Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “ab initio data”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 991 records · Page 55
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Glauber-Theory Calculations of High-Energy Nuclear Scattering Observables Using Variational Monte Carlo Wave Functions

Experiments using intermediate- to high-energy radioactive nuclear beams present numerous findings. Extracting important properties of physical observables relies on a firm theoretical analysis. Though Glauber theory is believed to work well, no convincing calculation has so far been done. Here, we perform ab initio Glauber theory calculations of both elastic differential cross sections and total reaction cross sections for p+ 12 C, 12 C+ 12 C, and 6 He+ 12 C systems. The wave functions of both 6 He and 12 C are generated by variational Monte Carlo calculations with spatial and spin-isospin correlations induced by realistic two- and three-nucleon potentials. Glauber’s phase-shift function is computed by Monte Carlo integration up to all orders of nucleon-nucleon multiple scatterings. We show an excellent performance of the Glauber description to the selected data on the above systems. We also find that the cumulant expansion of the phase-shift function converges rapidly up to the second order for the above systems. This finding will open up interesting applications for the analysis of high-energy nuclear experiments.

Horiuchi, W. [Osaka Metropolitan University (Japan↗
DOE OSTI2018

Ab Initio Study of the Electronic Structure, Elastic Properties, Magnetic Feature and Thermodynamic Properties of the Ba{sub 2}NiMoO{sub 6} Material

We report first-principles calculations of the elastic properties, electronic structure and magnetic behavior performed over the Ba{sub 2}NiMoO{sub 6} double perovskite. Calculations are carried out through the full-potential linear augmented plane-wave method within the framework of the Density Functional Theory (DFT) with exchange and correlation effects in the Generalized Gradient and Local Density Approximations, including spin polarization. The elastic properties calculated are bulk modulus (B), the elastic constants (C{sub 11}, C{sub 12} and C{sub 44}), the Zener anisotropy factor (A), the isotropic shear modulus (G), the Young modulus (Y) and the Poisson ratio (υ). Structural parameters, total energies and cohesive properties of the perovskite are studied by means of minimization of internal parameters with the Murnaghan equation, where the structural parameters are in good agreement with experimental data. Furthermore, we have explored different antiferromagnetic configurations in order to describe the magnetic ground state of this compound. The pressure and temperature dependence of specific heat, thermal expansion coefficient, Debye temperature and Grüneisen parameter were calculated by DFT from the state equation using the quasi-harmonic model of Debye. A specific heat behavior C{sub V} ≈ C{sub P} was found at temperatures below T = 400 K, with Dulong–Petit limit values, which is higher than those, reported for simple perovskites.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Quantitative x-ray scattering of free molecules

Advances in x-ray free electron lasers have made ultrafast scattering a powerful method for investigating molecular reaction kinetics and dynamics. Accurate measurement of the ground-state, static scattering signals of the reacting molecules is pivotal for these pump-probe x-ray scattering experiments as they are the cornerstone for interpreting the observed structural dynamics. Here, this article presents a data calibration procedure, designed for gas-phase x-ray scattering experiments conducted at the Linac Coherent Light Source x-ray Free-Electron Laser at SLAC National Accelerator Laboratory, that makes it possible to derive a quantitative dependence of the scattering signal on the scattering vector. A self-calibration algorithm that optimizes the detector position without reference to a computed pattern is introduced. Angle-of-scattering corrections that account for several small experimental non-idealities are reported. Their implementation leads to near quantitative agreement with theoretical scattering patterns calculated with ab-initio methods as illustrated for two x-ray photon energies and several molecular test systems.

74 ATOMIC AND MOLECULAR PHYSICS↗
NASA NTRS2001

Ab Initio Calculations of Anharmonic Vibrational Spectroscopy for Hydrogen Fluoride (HF)n (n=3,4) and Mixed Hydrogen Fluoride/Water (HF)n(H20)n (n=1,2,4) Clusters

