Large EA Research Articles

NMR analysis of structural geometry and molecular dynamics in perovskite-type N(CH3)4CdBr3 crystal near high-temperature phase transition.

The NMR chemical shifts, linewidths, spin-lattice relaxation times in the rotating system T1ρ, and spin-lattice relaxation times in the laboratory system T1 were evaluated for the perovskite-type N(CH3)4CdBr3 crystal, aiming to understand the changes in the structural geometry and molecular dynamics from phase I to phase II. From the temperature-dependence of the 1H, 13C, 14N, and 113Cd NMR chemical shifts, the structural geometry underwent a continuous change, without anomalous changes around (TC = 390 K). However, the linewidths in phase I were narrower than those in phase II, indicating that the motional averaging effects were caused by the rapid rotation of the N(CH3)4 group. Sudden changes in T1 and T1ρ were observed near TC, for which the activation energy Ea in phase I was approximately 12 times larger than that in phase II; the small Ea values in phase II indicate a large degree of freedom for the methyl group and CdBr6 octahedra, whereas the large Ea in phase I was primarily attributed to the overall N(CH3)4 and the 113Cd in the CdBr6 groups. Consequently, the phase transition mechanisms of N(CH3)4CdBr3 are related to reorientation of the N(CH3)4 group and the arrangement of the CdBr6 groups.

Theoretical insights into catalytic CO2 hydrogenation over single-atom (Fe or Ni) incorporated nitrogen-doped graphene

Developing highly efficient and cheap catalysts for the CO2 hydrogenation is the key to achieve CO2 conversion into clean energy. Herein, periodic density functional theory (DFT) calculations are performed to investigate possible reaction mechanisms for the hydrogenation of CO2 to formic acid (cis- or trans-HCOOH) product over a single Fe or Ni atom incorporated nitrogen-doped graphene (Fe-N3Gr or Ni-N3Gr) sheets. Our calculations found that the CO2 hydrogenation proceeds via a coadsorption mechanism to produce cis- or trans-HCOOH over Fe-N3Gr and Ni-N3Gr surfaces, which is classified into 2 steps: (1) the CO2 hydrogenation to form a formate (HCOO*) intermediate and (2) hydrogen abstraction to produce cis- or trans-HCOOH. The formation of trans-HCOOH over both Fe-N3Gr and Ni-N3Gr surfaces exhibit the obvious superiority due to the low barrier all through the whole channel. The highest energy barriers (Ea) in the case of trans-HCOOH formation on Fe-N3Gr and Ni-N3Gr surfaces are only 0.57 and 0.37 eV, respectively, which indicated that the CO2 hydrogenation to trans-HCOOH could be realized over these catalysts at low temperatures, especially the Ni-N3Gr surface. On the other hand, our findings show that the competitive reaction that produces CO and H2O is almost impossible or extremely difficult to proceeds under ambient conditions due to the large Ea for the formation of these side products. Moreover, the microkinetic modeling of the CO2 hydrogenation on both surfaces was investigated to confirm these results. Thus, the Fe-N3Gr and Ni-N3Gr catalysts reveal excellent catalytic activity and highly selective for CO2 hydrogenation to trans-HCOOH. This theoretical investigation not only provides a promising catalyst but also gives a deeper understanding of CO2 hydrogenation reaction.

Electronic Structure and Trap States of Two-Dimensional Ruddlesden–Popper Perovskites with the Relaxed Goldschmidt Tolerance Factor

