Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “dissociation”

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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Dissociative and double photoionization of CO from threshold to 90 A

Partial cross sections for molecular photoionization (CO(+)), dissociative photoionization (C(+) and O(+)), and dissociative double photoionization (C(2+)) in CO have been measured from their thresholds to 90 A using techniques of mass spectrometry. The results are compared with data reported previously. Several peaks observed in the cross section curves for dissociated fragments are tentatively assigned by comparing with those in the photoelectron spectra reported for CO. It is concluded that the shoulder in the total absorption cross section curve between 400 and 90 A results solely from the dissociative ionization processes.

Masuoka, T.↗
NASA NTRS1981

Nitrogen supply system based on hydrazine dissociation

Future long-duration manned space missions will require a method of generating N2 for cabin leakage makeup and repressurization. Life Systems, working with NASA, is developing a Nitrogen Supply Subsystem (NSS) based on the dissociation of N2H4 into a mixture of H2 and N2. The latter is separated to provide the makeup N2. Recent advances in specific hardware developments have resulted in the design and fabrication of a nominal 3.6 kg/day N2 generation module. The design integrates a N2H4 catalytic dissociator, three ammonia (NH3) dissociation stages and four H2 separation stages into a 33 kg, 14 cu dm module. A technique has been devised to alternate the NH3 dissociation and H2 separation stages to give high N2 purity in the product stream. Tests have shown the product stream to contain less than 0.5 percent H2 and 20 ppm NH3. This paper discusses the development and test activities of the NSS program. It reviews the design, configuration, operation and projected performance characteristics of a 4.4 kg/day NSS suitable for NASA's planned Space Operations Center.

Heppner, D. B.↗
NASA NTRS1984

The dissociation of subjective measures of mental workload and performance

Dissociation between performance and subjective workload measures was investigated in the theoretical framework of the multiple resources model. Subjective measures do not preserve the vector characteristics in the multidimensional space described by the model. A theory of dissociation was proposed to locate the sources that may produce dissociation between the two workload measures. According to the theory, performance is affected by every aspect of processing whereas subjective workload is sensitive to the amount of aggregate resource investment and is dominated by the demands on the perceptual/central resources. The proposed theory was tested in three experiments. Results showed that performance improved but subjective workload was elevated with an increasing amount of resource investment. Furthermore, subjective workload was not as sensitive as was performance to differences in the amount of resource competition between two tasks. The demand on perceptual/central resources was found to be the most salient component of subjective workload. Dissociation occurred when the demand on this component was increased by the number of concurrent tasks or by the number of display elements. However, demands on response resources were weighted in subjective introspection as much as demands on perceptual/central resources. The implications of these results for workload practitioners are described.

Yeh, Y. H.↗
NASA NTRS1987

In-Vacuum Dissociator for Atomic-Hydrogen Masers

Thermal control and vacuum sealing achieved while contamination avoided. Simple, relatively inexpensive molecular-hydrogen dissociator for atomic-hydrogen masers used on Earth or in vacuum of space. No air cooling required, and absence of elastomeric O-ring seals prevents contamination. In-vacuum dissociator for atomic hydrogen masers, hydrogen gas in glass dissociator dissociated by radio-frequency signal transmitted from surrounding 3-turn coil. Heat in glass conducted away by contacting metal surfaces.

Vessot, R. F.↗
NASA NTRS1989

The rate parameters for coupled rotation-vibration-dissociation phenomenon in H2

The effects of molecular rotation on coupled vibration-dissociation phenomena in H2 undergoing a nonequilibrium relaxation in a heating and cooling environment were studied theoretically. The rate coefficients for the collisional bound-bound and bound-free transitions, calculated by a quasi-classical trajectory method, were fed into the master equation, which was numerically solved to determine the rotational and vibrational population densities and bulk thermodynamic properties. Results indicate that the vibrational transition rates of H2 increase monotonically with the vibrational levels, faster than in the Landau-Teller (1936) model, and that the rotation of the molecules helps relax the low vibrational levels, serves as a temporary storage of vibrational energy during the relaxation, and thereby delays the dissociation process. The average energy loss due to the dissociation was determined to be about 80-90 percent of the total dissociation energy.

