bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical dispersion relations in amorphous semiconductors InSb and GeSe2
Authors: Ojima Takayuki , Adachi Sadao
Published: July 2002

The pseudodielectric-function spectra, ε(E)=ε1(E)+iε2(E), of amorphous (a-) InSb and GeSe2 semiconductors in the 1.5–5.5 eV photon-energy range at room temperature were measured by spectroscopic ellipsometry. The samples studied were prepared by radio frequency planar magnetron sputtering (a-InSb), and by the melt-quenching technique (a-GeSe2). The ε2(E) spectra for these semiconductors showed a single broad peak (a-InSb) and a double-peaked structure (a-GeSe2), respectively. The single broad peak found in a-InSb is typically observed in amorphous tetrahedral semiconductors. The double-peaked structure in the ε2(E) spectrum of a-GeSe2 closely resembles the a-Se and a-Te spectra and is described by a simple model consisting of two valence bands and a lower conduction band. The experimental ε2(E) spectra are analyzed using Jellison-Modine model [Appl. Phys. Lett. 69, 371 (1996)], and excellent agreement is achieved between the calculation and experiment over the entire range of photon energies. Dielectric-related optical constants, such as the complex refractive index, absorption coefficient, and normal-incidence reflectivity, of a-GeSe2 have also been presented.
Electrical properties of silicon and beryllium doped (AlyGa1−y)0.52In0.48P
Authors: Najda Stephen P. , Kean Alistair , Duggan Geoffrey
Published: July 2002

The electrical properties of silicon and beryllium doped (AlyGa1−y)0.52In0.48P grown by gas source molecular beam epitaxy were studied. Unintentionally doped (GaIn)P has a n-type background concentration of 5.1×1014 cm−3 and a free-carrier mobility of ∼3500 cm2/V s at room temperature. Hall measurements of n-(GaIn)P give a linear increase in the free-carrier concentration for values up to 4.0×1018 cm−3. Silicon doping of (GaIn)P and (Al0.7Ga0.3)0.52In0.48P reveals a linear increase in the impurity carrier concentration for values up to 8.0×1018 cm−3 by capacitance–voltage measurements. In contrast, the free electron concentration saturates at a value of 4.8×1017 cm−3 in (Al0.7Ga0.3)0.52In0.48P, due to Fermi-level pinning at the DX level. Beryllium doping of (GaIn)P reveals a linear increase in the Hall free-hole concentration for values up to 1.4×1019 cm−3 with a room-temperature mobility of ∼34 cm2/V s.
Time-integrated reflectivity of laser-induced back-ablated aluminum thin film targets
Authors: Bullock Anthony B. , Bolton Paul R. , Mayer Fred J.
Published: July 2002

A study of the time-integrated reflectivity of Al targets during laser-induced back ablation by 1064 nm, 10 ns laser pulses is reported. The Al target reflectance data is analyzed using a model which includes not only Al surface removal but also the possible production of Al plasma. Calculations based on a sharp Al film ablation fluence (Jth≈710 mJ/cm2) threshold agree with the reflectance data. Plasma reflectance contribution is found to be negligible for plasma electron densities of less than 0.3 critical density.
Thermal expansion of scanning tunneling microscopy tips under laser illumination
Authors: Grafström S. , Schuller P. , Kowalski J. , Neumann R.
Published: July 2002

The periodic thermal expansion of scanning tunneling microscopy (STM) tips arising under irradiation with power-modulated laser light has been investigated. The expansion was determined by comparison with a calibrated piezomotion measured in an STM, which was operated in the constant-current mode, and instrumental effects were corrected for. The experimental data concerning the frequency response of the thermal expansion for various geometries of the tip and for different positions of the laser focus are compared with theoretical results which were derived from a numerical solution of the equation of heat conduction. A very good agreement is found. The results are also interpreted in terms of simplified analytical expressions. Furthermore, the theoretical data are used to derive the response of the tip to fast transients of the light power as in the case of pulsed irradiation.
Effect of localized vibrations on the Si surface concentrations of H and D
Authors: Ipatova I. P. , Chikalova-Luzina O. P. , Hess K.
Published: July 2002

The equilibrium concentration of passivating adatoms in the system of Si crystal plus the gas of H2 (or D2) molecules is calculated. The effect of adatom localized vibrations on the equilibrium concentration is taken into account. It is shown that the substitution of D for H leads to an increase of the adatom concentration by 1–1.5 orders of magnitude.
Wide supercooled liquid region and soft magnetic properties of Fe56Co7Ni7Zr0–10Nb (or Ta)0–10B20 amorphous alloys
Authors: Inoue A. , Koshiba H. , Zhang T. , Makino A.
Published: July 2002