Two-dimensional Ruddlesden–Popper perovskites (2D RPPs) have been considered as promising building blocks for optoelectronic applications owing to optical properties comparable to the ones of 3D perovskites, together with superior stability. In addition, the more flexible structure adopted by such perovskites leads to a relaxation of the Goldschmidt tolerance factor (τ) requirement. Herein, we compare the crystalline and electronic structures, as well as the photophysics of two 2D perovskite single crystals (n-BA)2(MA)2Pb3I10 (BMAPI) and (n-BA)2(EA)2Pb3I10 (BEAPI) (n-BA = n-butylamine) containing small A-cations (MA, methylammonium) and large A-cations (EA, ethylammonium), respectively. The latter presents a relaxed τ (τEA > 1) compared with the requirement of a stable phase in 3D perovskites (τ < 1). Such relaxed τ is beneficial from the structural flexibility of the long organic cation bilayer and the pronounced lattice distortions in the 2D perovskite structures. We further elucidate how the greater lattice distortions concurrently modulate the electronic structure as well as trap densities in these 2D RPPs. The electronic band gap (Eg) of BEAPI (2.08 ± 0.03 eV) is ∼0.17 eV larger than the one of BMAPI (1.91 ± 0.03 eV). This is mainly because of a shift in the valence band maximum associated with the expansion of the Pb–I bond length in BEAPI. In addition, the overall trap state densities for BMAPI and BEAPI are calculated to be ∼2.18 × 1016 and ∼3.76 × 1016 cm–3, respectively, as extracted from the time-resolved photoluminescence studies. The larger trap density in BEAPI can be attributed to the stronger interfacial lattice distortion that sets in when large EA cations are contained into the inorganic crystal lattice. (Less)

The Effect of Chemical Reactivity on the Formation of Gaseous Oblique Detonation Waves

High-fidelity numerical simulations using a Graphics Processing Unit (GPU)-based solver are performed to investigate oblique detonations induced by a two-dimensional, semi-infinite wedge using an idealized model with the reactive Euler equations coupled with one-step Arrhenius or two-step induction-reaction kinetics. The novelty of this work lies in the analysis of chemical reaction sensitivity (characterized by the activation energy Ea and heat release rate constant kR) on the two types of oblique detonation formation, namely, the abrupt onset with a multi-wave point and a smooth transition with a curved shock. Scenarios with various inflow Mach number regimes M0 and wedge angles θ are considered. The conditions for these two formation types are described quantitatively by the obtained boundary curves in M0–Ea and M0–kR spaces. At a low M0, the critical Ea,cr and kR,cr for the transition are essentially independent of the wedge angle. At a high flow Mach number regime with M0 above approximately 9.0, the boundary curves for the three wedge angles deviate substantially from each other. The overdrive effect induced by the wedge becomes the dominant factor on the transition type. In the limit of large Ea, the flow in the vicinity of the initiation region exhibits more complex features. The effects of the features on the unstable oblique detonation surface are discussed.

Superior energy-storage properties in (Pb,La)(Zr,Sn,Ti)O3 antiferroelectric ceramics with appropriate La content

Abstract Antiferroelectric (AFE) ceramics based on Pb(Zr,Sn,Ti)O3 (PZST) have shown great potential for applications in pulsed power capacitors because of their fast charge-discharge rates (on the order of nanoseconds). However, to date, it has been proven very difficult to simultaneously obtain large recoverable energy densities Wre and high energy efficiencies η in one type of ceramic, which limits the range of applications of these materials. Addressing this problem requires the development of ceramic materials that simultaneously offer a large ferroelectric-antiferroelectric (FE-AFE) phase-switching electric field EA, high electric breakdown strength Eb, and narrow polarization-electric field (P-E) hysteresis loops. In this work, via doping of La3+ into (Pb1-1.5xLax)(Zr0.5Sn0.43Ti0.07)O3 AFE ceramics, large EA and Eb due to respectively enhanced AFE phase stability and reduced electric conductivity, and slimmer hysteresis loops resulting from the appearance of the relaxor AFE state, are successfully obtained, and thus leading to great improvement of the Wre and η. The most superior energy storage properties are obtained in the 3 mol% La3+-doped (Pb1-1.5xLax)(Zr0.5Sn0.43Ti0.07)O3 AFE ceramic, which simultaneously exhibits at room temperature a large Wre of 4.2 J/cm3 and a high η of 78%, being respectively 2.9 and 1.56 times those of (Pb1-1.5xLax)(Zr0.5Sn0.43Ti0.07)O3 AFE ceramics with x = 0 (Wre = 1.45 J/cm3, η = 50%) and also being superior to many previously published results. Besides, both Wre and η change very little in the temperature range of 25–125 °C. The large Wre, high η, and their good temperature stability make the Pb0.955La0.03(Zr0.5Sn0.43Ti0.07)O3 AFE ceramic attractive for preparing high pulsed power capacitors useable in various conditions.