Sharma, Surendra P.↗
NASA NTRS1990

Collision-induced gas phase dissociation rates

The Landau-Zener theory of reactive cross sections was applied to diatomic molecules dissociating from a ladder of vibrational states. The result predicts a dissociation rate that is quite well duplicated by an Arrhenius function having a preexponential temperature dependence of about T(sub -1/2), at least for inert collision partners. This relation fits experimental data reasonably well. The theory is then used to calculate the effect of vibrational nonequilibrium on dissociation rate. For Morse oscillators, the results are about the same as given by Hammerling, Kivel, and Teare in their analytic approximation for harmonic oscillators, though at very high temperature a correction for the partition function limit is included. The empirical correction for vibration nonequilibrium proposed by Park, which is a convenient algorithm for CFD calculations, is modified to prevent a drastic underestimation of dissociation rates that occurs with this method when vibrational temperature is much smaller than the kinetic temperature of the gas.

Hansen, C. Frederick↗
NASA NTRS1991

The generation of O(1S) from the dissociative recombination of O2(+)

The multichannel quantum defect theory (MQDT) method and large scale wave functions are applied to the calculation of the cross sections and rates for dissociative recombination of O2(+) along the 1Sigma-u(+) dissociative potential. Indirect dissociative recombination is accounted for by simultaneously including both the vibronic and electronic coupling to the intermediate Rydberg resonances. An enhanced MQDT approach involving a second-order K matrix is described. Cross sections and rates for the lowest three vibrational levels of the ion are reported. The shapes of the cross sections are discussed in terms of Fano's profile index. It is found that, for each of the three ion vibrational levels, the intermediate Rydberg resonances reduce the dissociative recombination rate below the direct recombination rate. Just above threshold, resonances with centers below threshold play an important role.

Guberman, Steven L.↗
NASA NTRS1992

Radiation enhanced dissociation of hydrogen in nuclear rockets

The effect of radiation-induced dissociation of hydrogen gas in nuclear rockets is studied. The dissociation degree is obtained by solving rate equations, which include the fast-ion induced dissociation and ionization of atomic and molecular hydrogens. Analytical formulas are used to estimate a change in the viscosity and the specific impulse. It was found that the fast-ion induced dissociation plays an important role in enhancing the specific impulse for nuclear rocket concepts using hydrogen gas at low pressures (less than 0.1 MPa) and low temperatures (less than 3000 K). It is also shown that the specific impulse is enhanced by mixing helium-3, lithium-6, boron-10, or uranium-235 with hydrogen.

Watanabe, Yoichi↗
NASA NTRS1994

Dissociative Recombination without a Curve Crossing

Ab initio calculations show that a curve crossing is not always needed for a high dissociative- recombination cross section. For HeH(+), in which no neutral states cross the ion potential curve, dissociative recombination is driven by the nuclear kinetic-energy operator on adiabatic potential curves. The kinetic-energy derivative operator allows for capture into repulsive curves that are outside of the classical turning points for the nuclear motion. The dominant dissociative route is the C (2)Sigma(+) state leading to H(n = 2) atoms. An analogous mechanism is proposed for the dissociative recombination of H3(+).

Guberman, Steven L.↗
NASA NTRS2003

Dissociative Ionization of Aromatic and Heterocyclic Molecules

Space radiation poses a major health hazard to humans in space flight. The high-energy charged particles in space radiation ranging from protons to high atomic number, high-energy (HZE) particles, and the secondary species they produce, attack DNA, cells, and tissues. Of the potential hazards, long-term health effects such as carcinogenesis are likely linked to the DNA lesions caused by secondary electrons in the 1 - 30 eV range. Dissociative ionization (DI) is one of the electron collision processes that can damage the DNA, either directly by causing a DNA lesion, or indirectly by producing radicals and cations that attack the DNA. To understand this process, we have developed a theoretical model for DI. Our model makes use of the fact that electron motion is much faster than nuclear motion and assumes DI proceeds through a two-step process. The first step is electron-impact ionization resulting in a particular state of the molecular ion in the geometry of the neutral molecule. In the second step the ion undergoes unimolecular dissociation. Thus the DI cross section sigma(sup DI)(sub a) for channel a is given by sigma(sup DI)(sub a) = sigma(sup I)(sub a) P(sub D) with sigma(sup I)(sub a) the ionization cross section of channel a and P(sub D) the dissociation probability. This model has been applied to study the DI of H2O, NH3, and CH4, with results in good agreement with experiment. The ionization cross section sigma(sup I)(sub a) was calculated using the improved binary encounter-dipole model and the unimolecular dissociation probability P(sub D) obtained by following the minimum energy path determined by the gradients and Hessians of the electronic energy with respect to the nuclear coordinates of the ion. This model is used to study the DI from the low-lying channels of benzene and pyridine to understand the different product formation in aromatic and heterocyclic molecules. DI study of the DNA base thymine is underway. Solvent effects will also be discussed.