An amorphous phase with a wide supercooled liquid region before crystallization was formed in Fe56Co7Ni7Zr10−xMxB20 (M=Nb or Ta, x=0–10 at. %) alloys by melt spinning. The glass transition temperature (Tg) and crystallization temperature (Tx) increase by the dissolution of 2% M and the degree of the increase is larger for Tx, leading to maximum ΔTx(=Tx−Tg) of 85 K at 2% Nb and 87 K at 2% Ta which are larger by about 20 K than the largest value for newly developed Fe–(Al, Ga)–(P,C,B,Si) amorphous alloys. The crystallization of the Nb-containing alloys occurs through two stages of amorphous (Am)→Am′+α-Fe+γ-Fe+Fe76Nb6B18 →α-Fe+γ-Fe+Fe76Nb6B18+Fe2Zr in the range less than about 6% Nb and Am→Am′+γ-Fe→γ-Fe+Co3Nb2B5+Ni8Nb in the range above 8% Nb. The change in the crystallization process with Nb content seems to reflect the easy precipitation of γ-Fe by the increase in the number of Fe–Nb pairs with weaker bonding nature as compared with the Fe–Zr pairs. The best soft magnetic properties were obtained at 2% Nb or 8% Ta. The saturation magnetization, coercive force, effective permeability at 1 kHz, and saturated magnetostriction in the annealed state for 300 s at 800 K are, respectively, 0.96 T, 2.0 A/m, 19 100, and 10×10−6 for the 10% Zr alloy, 0.75 T, 1.1 A/m, 25 000, and 12×10−6 for the 2% Nb alloy, and 0.85 T, 1.5 A/m 17 400, and 14×10−6 for the 8% Ta alloy. The Curie temperature is 531 K for the 2% Nb alloy and 538 K for the 8% Ta alloy. The success in synthesizing the new amorphous alloys with the wide supercooled liquid region and good soft magnetic properties is promising for future development as soft magnetic bulk amorphous alloys.
Temperature dependence of giant magnetoresistance properties of NiMn pinned spin valves
Authors: Mao Sining , Amin Nurul , Murdock Ed
Published: July 2002

The giant magnetoresistance response of NiMn pinned spin valves was studied at elevated temperature. Top spin valve films were made by ion beam sputtering and thermally treated to induce the strong unidirectional pinning field in the pinned layer. Both δR and δR/R decrease linearly with temperature. The sheet resistance of the spin valves also increases linearly with temperature. The exchange coupling between pinned layer and free layer decreases slightly and the coercivity of the free layer increases slightly. The temperature dependence of the exchange pinning field is unique in NiMn spin valves. The pinning field has a weakly increasing temperature dependence up to 200 °C, then decreases to zero at the blocking temperature of 380 °C. Samples with different thickness NiMn layers show different temperature dependencies. However, the blocking temperature is unchanged. The pinning fields of NiMn, FeMn, IrMn, and NiO spin valves were also measured up to 200 °C; NiMn pinned spin valves show the least dependence of pinning field at elevated temperatures.
Coercivity calculation of Sm2(Co,Fe,Cu,Zr)17 magnets
Authors: Katter M.
Published: July 2002

The coercivity of Sm2(Co,Fe,Cu,Zr)17 is calculated on the basis of a two dimensional model. To find local minima of the sum of the domain wall energy and the magnetostatic energy, the domain wall is divided into 1 nm long segments which are allowed to fluctuate randomly. With increasing field strength the domain wall is heavily bowed, forming the well known zig–zag domains. At higher field strengths, the domain wall is depinned first, from the edges of the 2/17 cells and later, from the intersection lines of the Z phase with the 1/5 boundary phase. For these two sites, the widths and the heights of the energy barriers for the movement of the domain walls are calculated in dependence of the applied magnetic field and compared with the thermal activation energy. As a result, the stronger pinning site is stable up to a local field strength of about 40 kA/cm. Since the domain wall generates a demagnetizing field of about 11 kA/cm at the critical position, the coercivity correlated to the stronger pinning site is reduced to 29 kA/cm at room temperature.
Changes in magnetic parameters of neutron irradiated SA 508 Cl. 3 reactor pressure vessel forging and weld surveillance specimens
Authors: Chi Se-Hwan , Chang Kee-Ok , Hong Jun-Hwa , Kuk Il-Hiun , Kim Chong-Oh
Published: July 2002

Irradiation-induced changes in the magnetic parameters and mechanical properties were measured and compared to explore possible correlations for reactor pressure vessel (RPV) forging and weld surveillance Charpy specimens which were irradiated to the neutron fluence of 2.3×1019 n/cm2 (E>1.0 MeV) in a typical pressurized water reactor environment at 290 °C. For mechanical property parameters, Vickers microhardness, tensile and Charpy impact tests were performed and saturation magnetization (Ms), remanence (Mr), coercivity (Hc), and Barkhausen noise amplitude (BNA) were measured for magnetic parameters for both unirradiated and irradiated specimens, respectively. Results of mechanical property measurements showed an increase in yield and tensile strength, Vickers microhardness, 30 ft. lb indexed RTNDT and a decrease in Charpy upper-shelf energy irrespective of forging and weld metals. Hysteresis loops appeared to turn clockwise, resulting in an increase in Hc, and BNA appeared to decrease after irradiation. Both magnetic parameters showed viable correlations to the changes in mechanical parameters (Vickers microhardness, Charpy upper shelf energy) due to irradiation. Even limited, the present study seems to show additional possibilities for the application of this magnetic method in monitoring the mechanical parameter changes due to neutron irradiation.
CoFe–Cu granular alloys: From noninteracting particles to magnetic percolation
Authors: Franco Victor , Batlle Xavier , Labarta Amı́lcar
Published: July 2002

CoFe–Cu granular films with ferromagnetic content ranging from 0.10 to 0.33 by volume were prepared by radio frequency sputtering. As-cast samples were rapidly annealed at various temperatures up to 750 °C to promote the segregation of CoFe particles within the metallic matrix. Magnetic and transport properties suggested that this family of samples may be classified into three groups: (i) below about 0.20 volume content of CoFe, all samples display the typical features of a granular solid constituted by a random distribution of nanometric CoFe particles within a Cu matrix, and the maximum magnetoresistance is about 20% at low temperature (giant magnetoresistance); (ii) for as-cast samples within 0.20 and 0.30 of volume concentration, magnetoresistance and magnetization display complex bimodal behavior and large metastable effects associated with the interparticle interactions, which stabilize a domain-like microstructure well below the volume percolation threshold (0.55), as already observed in CoFe–Ag(Cu) granular alloys. As a consequence of the large magnetic correlations, magnetoresistance is very low (1%–3%). Through annealing, the microstructure and therefore the transport properties evolve to those of a classical giant magnetoresistance system with large particles; and (iii) above about 0.30 of volume content (and still below the volume percolation threshold), as-cast samples display both anisotropic and giant magnetoresistance, as also observed in other granular alloys. Annealing leads to complete segregation and to the formation of large magnetic particles, which results in a transition from mixed behavior of both anisotropic and giant magnetoresistance (GMR) regimes to a giant magnetoresistance regime, with a maximum GMR of about 7%.
Study of microstructural behavior and nonadiabatic small polaron hopping conduction in BaTiO3 doped lead-vanadate glass and glass-ceramics dispersed with ferroelectric nanocrystals
Authors: Sadhukhan Manisha , Modak D. K. , Chaudhuri B. K.
Published: July 2002

