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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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2016

On the Detectability of CO Molecules in the Interstellar Medium via X-Ray Spectroscopy

We present a study of the detectability of CO molecules in the Galactic interstellar medium using high-resolution X-ray spectra obtained with the XMM-Newton Reflection Grating Spectrometer. We analysed 10 bright low mass X-ray binaries (LMXBs) to study the CO contribution in their line of sights. A total of 25 observations were fitted with the ISMabs X-ray absorption model which includes photoabsorption cross-sections for Oi, Oii, Oiii and CO. We performed a Monte Carlo (MC) simulation analysis of the goodness of fit in order to estimate the significance of the CO detection. We determine that the statistical analysis prevents a significant detection of CO molecular X-ray absorption features, except for the lines of sight towards XTE J1718-330 and 4U 1636-53. In the case of XTE J1817-330, this is the first report of the presence of CO along its line of sight. Our results reinforce the conclusion that molecules have a minor contribution to the absorption features in the O K-edge spectral region. We estimate a CO column density lower limit to perform a significant detection with XMM-Newton of N(CO) greater than 6 x 10(exp 16) per sq cm for typical exposure times.

ISM: structure↗
NASA NTRS1978

Low energy ionizing collisions between N2 and CO beam molecules and CO, N2, NO, CH4, and CO2 target molecules

Absolute total negative charge production cross sections for N2 + CO, CO + N2, CO + CO, N2 + NO, N2 + CH4, and N2 + CO2 collisions are reported, and a simple model of collisions is discussed. The cross sections were measured to within about 1 eV of their thresholds. Specific reaction channels were investigated by referring to mass spectrometric identification of the product ions scattered in the forward direction, and these product ion identifications were used to explain characteristic structures in the total charge production cross sections in the near-threshold regions. The extent of the importance of dissociative ionization and 'simple' ionization in the studied collisions at low energy is considered, and charge transfer cross sections for (CO)+ + CO, CO(+) + CH4, and N2(+) + CH4 are presented.

Utterback, N. G.↗
NASA NTRS1975

Proton transfer reactions from H3/+/ ions to N2, O2, and CO molecules

The rate constants for proton transfer from H3(+) ions to N2, O2, and CO have been measured as function of hydrogen-buffer-gas partial pressure. The rate constant for proton transfer from H3(+) to N2 shows a very large pressure dependence, increasing from 1.0 by 10 to the -9th power cu cm/s at low H2 partial pressures to 1.7 by 10 to the -9th power cu cm/s at high H2 partial pressures. The rate constants for proton transfer from H3(+) to O2 and CO are constant with partial pressure of H2. The roles of excess vibrational energy in H3(+) ions and of equilibrium between forward and back reactions are discussed. Back reaction is observed only for the reaction of H3(+) ions with O2, and an equilibrium constant of 2.0 (plus or minus 0.4) at 298 K has been determined. From these data, the proton affinity of O2 is deduced to be 0.47 (plus or minus 0.11) kcal/mole higher than that of H2.

Kim, J. K.↗
NASA NTRS1978

Collisional excitation of interstellar molecules - Linear molecules CO, CS, OCS, and HC3N

Rates for excitation of CO, CS, OCS, and HC3N by collisions with He atoms and H2 molecules are presented. These have been obtained from extensive theoretical calculations using methods of known reliability. In general, rates necessary for modeling interstellar molecular clouds with kinetic temperatures to 100 K have been included. Methods for fitting these rates in more compact form are discussed.

Green, S.↗
NASA NTRS1981

A theoretical study of selected singlet and triplet states of CO molecule

The results of the configuration calculations of six singlet electronic states and one triplet electronic state of CO are presented. The potential energy curves, spectroscopic constants, and electron transition moments are calculated, along with electronic dipole moment functions for three states. The self consistent field and configuration calculations used to obtain the electronic wave functions are described. The theoretical results are found to be in good agreement with the experimental measurements, and in the case of the dipole moment function calculations, preferable to them.

