Search NASA⌕ Search

SEARCH · Search NASA

Results for “Quantum Chemistry”

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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS2011

What's on the Surface? Physics and Chemistry of Delta-Doped Surfaces

Outline of presentation: 1. Detector surfaces and the problem of stability 2. Delta-doped detectors 3. Physics of Delta-doped Silicon 4. Chemistry of the Si-SiO2 Interface 5. Physics and Chemistry of Delta-doped Surfaces a. Compensation b. Inversion c. Quantum exclusion. Conclusions: 1. Quantum confinement of electrons and holes dominates the behavior of delta-doped surfaces. 2. Stability of delta-doped detectors: Delta-layer creates an approx 1 eV tunnel barrier between bulk and surface. 3. At high surface charge densities, Tamm-Shockley states form at the surface. 4. Surface passivation by quantum exclusion: Near-surface delta-layer suppresses T-S trapping of minority carriers. 5. The Si-SiO2 interface compensates the surface 6. For delta-layers at intermediate depth, surface inversion layer forms 7. Density of Si-SiO2 interface charge can be extremely high (>10(exp 14)/sq cm)

detectors↗
NASA NTRS1978

Photodissociation of CO2 and quenching of metastables

Investigations in four different areas were carried out to further our understanding of the chemistry of the atmospheres of Mars and Venus. CO2 photodissociation quantum yields were determined in the 1300-1500 A spectral region by measuring both CO and oxygen atoms. The O(1S) quantum yield was determined for CO2 photodissociation in the 1060-1175 A spectral region. The measurement resolves the differences between two earlier experiments, and demonstrates that the O(1S) yield is unity throughout most of the measured region. The pathways for the quenching of O(1S) by N2O, CO2, H2O and NO were investigated and the source of the Venus nightglow, detected by Venera 9 and 10, was investigated. What appears to be a new O2 band system, was detected although the identity of the transition is not yet evident.

Slanger, T. G.↗
NASA NTRS2003

Theoretical Studies of the Extra-terrestrial Chemistry of Biogenic Elements and Compounds

Results are presented on the following:(A) Ab initio quantum chemical studies of reactions in astrophysical ices.Theoretical electronic structure calculations were used to investigate reactions between formaldehyde (H2CO) and both hydrogen cyanide (HCN) and isocyanide (HNC) in search of other favorable reactions such as ammonia-formaldehyde addition, which was found in a recent theoretical study to be strongly enhanced when it occurs within cold ices.The present study examines further reactions between this product and H2CO in ices.(B) Heterogeneous hydrogenation of CO and H2CO on icy grain mantles.Formaldehyde (H2CO) and methanol (CH30H) are thought to be produced in the interstellar medium by the successive hydrogenation of carbon monoxide (CO) on grain surfaces. In the gas phase, the steps in which H adds to CO and H2CO possess modest barriers and are too inefficient to account for the observed abundances. Recent laboratory work has confirmed that formaldehyde and methanol are formed when H atoms are deposited on CO ice at 12 K. The present study employed ab initio quantum chemical calculations to investigate the impact of water ice on the sequential hydrogenation of CO.(C) Ice-bound condensed-phase reactions involving formic acid (HCOOH), methylenimine (CH2NH), hydrogen cyanide (HCN), hydrogen isocyanide (HNC), and ammonia ( 3) were investigated in order to characterize possible pathways to larger organic species that are efficient at the cold temperatures prevalent in cometary nuclei and the interstellar medium. (D) Pathways to glycine and other amino acids in ultraviolet-irradiated ices determined via quantum chemical modeling.(E) Photoionization in ultraviolet processing of astrophysical ice analogs at cryogenic temperatures.

Woon, David E.↗
NASA NTRS2000

Plasticity and Kinky Chemistry of Carbon Nanotubes

Since their discovery in 1991, carbon nanotubes have been the subject of intense research interest based on early predictions of their unique mechanical, electronic, and chemical properties. Materials with the predicted unique properties of carbon nanotubes are of great interest for use in future generations of aerospace vehicles. For their structural properties, carbon nanotubes could be used as reinforcing fibers in ultralight multifunctional composites. For their electronic properties, carbon nanotubes offer the potential of very high-speed, low-power computing elements, high-density data storage, and unique sensors. In a continuing effort to model and predict the properties of carbon nanotubes, Ames accomplished three significant results during FY99. First, accurate values of the nanomechanics and plasticity of carbon nanotubes based on quantum molecular dynamics simulations were computed. Second, the concept of mechanical deformation catalyzed-kinky-chemistry as a means to control local chemistry of nanotubes was discovered. Third, the ease of nano-indentation of silicon surfaces with carbon nanotubes was established. The elastic response and plastic failure mechanisms of single-wall nanotubes were investigated by means of quantum molecular dynamics simulations.