Multicomponent semiconducting oxide glasses like (80 V2O5–20 PbO)+xBaTiO3 (x=5–30 wt %) dispersed with nanocrystalline BaTiO3 have been prepared by a fast quenching technique. Results of microstructural study and transport properties (between 80 and 450 K) of these glasses and some glass ceramics have been reported in this article. It has been shown from x-ray diffraction, scanning electron microscopic, and other studies that homogeneous glasses are formed with wide concentrations of BaTiO3 (x⩽30 wt %). Transmission electron microscopic study, however, indicates the presence of nanocrystalline phases in the glass matrix. Mott’s variable range (nonadiabatic) hopping conduction mechanism is found to be valid at the low temperature regime (below θD/4, θD being the Debye temperature) while in the high temperature regime (above θD/2), the polaron hopping models of Schnakenberg as well as Emin and co-workers can quantitatively predict the conductivity data for all these special types of multicomponent glass-nanocrystal composites. The model parameters, obtained from best fit of the experimental data with these models, are consistent with the glass compositions. The dielectric constants of these glasses are found to be very high (comparable to that of bulk BaTiO3) and about two orders of magnitude higher than those of BaTiO3 free (80 V2O5–20 PbO) and other transition metal oxide glasses. This novel character is considered to be due to the embedded nanocrystalline BaTiO3 phases. The glass samples annealed at 300 °C for 9 h in air also showed nano and microcrystalline BaTiO3 phase along with traces of PbV2O6, PbTiO3, TiO2, and Pb2V2O7 phases. Broad anomaly (with a maximum around 390 K) is observed from the thermal variation of dielectric constant data of these partially annealed glass-ceramic samples. This anomaly resembles to the anomaly observed around the Curie temperature (∼393 K) in bulk ferroelectric BaTiO3 crystal.
Tight-binding calculations of electronic properties of AgI
Authors: Laref A. , Sekkal W. , Zaoui A. , Certier M. , Aourag H.
Published: July 2002

The empirical tight-binding method is used to calculate the electronic band structure, density of states, and dielectric response function of AgI. Effective masses of electrons and holes, and the refractive index are also calculated. The results are compared with other calculations.
The transmittance pattern in a mesoscopic nonuniform necklace like system
Authors: Mak Hon-Lung , Lin Hai-Qing , Pan Zhiwen , Gong Chang-De
Published: July 2002

The energy spectrum, the density of states, and the electronic transmittance pattern of a necklace like chain under the influence of magnetic field (uniform and nonuniform) and nonlinear impurity scattering (ordered and disordered) are discussed. A variety of quantum interference effects exhibited in the transmittance pattern are discussed, and physical explanations of these effects and their applications in designing quantum devices are analyzed.
Optical phonon confinement in zinc oxide nanoparticles
Authors: Rajalakshmi M. , Arora Akhilesh K. , Bendre B. S. , Mahamuni Shailaja
Published: July 2002

Effect of confinement is investigated on optical phonons of different symmetries in the nanoparticles of zinc oxide with wurtzite structure using Raman spectroscopy. An optical phonon confinement model is used for calculating the theoretical line shapes, which exhibit different asymmetric broadening and shifts, depending on the symmetries of phonon and their dispersion curves. The best fit to the data is found for particle diameters consistent with those estimated using x-ray diffraction.
Structural and magnetic properties of Fex–C1−x nanocomposite thin films
Authors: Babonneau D. , Briatico J. , Petroff F. , Cabioc’h T. , Naudon A.
Published: July 2002

Iron–carbon nanocomposite thin films with iron concentrations ranging from 12 to 74 at. % were grown by ion-beam sputtering codeposition at different substrate temperatures. The microstructure of the films was characterized by transmission electron microscopy, atomic force microscopy, extended x-ray absorption fine structure, and grazing incidence small-angle x-ray scattering. A granular morphology consisting of body-centered-cubic iron-rich nanoparticles (2–5 nm in diameter and 3–8 nm in height with a relatively sharp size distribution) regularly distributed within a more or less graphitic matrix was obtained. Structural properties as well as magnetic ones were found to depend strongly on composition, substrate temperature, and postdeposition treatments (annealing or Ar+ irradiation). The temperature dependence of the susceptibility exhibited a superparamagnetic response with blocking temperature in the range of 13–180 K. The maximum low-temperature (5 K) coercivity value obtained in this study was 850 Oe for the film with the lowest iron content (x=0.12). The saturation magnetization was found to be reduced compared to the corresponding bulk value for pure α-Fe, and increased with increasing substrate temperature. Otherwise, when increasing the iron content, a decrease in coercivity was observed in correlation with an increase in remanent magnetization.
Feasibility of FePt longitudinal recording media for ultrahigh density recording
Authors: Bae Seung-Young , Shin Kyung-Ho , Jeong Jae-Yoon , Kim Jung-Gi
Published: July 2002