Insulator-like behavior coexisting with metallic electronic structure in strained FeSe thin films grown by molecular beam epitaxy

This paper reports that ~10-nm-thick FeSe thin films exhibit insulator-like behavior in terms of the temperature dependence of their electrical resistivity even though bulk FeSe has a metallic electronic structure that has been confirmed by photoemission spectroscopy and first-principles calculations. This apparent contradiction is explained by potential barriers formed in the conduction band. Very thin FeSe epitaxial films with various [Fe]/[Se] were fabricated by molecular beam epitaxy and classified into two groups with respect to lattice strain and electrical properties. Lattice parameter a increased and lattice parameter c decreased with increasing [Fe]/[Se] up to 1.1 and then a levelled off and c began to decrease at higher [Fe]/[Se]. Consequently, the FeSe films had the most strained lattice when [Fe]/[Se] was 1.1, but these films had the best quality with respect to crystallinity and surface flatness. All the FeSe films with [Fe]/[Se] of 0.8-1.9 exhibited insulator-like behavior, but the temperature dependences of their electrical resistivities exhibited different activation energies Ea between the Se-rich and Fe-rich regions; i.e., Ea were small (a few meV) up to [Fe]/[Se]=1.1 but jumped up to ~25 meV at higher [Fe]/[Se]. The film with [Fe]/[Se]=1.1 had the smallest Ea of 1.1 meV and exhibited an insulator-superconducting transition at 35 K with zero resistance under gate bias. The large Ea of the Fe-rich films was attributed to the unusual lattice strain with tensile in-plane and relaxed out-of-plane strains. The large Ea of films with [Fe]/[Se]>1.1 resulted in low mobility with a high potential barrier of ~50 meV in the conduction band for percolation carrier conduction compared with that of the [Fe]/[Se]=1.1 film (~17 meV). Therefore, the Fe-rich films exhibited remarkable insulator-like behavior similar to a semiconductor despite their metallic electronic structure.

Influence of Channel Layer Thickness on the Instability of Amorphous SiZnSnO Thin Film Transistors Under Negative Bias Temperature Stress

In this study, amorphous silicon‐zinc‐tin‐oxide thin film transistors (a‐SZTO TFTs) are fabricated by radio‐frequency magnetron sputtering at room temperature, and the influence of various channel thicknesses on their electrical performance and stability is reported. Under the negative bias temperature stress, the transfer curve exhibits threshold voltage shift in the negative direction and degradation of subthreshold swing. In addition, the hump effect occurs in the thick channel, which is primarily due to an increase in total trap density from 5.0 × 1011 to 3.5 × 1012 cm−2 with an increase in the channel layer thickness from 12 to 72 nm. These results agree well with the increase in the bulk trap density because all a‐SZTO TFTs have the same interface; therefore, the interface trap density is excluded. Thicker SZTO TFTs show the hump effect, as they have more donor‐like states in the shallow level. Furthermore, temperature stress at 300–333 K and the activation energy (Ea) falling rate are calculated for a‐SZTO TFTs. The Ea falling rate decreases from 0.103 to 0.010 eV V−1 with increasing channel thickness. Consequently, an a‐SZTO TFT with a 12‐nm channel layer thickness shows a large Ea falling rate (0.103 eV V−1) and a small threshold voltage shift of 4.74 V without the hump effect and degraded electrical performance.

