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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.

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At least 829 records · Page 46
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Adsorption on transition metal surfaces: Transferability and accuracy of DFT using the ADS41 dataset

We present a benchmarking study of adsorption energies on transition metal surfaces computed with select functionals across different density functional theory codes. In addition to gradient corrected functionals, we evaluate the accuracies of representative metaGGAs, including MS2, SCAN, and SCAN+rVV10 , as well as a short-range screened hybrid functional, HSE06. The study shows that the challenge of finding a functional that can simultaneously capture both covalent and noncovalent molecule-surface interactions persists, with no single functional in the benchmarking study with average errors < 0.2 eV. We find that HSE06 on average does not improve the accuracy compared to PBE for the surface chemistry of transition metals. The BEEF-vdW dispersion-corrected generalized gradient approximation (GGA) and the MS2 metaGGA yield the lowest errors in both chemisorption and dispersion energies, demonstrating that moving up the Jacob's ladder of functionals to screened hybrids does not necessarily improve the description of transition metal surface chemistry.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Extensive gene content variation in the Brachypodium distachyon pan-genome correlates with population structure

While prokaryotic pan-genomes have been shown to contain many more genes than any individual organism, the prevalence and functional significance of differentially present genes in eukaryotes remains poorly understood. Whole-genome de novo assembly and annotation of 54 lines of the grass Brachypodium distachyon yield a pan-genome containing nearly twice the number of genes found in any individual genome. Genes present in all lines are enriched for essential biological functions, while genes present in only some lines are enriched for conditionally beneficial functions (e.g., defense and development), display faster evolutionary rates, lie closer to transposable elements and are less likely to be syntenic with orthologous genes in other grasses. Our data suggest that differentially present genes contribute substantially to phenotypic variation within a eukaryote species, these genes have a major influence in population genetics, and transposable elements play a key role in pan-genome evolution.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Measurement of Λ(1520) production in pp collisions at $\sqrt{s}$ = 7 TeV and p–Pb collisions at $\sqrt{s}$$_ {NN}$ = 5.02

The production of the Λ(1520) baryonic resonance has been measured at midrapidity in inelastic pp collisions at $\sqrt{s}$=7 TeV and in p–Pb collisions at $\sqrt{s}$$_ {NN}$=5.02 TeV for non-single diffractive events and in multiplicity classes. The resonance is reconstructed through its hadronic decay channel Λ(1520) →pK - and the charge conjugate with the ALICE detector. The integrated yields and mean transverse momenta are calculated from the measured transverse momentum distributions in pp and p–Pb collisions. The mean transverse momenta follow mass ordering as previously observed for other hyperons in the same collision systems. A Blast-Wave function constrained by other light hadrons (π, K, K$^0_S$, p, Λ) describes the shape of the Λ(1520) transverse momentum distribution up to 3.5 GeV/c in p–Pb collisions. In the framework of this model, this observation suggests that the Λ(1520) resonance participates in the same collective radial flow as other light hadrons. The ratio of the yield of Λ(1520) to the yield of the ground state particle Λ remains constant as a function of charged-particle multiplicity, suggesting that there is no net effect of the hadronic phase in p–Pb collisions on the Λ(1520) yield.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Parameterized yields of semivolatile products from isoprene oxidation under different NOx levels: impacts of chemical aging and wall-loss of reactive gases

We developed a new parameterization for the yields of semi-volatile/intermediate volatility products from isoprene oxidation that took into account the chemical aging under different NOx levels, including functionalization and fragmentation reactions within the gas phase, oligomerization and photolysis within the condensed phase, as well as the loss of particles and gases to chamber walls. We used a box model to fit the dynamic evolution of measured secondary organic aerosol (SOA) concentrations from chamber experiments. The explicit inclusion of multigenerational gas phase chemistry and SOA oligomerization/photolysis during fitting itself had large impacts on the fitted yields that relate to the initial volatility distribution of isoprene oxidation products. During further multigenerational aging of these initial organics, we varied the branching ratio between functionalization and fragmentation. The best fits suggested increasing amounts of fragmentation with increasing initial NOx levels for mixed experiments. Using a box model to simulate evolution of SOA in the atmosphere at constant dilution rate (in absence of wall losses), we found that the yields determined by including different chemical scenarios during fitting changed predicted SOA mass concentrations substantially over aging timescale of 1-2 days. Our results demonstrated the need for better constraining smog-chamber-derived volatility distributions of both gas- and particle-phase SOA constituents with measurements.