Srivastava, Deepak↗
NASA NTRS1992

The effects of molecular structure on the electrical conductivity of polymers

The role of Quantum Theoretical Methods is both predictive and supportive of experimental results in Chemistry. Present day methods are able to calculate vibrational spectra and stereochemical interactions for molecules of moderate size (up to 20 atoms). As for the predictive side, the electronic structure of molecules and polymers can be calculated in order to narrow down the field of many potential candidates, which would have the novel properties looked for. The following has been accomplished at the Rutgers Camden Chemistry Department as results of calculations on molecular and polymeric systems of interest to the Polymers Branch of the NASA Lewis Research Center, under Grant NAG3-956.

Burke, Luke A.↗
NASA NTRS1993

Quantum chemical study of methane oxidation species

The research funded by this project has focused on quantum chemical investigations of molecular species thought to be important in the chemistry of the earth's upper and lower atmospheres. The body of this report contains brief discussions of the results of the several phases of this investigation. In many instances these results have been presented at scientific meetings and/or published in refereed journals. Those bibliographic references are given. In addition to the study of specific chemical systems, there were several phases during the course of this investigation where much of the effort went into the development and modification of computer codes necessary to carry out these calculations on the wide range of computer equipment used during this study. This type of code maintenance and development work did not generally result in publications and presentations, but a brief review is given.

Jackels, Charles F.↗
NASA NTRSDate not supplied

Self-consistent Quantum Iteratively Sparsified Hamiltonian Algorithm (SQuISH)

Due to coherence time limitations, reducing the resources required to run quantum algorithms and simulate physical systems on a quantum computer is crucial. With regards to Hamiltonian simulation, a significant effort has focused on building efficient algorithms using various factorizations and truncations, typically derived from the Hamiltonian alone. We introduce a new paradigm for improving Hamiltonian simulation and reducing the cost of ground state problems based on ideas recently developed for classical chemistry simulations. The key idea is that one can find efficient ways to reduce resources needed by quantum algorithms by making use of two key pieces of information: the Hamiltonian operator and an approximate ground state wavefunction. We refer to our algorithm as the self-consistent quantum iteratively sparsified Hamiltonian (SQuISH). By performing our scheme iteratively, one can drive SQuISH to create an accurate wavefunction using a truncated, resource-efficient Hamiltonian. By utilizing this more compact Hamiltonian, our algorithm provides an approach to reduce the gate complexity of ground state calculations on quantum hardware. As proof of principle, we implement SQuISH using configuration interaction for small molecules and coupled cluster for larger systems. Through our combination of approaches, we demonstrate how it performs on a range of systems, the largest of which would require more than 200 qubits to run on quantum hardware.

Diana Chamaki↗
NASA NTRS1994

The Production of NO subscript 2 from the Photolysis of Peroxyacetyl Nitrate

PAN vapor was photolyzed at 248 nm and the NO subscript 2 photoproduct was detected by laser induced fluorescence (LIF). By comparison to the NO subscript 2 production from the photolysis of HNO subscript 3 under identical experimental conditions, we have obtained a relative quantum yield for the production of NO subscript 2. The implications of these results for atmospheric PAN chemistry will be discussed.

Peroxyacetyl nitrate fluorescence↗
NASA NTRSDate not supplied

A Look at the Truths and Misconceptions of the Variational Quantum Eigensolver and the Implications of Overparameterization

In this work, we investigate loss landscapes of the variational quantum eigensolver (VQE) by quantifying the number of local minima through empirical analyses. We focus on minimal models in chemistry and physics so that we can do a complete analysis using more computationally expensive tools. We employ Hessian eigenvalue calculations and the nudged elastic band algorithm to characterize these landscapes. Our results expand upon the existing literature by highlighting the optimization challenges faced by VQE. We find that, as the number of parameters in our ansatz increases, the number of basins increases while the corresponding loss function values converge toward the global minimum value. This observation implies that overparameterization may lead to an ``effective convexity'' in VQE loss landscapes, a phenomenon supported by theoretical and numerical work in classical machine learning.

quantum computing↗
NASA NTRS1989

Superaromatics: The key to a unified cosmic dust theory

The theory of Superaromatics, the key to a unified cosmic dust theory, was constructed by analyzing several thousand astronomical features covering every major aspect of astrophysics and astrochemistry relating to dust. To insure consistency between disciplines, the logical structure of the conclusions in each field was checked rather than accepting the current consensus. No substantial contradictory features are known to the author. The analysis falls into seven major parts: (1) kinetics of grain formation and destruction; (2) optical spectra of the interstellar medium (ISM); (3) meteorite interplanetary dust particle (IPD) chemistry; (4) structure and chemistry of the interstellar medium arising from surface catalysis; (6) dynamics of circumstellar and interstellar dust clouds, including galactic morphology; and (7) the chemistry and physics of previously unidentified compounds. Only tentative conclusions are presented here. The principle conclusion is that quantum mechanics as it is normally formulated is incomplete. The probable cause is that it is formulated with complex numbers rather than the more fundamental quaternion system. The manifestation in astrochemistry is that the most stable compounds are superaromatic and exotic enough to confound most classical analysis.