High temperature‐insensitive ferro‐/piezoelectric properties and nanodomain structures of Pb(In1/2Nb1/2)O3–PbZrO3–Pb(Mg1/3Nb2/3)O3–PbTiO3 relaxor single crystals

AbstractFor rhombohedral (R) Pb(In1/2Nb1/2)O3–PbZrO3–Pb(Mg1/3Nb2/3)O3–PbTiO3 (PIN–PZ–PMN–PT) relaxor single crystal, high temperature‐insensitive behaviors under different external stimuli were observed (remnant polarization Pr from 30°C to 180°C and piezoelectric strain d33* from 30°C to 116°C). When electric field E ≥ 50 kV/cm in the case of an activation field Ea = 40‐50 kV/cm was applied, it was found that the domain switching was accompanied by a phase transition. The high relaxor nature of the R phase PIN–PZ–PMN–PT was speculated to account for the large Ea and high piezoelectric response. The short‐range correlation lengths extracted from the out‐of‐plane (OP) and in‐plane (IP) nanodomain images, were 64 nm and 89 nm, respectively, which proved the high relaxor nature due to In3+ and Zr4+ ions entering the B‐site in the ABO3‐lattice and enhancing the disorder of B‐site cations in the R phase PIN–PZ–PMN–PT. The switching process of R nanodomain variants under the step‐increased tip DC voltage was visually revealed. Moreover, the time‐dependent domain evolution confirmed the high relaxor nature of the R phase PIN–PZ–PMN–PT single crystal.

Arbitrary electron acoustic waves in degenerate dense plasmas

A theoretical investigation is carried out of the nonlinear dynamics of electron-acoustic waves in a collisionless and unmagnetized plasma whose constituents are non-degenerate cold electrons, ultra-relativistic degenerate electrons, and stationary ions. A dispersion relation is derived for linear EAWs. An energy integral equation involving the Sagdeev potential is derived, and basic properties of the large amplitude solitary structures are investigated in such a degenerate dense plasma. It is shown that only negative large amplitude EA solitary waves can exist in such a plasma system. The present analysis may be important to understand the collective interactions in degenerate dense plasmas, occurring in dense astrophysical environments as well as in laser–solid density plasma interaction experiments.

Changes in the Autonomic Nervous System and Moods of Advanced Cancer Patients by Mindfulness Art Therapy Short Version

The aim of this study was to investigate changes in the Autonomic Nervous System (ANS) and moods before and after participation in a Mindfulness Art Therapy Short version (MATS). The study design was non-randomized controlled trial in intervention study. Participants were 10 Japanese patients with advanced cancer. They received the MATS in one session, which consisted of mindfulness practices and making arts. Their Autonomic Nervous System (sympathetic nervous, parasympathetic nervous) physiologically and mood (Tense Arousal: TA, Energetic Arousal: EA) psychologically were measured before and after the MATS. The results showed that the level of parasympathetic nervous system decreased and that the sympathetic nervous system increased in small effect size. The TA decreased in a large effect size and EA increased in a middle effect size. These results suggested that the MATS might activate physiologically, alleviate tension and increase energy psychologically.

Proton-Conductivity of Amorphous Aluminum Phosphate Thin Films under Anhydrous Conditions

The proton conductivity σ across 100 nm thick, amorphous aluminum phosphate thin films under anhydrous conditions was investigated. The densely packed glass films were uniformly formed without formation of pinholes and clacks over the electrode substrate by multiple spin-coating with a mixed precursor sol, as checked by transmission electron microscopy. X-ray absorption spectroscopy, and Fourier transform infrared indicated that the Al-rich films were mainly composed of alumina and phosphate mixed glass phase, but the P-rich films involved a large amount of the aluminum metaphosphate glass moiety. σ abruptly changed with Al/P ratio owing to this variation of glass network structure. The Al-rich films revealed the large activation energy Ea of about 1.0 eV, but the P-rich films revealed the small Ea of about 0.2 eV above 200°C and they kept the value on the order of 10−5 S cm−1 at the temperatures. Consequently, the σ of P-rich films were one order of magnitude higher than that of the others at around 300°C.

Inferential Statistics

Inferential Statistics

Kinetic neutron diffraction study ofNb3Sn phase formation in superconducting wires

The kinetics of Nb3Sn phase formation in commercial multifilamentary wires have been studiedas a function of time and temperature using time-resolved, in situneutron diffraction. This work shows that at higher temperatures theNb3Sn phaseforms in a fraction of the recommended annealing time. A temperature-independent Avrami exponent ofn = 0.51 ± 0.01 wasobserved, indicating a diffusion-controlled growth mechanism, and a large apparent activation energyof Ea = 10 ± 1 eV is reported where the energies of nucleation and growth both contribute.

