laser plasma instabilities, which have a very rapid response time. When combining PS and temporal methods, such as smoothing by spectral dispersion (SSD), PS can reduce the rms of the temporally smoothed illumination by an additional factor of √. However, it has generally been thought that in order to achieve this reduction of √, the increased divergence of the beam from PS must exceed the divergence of SSD. It is also shown here that, over the time scales of interest to direct or indirect drive ICF, under some conditions PS can reduce the smoothed illumination rms by nearly √ even when the PS divergence is much smaller than that of SSD.
Scattering mechanisms limiting two-dimensional electron gas mobility in Al0.25Ga0.75N/GaN modulation-doped field-effect transistors
Authors: Antoszewski J. , Gracey M. , Dell J. M. , Faraone L. , Fisher T. A. , Parish G. , Wu Y.-F. , Mishra U. K.
Published: July 2002

In order to characterize the electron transport properties of the two-dimensional electron gas (2DEG) in AlGaN/GaN modulation-doped field-effect transistors, channel magnetoresistance has been measured in the magnetic field range of 0–12 T, the temperature range of 25–300 K, and gate bias range of +0.5 to −2.0 V. By assuming that the 2DEG provides the dominant contribution to the total conductivity, a one-carrier fitting procedure has been applied to extract the electron mobility and carrier sheet density at each particular value of temperature and gate bias. Consequently, the electron mobility versus 2DEG sheet density has been obtained for each measurement temperature. Theoretical analysis of these results suggests that for 2DEG densities below 7×1012 cm−2, the electron mobility in these devices is limited by interface charge, whereas for densities above this level, electron mobility is dominated by scattering associated with the AlGaN/GaN interface roughness.
Spin dependent tunneling devices fabricated for magnetic random access memory applications using latching mode
Authors: Wang D. , Tondra M. , Pohm A. V. , Nordman C. , Anderson J. , Daughton J. M. , Black W. C.
Published: July 2002

Spin dependent tunneling (SDT) devices were fabricated as building blocks for magnetic random access memory (MRAM) applications using latching electronics. The basic SDT structure was NiFeCo/Al2O3/CoFe/IrMn deposited using rf diode sputtering. The SDT structures and the word and torque coils were patterned using standard photolithography techniques. The junction magnetoresistance was 25.6%, the switching field was 12 Oe, the junction resistance-area product was 116 kΩ μm2, and the pinning field was 150 Oe. There were two legs of SDT resistors in a latch cell, with each leg consisting of at least one pair of junctions. The basic latching function of the devices was evaluated using external electronics. The two memory states per cell were demonstrated by passing a current of 22 mA with both polarities through the on-chip word coil. This translates to a field efficiency of about 1 Oe/mA for the word coil, which can be further improved by adding a magnetic keeper layer. The raw output voltage change was 21 mV for a SDT cell with four junctions and 4.5 kΩ resistance in each leg using a 50 μA sense current. These results show great potential for SDT materials to be used in high speed and low power MRAM applications with latching mode.
Metastable phases induced by ion irradiation in the equilibrium immiscible Fe–Cu system
Authors: Yang G. W. , Lai W. S. , Lin C. , Liu B. X.
Published: July 2002

Anomalous structural evolution was induced by room-temperature 200 keV xenon ion irradiation and it results in the formation of various new metastable phases in the equilibrium immiscible Fe–Cu system. First, nanosized quasicrystals were formed in an amorphous matrix through a two-step transition of crystal to amorphous to quasicrystal in Fe70Cu30 multilayered films. The real compositions of the amorphous matrix and quasicrystals were determined to be close to Fe70Cu30 and Fe50Cu50, respectively. Moreover, the same icosahedral phase was also obtained in another similarly designed Fe50Cu50 multilayered sample upon 850 °C thermal annealing, confirming the existence of such a metastable state. Second, amorphous alloys were formed in a composition range of 30–50 at. % of Cu. Third, a Cu-based face-centered-cubic (fcc) solid solution was formed at an alloy composition of about Fe30Cu70 and, interestingly, another fcc structured metastable crystalline phase was obtained at a composition very close to that of Fe50Cu50. A Gibbs free energy diagram of the Fe–Cu system was calculated, with special consideration of excess interfacial free energy stored in the multilayered films, within the framework of Miedema’s model and it gives a reasonable thermodynamic explanation to the metastable phase formation observed. The amorphous-to-quasicrystal transition is also discussed in terms of the similarity in the atomic configuration between the icosahedral and amorphous short-range orders. Furthermore, molecular dynamics study showed that Fe and Cu could be mixed on an atomic scale in the metastable phases observed.
In-plane lattice thermal conductivity of a quantum-dot superlattice
Authors: Khitun A. , Balandin A. , Liu J. L. , Wang K. L.
Published: July 2002