Xing, Li↗
DOE OSTI2023

Mapping the influence of ligand electronics on the spectroscopic and 1 O 2 sensitization characteristics of Pd( ii ) biladiene complexes bearing phenyl–alkynyl groups at the 2- and 18-positions

Photodynamic therapy (PDT) is a promising treatment for certain cancers that proceeds via sensitization of ground state 3 O 2 to generate reactive 1 O 2 . Classic macrocyclic tetrapyrrole ligand scaffolds, such as porphyrins and phthalocyanines, have been studied in detail for their 1 O 2 photosensitization capabilities. Despite their compelling photophysics, these systems have been limited in PDT applications because of adverse biological side effects. Conversely, the development of non-traditional oligotetrapyrrole ligands metalated with palladium (Pd[DMBil1]) have established new candidates for PDT that display excellent biocompatibility. Herein, the synthesis, electrochemical, and photophysical characterization of a new family of 2,18-bis(phenylalkynyl)-substituted Pd II 10,10-dimethyl-5,15-bis(pentafluorophenyl)-biladiene (Pd[DMBil2-R]) complexes is presented. These second generation biladienes feature extended conjugation relative to previously characterized Pd II biladiene scaffolds (Pd[DMBil1]). We show that these new derivatives can be prepared in good yield and, that the electronic nature of the phenylalkynyl appendages dramatically influence the Pd II biladiene photophysics. Extending the conjugation of the Pd[DMBil1] core through installation of phenylacetylene resulted in a ~75 nm red-shift of the biladiene absorption spectrum into the phototherapeutic window (600–900 nm), while maintaining the Pd II biladiene's steady-state spectroscopic 1 O 2 sensitization characteristics. Varying the electronics of the phenylalkyne groups via installation of electron donating or withdrawing groups dramatically influences the steady-state spectroscopic and photophysical properties of the resulting Pd[DMBil2-R] family of complexes. The most electron rich variants (Pd[DMBil2-N(CH3)2]) can absorb light as far red as ~700 nm but suffer from significantly reduced ability to sensitize formation of 1 O 2 . By contrast, Pd[DMBil2-R] derivatives bearing electron withdrawing functionalities (Pd[DMBil2-CN] and Pd[DMBil2-CF3]) display 1 O 2 quantum yields above 90%. The collection of results we report suggest that excited state charge transfer from more electron-rich phenyl-alkyne appendages to the electron deficient biladiene core circumvents triplet sensitization. The spectral and redox properties, as well as the triplet sensitization efficiency of each Pd[DMBil2-R] derivative is considered in relation to the Hammett value (σp) for each biladiene's R-group. More broadly, the results reported in this study clearly demonstrate that biladiene redox properties, spectral properties, and photophysics can be perturbed greatly by relatively minor alterations to biladiene structure.

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

Measurement of the nuclear modification factor for muons from charm and bottom hadrons in Pb+Pb collisions at 5.02 TeV with the ATLAS detector

Heavy-flavour hadron production provides information about the transport properties and microscopic structure of the quark–gluon plasma created in ultra-relativistic heavy-ion collisions. A measurement of the muons from semileptonic decays of charm and bottom hadrons produced in Pb+Pb and pp collisions at a nucleon–nucleon centre-of-mass energy of 5.02 TeV with the ATLAS detector at the Large Hadron Collider is presented. The Pb+Pb data were collected in 2015 and 2018 with sampled integrated luminosities of 208 μb –1 and 38 μb –1 , respectively, and pp data with a sampled integrated luminosity of 1.17 pb –1 were collected in 2017. Muons from heavy-flavour semileptonic decays are separated from the light-flavour hadronic background using the momentum imbalance between the inner detector and muon spectrometer measurements, and muons originating from charm and bottom decays are further separated via the muon track's transverse impact parameter. Differential yields in Pb+Pb collisions and differential cross sections in pp collisions for such muons are measured as a function of muon transverse momentum from 4 GeV to 30 GeV in the absolute pseudorapidity interval |n| < 2. Nuclear modification factors for charm and bottom muons are presented as a function of muon transverse momentum in intervals of Pb+Pb collision centrality. The bottom muon results are the most precise measurement of b quark nuclear modification at low transverse momentum where reconstruction of B hadrons is challenging. The measured nuclear modification factors quantify a significant suppression of the yields of muons from decays of charm and bottom hadrons, with stronger effects for muons from charm hadron decays.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Microbial sensitivity to temperature and sulfate deposition modulates greenhouse gas emissions from peat soils