Anharmonic vibrational frequencies and intensities are computed for hydrogen fluoride clusters (HF)n with n=3,4 and mixed clusters of hydrogen fluoride with water (HF)n(H2O)n where n=1,2. For the (HF)4(H2O)4 complex, the vibrational spectra are calculated at the harmonic level, and anharmonic effects are estimated. Potential energy surfaces for these systems are obtained at the MP2/TZP level of electronic structure theory. Vibrational states are calculated from the potential surface points using the correlation-corrected vibrational self-consistent field (CC-VSCF) method. The method accounts for the anharmonicities and couplings between all vibrational modes and provides fairly accurate anharmonic vibrational spectra that can be directly compared with experimental results without a need for empirical scaling. For (HF)n, good agreement is found with experimental data. This agreement shows that the MP2 potential surfaces for these systems are reasonably reliable. The accuracy is best for the stiff intramolecular modes, which indicates the validity of MP2 in describing coupling between intramolecular and intermolecular degrees of freedom. For (HF)n(H2O)n experimental results are unavailable. The computed intramolecular frequencies show a strong dependence on cluster size. Intensity features are predicted for future experiments.

Chaban, Galina M.↗
DOE OSTI2022

Ab Initio Evaluation of Uranium Carbide S(α,β) and Thermal Neutron Cross Sections

Uranium Carbide (UC) is a nuclear fuel material which offers better neutron economy and lower fuel-cycle costs compared to conventional mixed-oxide fuels. UC’s lattice binding and dynamical properties impact thermal neutron scattering and low temperature epithermal resonance absorption. The Thermal Scattering Law (TSL) describes the scattering system available energy and momentum transfer states. There is no TSL evaluation for UC in the ENDF/B-VIII.0 database; herein, ab-initio lattice dynamics (AILD) techniques are invoked to calculate the phonon spectrum for UC using spin-orbit-coupling density functional theory (DFT). The TSLs, inelastic and elastic thermal scattering cross sections for Uranium and Carbon in UC, respectively, are calculated in FLASSH for use in higher fidelity reactor design calculations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

Electronic structure, thermodynamic properties and hydrogenation of LaPtIn and CePtIn compounds by ab-initio methods

The electronic structures and thermodynamic properties of LaPtIn and CePtIn are studied by means of ab-initio full-relativistic full-potential local orbital basis (FPLO) method within densities functional (DFT) methodologies. We have also examined the influence of hydrogen on the electronic structure and stability of CePtInH and LaPtInH systems. The positions of the hydrogen atoms have been found from the minimum of the total energy. Our calculations have shown that band structure and topology of the Fermi surfaces changed significantly during the hydrogenation. The thermodynamic properties (bulk modulus, Debye temperatures, constant pressure heat capacity) calculated in quasi-harmonic Debye-Grüneisen model are in a good agreement with the experimental data. We have applied different methods of the calculation of the equation of states (EOS) (Murnaghan, Birch-Murnaghan, Poirier–Tarantola, Vinet). The thermodynamic properties are presented for the pressure 0<P<9 GPa and the temperature range 0<T<300 K. - Highlights: • Full relativistic band structure of LaPtIn and CePtIn. • Fermi surface of LaPtIn, LaPtInH, CePtIn, CePtInH. • Effect of hydrogenation on the electronic structure of LaPtIn and CePtIn. • Thermodynamic properties in the quasi-harmonic Debye-Grüneisen model.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

High-throughput computation of electric polarization in solids via Berry flux diagonalization

Electric polarization in the absence of an externally applied electric field is a key property of polar materials, but the standard interpolation-based ab initio approach to compute polarization differences within the modern theory of polarization presents challenges for automated high-throughput calculations. Berry flux diagonalization [J. Bonini et al., Phys. Rev. B 102, 045141 (2020)] has been proposed as an efficient and reliable alternative, though it has yet to be widely deployed. Here, we assess Berry flux diagonalization using ab initio calculations of a large set of materials, introducing and validating heuristics that ensure branch alignment with a minimal number of intermediate interpolated structures. Our automated implementation of Berry flux diagonalization succeeds in cases where prior interpolation-based workflows fail due to band-gap closures or branch ambiguities. Benchmarking with ab initio calculations of 176 candidate ferroelectrics, we demonstrate the efficacy of the approach on a broad range of insulating materials and obtain accurate effective polarization values with fewer interpolated structures than prior automated interpolation-based workflows. Our real-space heuristics that can predict gauge stability a priori from ionic displacements enable a general automated framework for reliable polarization calculations and efficient high-throughput screening of chemically and structurally diverse polar insulators. These results establish Berry flux diagonalization as a robust and efficient method to compute the effective polarization of solids and to accelerate the data-driven discovery of functional polar materials.