We have theoretically investigated the in-plane lattice thermal conductivity of a quantum-dot superlattice. The calculations were carried out for a structure that consists of multiple layers of Si with randomly distributed Ge quantum dots separated by wetting layers and spacers. Our model takes into account scattering of acoustic phonons on spherical quantum dots, and corresponding modification of the phonon dispersion relation. The finite acoustic mismatch between Si and Ge is also taken into account. The obtained results are important for the most recently suggested applications of SiGe quantum-dot superlattices for thermoelectric devices.
The submillimeter wave spectrum of the protonated and deuterated carbon dioxide
Authors: Bogey Marcel , Demuynck Claire , Destombes Jean-Luc
Published: July 2002

The submillimeter wave spectrum of the protonated carbon dioxide has been investigated in the 340–406 GHz frequency range by using a phase locked submillimeter carcinotron. A magnetically confined glow discharge in a mixture of CO2, H2/D2, and Ar has been used to produce the molecular ions. The rotational lines investigated are characterized by 15≤J≤18, Ka ≤5 for HCO+2 and 16≤J≤19, Ka ≤6 for DCO+2. From the analysis of the spectra, accurate molecular constants have been derived, leading to the prediction of transitions of astrophysical interest.
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o study of the alkali and alkaline-earth monohydroxides
Authors: Bauschlicher Charles W. , Langhoff Stephen R. , Partridge Harry
Published: July 2002

The structure and energetics of the alkali and alkaline-earth monohydroxides are studied at both the self-consistent-field and singles plus doubles configuration-interaction level using Gaussian basis sets of at least triple-zeta plus double polarization quality. BeOH is found to be bent, with a very flat bending potential. MgOH is found to be linear, and all remaining alkali and alkaline-earth hydroxides are known to be linear. Our recommended dissociation energies, D0, in eV are LiOH (4.64), NaOH (3.51), KOH (3.61), RbOH (3.58), CsOH (3.78), BeOH (4.70), MgOH (3.31), CaOH (4.15), SrOH (4.19), and BaOH (4.6). The dissociation energies are estimated to be accurate to 0.10 eV, except for BaOH where the estimated uncertainty is at least 0.2 eV owing to the use of a relativistic effective core potential. The theoretical dissociation energies are shown to have a strong correlation with those of the corresponding fluorides and oxides.
Total absorption and photoionization cross sections of water vapor between 100 and 1000 Å
Authors: Haddad G. N. , Samson James A. R.
Published: July 2002

Total absorption and photoionization cross sections of water vapor have been measured between 100 and 1000 Å with an accuracy of ±3%. Recent calculations are shown to be in reasonable agreement with the present data.
Homodyne photon-correlation spectroscopy of a supercooled liquid: 1,3,5-Tri-α-naphthyl benzene
Authors: Zhu X. R. , Wang C. H.
Published: July 2002

Homodyne depolarized photon-correlation functions of 1,3,5-tri-α-naphthyl benzene (TαNB) have been measured at the 90° scattering angle in the temperature range of 75–110 °C. The correlation functions are analyzed in terms of a fractional exponential function and a modified constrained regularization method originally developed by Provencher. The results from both methods of data analysis are in agreement. The temperature dependence of the mean orientational relaxation time when fitted to the Arrhenius equation, gives an apparent activation energy E=85.3 kcal/mol. The Antoine–WLF equation provides a better fit of the mean reorientational relaxation time data. It is also found that orientational time τ̄ is linearly proportional to η/T, indicating that the Debye–Stokes–Einstein equation is applicable to describe molecular reorientation in the supercooled TαNB liquid.
Microscopic frictional forces on molecular motion in liquids. Picosecond rotational diffusion in alkanes and alcohols
Authors: Ben-Amotz Dor , Scott Thomas W.
Published: July 2002