Thermostability of Irreversible Unfolding α-Amylases Analyzed by Unfolding Kinetics

For most multidomain proteins the thermal unfolding transitions are accompanied by an irreversible step, often related to aggregation at elevated temperatures. As a consequence the analysis of thermostabilities in terms of equilibrium thermodynamics is not applicable, at least not if the irreversible process is fast with respect the structural unfolding transition. In a comparative study we investigated aggregation effects and unfolding kinetics for five homologous alpha-amylases, all from mesophilic sources but with rather different thermostabilities. The results indicate that for all enzymes the irreversible process is fast and the precedent unfolding transition is the rate-limiting step. In this case the kinetic barrier toward unfolding, as measured by unfolding rates as function of temperature, is the key feature in thermostability. The investigated enzymes exhibit activation energies (E(a)) between 208 and 364 kJmol(-1) and pronounced differences in the corresponding unfolding rates. The most thermostable alpha-amylase from Bacillus licheniformis (apparent transition temperature, T(1/2) approximately 100 degrees C) shows an unfolding rate which is four orders of magnitude smaller as compared with the alpha-amylase from pig pancreas (T(1/2) approximately 65 degrees C). Even with respect to two other alpha-amylases from Bacillus species (T(1/2) approximately 86 degrees C) the difference in unfolding rates is still two orders of magnitude.

Participation of (η3-Allyl)ruthenium(II) Complexes in C−C Bond Formation and C−C Bond Cleavage. A Theoretical Study

Coupling reactions of formaldehyde with RuBr(η3-C3H5)(CO)3 (R1), [Ru(η3-C3H5)(HCHO)(CO)3]+ (I2), and RuBr(η3-C3H5)(HCHO)(CO)2 (I3) were theoretically investigated with ab initio MP2-MP4(SDQ), CCSD(T), and DFT(B3LYP) methods. In R1, the coupling reaction takes place through two transition states, as follows: coordination of formaldehyde with the ruthenium(II) center occurs through the first transition state, to afford an (η1-allyl)ruthenium(II) formaldehyde complex, RuBr(η1-C3H5)(HCHO)(CO)3, as an intermediate, and then C−C bond formation between the η1-allyl ligand and formaldehyde takes place through the second transition state, to afford The activation energy (Ea) is 19.9 (12.0) kcal/mol for the first transition state and 12.5 (5.4) kcal/mol for the second transition state, where the values given without parentheses are Ea values calculated with the MP4(SDQ) method and the values in parentheses are those calculated with the DFT method. In I2 and I3, the coupling reaction proceeds through one transition state, to afford and with considerably larger Ea values of 50.7 (30.6) and 34.8 (32.0) kcal/mol, respectively. Even in I2, however, the allyl−aldehyde coupling reaction easily occurs through two transition states like that of R1, when one more formaldehyde molecule coordinates with the ruthenium(II) center; the Ea value is 10.5 (4.6) kcal/mol for the first transition state and 13.6 (6.7) kcal/mol for the second transition state. In this case, one formaldehyde molecule plays the role of a spectator ligand and the second formaldehyde undergoes a coupling reaction with the allyl ligand. From these results, it should be concluded that the allyl−aldehyde coupling reaction proceeds easily in the coordinatively saturated (η3-allyl)ruthenium(II) complex and that the coordinatively unsaturated (η3-allyl)ruthenium(II) complex becomes reactive when two molecules of formaldehyde coordinate with the ruthenium(II) center. IRC calculation of the allyl−aldehyde coupling reaction of R1 clearly shows that the C−C bond formation between the η1-allyl ligand and formaldehyde occurs after the second transition state concomitantly with the bond alternation in the η1-allyl ligand. Electron redistribution in the reaction indicates that the allyl−aldehyde coupling reaction is understood in terms of electrophilic attack of formaldehyde to the allyl ligand. Reverse C−C bond cleavage proceeds with a moderate Ea value of 16.6 (13.5) kcal/mol in to afford [Ru(η3-C3H5)(HCHO)(CO)3]+, with a similar Ea value of 19.6 (11.1) kcal/mol in to afford RuBr(η3-C3H5)(CO)3 + HCHO, and with a considerably large Ea value of 27.0 (26.8) kcal/mol in to afford RuBr(η3-C3H5)(HCHO)(CO)2. is the best for this C−C bond cleavage. This is because the coordinatively unsaturated complex with electron-accepting ligands yields a stable (η3-allyl)ruthenium(II) complex in which the η3-allyl ligand is strongly electron donating and needs two coordination sites. Though the C−C bond cleavage of occurs with a moderate Ea value, this reaction is much less exothermic than that of