Abstract Peatlands are among the largest natural sources of atmospheric methane (CH 4 ) worldwide. Microbial processes play a key role in regulating CH 4 emissions from peatland ecosystems, yet the complex interplay between soil substrates and microbial communities in controlling CH 4 emissions as a function of global change remains unclear. Herein, we performed an integrated analysis of multi‐omics data sets to provide a comprehensive understanding of the molecular processes driving changes in greenhouse gas (GHG) emissions in peatland ecosystems with increasing temperature and sulfate deposition in a laboratory incubation study. We sought to first investigate how increasing temperatures (4, 21, and 35°C) impact soil microbiome–metabolome interactions; then explore the competition between methanogens and sulfate‐reducing bacteria (SRBs) with increasing sulfate concentrations at the optimum temperature for methanogenesis. Our results revealed that peat soil organic matter degradation, mediated by biotic and potentially abiotic processes, is the main driver of the increase in CO 2 production with temperature. In contrast, the decrease in CH 4 production at 35°C was linked to the absence of syntrophic communities and the potential inhibitory effect of phenols on methanogens. Elevated temperatures further induced the microbial communities to develop high growth yield and stress tolerator trait‐based strategies leading to a shift in their composition and function. On the other hand, SRBs were able to outcompete methanogens in the presence of non‐limiting sulfate concentrations at 21°C, thereby reducing CH 4 emissions. At higher sulfate concentrations, however, the prevalence of communities capable of producing sufficient low‐molecular‐weight carbon substrates for the coexistence of SRBs and methanogens was translated into elevated CH 4 emissions. The use of omics in this study enhanced our understanding of the structure and interactions among microbes with the abiotic components of the system that can be useful for mitigating GHG emissions from peatland ecosystems in the face of global change.

AminiTabrizi, Roya↗
DOE OSTI2019

Multimodal Chemical Imaging for Linking Adhesion with Local Chemistry in Agrochemical Multicomponent Polymeric Coatings

Seed coatings improve germination and offer higher crop yields through a blend of active ingredients (such as insecticides and fungicides), polymers, waxes, fillers, and pigments. To reach their full potential, fundamental formulation challenges bridging structure and function need to be addressed. In some instances, during industrial-volume packing and transportation, coated seeds do not flow well through elevators, conveyers, and applicators, which may reduce yield and add cost. In this work, we illustrate a combinatorial chemical imaging approach to study seed coatings at the microscale to link chemical and physical properties responsible for low seed flowability. The local chemical composition was examined using time-of-flight secondary ion mass spectrometry (ToF-SIMS) and at comparable length scales, the local adhesive properties were examined using atomic force microscopy (AFM) force volume mapping. The link between the chemical and the adhesive properties was established by non-negative matrix factorization (NMF). The correlative multimodal imaging approach developed here utilizing AFM force volume mapping, ToF-SIMS chemical mapping, and data analytics offers a path for linking function with localized chemistry when investigating multicomponent soft material systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Conditions for translation and scaling invariance of the neutron diffusion equation