The rotational diffusion times of the nonpolar solutes p-terphenyl, p-quaterphenyl, and 9,10-diphenylanthracene dissolved in n-alkane and n-alcohol solvents are reported. The observed microscopic frictional coefficients approximate the predictions of ‘‘slip’’ hydrodynamics in n-alkanes. Substantially lower friction is found in n-alcohols of comparable viscosity. Large deviations are also observed in branched alkane and dialcohol solvents. These differences are interpreted as an indication of nonhydrodynamic behavior in the microscopic rotational friction. Comparison with the results of other recent studies supports this interpretation and also indicate that charged solutes experience higher friction than the neutral solutes used in this study. The difference between charged and uncharged solutes is attributed to the larger effective volume of charged species, as well as to dielectric friction and solvation environment effects. A new picosecond spectroscopic technique based on stimulated emission gain anisotropy relaxation is used to perform the experiments.
Correlation crystal field analyses with orthogonal operators
Authors: Reid Michael F.
Published: July 2002

The construction of orthogonal operators to represent correlation crystal field (CCF) effects in the f N configuration of lanthanide and actinide ions is discussed. The approach of B. R. Judd [J. Chem. Phys. 66, 3163 (1977)] is extended to make all the operators orthogonal. The spin-correlated crystal field (SCCF) parametrization that has been successful in removing several long-standing anomalies from crystal field fits involves only two of the two-electron orthogonalized operators. We calculate values of the orthogonal CCF parameters from recent ab initio results. On the basis of these calculations the sixth rank SCCF operators are predicted to be very important. Fits using various combinations of the CCF parameters are reported for Ho3+ and Gd3+in LaCl3. For these systems we only obtain consistent results for the parameters associated with the sixth rank SCCF.
The analytic evaluation of energy first derivatives for two-configuration self-consistent-field configuration interaction (TCSCF-CI) wave functions. Application to ozone and ethylene
Authors: Lee Timothy J. , Allen Wesley D. , Schaefer Henry F.
Published: July 2002

An efficient formulation for the analytic evaluation of two-configuration self-consistent-field configuration interaction (TCSCF-CI) energy first derivatives is presented. Use is made of the Z-vector approach of Handy and Schaefer. The procedure outlined does not require the transformation of derivative integrals. We have applied the new procedure to the ground states of ozone and ethylene. For ozone, the (DZP) TCSCF-CI procedure yields a structure which is much improved relative to that obtained using a single-reference description. However, the incorrect ordering of the harmonic vibrational frequencies ω1(a1) and ω3(b2), which was first found using a TCSCF description of O3, remains at the TCSCF-CI level of theory. Anharmonic vibrational frequencies (utilizing TCSCF-CI harmonic frequencies and SCF anharmonic corrections) are reported for ethylene. With a DZP basis set, 11 of the 12 TCSCF-CI fundamental frequencies of C2H4 agree very well with experiment, the mean absolute error being 2.4%. However, the infrared inactive ν8=799 cm−1 is 15.0% below the accepted experimental value. The utilization of a TZ2P basis set resolves this discrepancy. The TZ2P TCSCF-CI ν8=922 cm−1 is 1.9% below experiment, and the average absolute error of all of the TZ2P fundamentals is only 2.6%.
Rotationally resolved laser spectroscopy of tetracene and its van der Waals complexes with inert gas atoms
Authors: van Herpen W. M. , Meerts W. Leo , Dymanus A.
Published: July 2002

By using a molecular beam apparatus in combination with a single frequency dye laser we were able to resolve several rovibronic bands in the S1 electronic state of tetracene (C18H12) and its van der Waals complexes with inert gas atoms. The spectra of tetracene have been assigned and rotational constants were derived for the S0 and S1 electronic state. The existence of perturbations in the rotational spectra of the van der Waals complexes is demonstrated.
Semiclassical dynamics in Liouville space: Application to molecular electronic spectroscopy
Authors: Yan Yi Jing , Mukamel Shaul
Published: July 2002

A semiclassical theory of molecular dynamics and electronic spectroscopy, based on the propagation of a Liouville-space generating function (LGF) is developed. The method is particularly useful for treating the dynamics of systems, consisting of coupled classical and quantum degrees of freedom. Applications to intramolecular and intermolecular dynamics, correlation functions, and spectral line shapes in linear and nonlinear optical measurements are developed. The electronic absorption line shapes and Raman excitation profiles of model anharmonic molecules at finite temperatures are calculated as a demonstration.
The dynamics of polar solvation: Inhomogeneous dielectric continuum models
Authors: Castner Edward W. , Fleming Graham R. , Bagchi Biman , Maroncelli Mark
Published: July 2002