The feasibility of chemically ordered, ultrathin FePt longitudinal media for ultrahigh recording density is discussed with the basic magnetic and structural properties which can be obtained under acceptable thin film processing condition, as well as preliminary read/write test. High coercivity (≫3000 Oe) could be achieved even in the film with very low Mrt (≪0.3 memu/cm2) at moderate annealing temperature (375–450 °C). However, rapid degradation of crystallographic texture with thickness, in the absence of proper template layer, results in very low coercivity squareness (S*∼0.2), which may be detrimental to recording application. Media noise, particularly exchange coupling induced transition noise, may not be a critical problem, by virtue of extremely small grain size (≃5 nm) and high Ku.
Tertiary recrystallization and magnetic induction under various annealing atmospheres in thin-gauged 3% Si–Fe strip
Authors: Chai K. H. , Heo N. H. , Na J. G. , Lee S. L.
Published: July 2002

Surface-energy-induced secondary or tertiary recrystallization by grains with a specific surface plane can be freely governed in thin-gauged 3% Si–Fe strips by controlling the bulk content of sulfur and annealing atmosphere. During a vacuum or hydrogen annealing process, a convex profile in segregated-sulfur concentration is formed due to evaporation or desorption of segregated sulfur as a hydrogen sulfide, corresponding to a trough in magnetic induction. High magnetic induction is obtained after the annealing treatments. Final annealing under an argon atmosphere caused a saturation in segregated-sulfur concentration with annealing time. Under this extremely high segregated sulfur, grains of high index crystal plane including {111} continued to grow, resulting in low magnetic induction.
Mass distribution of ejected molecules and clusters in noncascade sputtering processes
Authors: King B. V. , Ziv A. R. , Lin S. H. , Tsong I. S. T.
Published: July 2002

A model of noncascade sputtering is proposed to explain the mass distribution observed by MacFarlane and co-workers in the sputtering of insulin by 90 MeV 127I20+ ions. The ejection of molecular ions from insulin is considered to be induced by vibrational excitation. The ensuing calculations using RRKM theory show that the relative abundance of the ejected species can be fitted to our model yielding realistic values for both the energy deposited by the incident ion and the activation energies required for the ejection of the molecular species.
Relativistic configuration interaction calculations of the low-lying states of TlF
Authors: Balasubramanian K.
Published: July 2002

Relativistic configuration interaction calculations (including spin-orbit interaction) are carried out for the nine low-lying ω–ω states arising from the 1Σ+, 3Π, 1Π, 3Σ−, 3Σ+, and 3Δ Λ-S states of TlF. Our calculations confirm the earlier assignment of experimentally observed spectra to some of these states. We have calculated the spectroscopic properties of both experimentally observed states (1Σ+0+, 3Π0+, 3Π1, 1Π1) and 3Π0−, 3Π2, 0−(II), 2(II), and 0+(III) states. The calculated spectroscopic properties are in good agreement with experimental values. The potential energy curves of the excited states of TlF [3Π0+, 3Π1, 3Π2, 3Π0−, 0−(II), 0+(III), and 2(II)] contain maxima thus confirming the recent experimental observations which predict potential barriers in the excited Π states. Vibrational bands higher than ν′=3 for 3Π0+ and ν′=8 for 3Π1 could not be observed. The present calculations explain this based on the crossing of repulsive 0− (I) state with 3Π0+ and 3Π1 thus leading to predissociation.
Two-photon electronic spectroscopy of Cs2GeF6:Mn4+
Authors: Chien Ring-Ling , Berg John M. , McClure Donald S. , Rabinowitz Paul , Perry Bruce N.
Published: July 2002

The spectrum of the d→d transitions of Mn+4 in Cs2GeF6 has been observed by means of two-photon spectroscopy using a tunable infrared laser. The g→g two-photon spectrum is fully allowed and therefore, shows the true electronic origins and symmetric vibrational sidebands without any interfering odd parity vibrations. The resulting spectra for each of the four electronic states studied (2Eg,2T1g,4T2g,a 4T1g), a 4T1g), are free of lattice mode and enabling mode complications and provide data for the analysis of Jahn–Teller effects, spin-orbit coupling, and other dynamical processes at the impurity ion. In the 4T2g, state there is clear evidence both in the quenching of the origin quartet, and in the vibronic structure for both e- and t2-type Jahn–Teller distortions. Each of the four states shows a specific, and a different mode of coupling to the lattice. Many other spectroscopic details are revealed, none of which were evident in the one-photon spectra.
Computations of the phase equilibrium, elastic constants, and viscosities of a hard-rod nematic liquid crystal
Authors: Lee Sin-Doo , Meyer Robert B.
Published: July 2002

Using an iterative solution to the Onsager integral equation for the orientational distribution function of spherocylinders in the nematic liquid crystal phase, we have studied several aspects of the Onsager theory of nematic ordering. We find that the isotropic–nematic coexistence region becomes narrower as the ionic strength of the solution decreases. We also calculate the curvature elastic constants and the nematodynamic viscosities of the nematic phase as a function of particle concentration. The results are compared to experimental data.
Corrections to preaveraging approximation within the Kirkwood–Riseman model for flexible polymers: Calculations to second order in ε with both hydrodynamic and excluded volume interactions
Authors: Wang Shi-Qing , Douglas Jack F. , Freed Karl F.
Published: July 2002