Cooper, D. M.↗
DOE OSTI2021

Structural Characterization of Two CO Molecules Bound to the Nitrogenase Active Site

As an approach towards unraveling the nitrogenase mechanism, we have studied the binding of CO to the activesite FeMo-cofactor. CO is not only an inhibitor of nitrogenase, but it is also a substrate, undergoing reduction to hydrocarbons (Fischer–Tropsch-type chemistry). The CC bond forming capabilities of nitrogenase suggest that multiple CO or COderived ligands bind to the active site. Herein, we report a crystal structure with two CO ligands coordinated to the FeMo-cofactor of the molybdenum nitrogenase at 1.33 resolution. In addition to the previously observed bridging CO ligand between Fe2 and Fe6 of the FeMo-cofactor, a new ligand binding mode is revealed through a second CO ligand coordinated terminally to Fe6. While the relevance of this state to nitrogenase-catalyzed reactions remains to be established, it highlights the privileged roles for Fe2 and Fe6 in ligand binding, with multiple coordination modes available depending on the ligand and reaction conditions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Shaping attosecond pulses by controlling the minima in high-order harmonic generation through alignment of CO 2 molecules

In this paper, we report a simple method for generating shaped attosecond pulses by using a CO 2 molecule. Unlike most other molecules, owing to its unique energy and angle dependence and the presence of deep minima in the photoionization transition dipole moment, the shape of harmonic spectra, especially the position and depth of minima, can be readily controlled by tuning the degree of alignment. The sensitive alignment dependence of the minima is due to the coherent interference of a laser-induced dipole from each molecule when CO 2 molecules are moderately aligned, but not when they are well aligned or when they are isotropically distributed. Such a sensitivity offers a simple way of controlling the spectral amplitude and phase of the generated harmonics and thus shaping the generated attosecond pulses, for example, producing structured attosecond pulses by splitting a single burst into two. We illustrate how such pulses are generated and how to characterize them. This method offers a simple way to shape attosecond pulses at the generation step. It can be easily implemented experimentally to generate attosecond pulses with strong phase variations for unique applications.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2020

How Rh surface breaks CO 2 molecules under ambient pressure

Utilization of carbon dioxide (CO 2 ) molecules leads to increased interest in the sustainable synthesis of methane (CH 4 ) or methanol (CH 3 OH). The representative reaction intermediate consisting of a carbonyl or formate group determines yields of the fuel source during catalytic reactions. However, their selective initial surface reaction processes have been assumed without a fundamental understanding at the molecular level. Here, we report direct observations of spontaneous CO 2 dissociation over the model rhodium (Rh) catalyst at 0.1 mbar CO 2 . The linear geometry of CO 2 gas molecules turns into a chemically active bent-structure at the interface, which allows non-uniform charge transfers between chemisorbed CO 2 and surface Rh atoms. By combining scanning tunneling microscopy, X-ray photoelectron spectroscopy at near-ambient pressure, and computational calculations, we reveal strong evidence for chemical bond cleavage of O-CO* with ordered intermediates structure formation of (2 × 2)-CO on an atomically flat Rh(111) surface at room temperature.

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

Genetic-algorithm retrieval of the molecular alignment distribution with high-order harmonics generated from transiently aligned CO 2 molecules

Using genetic algorithm, we propose a method to retrieve the alignment distribution of transiently aligned CO 2 molecules from the high-order harmonic generation (HHG) spectra. The retrieval method is based on the quantitative rescattering (QRS) model where averaged photorecombination transition dipole can be factored out from the parallel (or perpendicular) harmonic spectra after the propagation of the harmonic fields in the gas medium. We examine how the retrieved alignment distributions are affected by uncertainty in alignment dependent ionization probability and on multiple orbital contribution to the HHG. We further confirm that alignment distribution is more accurately retrieved by using the minima in the HHG spectra driven by a long-wavelength laser. In addition, we show that earlier experimental data on the ratios between the perpendicular and the parallel HHG components of aligned CO 2 molecules are in better agreement with the QRS model if the macroscopic propagation and multiple orbital interference are included in the theoretical calculation.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2025

Multigas Adsorption with Single-Site Cooperativity in a Metal-Organic Framework

Cooperative gas adsorption in metal-organic frameworks (MOFs) is a rare phenomenon that generally involves long-range communication between multiple binding sites. We demonstrate a MOF containing cobalt(II)-methyl sites that selectively and reversibly capture two carbon monoxide (CO) molecules per site, leading to record-high adsorption capacities at ambient temperatures and pressures. Gas adsorption and structural, spectroscopic, and computational analyses support a mechanism in which binding of one CO molecule triggers a spin transition, followed by binding of a second CO molecule and migratory insertion of the first CO molecule into the cobalt-methyl bond to form an acetyl. The greater binding affinity associated with the second CO results in sigmoidal adsorption isotherms, a hallmark of cooperativity and phase-change materials, despite the absence of long-range interactions within the framework.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Lattice expansion and ligand twist during CO2 adsorption in flexible Cu bipyridine metal–organic frameworks