The influence of an inhomogeneous dielectric response on the dynamics of solvation of ions and dipoles is investigated. Solvent models considered include discrete shell models as well as models in which the solvent dielectric constant varies continuously as a function of distance from a spherical solute. The effect of such dielectric inhomogeneity is to introduce additional, slower relaxation times into the solvation response when compared to the homogeneous case. For all models studied, the deviation of the average relaxation time from that predicted for a homogeneous continuum solvent increases as the dielectric constant and the length parameter, which specifies the rapidity of approach to bulk behavior, increase. For a given solvent model the solvation response to a change in a point dipole moment is slower than the response to a charge jump. The continuum results are compared to a recent molecular model based on the mean spherical approximation. The comparison suggests that deviations from homogeneous continuum behavior in the molecular model can be accounted for by inhomogeneity of the solvent dielectric constant extending only over the first solvation shell. Predictions of inhomogeneous continuum models are also compared to experimental data. Both the observed dependence of average relaxation time on dielectric constant, and the detailed time dependence of the relaxation in high dielectric constant solvents can be rationalized on the basis of such models.
Polymer/metal interfaces studied by carbon near-edge x-ray absorption fine structure spectroscopy
Authors: Jordan-Sweet J. L. , Kovac C. A. , Goldberg M. J. , Morar J. F.
Published: July 2002

Interaction of polyimide and two simple organic polymers with an evaporated chromium metal overlayer was studied by surface-sensitive carbon 1s near-edge x-ray absorption fine structure (NEXAFS) spectroscopy. The technique was used to measure unoccupied electronic states in the polymers. Assignments of C1s→π* transitions in poly(pyromellitimido oxydianiline) (PMDA-ODA polyimide) were based upon transitions measured for model polymers which contained structural subunits of the polyimide. Changes in the NEXAFS spectrum of each polymer were observed after sequential depositions of chromium. Abrupt changes in the carbonyl C1s→π* transition peaks show that the carbonyl groups on these polymers are sites for initial interaction with chromium. No evidence was seen for the formation of Cr–arene complexes on any of the polymer surfaces.
Measurement and prediction of Raman Q-branch line self-broadening coefficients for CO from 400 to 1500 K
Authors: Rosasco G. J. , Rahn L. A. , Hurst W. S. , Palmer R. E. , Dohne S. M.
Published: July 2002

The J and temperature dependence of the self-broadening coefficients for the Raman Q-branch lines of pure CO have been experimentally determined for Q(J) transitions with J=0–38 and for temperatures in the range 400–1500 K. It is shown that a fitting law, based on a modified exponential energy-gap model for the rates of state-to-state rotationally inelastic collisions, can account for the observed J dependence. The two parameters that determine the J dependence are found to be essentially independent of temperature. A temperature scaling function, recently proposed for N2, is added to the basic rate law, and accurate predictions of both the J and the T dependence of these coefficients and those previously reported at 298 K are obtained. This rate law model, used in conjunction with a relaxation matrix description of the Q-branch spectrum, is shown to give good agreement with the observed, partially collapsed spectrum at 2.8 atm and 295 K.
The millimeter- and submillimeter-wave spectrum of dichlorocarbene CCl2: Electronic structure estimated from the nuclear quadrupole coupling constants
Authors: Fujitake Masaharu , Hirota Eizi
Published: July 2002

The pure rotational spectrum of CCl2 in the ground state was observed for the first time in the millimeter- and submillimeter-wave region. The CCl2 molecule was generated directly in a free space cell by a dc glow discharge in CCl4 . Several transitions showed hyperfine splittings arising from the nuclear quadrupole coupling of two Cl atoms. Analysis of the observed spectrum yielded the rotational, centrifugal distortion, and nuclear quadrupole coupling constants of the C35 Cl2 species. The r0 structure was derived from the rotational constants to be r0 (C–Cl)=1.7157 Å and θ0 (ClCCl)=109.2°. The ionic and π character of the C–Cl bond were estimated from the nuclear quadrupole coupling constants to be 0.26 and 0.32, respectively.
Density functional approximation for hard-body liquid crystals
Authors: Somoza A. M. , Tarazona P.
Published: July 2002