Manuel, Lawrence R.↗
NASA NTRS2012

Revisions to Photochemical Data for Use in Atmospheric Modeling

Solar and stellar flux incident on an atmosphere can cause molecules to dissociate into highly reactive species and allows for photochemical processes to play a fundamental role in atmospheric chemistry. While models have tried to simulate such processes, they are extremely sensitive to photoabsorption cross-sections and quantum yields: two parameters that are important in determining the photodissociation rate, and hence the lifetime, of atmospheric compounds. Obtaining high-resolution and current data for these parameters is therefore highly desirable. Due to this, database and literature searches for high-quality cross-sections and quantum yields were performed and compiled for KINETICS, a Caltech/JPL Chemical Transport Model that can be used in modeling planetary atmospheres. Furthermore, photodissociation rates determined by running a Titan 1-D model were used to verify the completeness of these latest revisions.

Chemical Transport Model (CTM)↗
NASA NTRS1977

A new concept in laser-assisted chemistry - The electronic-field representation

Electronic-field representation is proposed as a technique for laser-assisted chemistry. Specifically, it is shown that several field-assisted chemical processes can be described in terms of mixed matter-field quantum states and their associated energies. The technique may be used to analyze the effects exerted by an intense laser on both bound and unbound molecular systems, and to investigate other field-induced effects including multiphoton processes, emission, and photodissociation.

George, T. F.↗
NASA NTRS1992

Chemistry of the outer planets

Various aspects were studied of past or present chemistry in the atmospheres of the outer planets and their satellites using lab simulations. Three areas were studied: (1) organic chemistry induced by kinetically hot hydrogen atoms in the region of Jupiter's atmosphere containing the ammonia cirrus clouds; (2) the conversion of NH3 into N2 by plasmas associated with entry of meteors and other objects into the atmosphere of early Titan; and (3) the synthesis of simple hydrocarbons and HCN by lightning in mixtures containing N2, CH4, and NH3 representing the atmospheres of Titan and the outer planets. The results showed that: (1) hot H2 atoms formed from the photodissociation of NH3 in Jupiter's atmosphere could account for some of the atmospheric chemistry in the ammonia cirrus cloud region; (2) the thermalization of hot H2 atoms in atmospheres predominated by molecular H is not as rapid as predicted by elastic collision theory; (3) the net quantum loss of NH3 in the presence of a 200 fold excess of H2 is 0.02, much higher than was expected from the amount of H2 present; (4) the conversion of NH3 into N2 in plasmas associated with infalling meteors is very efficient and rapid, and could account for most of the N2 present on Titan; (5) the yields of C2H2 and HCN from lightning induced chemistry in mixtures of CH4 and N2 is consistent with quenched thermodynamic models of the discharge core; and (6) photolysis induced by the UV light emitted by the gases in the hot plasmas may account for some, if not most, of the excess production of C2H6 and the more complex hydrocarbons.

Scattergood, Thomas W.↗
NASA NTRS2014

Novel Materials, Processing and Device Technologies for Space Exploration with Potential Dual-Use Applications

We highlight results of a broad spectrum of efforts on lower-temperature processing of nanomaterials, novel approaches to energy conversion, and environmentally rugged devices. Solution-processed quantum dots of copper indium chalcogenide semiconductors and multiwalled carbon nanotubes from lower-temperature spray pyrolysis are enabled by novel (precursor) chemistry. Metal-doped zinc oxide (ZnO) nanostructured components of photovoltaic cells have been grown in solution at low temperature on a conductive indium tin oxide substrate. Arrays of ZnO nanorods can be templated and decorated with various semiconductor and metallic nanoparticles. Utilizing ZnO in a more broadly defined energy conversion sense as photocatalysts, unwanted organic waste materials can potentially be repurposed. Current efforts on charge carrier dynamics in nanoscale electrode architectures used in photoelectrochemical cells for generating solar electricity and fuels are described. The objective is to develop oxide nanowire-based electrode architectures that exhibit improved charge separation, charge collection and allow for efficient light absorption. Investigation of the charge carrier transport and recombination properties of the electrodes will aid in the understanding of how nanowire architectures improve performance of electrodes for dye-sensitized solar cells. Nanomaterials can be incorporated in a number of advanced higher-performance (i.e. mass specific power) photovoltaic arrays. Advanced technologies for the deposition of 4H-silicon carbide are described. The use of novel precursors, advanced processing, and process studies, including modeling are discussed from the perspective of enhancing the performance of this promising material for enabling technologies such as solar electric propulsion. Potential impact(s) of these technologies for a variety of aerospace applications are highlighted throughout. Finally, examples are given of technologies with potential spin-offs for dual-use or terrestrial applications.