The polymer hydrodynamic radius RH is calculated to second order in the ε=4−d (d is the dimension) perturbation theory using the Kirkwood–Riseman model in conjunction with the renormalization group. Excluded volume effects on RH are modeled by the two-parameter theory, and the hydrodynamic radius is evaluated both with and without the preaveraging approximation. These second order in ε calculations are then used to evaluate the leading corrections in ε to the preaveraging approximation for RH. Gaussian and self-avoiding chains in three dimensions yield nondraining limit preaveraging corrections of 26% and 16%, respectively, whereas simulations by Zimm and others using the same rigid body model of dynamics produce only about a 12% correction for Gaussian chains. It thus appears that the dynamical renormalization group theory only provides a qualitative prediction of the preaveraging error to this order in the ε-perturbation theory.
The adsorption and thermal decomposition of water on clean and oxygen-predosed Al(111)
Authors: Crowell J. E. , Chen J. G. , Hercules D. M. , Yates J. T.
Published: July 2002

The adsorption of water on both clean and oxygen-predosed Al(111) has been studied by vibrational spectroscopy using electron energy loss spectroscopy (EELS). At 130 K, adsorption on either surface is competitively associative and dissociative. The dominant dissociation product is a hydroxyl species. On the clean surface, adsorption is predominantly molecular, while in the presence of oxygen, adsorption is predominantly dissociative. In contrast to the low temperature behavior, adsorption of water on clean Al(111) at 300 K is completely dissociative, resulting in oxygen adsorption and surface oxidation. Adsorbed hydroxyl species can be produced at 300 K by prolonged water exposure. Upon heating a low-temperature water layer adsorbed on either surface, molecular water desorption and further decomposition both occur. The production of adsorbed hydroxyl species from water reaches a maximum at 250 K on the clean surface and at 350 K on the oxygen-predosed surface. The hydroxyl species decompose above these temperatures to evolve hydrogen and further oxidize the Al(111) surface.
One- and two-photon spectroscopy of the 3E
g state of NaF:Cu+: Observation and analysis of vibronic fine structure
Authors: Berg John M. , Chien Ring-Ling , McClure Donald S.
Published: July 2002

One- and two-photon laser excitation spectra of the 1A1g→3Eg transition of NaF:Cu+ are reported, these being the first direct observations of the lowest d9s excited state of Cu+ in an alkali halide host. The spin–orbit splitting of the 3Eg vibronic origin is directly measured, and can be compared with values inferred from studies of the temperature and magnetic field dependence of the emission lifetime. Clear vibrational progressions based on both spin–orbit origins are assigned to odd parity local modes of t1u symmetry. We also report high resolution emission spectra which reveal evidence of a corresponding local mode in the ground state with a fundamental frequency significantly higher than that observed in any of the d9s excited states. We model these spectroscopic data and those of the 1Eg and 1T2g states within the adiabatic approximation using three-parameter anharmonic vibrational potentials, evaluating the energies and wave functions by a variational procedure. Good fits are obtained for most spectroscopic features. Those features which are not accommodated by the adiabatic model potentials are accounted for by nonadiabatic vibronic coupling.
An ESR study on solvated electrons in water and alcohols: Difference in the g factor and related analysis of the electronic state by MO calculation
Authors: Shiraishi Hirotsugu , Ishigure Kenkichi , Morokuma Keiji
Published: July 2002

An induction-detecting ESR spectrometer system, capable of μs time resolution, has been set up, and measurements were made on the radiolytically produced solvated electrons in water, methanol, ethanol, and mixtures of water and these alcohols. The spectrum of the solvated electron was a singlet in all these solvents. The g factor of the hydrated electron was measured to be 2.000 47±0.000 07 at 22 °C in reasonable agreement with the reported data. While this value is significantly smaller than the free electron g factor, the corresponding g factors in methanol and in ethanol, respectively 2.002 05±0.000 07 and 2.001 97±0.000 07 at 22 °C, were found much closer to it. In both methanol–water and ethanol–water mixtures the g factor of the solvated electron varied approximately in proportion to the mole fraction. The g shift of the hydrated electron was interpreted as arising from spin density in the proximity of oxygen nuclei of water molecules. Ab initio MO calculations were performed for an anionic cluster of water and that of methanol, assuming a cavity-like structure. The result showed that while in a water cluster the spin population on oxygen 2p atomic orbitals was in fact significant, the corresponding orbital spin population was smaller in a methanol cluster especially with a dipole-oriented model. The difference was considered to be related to increased diffuseness of the half-occupied orbital in the latter cluster.
Polarized D2 Stokes–Raman Q branch broadened by He: A numerical calculation
Authors: Blackmore Robert , Green Sheldon , Monchick Louis
Published: July 2002

The high pressure dependence of the linewidths of the D2 polarized Q branch of the Stokes Raman ν=0→1 transition is calculated numerically and compared with the experimental linewidths. These linewidths are computed using the Shafer–Gordon formula for the line broadening cross section. The requisite S matrices are determined from an ab initio D2–He interparticle potential averaged over D2 vibrational wave functions. These wave functions were also calculated with an ab initio D–D potential. Thus, there were no adjustable parameters for the linewidth calculations. In the high pressure limit, the calculated linewidths matched the experimental linewidths to within about 5%.
Molecular bonding with scandium: Diatomics ScH, ScO, ScC, and ScN
Authors: Jeung G. H. , Koutecký J.
Published: July 2002