We present a density functional approximation for the free energy of a system of hard bodies with arbitrary shape and orientational distribution. For systems with homogeneous density it reduces to existing treatments, which describe the isotropic liquid and the nematic liquid crystal. The treatment of the inhomogeneous density allows the study of smectic and crystal phases. We applied the approximation to a system of parallel hard spherocylinders, for which we compare the nematic to smectic-A phase transition with recent computer simulation data. We also study a system of oblique cylinders and show that smectic-C phase may appear as the result of packing effects in systems of hard bodies.
Structure of the hard ellipsoid fluid
Authors: Talbot J. , Kivelson D. , Allen M. P. , Evans G. T. , Frenkel D.
Published: July 2002

Molecular-dynamics calculations are reported on fluids of hard ellipsoids over a range of densities and for several ellipsoidal aspect ratios. The pair correlation functions obtained from the simulations are expressed as functions of the minimum surface-to-surface separation, s, measured along the surface normal, ŝ, and angles measured relative to the surface normal. Both isotropic and orientational correlations exhibit simpler behavior in the surface-to-surface than in the more customary center-to-center coordinate representation. For the hard-ellipsoid fluid, the isotropic part of the pair correlation function, giso(s), behaves much like that of a hard-sphere fluid. The surface-to-surface coordinates are well suited for studying pressure and collision rates because these properties depend upon surface contact distributions. They are also useful for studying the orientational order parameter, g2, because they enable one to readily identify a long-range part and geometrical excluded volume contribution.
Multidimensional variational Gaussian wave packet dynamics with application to photodissociation spectroscopy
Authors: Coalson Rob D. , Karplus Martin
Published: July 2002

The McLachlan variational principle for the time-dependent Schrödinger equation is utilized in conjunction with extant localized Guassian wave packet technology to deduce equations of motion for general multidimensional Gaussians. These equations of motion are characterized by the same simplicity as the local quadratic expansion results of Heller [J. Chem. Phys. 62, 1544 (1975)]. However, the resultant variational wave packet evolution is shown to be an improvement over its local quadratic analog as a tool for computing certain photodissociation spectra. Numerical examples drawn from the Beswick–Jortner model of ICN photodissociation [Chem. Phys. 24, 1 (1977)] are presented.
The theory of electronic intensity in solution or condensed media
Authors: Iweibo Idowu , Obi-Egbedi Nelson O. , Chongwain Paul T. , Lesi Abiodun F. , Abe Takehiro
Published: July 2002

Based on microscopic and macroscopic models for the description of the electronic intensity of an ensemble of absorbing molecules in solution or condensed media, rigorous and general expressions have been derived for the integral Einstein B coefficient and the oscillator strength by means of the classical and the quantum mechanical methods. The two approaches are shown to yield in all essential points the same results. The present expressions are formulated to accommodate various field models and molecular shapes and to permit the distinction and/or selection of a model that best describes a spectroscopic or molecular property or the physical condition of the molecular ensemble. The merit of the present description relative to some previous derivations is examined.
The phase transitions of ferroelastic K2SeBr6: A calorimetric and x-ray diffraction study
Authors: Abriel Walter , White Mary Anne
Published: July 2002

Guinier x-ray powder diffraction data in the temperature range from T=10 to 290 K, and heat capacity measurements from T=40 to 280 K indicate three phases for K2SeBr6. The high-temperature cubic structure [K2PtCl6 -type, space group Fm3̄m; a=10.4211(7) Å at T=290 K] transforms at 237.8±0.3 K with ΔStr=(1.36±0.02) J K−1 mol−1 to a tetragonal phase with a Rb2TeI6 -type structure [space group P4/mnc; a=7.313(1) Å, c=10.474(2) Å at T=220 K]. A second phase transition at 215±1 K [ΔStr=(0.54±0.01) J K−1 mol−1 ] results in a monoclinic phase with a K2TeBr6 -type structure [space group P21/n; a=7.265(3) Å, b=7.265(3) Å, c=10.438(4) Å, β=89.66(5)° at T=80 K]. Both transitions can be interpreted in terms of softening of rotary phonons at the X edge of the Brillouin zone. From the thermal parameters of a single crystal x-ray structure determination at T=293 K, this low-temperature instability can be predicted. The results agree with comparable data of ferroelastic K2TeBr6 and refute some earlier speculations concerning the phase transitions in K2SeBr6.
The vibrational frequencies of ozone
Authors: Lee Timothy J. , Scuseria Gustavo E.
Published: July 2002