Poteshman, Abigail N. [University of Chicago, IL (↗
DOE OSTI2013

Fourier-transform spectroscopy of (4){sup 1}Σ{sup +} → A {sup 1}Σ{sup +} − b {sup 3}Π, A {sup 1}Σ{sup +} − b {sup 3}Π → X{sup 1}Σ{sup +}, and (1){sup 3} Δ{sub 1} → b{sup 3}Π{sub 0±} transitions in KCs and deperturbation treatment of A {sup 1}Σ{sup +} and b {sup 3}Π states

High resolution Fourier-transform spectroscopy data of term values in the spin-orbit (SO) coupled first excited A {sup 1}Σ{sup +} and b{sup 3}Π{sub 0±} states in KCs were obtained from (4){sup 1}Σ{sup +} → A {sup 1}Σ{sup +} − b {sup 3}Π, A {sup 1}Σ{sup +} − b {sup 3}Π → X{sup 1}Σ{sup +}, and (1){sup 3}Δ{sub 1} → b{sup 3}Π{sub 0±} spectra of laser-induced fluorescence (LIF). About 3000 new rovibronic term values of the A {sup 1}Σ{sup +} and b {sup 3}Π{sub Ω} states were obtained with an uncertainty about 0.01 cm{sup −1} and added to the previously obtained 3439 term values in Kruzins et al. [Phys. Rev. A 81, 042509 (2010)] and 30 term values of the b {sup 3}Π{sub 0{sup +}} state levels below the A {sup 1}Σ{sup +} state in Tamanis et al. [Phys. Rev. A 82, 032506 (2010)]. The data field was extended considerably, going down to vibrational level v{sub b} = 0 and up in energy to 13 814 cm{sup −1}, as compared to previously achieved v{sub b} = 14 and E = 13 250 cm{sup −1}. Overall 6431 e-symmetry term values of {sup 39}K{sup 133}Cs were included in 4 × 4 coupled-channel deperturbation analysis. The analytical Morse-Long-Range (MLR) function yielded empirical diabatic potentials for the A {sup 1}Σ{sup +} and b {sup 3}Π{sub 0{sup +}} states while the morphing of the SO ab initio points [J. T. Kim et al., J. Mol. Spectrosc. 256, 57 (2009)] provided the empirical diagonal and off-diagonal SO functions. Overall 98.5% of the fitted term values were reproduced with a rms (root mean square) uncertainty of 0.004 cm{sup −1}. The reliability of the model is proved by a good agreement of predicted and measured term values of the {sup 41}K{sup 133}Cs isotopologue, as well as of measured and calculated intensities of (4){sup 1}Σ{sup +} → A {sup 1}Σ{sup +} − b {sup 3}Π LIF progressions. Direct-potential-fit of low-lying v{sub b} levels of the b {sup 3}Π{sub 0{sup −}} component yielded the MLR potential which represents the 204 f-symmetry experimental term values with a rms uncertainty of 0.002 cm{sup −1}. The Ω-doubling of the b {sup 3}Π{sub 0} sub-state demonstrates a pronounced v{sub b}-dependent increase.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Macromolecular phasing using diffraction from multiple crystal forms

A phasing algorithm for macromolecular crystallography is proposed that utilizes diffraction data from multiple crystal forms – crystals of the same molecule with different unit-cell packings (different unit-cell parameters or space-group symmetries). The approach is based on the method of iterated projections, starting with no initial phase information. The practicality of the method is demonstrated by simulation using known structures that exist in multiple crystal forms, assuming some information on the molecular envelope and positional relationships between the molecules in the different unit cells. With incorporation of new or existing methods for determination of these parameters, the approach has potential as a method for ab initio phasing.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Atomic Diffusivities of Yttrium, Titanium and Oxygen Calculated by Ab Initio Molecular Dynamics in Molten 316L Oxide-Dispersion-Strengthened Steel Fabricated via Additive Manufacturing