The spectroscopic and chemical properties of some typical diatomics of scandium are calculated using a nonempirical HF pseudopotential and multireference single-and-double configuration interaction. The potential energy curves of ScO, where the ground state (2∑+) is clearly separated from other low-lying states (2Δ,2Π, and 4Π), are in good agreement with experimental data, and the strong bonding is paralleled with a significant ionic nature. All six lowest states (1∑+,3∑+,1Π,3Π,1Δ, and 3Δ) of ScH dissociating into the ground state atoms have a common bonding orbital and they can only be distinguished from each other by the orbital(s) used by the two nonbonding Sc electrons and their relative spin dispositions. The ScC molecule has about the same stability as ScH with respect to dissociation of the ground state, but the former shows a more complicated bonding nature in its lowest states (2∑+,2Π,2Δ,4∑−,4∑+,4Π, and 4Δ). Highly degenerate bound states 5Δ,5Π, and 3∑− of ScN appear to be the least bonding among the heteronuclear diatomics studied here. The estimated binding energies obtained from these calculations are about 2.0 eV for ScH and ScC, and 1.0 eV for ScN. The different characteristics of the lowest Sc atomic states which are due to different 3d and 4s occupations are analyzed.
Theoretical study of the A′ 5Σ+g and C″ 5Πu states of N2: Implications for the N2 afterglow
Authors: Partridge Harry , Langhoff Stephen R. , Bauschlicher Charles W. , Schwenke David W.
Published: July 2002

Theoretical spectroscopic constants are reported for the A′ 5Σ+g and C″ 5Πu states of N2 based on CASSCF/MRCI calculations employing large ANO Gaussian basis sets. Our calculated A′ 5Σ+g potential differs qualitatively from previous calculations in that the inner well is significantly deeper (De ≊3450 cm−1). The potential also has a substantial barrier (≊500 cm−1) to dissociation with a maximum near 4.3 a0, and then a shallow (≊47 cm−1) van der Waals minimum near 6.3 a0. We suggest that it is the v=4 and v=5 levels that are involved in predissociating the a 1Πg and B 3Πg states, as opposed to v=0 and v=1 proposed by Verma. The deeper well in the A′ 5Σ+g state provides considerable support for the theory of Berkowitz, Chupka, and Kistiakowsky who proposed that A′ 5Σ+g is the primary precursor state involved in the yellow Lewis–Rayleigh afterglow of nitrogen. The theoretical De for the C″ 5Πu state is also much larger than previous estimates. The previously unassigned Hermann infrared system (HIR) band positions correspond exceptionally well to our theoretical values for the C″ 5Πu →A′ 5Σ+g transition. This and other considerations lead to a rather convincing assignment of this transition as the HIR system. Einstein coefficients and radiative lifetimes are presented for this transition. Since the natural radiative lifetime of this state is much longer than experimental estimates, the C″ 5Πu state may derive its actual lifetime through interaction with the C 3Πu state.
Pressure effects on kinetics and decay processes in xenon after selective photoexcitation
Authors: Moutard P. , Laporte P. , Subtil J.-L. , Damany N. , Damany H.
Published: July 2002

Kinetics associated with the decay of the low-lying excited states of xenon is investigated in a density range 2.5×1018 to 2.5×1020 atoms cm−3 (pressure range between 104 and 106 Pa). Three different experiments are performed, i.e., two-photon excitation of 6p atomic states or 0+g molecular states, VUV one-photon excitation of the 6s[3/2]1 and 6s′[1/2]1 atomic states, and laser probing of intermediate transient species. The basic experimental data are the time-resolved second continuum excimer fluorescence at ∼173 nm and the photoionization current. It is found that all excitation decays through 6s[3/2]1 or 6s[3/2]2 with a branching ratio 9/1. Part of the 6s[3/2]1 species (70%) decay subsequently via the 6s[3/2]2 level. The effectiveness of these atomic intermediate steps is directly demonstrated by the transient laser probing. This result, the time analysis, and the discussion allow to set a clear basis to the involved processes and to rule out part of the models proposed in the literature. In particular, the hypothesis of infrared decay from attractive high-lying molecular states to the lowest lying excimer states 0+u /6s[3/2]1 and 1u0−u /6s[3/2]2 is rejected. The data treatment, with the help of 2 or 2×2 exponential formula depending on density, is discussed. It takes into account the instrumental response so that kinetics information is reached down to the nanosecond range. In particular, the 0+u, v≊0/6s[3/2]1 relaxed excimer lifetime is found to be 4.5(5) ns, and that of the 1u,0−u /6s[3/2]2 state 103(2)ns.
The microwave spectrum of SiF+
Authors: Petrmichl Rudolph H. , Peterson Kirk A. , Woods R. Claude
Published: July 2002

The first detection of the silicon monofluoride cation by spectroscopic means has been achieved at millimeter and submillimeter wavelengths. Frequencies of rotational transitions spanning a range of J values from 1 to 14 and all vibrational states from v=0 to 15 were precisely measured. Lines of 29 SiF+ up to v=4 and 30 SiF+ up to v=3 were also included in this study. These data were all well fit by a standard Dunham expansion with eight terms, with no requirement for a Watson type ΔSi01 parameter, describing breakdown of the Born–Oppenheimer approximation, to explain the isotope dependence. The parameters Be (or re ), ωe , and the Dunham potential constants a1 –a5 were well determined from this analysis and showed very satisfying agreement with the results of our recent large basis set MP4SDQ and CI calculations, which we had used to determine the search range for locating the spectrum of SiF+ . The final results are re =1.526 495 0(2) Å and ωe =1050.7(2) cm−1.
Selective excitation and analysis of NaF:Cu+ electronic transitions using two-color, two-photon spectroscopy
Authors: Berg John M. , McClure Donald S.
Published: July 2002