The equilibrium structure and harmonic frequencies of ozone have been determined at various levels of coupled-cluster theory using large one-particle basis sets. We have used the singles and doubles coupled-cluster (CCSD) method, the recently proposed CCSD(T) method, and the CCSDT-1 method. The largest one-particle basis sets utilize the atomic natural orbital (ANO) general contraction scheme and contain up through g-type functions. It is shown that f-type functions are essential for obtaining quantitative accuracy in the equilibrium structure and the harmonic frequencies (i.e.,±0.003 Å and ± 30 cm−1). The CCSD(T) level of theory in conjunction with a [4s 3p 2d 1f] ANO basis set is found to yield an equilibrium geometry and harmonic frequencies in excellent agreement with experiment. At this level of theory the harmonic frequencies are ω1(a1)=1152, ω2(a)1=717, and ω3(b2)=1057 cm−1 to be compared with the experimental values of 1135, 716, and 1089 cm−1, respectively. This success encouraged us to determine the cubic and quartic force constants and evaluate the anharmonic corrections to the fundamental vibrational frequencies. This level of theory is shown to be quite good for the a1 vibrational modes, but some of the cubic force constants involving ω3(b2) are shown to have large errors leading to an anharmonic correction for the asymmetric stretch that is about a factor of 2 too large.
The microwave spectrum of the equatorial conformer of chlorocyclopentane
Authors: Groner P. , Lee Min Joo , Durig J. R.
Published: July 2002

The microwave spectrum of chlorocyclopentane has been reinvestigated. The ground state and two vibrationally excited states of the equatorial conformation of c-C5H935Cl have been identified. The ground state rotational constants are A=6424.51(14) MHz, B=1832.304(6) MHz, C=1523.163(5) MHz. The spectrum of the 37Cl substituted species has also been assigned. For the previously reported axial conformer of c-C5H935Cl, additional transitions have been measured in the ground state and the first excited state of the lowest frequency motion and the spectrum of another vibrationally excited state has been assigned. The experimental rotational constants have been used to derive plausible molecular structures for both conformers. The experimental quadrupole coupling constants are compatible with the proposed structures.
Gaussian functions in Hylleraas-configuration-interaction calculations. VI. The first excited state of H+3
Authors: Preiskorn A. , Frye D. , Clementi E.
Published: July 2002

The Hylleraas-configuration-interaction (H-CI) method has been applied to the first 3Σ+u excited state of the H+3 molecular ion. Besides the ground state, this is the only known bound state of H+3, albeit with a very weak minimum of 8.428 kcal/mol. The equilibrium geometry and the minimum energy have been determined. The Hylleraas-CI energy of −1.116 102 7 a.u. at an equidistant nuclear separation of 2.454 bohr is the lowest reported so far. The vibrational force constants and vibrational frequencies also have been computed.
Configuration interaction and Hylleraas configuration interaction methods in valence bond theory. Diatomic two-electron systems
Authors: Cencek Wojciech , Komasa Jacek , Rychlewski Jacek
Published: July 2002

A method to construct configuration interaction (CI) and Hylleraas configuration interaction (Hylleraas–CI) wave functions of the valence bond type from Cartesian Gaussians for diatomic two-electron systems is presented. It is shown that this approach has many advantages in comparison with the usual molecular-orbital (MO) procedure and enables efficient optimization of nonlinear parameters. Sample results for the ground state of H2 are reported. In the case of CI they are better than all CI results obtained previously with Gaussian functions. The presented Hylleraas–CI function gives an error of about 2.8 cm−1 compared with the exact value.
Infrared spectroscopy and equilibrium structure of H2O+(X̃ 2B1)
Authors: Huet T. R. , Pursell C. J. , Ho W. C. , Dinelli B. M. , Oka T.
Published: July 2002

A color center laser spectrometer along with velocity modulation detection was used to record the absorption spectrum of H2O+ produced in an AC glow discharge between 3180 and 3390 cm−1 with a gas mixture of He/H2O. The predominant role of the reaction of metastable helium with H2O has been observed. The H2O+ ion is also present in the spectra recorded between 3100 and 3600 cm−1 with a gas mixture of He/H2/O2 and some features are illustrated. The ν1 and ν2+ν3−ν2 bands have been assigned and the previous analysis of the ν3 band [J. Mol. Spectrosc. 127, 1 (1988)] has been extended. The ν1 and ν3 states have been fitted together taking into account the vibration–rotation interaction. The molecular constants have been obtained for the ν1 and ν2+ν3 states and they have been improved in the case of the ν3 and the ground vibrational states. The equilibrium structure has been derived [re=0.9992(6) Å, θe=109.30(10)°] and the quadratic and cubic force field constants have been evaluated.