Oxide-dispersion-strengthened (ODS) steels have long been viewed as a prime solution for harsh environments. However, conventional manufacturing of ODS steels limits the final product geometry, is difficult to scale up to large components, and is expensive due to multiple highly involved, solid-state processing steps required. Additive manufacturing (AM) can directly incorporate dispersion elements (e.g., Y, Ti and O) during component fabrication, thus bypassing the need for an ODS steel supply chain, the scale-up challenges of powder processing routes, the buoyancy challenges associated with casting ODS steels, and the joining issues for net-shape component fabrication. In the AM process, the diffusion of the dispersion elements in the molten steel plays a key role in the precipitation of the oxide particles, thereby influencing the microstructure, thermal stability and high-temperature mechanical properties of the resulting ODS steels. In this work, the atomic diffusivities of Y, Ti, and O in molten 316L stainless steel (SS) as functions of temperature are determined by ab initio molecular dynamics simulations. The latest Vienna Ab initio Simulation Package (VASP) package that incorporates an on-the-fly machine learning force field for accelerated computation is used. At a constant temperature, the time-dependent coordinates of the target atoms in the molten 316L SS were analyzed in the form of mean square displacement in order to obtain diffusivity. The values of the diffusivity at multiple temperatures are then fitted to the Arrhenius form to determine the activation energy and the pre-exponential factor. Given the challenges in experimental measurement of atomic diffusivity at such high temperatures and correspondingly the lack of experimental data, this study provides important physical parameters for future modeling of the oxide precipitation kinetics during AM process.

Chemistry↗
DOE OSTI2019

Second spectrum of Manganese (Mn II), Part II: Revised fine and hyperfine structure analysis of odd-parity levels

In the first part of this global work, we have achieved the fine and hyperfine structure (fs and hfs) parametric study of even-parity levels, which confirmed in the whole the well-founded basis of previous analyses. Unfortunately, in the present work devoted to odd-parity levels, some divergences appear. For instance, the three levels w{sup 5}P{sub 3}, w{sup 5}P{sub 2}, w{sup 5}P{sub 1} located respectively at 86898, 86937 and 86961 cm{sup −1} should not belong to the 3d{sup 4}({sup 5}D)4s4p configuration, as indicated earlier, but rather to 3d{sup 5}({sup 4}P)5p. In the other hand, the levels whose energies are: 88 840, 89 079 and 89 429 cm{sup −1} should belong this time to 3d{sup 4}({sup 5}D)4s4p instead of 3d{sup 5}5p, as mentioned previously. Our analysis is strengthened when using experimental hfs data as finger prints, even if the comparison between these experimental hfs data, given in the literature, and our calculated results also shows in numerous cases some notable discrepancies, concerning particularly the sign of the electric quadrupole factor. The main monoelectronic hfs parameter values, extracted from our least square fitting procedure, are: a{sub 3d}{sup 01}(3d{sup 5}4p)= 17.58 mK, b{sub 3d}{sup 02}(3d{sup 5}4p)= 10.27 mK, a{sub 3d}{sup 01} (3d{sup 4}4s4p)= 18.74 mK and a{sub 4s}{sup 10}(3d{sup 4}4s4p)= 274.9 mK. These parameter values, displayed for the first time, were analyzed and compared with ab-initio calculations. As in the first part, we conclude this work by giving the predicted hfs A and B constants of low-lying levels of these two configurations, whose splitting are not yet measured.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2016

Ab-initio study of thermal expansion in pure graphene

Graphene is a zero band gap semiconductor with exceptionally high thermal conductivity. The electronic properties having been studied, therole of phonon in contributing to thermal expansion, thermal conductivity and other thermodynamic properties, is required to be investigated. This paper focuses more on thermal expansion. Some others results like phonon dispersion, Grüneisenparameters and bulk modulus,which are essential to estimation of thermal expansion, are also presented. The dynamical matrix was calculated using VASP code using both DFT and DFPT and the phonon frequencies were calculated using phonopy code under harmonic approximation. The linear thermal expansion coefficient of graphene is found to be strongly dependent on temperature but remains negative upto 470 K and positive thereafter, with a room temperature value of −1.44×10{sup −6}. The negative expansion coefficient is very interesting and is found to be in conformity with experimental as well as with recent theoretical estimates. There is only qualitative agreement of our results with experimental data and motivates further investigation, primarily on the high negative values of Grüneisen parameters.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2023

Fluorine spillover for ceria- vs silica-supported palladium nanoparticles: A MD study using machine learning potentials