Flexible metal–organic frameworks (MOFs) can show exceptional selectivity and capacity for adsorption of CO 2 . The incorporation of CO 2 into flexible MOFs that have Cu 2+ coordination centers and organic pillar ligands is accompanied by a distortion of the framework lattice arising from chemical interactions between these components and CO 2 molecules. CO 2 adsorption yields a reproducible lattice expansion that is enabled by the rotation of the pillar ligands. The structures of Cu 2 (pzdc) 2 (bpy) and Cu 2 (pzdc) 2 (bpe), CPL-2 and CPL-5, were evaluated using in situ synchrotron X-ray powder diffraction at room temperature at CO 2 gas pressures up to 50 atm. The structural parameters exhibit hysteresis between pressurization and depressurization. The pore volume within CPL-2 and CPL-5 increases at elevated CO 2 pressure due to a combination of the pillar ligand rotation and the overall expansion of the lattice. Volumetric CO 2 adsorption measurements up to 50 atm reveal adsorption behavior consistent with the structural results, including a rapid uptake of CO 2 at low pressure, saturation above 20 atm, and hysteresis evident as a retention of CO 2 during depressurization. Finally, a significantly greater CO 2 uptake is observed in CPL-5 in comparison with predictions based on CO 2 pressure-induced expansion of the pore volume available for adsorption, indicating that the flexibility of the CPL structures is a key factor in enhancing adsorption capacity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Robust control of the minima of high-order harmonics by fine-tuning the alignment of CO 2 molecules for shaping attosecond pulses and probing molecular alignment

In a recent paper, we reported that the position and depth of the minima in the harmonic spectra of CO 2 molecules can be dramatically manipulated by a slight change of the degree of alignment, thus providing a convenient method of shaping attosecond pulses which could lead to the splitting of a typical single attosecond burst into two. Here, we demonstrate that harmonic minima can also be dramatically controlled by changing the pump-probe angles to shape attosecond pulses. In the meanwhile, since the pump-probe angle-dependent harmonic spectra are very sensitive to the degree of alignment, harmonic spectra can also be used to calibrate the alignment distribution of molecules. In this work we identify such robust control of harmonic generation is due to the optical property of CO 2 and the coherent harmonic emission from the oriented molecules. The photoionization transition dipoles (PITDs) of CO 2 exhibit deep minima that change rapidly with molecular orientations accompanied by large phase changes of π in PITDs, thus leading to strong interference when the dipoles are added up coherently.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2020

Pt-Assisted Carbon Remediation of Mo2C Materials for CO Disproportionation

Using the CO disproportionation (Boudouard) reaction as a probe reaction, an in-depth analysis of temperature-programmed pulse response data shows that the addition of Pt to Mo2C mitigates deactivation of Mo active sites by acting as a carbon collector. CO2 production on Mo2C and Pt/Mo2C materials is dependent on both the activation energy and the CO surface concentration. Detailed plane-wave density functional theory calculations of the CO adsorption and disproportion reactions on Mo2C-supported Pt nanoparticles (NPs) are reported. The Mo2C was modeled by the ß-Mo2C (100) surface, and the Pt/Mo2C interface was modeled by the addition of 12 Pt atoms to the Mo2C (100) surface (12Pt@Mo2C). The potential energy surfaces of the Boudouard reaction were calculated on pure Mo2C, 12Pt@Mo2C, and Pt (111) surfaces. CO dissociation readily occurs on the Mo2C (100) surface, but not on the Pt (111) surface, with the former being exothermic and the latter being endothermic. At the Pt/Mo2C interface, CO dissociation is still exothermic, but with a larger energy barrier. The Boudouard reaction takes place on the Mo2C region, where CO2 is formed from a surface O atom dissociated from one CO molecule in reaction with another CO molecule, leaving one C atom on the surface. C adsorption is preferential on the Pt site in comparison to the Mo site. The supported Pt domains can collect the remaining C atoms, facilitating further CO2 formation on the active Mo sites. A Bader charge analysis shows that the surface metal-carbon bond is a mixture of covalent and ionic bonds, whereas the surface metal-oxygen bond is ionic. Electron localization function (ELF) and partial charge density calculations agree well with the Bader charge analysis. These computational results are consistent with experimental observations of the interaction of CO with Mo2C nanotube supported Pt domains in the transient regime under far from equilibrium conditions. The Boudouard reaction is an important side reaction, and the unexpected role found for Pt as a carbon collector, with Mo serving as a disproportionation site, provides a unique vantage point for understanding carbon and coke formation on catalytic materials.