Nonresonant, one-color and two-color, two-photon excitation spectra of d10→d9s transitions in NaF:Cu+ at T<15 K are presented. The two-color method is shown to provide a means of using the symmetry selectivity of two-photon excitation to its fullest extent to separate cleanly bands normally distorted or obscured by other transitions. The spectra give unambiguous assignments and accurate energies of the T2g(3T2g) and Eg(3T2g) electronic states within the d9s excited state manifold. Vibronic fine structure is observed at the electronic origins of transitions to each of these states. This structure aids in band assignment and in analysis of the symmetric mode vibrational potentials in the excited states. Band intensities are analyzed and vibronic fine-structure linewidths are interpreted in terms of nonradiative relaxation. These new data require a reassessment of the assignment of the bands previously attributed entirely to transitions to the 1Eg state. It is suggested that Jahn–Teller splitting does not distort this state to a spectroscopically observable degree, contrary to earlier interpretations of the spectra, and that only the lower energy of the two Eg bands originates from transitions to the state ofprimarily singlet character. Observed spin–orbit coupled energy levels are modeled using crystal field splittings, singlet–triplet splittings, and the Cu+3d spin–orbit constant as variable parameters. The resulting fit gives energies and intensities which are in agreement with all measured experimental values if ζ3d is approximately equal to its free ion value.
Desorption and trapping of argon at a 2H–W(100) surface and a test of the applicability of detailed balance to a nonequilibrium system
Authors: Rettner C. T. , Schweizer E. K. , Mullins C. B.
Published: July 2002

Molecular beam techniques have been used to probe the dynamics of the trapping and trapping–desorption of Ar at a hydrogen-saturated W(100) surface. Trapping probabilities have been measured as a function of incidence energy Ei, and angle θi for a surface temperature Ts of 85 K. We find that this probability scales approximately with Ei  cos θi, rather than Ei or the so-called ‘‘normal energy’’ Ei  cos2 θi. Trapping probabilities approach unity for low energies, falling to 0.5 and 0.05 for Ei  cos θi ∼30 and 100 meV, respectively. The time-of-flight distributions of scattered Ar are clearly bimodal in many cases, having both direct–inelastic and trapping–desorption components. The latter component has been characterized over a wide range of conditions to provide information on the desorption of Ar from this surface. We find that desorbing species emerge with a near-cosine angular distribution for Ts ≂85 K. However, these distributions become increasingly noncosine as Ts is raised, becoming substantially broader than cosine. In addition, at the lowest temperature employed (∼85 K), the velocity distributions of the desorbing atoms are well described by Maxwell–Boltzmann distributions characteristic of the surface temperature. At higher temperatures, these distributions are still approximately Boltzmann, but the characteristic temperature falls below Ts. The ‘‘lag’’ between this effective temperature and Ts increases with Ts and is most pronounced for atoms desorbing at angles close to the normal. We show that the desorption results are very close to the predictions of a model in which angular and velocity distributions for desorption are synthesized by applying detailed balance arguments to the trapping data. Similarly the trapping results are close to trapping curves extracted from the desorption data.
Ionization and temperature dependent attachment cross section measurements in C3F8 and C2H3Cl
Authors: Chantry P. J. , Chen C. L.
Published: July 2002

Total ionization and attachment cross sections have been measured in C3F8 at 330 K using an electron beam and a total ion collection technique, calibrated by similar measurements on N2O and Xe. Our total ionization cross section is similar in general shape to a previous measurement of this type, but with typically half the magnitude. The ionization threshold cannot be accurately derived from these measurements, due to severe upward curvature immediately above threshold. The positive-ion signal rises above the background at 13.0±0.1 eV, to be regarded as a lower limit to the true threshold. An overall ionization cross section with a threshold at 13.3 eV is recommended, based on threshold data from photoelectron spectroscopy and the present data between 14 and 80 eV. The room temperature total attachment cross section peaks at 2.8 eV with a value of 1.75×10−17 cm2. This is 14 times smaller than the only other measurement of this type we are aware of. There is much better agreement with two more recently reported values unfolded from swarm experiments. The temperature dependence of the predominant dissociative attachment process, involving F− production, was studied in a different apparatus using a mass filter and ion pulse counting. At 730 K the peak cross section has increased by ∼60% and the threshold is lower by 1.1 eV. This second type of measurement was used to study the predominant dissociative attachment process in C2H3Cl, involving Cl− production. At 290 K this has a threshold at 0.85 eV and a peak at 1.35 eV of 3.2×10−17 cm2, in good agreement with recent work elsewhere. At 850 K the cross section at the peak is 2.6 larger, and lower in energy by 0.33 eV, while at 0 eV it has reached 6×10−18 cm2. At higher temperatures effects ascribed to thermal dissociation of the C2H3Cl were observed. The implications of the present results regarding the use of these gases in diffuse discharge switches are discussed.
Liquid polymer conformation on solid surfaces
Authors: Novotny V. J. , Hussla I. , Turlet J.-M. , Philpott M. R.
Published: July 2002

Infrared spectra of thin films of polyperfluoroethers on metal and silicon dioxide surfaces were obtained for films with thicknesses between 1 and 1000 nm by p-polarized reflection and modulated polarization techniques. Changes in frequencies and relative intensities of vibrational peaks with film thickness suggest that the conformation of liquid polymers on surfaces is unlike bulk conformation, with polymer chains extended preferentially along the surface.
Slit jet infrared spectroscopy of NeHF complexes: Internal rotor and J-dependent predissociation dynamics
Authors: Nesbitt D. J. , Lovejoy C. M. , Lindeman T. G. , ONeil S. V. , Clary D. C.
Published: July 2002