Lie group methods are applied to the time-dependent, monoenergetic neutron diffusion equation in materials with spatial and time dependence. To accomplish this objective, the underlying 2nd order partial differential equation (PDE) is recast as an exterior differential system so as to leverage the isovector symmetry analysis approach. Some of the advantages of this method as compared to traditional symmetry analysis approaches are revealed through its use in the context of a 2nd order PDE. In this context, various material properties appearing in the mathematical model (e.g., a diffusion coefficient and macroscopic cross section data) are left as arbitrary functions of space and time. The symmetry analysis that follows is restricted to a search for translation and scaling symmetries; consequently the Lie derivative yields specific material conditions that must be satisfied in order to maintain the presence of these important similarity transformations. The principal outcome of this work is thus the determination of analytic material property functions that enable the presence of various translation and scaling symmetries within the time-dependent, monoenergetic neutron diffusion equation. The results of this exercise encapsulate and generalize many existing results already appearing in the literature. While the results contained in this work are primarily useful as phenomenological guides pertaining to the symmetry behavior of the neutron diffusion equation under certain assumptions, they may eventually be useful in the construction of exact solutions to the underlying mathematical model. Furthermore, the results of this work are also useful as a starting point or framework for future symmetry analysis studies pertaining to the neutron transport equation and its many surrogates.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

Study of Cylindrical Polytropes with Cosmological Constant

In this paper, we study cylindrically symmetric perfect fluid distribution in the presence of cosmological constant satisfying two cases of polytropic equation of state. The corresponding structure equations are formulated and solved through numerical technique. The resulting polytropic models turn out to be physically viable as they satisfy all the energy conditions. Finally, we analyze the stability of polytropes by applying perturbations on matter variables via polytropic constant as well as polytropic index and construct the force distribution function. It is found that compact object is stable for feasible choice of perturbed polytropic constant in each case while the perturbation in polytropic index yields stable results only for the first case.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2025

Atomistic Investigation of Plastic Deformation and Dislocation Motion in Uranium Mononitride

Uranium mononitride (UN) is a promising advanced nuclear fuel due to its high thermal conductivity and high fissile density. However, many aspects of its mechanical behavior, particularly at reactor-relevant conditions, remain unclear. In this study, molecular dynamics (MD) simulations were employed to investigate the deformation behavior and dislocation motion in UN. We found that the Kocevski potential predicts the principal slip system as $\frac{1}{2}$ $\langle110\rangle${110}, aligning with experimental data. On the other hand, the Tseplyaev potential predicts slip to primarily occur on $\frac{1}{2}$ $\langle110\rangle${111}. MD simulations of stress–strain behavior were used to estimate the nanoindentation hardness, revealing that the Kocevski potential accurately predicts hardness even though it fails to model dynamic plasticity. Complete dislocation mobility functions have been fitted for the edge and screw dislocations in both the thermally activated and phonon-drag regimes. The 300 K linear mobility of the edge dislocation using the Tseplyaev potential was found to be 817 Pa -1 ·s -1 , whereas that of the screw dislocation using the Kocevski potential was found to be 4546 Pa -1 ·s -1 . At intermediate stresses, we observed that the subsonic steady-state motion of the edge dislocation in UN is intermittently interrupted by velocity jumps, reaching the average sound velocity. Finally, the threshold Schmid stress is calculated as 179–197 MPa, which gives an upper-limit estimate of the uniaxial yield stress of polycrystalline UN of 548–603 MPa. These findings, including the fitted dislocation mobility function, provide essential input for future plasticity and dislocation dynamics models of nuclear fuels.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Atomic Molybdenum for Synthesis of Ammonia with 50% Faradic Efficiency

The electrochemical dinitrogen (N 2 ) reduction reaction (NRR) under ambient conditions has gained significant interest as an environmentally friendly alternative to the traditional Haber–Bosch process for the synthesis of ammonia (NH 3 ). However, up to now, most of the reported NRR electrocatalysts with satisfactory catalytic activities have been hindered by the large overpotential in N 2 activation. The preparation of highly efficient Mo-based NRR electrocatalyst in acidic electrolytes under ambient conditions is demonstrated here, consisting of stabilized single Mo atoms anchored on holey nitrogen-doped graphene synthesized through a convenient potassium-salt-assisted activation method. At -0.05 V versus a reversible hydrogen electrode (RHE), an electrode consisting of the resultant electrocatalyst immobilized on carbon fiber paper can attain an exceptional Faradaic efficiency of 50.2% and a NH3 yield rate of 3.6 µg h -1 mg cat -1 with low overpotentials. Density functional theory calculations further unveil that compared to the original graphene without holes, the edge coordinated Mo atoms and the existence of vacancies on holey graphene lower the overpotential of N 2 reduction, thereby promoting the NRR catalytic activity. Finally, this work could provide new guidelines for future designs in single-atom catalysis that would be beneficial to ambient N 2 fixation, and replacement of classical synthesis processes that are very energy-intensive.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Inverse design of two-dimensional graphene/h-BN hybrids by a regressional and conditional GAN