C−H Bond Activation of Benzene and Methane by M(η2-O2CH)2(M = Pd or Pt). A Theoretical Study

C−H bond activations of benzene and methane by M(η2-O2CH)2 (M = Pd or Pt) are theoretically investigated with density functional theory (DFT), MP2-MP4(SDQ), and CCSD(T) methods. The C−H bond activation of benzene takes place with activation energies (Ea) of 16.1 and 21.2 kcal/mol and reaction energies (ΔE) of −16.5 and −25.8 kcal/mol for M = Pd and Pt, respectively, to afford M(η2-O2CH)(C6H5)(η1-HCOOH), where MP4(SDQ) values are given hereafter and a negative ΔE value represents that the reaction is exothermic. The C−H bond activation of methane proceeds with Ea values of 21.5 and 17.3 kcal/mol and ΔE values of −8.3 and −13.3 kcal/mol for M = Pd and Pt, respectively, to afford M(η2-O2CH)(CH3)(η1-HCOOH). However, C−H bond activations of benzene and methane by Pd(PH3)2 need a large Ea value, and these reactions are significantly endothermic: Ea = 26.5 kcal/mol and ΔE = 22.1 kcal/mol for benzene and Ea = 34.7 kcal/mol and ΔE = 31.5 kcal/mol for methane. Also, the C−H bond activation of methane by Pt(PH3)2 needs a large Ea value (28.1 kcal/mol) with moderate endothermicity (ΔE = 7.0 kcal/mol), while the C−H bond activation of benzene by Pt(PH3)2 occurs with a moderate Ea value (17.3 kcal/mol) and a negative ΔE value (−3.9 kcal/mol). From these results, the following conclusions are presented: (1) Pd(η2-O2CH)2 can perform easily the C−H bond activations of benzene and methane but Pd(PH3)2 cannot. This is because the formate ligand assists the C−H bond activation through formation of a strong O−H bond. (2) Pt(η2-O2CH)2 more easily performs the C−H bond activation of methane but much less easily the C−H bond activation of benzene than Pd(η2-O2CH)2, because the intermediate, Pt(II)−benzene complex, is too stable. (3) Benzene more easily undergoes C−H bond activation than does methane. The higher reactivity of benzene is interpreted in terms of M−C6H5 and M−CH3 bond energies and the bonding interaction of benzene π and π* orbitals with M d orbitals. Analysis of electron distribution implicitly indicates that the C−H bond activation by M(η2-O2CH)2 is characterized to be heterolytic C−H bond fission, while the C−H bond activation by M(PH3)2 is characterized to be homolytic C−H bond fission.

Photoelectron spectroscopy of copper cyanide cluster anions: On the possibility of linear and ring structures