Direct absorption tunable difference frequency IR spectroscopy in a slit jet supersonic expansion has been used to observe complexes of Ne with HF for the first time. Spectra of both the weak HF stretch fundamental (1000)←(0000) and the 10–20 fold more intense bend and stretch combination band (111e,f0)←(0000) transitions are observed, and illustrate several interesting dynamical features. The large ratio of combination band to fundamental intensity is evidence for a highly isotropic potential with respect to HF rotation. The HF bend vibration is thus better thought of as nearly free internal rotor motion with a nearly good space fixed quantum number, jHF =1. Weak anisotropy in the potential permits the jHF=1 (Πebend) levels to relax intramolecularly to jHF =0 (Σ) levels, leading to predissociative line broadening in the sub-Doppler slit jet spectra. This observed dissociation of NeHF with 44 cm−1 of internal excitation provides a rigorous upper limit to the binding energy. The Πfbend levels, on the other hand, have no lower energy internal rotor states of the correct parity to relax into, and thus the (111f0) ←(0000) spectra exhibit linewidths limited by the apparatus resolution. The internal relaxation of the jHF=1 (Πebend) levels results from Coriolis mixing with the Σbend states (1200) by overall rotation of the NeHF complex, and thus the lifetimes depend dramatically on J. The J-dependent predissociation rates observed are in remarkably quantitative agreement with quantum scattering calculations on the CEPA ab initio surface of ONeil and co-workers.
Leading concentration correction to polymer dynamic self-structure factor
Authors: Perico Angelo , La Ferla Roberto , Freed Karl F.
Published: July 2002

The discrete chain representation of multiple scattering theory of the concentration dependence of the hydrodynamics of polymer solutions is applied to the calculation of the leading concentration correction to the dynamic structure factor S(k,t) and its first and second cumulants of individual labeled Gaussian chains in theta solutions at nonzero concentrations. Contributions are separated into those from overall translational and internal chain motions as well as couplings between different internal modes and between translation and internal modes, coupling that are introduced by interchain hydrodynamic interactions. The separate contributions are analyzed as a function of k and of t in order to isolate regions where certain contributions are dominant. As expected, short times and larger k tend to favor contributions from internal chain dynamics, while longer times and smaller k make concentration dependent translational effects predominate. Computations for shorter chains are extrapolated to provide the asymptotic long chain behavior.
Parallel vibrational states of CH3I in the high resolution infrared spectrum from 2770 to 2900 cm−1
Authors: Lattanzi F.
Published: July 2002

The analysis of the high resolution infrared spectrum of CH3I between 2770 and 2900 cm−1, where only parallel transitions are observed, allowed the identification of the complex branch origin patterns of the interacting parallel system 2ν05, ν3+ν∓15 +ν±16, 2ν3+2ν06. The values of vibrational frequencies, vibration–rotation parameters affecting the K structures, and interaction parameters have been estimated by a least squares fit of the observed transition wave numbers.
First laboratory observation of niobium monosulphide in the gas phase
Authors: Simard B. , Masoni C. , Hackett P. A.
Published: July 2002

The diatomic molecule NbS has been observed for the first time by laser-induced fluorescence at low resolution in a supersonic molecular beam following expansion of a CS2/He (1:100) mixture through a laser-produced plasma of niobium atoms. Two band systems have been observed in the visible (400–700 nm); a strong one and a weaker one. The strong one has its origin near 15 670 cm−1 and is shown to belong to the C 4Σ−–X 4Σ− system. The weaker one has its origin likely at 15 215 cm−1 and is attributed to the 2Σ+–X 4Σ−1/2 system. The latter system is observed owing to the 2Σ+(σ1δ2)∼C4Σ−1/2 (δ2σ*1) perturbation induced by the spin–orbit operators. This perturbation has been characterized through vibrational energy shifts, vibronic lifetimes, and analysis of the perturbation matrix elements. This enables direct determination of the large second-order spin–orbit splittings in the C 4Σ− and X 4Σ− states.

In the ground state, the splitting which is due to the isoconfigurational 〈2Σ+‖Hso‖X 4Σ−〉 interaction element has been established to be 63 cm−1 and is independent of the vibrational energy content. In the C state, the spin–orbit splitting arises from two interactions; one due to the isoconfigurational 〈2Σ+‖Hso‖C 4Σ−〉 interaction and the other to the 〈2Σ−(σ1δ2), (v+1)‖Hso‖C 4Σ−(δ2σ*1),v〉 interaction. The former interaction splits the C 4Σ−3/2 and C 4Σ−1/2 components by about 63 cm−1, as in the ground X 4Σ− state again independent of the vibrational energy content. The second interaction which becomes negligible at v(C 4Σ−)≥4 shifts the C 4Σ− (v=0,1,2,3) levels to lower wave numbers by 18, 15, 11, and 5 cm−1, respectively. From a Franck–Condon analysis, the electronic part of the molecular matrix elements 〈2Σ+(σ1δ2), v′‖Hso‖C 4Σ−(δ2σ1*),v″〉 is estimated to be 57 cm−1. Other molecular parameters such as vibrational frequencies and anharmonicities, radiative lifetimes, Franck–Condon factors, mixing coefficients, and approximate bond lengths are reported and discussed.
Bond-selected bimolecular chemistry: H+HOD(4νOH)→OD+H2
Authors: Sinha Amitabha , Hsiao Mark C. , Crim F. Fleming
Published: July 2002

The reaction of HOD containing four quanta of O–H bond stretching vibration with H atoms produces OD fragments almost exclusively. Vibrational overtone excitation prepares HOD(4νOH) that reacts with H atoms formed in a microwave discharge. The endothermic reaction of water with hydrogen atoms does not occur for ground vibrational state water but proceeds at roughly the gas kinetic collision rate for the vibrationally excited molecule. The production of OD fragments from HOD(4νOH) in the reaction is at least two orders of magnitude more efficient than the production of OH, indicating very selective reaction of the vibrationally excited bond.