Design of materials with desired properties is currently laborious and heavily relies on intuition of researchers through a trial-and-error process. To tackle this challenge, in this work we propose a novel regressional and conditional generative adversarial network (RCGAN) for inverse design of representative two-dimensional materials, the graphene and boron-nitride (BN) hybrids. RCGAN incorporates a supervised regressor network, thus overcoming the common technical barrier in the traditional unsupervised GANs, which cannot generate data when fed with continuous and quantitative labels. RCGAN can autonomously generate graphene/BN hybrids given any target bandgap values. These structures are distinguished from the ones used for training and exhibit high diversity for a given bandgap. Moreover, they exhibit high fidelity, yielding bandgaps within ~10% MAE F of the desired bandgaps as validated by density functional theory (DFT) calculations. Analysis by the principle component analysis (PCA) and modified locally linear embedding (MLLE) reveals that the generator has successfully generated structures following the statistical distribution of the real structures. It implies the possibility of the RCGAN in recognizing physical rules hidden in the high-dimensional data. The novel strategy for designing regressional GAN architecture together with the successful application to inverse design of materials would inspire further exploration in research fields beyond materials.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Mechanical properties, strain hardening, and fracture behavior of ultrasonic additively manufactured Zircaloy-4 after low-temperature neutron irradiation

Ultrasonic additive manufacturing (UAM) is a solid-state, layer-by-layer advanced manufacturing process that has the potential to create custom spatially controlled composites with embedded wires and sensors for nuclear component manufacture. For this work, to assess the feasibility of using UAM for nuclear-relevant materials research, the technique was used to produce a 3.5-mm-thick Zircaloy-4 plate for irradiation testing. The UAM Zircaloy-4 specimens were irradiated in the High Flux Isotope Reactor at a target irradiation temperature of 117 °C to 2.9 displacements per atom (dpa) to assess differences in irradiation-hardening behavior as a function of alloy processing path. The UAM and reference baseplate (BP) materials increased in yield strength by 372±27 MPa and 346±21 MPa, respectively, and both suffered significant reductions in uniform and total elongation attributed to irradiation hardening at low-temperature. Although the materials had similar nanoscale defect structures, including nanoscale black dot/loop features and strain-induced dislocation channels, the UAM material’s processing-related defects resulted in accelerated strain localization and failure as demonstrated by lower post-irradiation uniform elongation of UAM specimens (0.5 %) compared to BP (1.5 %) material. The UAM material also showed considerable anisotropy in mechanical response due to crack propagation along weld boundaries, resulting in differences in strength & ductility when tested parallel and perpendicular to the prior UAM build orientation. Therefore, although the fundamental irradiation response of UAM-processed Zircaloy-4 was phenomenologically comparable to that of BP reference material, additional optimization of the UAM processing is needed to produce irradiation-resistant and nuclear-relevant materials.

Digital image correlation↗
DOE OSTI2017

Naphthylbipyrrole-Containing Amethyrin Analogue: A New Ligand for the Uranyl (UO 2 2+ ) Cation

Using naphthobipyrrole as a functional building block, a new expanded porphyrin, naphtho-isoamethyrin, was prepared in 85% yield under acid catalyzed [4+2] MacDonald coupling conditions. Here, treatment of naphtho-isoamethyrin with the non- aqueous uranyl silylamide salt, [UO 2 [N(SiMe 3 ) 2 ] 2 ·2THF], yielded the corresponding uranyl complex. Upon metalation, naphtho-isoamethyrin undergoes a 2-electron oxidation to yield a formal 22 π-electron aromatic species, as inferred from 1H NMR and UV-vis spectroscopy, as well as cyclic voltammetry.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Cooperative Metal+Ligand Oxidative Addition and Sigma-Bond Metathesis: A DFT Study