Supported metallic nanoparticles play a central role in catalysis. However, predictive modeling is particularly challenging due to the structural and dynamic complexity of the nanoparticle and its interface with the support, given that the sizes of interest are often well beyond those accessible via traditional ab initio methods. With recent advances in machine learning, it is now feasible to perform MD simulations with potentials retaining near-density-functional theory (DFT) accuracy, which can elucidate the growth and relaxation of supported metal nanoparticles, as well as reactions on those catalysts, at temperatures and time scales approaching those relevant to experiments. Furthermore, the surfaces of the support materials can also be modeled realistically through simulated annealing to include effects such as defects and amorphous structures. We study the adsorption of fluorine atoms on ceria and silica supported palladium nanoparticles using machine learning potential trained by DFT data using the DeePMD framework. We show defects on ceria and Pd/ceria interfaces are crucial for the initial adsorption of fluorine, while the interplay between Pd and ceria and the reverse oxygen migration from ceria to Pd control spillover of fluorine from Pd to ceria at later stages. In contrast, silica supports do not induce fluorine spillover from Pd particles.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

FINETUNA: fine-tuning accelerated molecular simulations

Abstract Progress towards the energy breakthroughs needed to combat climate change can be significantly accelerated through the efficient simulation of atomistic systems. However, simulation techniques based on first principles, such as density functional theory (DFT), are limited in their practical use due to their high computational expense. Machine learning approaches have the potential to approximate DFT in a computationally efficient manner, which could dramatically increase the impact of computational simulations on real-world problems. However, they are limited by their accuracy and the cost of generating labeled data. Here, we present an online active learning framework for accelerating the simulation of atomic systems efficiently and accurately by incorporating prior physical information learned by large-scale pre-trained graph neural network models from the Open Catalyst Project. Accelerating these simulations enables useful data to be generated more cheaply, allowing better models to be trained and more atomistic systems to be screened. We also present a method of comparing local optimization techniques on the basis of both their speed and accuracy. Experiments on 30 benchmark adsorbate-catalyst systems show that our method of transfer learning to incorporate prior information from pre-trained models accelerates simulations by reducing the number of DFT calculations by 91%, while meeting an accuracy threshold of 0.02 eV 93% of the time. Finally, we demonstrate a technique for leveraging the interactive functionality built in to Vienna ab initio Simulation Package (VASP) to efficiently compute single point calculations within our online active learning framework without the significant startup costs. This allows VASP to work in tandem with our framework while requiring 75% fewer self-consistent cycles than conventional single point calculations. The online active learning implementation, and examples using the VASP interactive code, are available in the open source FINETUNA package on Github.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2018

Grain-Boundary Shear-Migration Coupling in Al Bicrystals. Atomistic Modeling

The energy of grain boundary shears is calculated for symmetric grain boundaries (GBs) using ab initio methods and molecular-dynamic modeling in order to elucidate mechanisms that control GB shear-migration coupling in typical symmetric GBs, such as Σ3 (111), Σ5 (012), Σ5 (013) and Σ11 (113) tilt GBs, in Al bicrystal. The energy of generalized grain-boundary stacking faults (GB–SF) is determined, and the preferred directions and the energy barrier are established for grain-boundary slippage. It is shown that the relative slippage of neighboring grains at certain directions of particle shears is accompanied by conservative migration of GB in the direction perpendicular to its plain. The modeling data are comparative to known grain-boundary shear-migration coupling mechanisms in Al.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Predicting defect behavior in B2 intermetallics by merging ab initio modeling and machine learning

We present a combination of machine learning and high throughput calculations to predict the points defects behavior in binary intermetallic (A-B) compounds, using as an example systems with the cubic B2 crystal structure (with equiatomic AB stoichiometry). To the best of our knowledge, this work is the first application of machine learning-models for point defect properties. High throughput first principles density functional calculations have been employed to compute intrinsic point defect energies in 100 B2 intermetallic compounds. The systems are classified into two groups: (i) those for which the intrinsic defects are antisites for both A and B rich compositions, and (ii) those for which vacancies are the dominant defect for either or both composition ranges. The data was analyzed by machine learning-techniques using decision tree, and full and reduced multiple additive regression tree (MART) models. Among these three schemes, a reduced MART (r-MART) model using six descriptors (formation energy, minimum and difference of electron densities at the Wigner-Seitz cell boundary, atomic radius difference, maximal atomic number and maximal electronegativity) presents the highest fit (98 %) and predictive (75 %) accuracy. This model is used to predict the defect behavior of other B2 compounds, and it is found that 45 % of the compounds considered feature vacancies as dominant defects for either A or B rich compositions (or both). The ability to predict dominant defect types is important for the modeling of thermodynamic and kinetic properties of intermetallic compounds, and the present results illustrate how this information can be derived using modern tools combining high throughput calculations and data analytics.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2025