solid state devices↗
NASA NTRS2017

Revised Models of Interstellar Nitrogen Isotopic Fractionation

Nitrogen-bearing molecules in cold molecular clouds exhibit a range of isotopic fractionation ratios and these molecules may be the precursors of 15N enrichments found in comets and meteorites. Chemical model calculations indicate that atom-molecular ion and ion-molecule reactions could account for most of the fractionation patterns observed. However, recent quantum-chemical computations demonstrate that several of the key processes are unlikely to occur in dense clouds. Related model calculations of dense cloud chemistry show that the revised 15N enrichments fail to match observed values. We have investigated the effects of these reaction rate modifications on the chemical model of Wirstrom et al. (2012) for which there are significant physical and chemical differences with respect to other models. We have included 15N fractionation of CN in neutral-neutral reactions and also updated rate coefficients for key reactions in the nitrogen chemistry. We find that the revised fractionation rates have the effect of suppressing 15N enrichment in ammonia at all times, while the depletion is even more pronounced, reaching 14N/15N ratios of >2000. Taking the updated nitrogen chemistry into account, no significant enrichment occurs in HCN or HNC, contrary to observational evidence in dark clouds and comets, although the 14N/15N ratio can still be below 100 in CN itself. However, such low CN abundances are predicted that the updated model falls short of explaining the bulk 15N enhancements observed in primitive materials. It is clear that alternative fractionating reactions are necessary to reproduce observations, so further laboratory and theoretical studies are urgently needed.

Wirstrom, E. S.↗
NASA NTRS2017

Revised Models of Interstellar Nitrogen Isotopic Fractionation

Nitrogen-bearing molecules in cold molecular clouds exhibit a range of isotopic fractionation ratios and these molecules may be the precursors of 15N enrichments found in comets and meteorites. Chemical model calculations indicate that atom–molecular ion and ion–molecule reactions could account for most of the fractionation patterns observed. However, recent quantum-chemical computations demonstrate that several of the key processes are unlikely to occur in dense clouds. Related model calculations of dense cloud chemistry show that the revised 15N enrichments fail to match observed values. We have investigated the effects of these reaction rate modifications on the chemical model of Wirström et al. (2012) for which there are significant physical and chemical differences with respect to other models. We have included 15N fractionation of CN in neutral–neutral reactions and also updated rate coefficients for key reactions in the nitrogen chemistry. We find that the revised fractionation rates have the effect of suppressing 15N enrichment in ammonia at all times, while the depletion is even more pronounced, reaching 14N/15N ratios of >2000. Taking the updated nitrogen chemistry into account, no significant enrichment occurs in HCN or HNC, contrary to observational evidence in dark clouds and comets, although the 14N/15N ratio can still be below 100 in CN itself. However, such low CN abundances are predicted that the updated model falls short of explaining the bulk 15N enhancements observed in primitive materials. It is clear that alternative fractionating reactions are necessary to reproduce observations, so further laboratory and theoretical studies are urgently needed.

astrochemistry – molecular processes – comets: gen↗
NASA NTRS2017

Revised Models of Interstellar Nitrogen Isotopic Fractionation

Nitrogen-bearing molecules in cold molecular clouds exhibit a range of isotopic fractionation ratios and these molecules may be the precursors of 15N enrichments found in comets and meteorites. Chemical model calculations indicate that atom–molecular ion and ion–molecule reactions could account for most of the fractionation patterns observed. However, recent quantum-chemical computations demonstrate that several of the key processes are unlikely to occur in dense clouds. Related model calculations of dense cloud chemistry show that the revised 15N enrichments fail to match observed values. We have investigated the effects of these reaction rate modifications on the chemical model of Wirström et al. (2012) for which there are significant physical and chemical differences with respect to other models. We have included 15N fractionation of CN in neutral–neutral reactions and also updated rate coefficients for key reactions in the nitrogen chemistry. We find that the revised fractionation rates have the effect of suppressing 15N enrichment in ammonia at all times, while the depletion is even more pronounced, reaching 14N/15N ratios of >2000. Taking the updated nitrogen chemistry into account, no significant enrichment occurs in HCN or HNC, contrary to observational evidence in dark clouds and comets, although the 14N/15N ratio can still be below 100 in CN itself. However, such low CN abundances are predicted that the updated model falls short of explaining the bulk 15N enhancements observed in primitive materials. It is clear that alternative fractionating reactions are necessary to reproduce observations, so further laboratory and theoretical studies are urgently needed.

astrochemistry – molecular processes – comets: gen↗