Pt-assisted carbon remediation, Pt/Mo2C interface,↗
DOE OSTI2025

Automated Construction of Artificial Lattice Structures with Designer Electronic States

Manipulating matter with a scanning tunneling microscope (STM) enables the creation of atomically defined artificial structures that host designer quantum states. However, the time-consuming nature of the manipulation process, coupled with the sensitivity of the STM tip, constrains the exploration of diverse configurations and limits the size of the designed features. In this study, we present a reinforcement learning (RL)-based framework for creating artificial structures by spatially manipulating carbon monoxide (CO) molecules on a copper substrate by using the STM tip. The automated workflow combines molecule detection and manipulation, employing deep-learning-based object detection to locate CO molecules and linear assignment algorithms to allocate these molecules to designated target sites. We initially perform molecule maneuvering based on randomized parameter sampling for sample bias, tunneling current set point, and manipulation speed. This data set is then structured into an action trajectory used to train an RL agent. The model is subsequently deployed on the STM for real-time fine-tuning of the manipulation parameters during structure construction. Our approach incorporates path-planning protocols coupled with active drift compensation to enable atomically precise fabrication of structures with significantly reduced human input while realizing larger-scale artificial lattices with the desired electronic properties. Furthermore, using our approach, we demonstrate the automated construction of an extended artificial graphene lattice and confirm the existence of a characteristic Dirac point in its electronic structure. Further challenges regarding the RL-based structural assembly scalability are discussed.

Algorithms↗
DOE OSTI2020

Heterotrimetallic Mixed‐Valent Molecular Precursors Containing Periodic Table Neighbors: Assignment of Metal Positions and Oxidation States

Abstract A known trinuclear structure was used to design the heterobimetallic mixed‐valent, mixed‐ligand molecule [Co II (hfac) 3 −Na−Co III (acac) 3 ] ( 1 ). This was used as a template structure to develop heterotrimetallic molecules [Co II (hfac) 3 −Na−Fe III (acac) 3 ] ( 2 ) and [Ni II (hfac) 3 −Na−Co III (acac) 3 ] ( 3 ) via isovalent site‐specific substitution at either of the cobalt positions. Diffraction methods, synchrotron resonant diffraction, and multiple‐wavelength anomalous diffraction were applied beyond simple structural investigation to provide an unambiguous assignment of the positions and oxidation states for the periodic table neighbors in the heterometallic assemblies. Molecules of 2 and 3 are true heterotrimetallic rather than a statistical mixture of two heterobimetallic counterparts. Trinuclear platform 1 exhibits flexibility in accommodating a variety of di‐ and trivalent metals, which can be further utilized in the design of molecular precursors for the NaMM′O 4 functional oxide materials.

Han, Haixiang↗
NASA NTRS1986

Carbon monoxide production in low energy oxygen ion bombardment of pyrolytic graphite and Kapton surfaces

The results of an investigtion of the interaction of low energy oxygen ions with pyrolytic graphite and Kapton surface are reported. CO molecules emitted from the surface as a result of the ion bombardment were detected by a mass spectrometer. Because the ion-induced signals were small compared to that arising from the CO background pressure in the vacuum system, the ion beam was modulated and the modulated component of the CO signal measured with a lock-in amplifier. The quantum yield (CO molecules emitted per incident oxygen ion) for graphite rose from 1.9 at 4.5 eV ion energy to 6.6 at 465 eV. Comparable yields were obtained for Kapton. The large size of the yields suggests contributions to the reaction process from the background O2 molecules in the vacuum system.

Horton, C. C.↗