A computational study of the experimentally proposed mechanism of alkyne diboration by a PDICo complex yielded two fundamental catalytic steps that undergo remarkable electronic changes, PDI = bis(imino)-pyridine. The reactions are envisaged via DFT (density functional theory) and MCSCF (multi-configuration self-consistent field) simulations as (i) a cooperative metal+ligand oxidative addition, and (ii) a sigma-bond metathesis induced ligand-to-metal charge transfer. Analysis of the bonding of pertinent intermediates/TSs also yielded important insight that may be illuminating with regards to the larger field of green catalysis that seeks to ennoble base metals through synergy with potentially redox non-innocent (RNI) ligands. For the present case, massive changes in electronic structure do not incur massive energetic penalties. Finally, in conjunction with previous research, one may postulate that structural and energetic “fluidity” among several electronic states of RNI-M 3d along the reaction coordinate is an essential signature of redox cooperativity and thus ennoblement.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Mechanistic Insights into Visible-Light-Induced ATRA Reactions Powered by the Symbiotic Relationship between Cu(II)/Cu(I) Phenanthroline Complexes

As photoredox catalysis continues to yield promising chemical transformations, there is an increased need to understand how specific photocatalysts function to improve reaction efficiencies while expanding their scope. Copper-phenanthroline-based photocatalysts such as Cu II (dap)Cl 2 (dap = 2,9-di(p-anisyl)-1,10-phenanthroline) and [Cu I (dap) 2 ]Cl were both found to be equally capable of olefin activation through electrophilic atom transfer radical addition (ATRA) reactions. Although these molecular catalysts have proven successful, many intermediates suggested in the proposed catalytic cycles have never been detected. One undetermined aspect in this chemistry is related to how one equivalent of Cu II (dap)Cl 2 generates half of an equivalent of [Cu I (dap) 2 ] + during the photocatalytic sequence. To this end, we initially used more synthetically accessible model systems, namely, [Cu I (dpp) 2 ]Cl and Cu II (dpp)Cl 2 (dpp = 2,9-diphenyl-1,10-phenanthroline), to glean detailed mechanistic insights into this unusual symbiotic relationship. We directly detected several intermediates involved in the ATRA photocatalytic cycle using these model chromophores in conjunction with electronic spectroscopy, infrared matrix-assisted laser desorption electrospray ionization (IR-MALDESI) mass spectrometry, electronic structure calculations, EPR spin-trap experiments, and 1 H NMR spectroscopy. We found that the unique ligand lability and coordinating properties of acetonitrile enable both the in situ oxidation of [Cu I (dpp) 2 ] + by tosyl chloride into Cu II (dpp)Cl 2 and the visible-light-induced homolysis of the Cu II –Cl bond, which initiates the conversion to the Cu I species [Cu I (dpp) 2 ][Cu I Cl 2 ]. Here, the combined findings from the present study of the catalytic cycle demonstrate that the symbiotic relationship between Cu II (dpp)Cl 2 and [Cu I (dpp) 2 ] + , as well as between Cu II (dap)Cl 2 and [Cu I (dap) 2 ] + , is the critical factor enabling the ATRA photoreaction by departing from either photocatalyst.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

A multi-plate velocity-map imaging design for high-resolution photoelectron spectroscopy

A velocity map imaging (VMI) setup consisting of multiple electrodes with three adjustable voltage parameters, designed for slow electron velocity map imaging applications, is presented. The motivations for this design are discussed in terms of parameters that influence the VMI resolution and functionality. Particularly, this VMI has two tunable potentials used to adjust for optimal focus, yielding good VMI focus across a relatively large energy range. It also allows for larger interaction volumes without significant sacrifice to the resolution via a smaller electric gradient at the interaction region. All the electrodes in this VMI have the same dimensions for practicality and flexibility, allowing for relatively easy modifications to suit different experimental needs. We have coupled this VMI to a cryogenic ion trap mass spectrometer that has a flexible source design. The performance is demonstrated with the photoelectron spectra of S- and CS 2 - . The latter has a long vibrational progression in the ground state, and the temperature dependence of the vibronic features is probed by changing the temperature of the ion trap.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