The electronic properties of copper cyanide cluster anions [Cun(CN)m−; n=1–6, m=1–6] were studied using photoelectron spectroscopy (PES) with a magnetic-bottle type electron spectrometer. Both the anions and the cations of the Cun(CN)m cluster were generated by laser vaporization of a molded copper cyanide rod in a He carrier gas. In the mass spectra, abundant clusters were produced at the composition of (n,m)=(n,n+1;n=1−6) and (n,n;n=4 and 5) for the anions, whereas more abundant clusters were observed at (n, n−1; n=1−9) for the cations. The stability of Cun(CN)n+1− and Cun(CN)n−1+ clusters is attributed to their electronic structure, where ionic Cu+ and CN− are linked alternately in a linear geometry. The PES spectra of the Cun(CN)m− anions show that the (n,n+1) clusters exhibit an extremely large EA of above 4.5 eV, while the EA’s of the less abundant (n,n) clusters increase monotonously with cluster size from 1.3 eV (n=1) to 3.12 eV (n=6), except for n=4 and 5. Together with theoretical calculations by the density functional theory (DFT), two different linear isomers have been found for (n,n) clusters, where CN takes a opposite direction toward Cu. For Cu4(CN)4− and Cu5(CN)5−, moreover, the PES spectra show two components of distinctly different peak shape, suggesting that a ring isomer should coexist with the linear ones.

The Local Topography of Uruk Sulcus and Galileo Regio Obtained from Stereo Images

High resolution (<100 m/pixel) stereo images obtained by the Galileo SSI camera are analyzed using photogrammetric techniques to derive local Digital Terrain Models (DTMs) of Ganymede's surface. The models cover areas of 22 × 56 km in Uruk Sulcus and 63 × 102 km in Galileo Regio and have spatial resolutions of 500 m/pixel and 1000 m/pixel, respectively. For Uruk Sulcus, the DTM features a wave-like topography with wavelengths of 2–6 km and amplitudes of up to 500m. Individual topographic highs show asymmetric shapes with slopes of up to 20° and terracing. The terrain model in Galileo Regio has isolated knobs, furrows of up to 10 km in width, and ridges of up to 1 km in height. Surface roughness in Galileo Regio at DTM scales is markedly higher than in Uruk Sulcus. Bowl-shaped craters are identified in the models with depth to diameter ratios of about 1:12 (Uruk Sulcus) and 1:9 (Galileo Regio). This is in approximate agreement with data for simple craters measured in Voyager images. The large complex 20-km crater Ea is found to have a central dome 300 m above the crater floor, reaching more than half of the crater rim's height. These unique topographic data, at far higher resolution than what could be derived from Voyager images, will provide new insights into the formation of Ganymede's surface.

Ab initio MO studies of neutral and anionic SiCn clusters (n=2–5)

The geometries and energies of SiCn and SiCn− (n=2–5) were investigated with ab initio calculations including electron correlation effects with the MP2/6-31G* method, followed by MP4 and CCSD(T) single-point calculations to determine the most stable isomers. The adiabatic electron affinities (AEA) were evaluated with the ΔMP4 method. Because of the complexity of the electronic structure of SiC2, its AEA was calculated at the CCSD(T)/aug cc-pVTZ//CCSD(T)/aug cc-pVDZ level of approximation. For the neutral SiCn clusters, the isomer having a triplet ground state has large EA, whereas the isomer having a singlet ground state has small EA. This is attributed to the bonding character between Si and C atoms in the orbital occupied by the extra electron. The calculated EA was used to assign the photoelectron spectra of SiCn− reported previously. Furthermore, the effects of Renner–Teller splitting for the linear isomers of anions are discussed.

PHOTOELECTRON SPECTROSCOPY OF BINARY-METAL CLUSTER ANIONS CONTAINING SULFUR ATOM

Photoelectron spectra of [Formula: see text] (M= Al , Cu, Ag, and Au) cluster anions were measured at the photon energies of 3.49 and 4.66 eV using a magnetic-bottle electron spectrometer having ~60-meV resolution. The electron affinities of AlS−, CuS−, AgS−, and AuS− are 2.60(3), 2.10(3), 2.09(3), and 2.44(3) eV, respectively. The large EA of AlS− is attributed to large stability by six bonding electrons, and a new electronic state of A ′ 2Π can be found 0.4 eV above the AlS ground state, which is in agreement with a theoretical calculation. In the photoelectron spectrum of AuS−, two peaks due to a splitting by the L–S coupling could be observed, and the amount of the splitting is 0.18(2) eV. The results of aluminum clusters containing sulfur atom will also be presented.