Experimental determination of the magnetic anisotropy in five-coordinated Co( II ) field-induced single molecule magnets

Magnetic anisotropy of the central metal atom is a crucial property of single molecule magnets (SMMs). Small structural changes can alter the magnetic properties, and accurate experimental methods to investigate magnetic anisotropy are therefore critical. Here, we investigate two five-coordinated Co( II ) SMMs, [CoCl 2 Cltpy] (1) and [CoBr 2 Cltpy] (2) (Cltpy = 4′-chloro-2,2′:6′,2′′-terpyridine), through multiple techniques. Ab initio theoretical calculations performed on the two compounds show that both possess axial magnetic anisotropy with the magnetic easy axis pointing towards one of the terminal halogen atoms. Theoretical calculations on SMMs are typically done on isolated molecular species, and to validate this approximation the magnetic anisotropy was further studied through experimental techniques. EPR measurements confirm an axial anisotropy of 1, and magnetic measurements provide experimental Zero-Field Splitting (ZFS) parameters, showing that the values from theoretical calculations are slightly overestimated. The X-ray electron density determined from 20 K single-crystal synchrotron X-ray diffraction data provides estimated d-orbital populations also suggesting axial magnetic anisotropy in both systems, and furthermore suggesting a more pronounced axiality in 1 compared to 2. This is in good agreement with the results obtained from both magnetic measurements and theoretical calculations. The magnetic anisotropy of 1 is quantified experimentally through polarized powder neutron diffraction via the site susceptibility method, confirming an axial magnetic anisotropy of the compound. A slight deviation in the easy axis direction is observed between experimental and theoretical results. This, together with the overestimation of the ZFS parameters from theoretical calculations, shows that experimental investigation of the magnetic anisotropy of SMMs is of high relevance. Magnetic anisotropy of the central metal atom is a crucial property of single molecule magnets (SMMs).

Slavensky, Hannah H. [Aarhus Univ. (Denmark)] (ORC↗
DOE OSTI2016

Probing the electronic structure and Au—C chemical bonding in AuC{sub n}{sup −} and AuC{sub n}H{sup −} (n = 2, 4, and 6) using high-resolution photoelectron spectroscopy

We report a joint photoelectron spectroscopy and theoretical study on AuC{sub 4}{sup −}, AuC{sub 6}{sup −}, and AuC{sub n}H{sup −} (n = 2, 4, and 6) using high-resolution photoelectron imaging and ab initio calculations. The ground state of AuC{sub 2}H{sup −}, AuC{sub 4}H{sup −}, and AuC{sub 6}H{sup −} is found to be linear, while that of AuC{sub 4}{sup −} and AuC{sub 6}{sup −} is bent. All the species are found to be linear in their neutral ground states. The electron affinities (EAs) are measured to be 3.366(1) and 3.593(1) eV for AuC{sub 4} and AuC{sub 6}, respectively. Both bending and stretching frequencies are resolved in the spectra of AuC{sub 4}{sup −} and AuC{sub 6}{sup −}. High-resolution data of AuC{sub n}H{sup −} reveal major vibrational progressions in the Au—C stretching and bending modes. AuC{sub 2}H{sup −} has a ground state stretching frequency of 445(10) cm{sup −1} and a bending frequency of 260(10) cm{sup −1}; AuC{sub 4}H{sup −} has a ground state stretching frequency of 340(10) cm{sup −1}; AuC{sub 6}H{sup −} has a ground state stretching frequency of 260(10) cm{sup −1} and a bending frequency of 55(10) cm{sup −1}. The EAs are measured to be 1.475(1), 1.778(1), and 1.962(1) eV for AuC{sub 2}H, AuC{sub 4}H, and AuC{sub 6}H, respectively. The strength of the Au—C bond decreases as the number of carbon atoms increases. The current study provides a wealth of electronic structure information about AuC{sub 4}{sup −}, AuC{sub 6}{sup −}, and AuC{sub n}H{sup −} (n = 2, 4, and 6) and their corresponding neutrals.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