Huo, Winifred M.↗
DOE OSTI2025

2025 ASMS Investigation of the Collision-Induced Dissociation Mechanism of Protonated TODGA with IRIS

Title (20 words): Investigation of the Collision-Induced Dissociation Mechanism of Protonated TODGA with IRIS Introduction (120 words): One of the challenges facing wide-spread adoption of nuclear power is the development of efficient separation processes for used nuclear fuel. The molecules in separation processes are subjected to an extreme environment due to the high radiation fields from the used fuel and highly acidic media used for fuel dissolution, which results in significant molecular degradation, leading to reduced process efficiency. These degradation products must be identified and studied so mitigation strategies can be developed to maintain process efficiency. However, complex systems can have many degradation products, complicating identification. Untargeted analysis tools could be used to understand radiation chemistry in complex systems. However, this would necessitate improved understanding of the gas-phase fragmentation mechanisms of fuel cycle molecules like tetraoctyldiglycolamide (TODGA). Methods (120 words): The gas-phase fragmentation of protonated TODGA was investigated using collision-induced dissociation (CID), resonance ejection, and infrared ion spectroscopy (IRIS). CID and resonance ejection experiments were conducted using a Bruker Daltonics (Bremen, Gemany) SolariX XR fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. IRIS spectra of protonated TODGA and its two CID fragmentation products were measured using a modified Bruker amaZon Speed ETD 3D quadrupole ion trap mass spectrometer coupled to the Free Electron Lasers for Infrared eXperiments (FELIX) free electron laser. Measured spectra were compared with density functional theory (DFT) calculations using the Gaussian 16, Revision C.02 software package with the ?B97X-D functional and def2-TZVPP basis sets. Candidate structures were generated using the CREST 3.0 conformational sampling software tool. Preliminary Data (300 words): Collision-induced dissociation of protonated TODGA ([C36H73N2O3]+, m/z=581.562) results two fragment ions, one at m/z=340.285 assigned as [C20H38NO3]+ and the other at m/z=312.290, assigned as [C19H38NO2]+. Based on the assigned formula and the structure of protonated TODGA, the fragment at m/z=340.285 is likely formed from elimination of neutral dioctylamine. Comparison of the IRIS spectrum of m/z=340.285 with DFT predictions suggests it contains a ring structure, and is assigned as N-octyl-N-(6-oxo-1,4-dioxan-2-ylidene)octan-1-aminium. Based on this structure and the structure of protonated TODGA, we hypothesize this fragment formed from elimination of neutral dioctylamine followed by a ring closure mechanism. Comparison of the IRIS spectrum of the fragment at m/z=312.290 with DFT predictions also indicated the presence of a ring structure, assigned as N-(1,3-dioxolan-4-ylidene)-N-octyloctan-1-aminium. This product could be formed from elimination of carbon monoxide from the ring of m/z=340.285 as a sequential fragmentation or formed directly from protonated TODGA via elimination of neutral N,N-dioctylformamide followed by a ring closure. Resonance ejection experiments where m/z=340 was continuously ejected from the IRC cell showed no decrease in intensity of m/z=312.290 across several collision energies, suggesting that the later, direct formation mechanism, dominates. The location of the ionizing proton in protonated TODGA is important for modeling the fragmentation mechanisms. DFT calculations suggested that the position of bands involving the coupled vibrations of the amide C—N and C=O bonds in TODGA are the most sensitive to proton location. Evaluation of the IRIS spectrum of protonated TODGA suggests that the ionizing proton is located between the two amid oxygens. This protonation location was calculated to lie approximately 30 kJ/mol lower in energy than the next lowest energy location, with the proton located solely on one of the amide oxygens. Novel aspect (20 words): Infrared ion spectroscopy combined with resonance ejection experiments and density functional theory to probe the collision-induced dissociation mechanism of tetraoctyldiglycolamide.

37 - INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL C↗
DOE OSTI2026

From dynamics to kinetics for the dissociation of •QOOH radicals derived from isopentane

Thermal dissociation rates for hydroperoxyalkyl (•QOOH) radicals are challenging to measure due to their inherent instability. Recent dynamics experiments have demonstrated that in situ synthesis of •QOOH radicals in a supersonic expansion in combination with IR action spectroscopy provides an effective route to accurately map their energy-resolved dissociation rates. Collaborative theoretical analyses provide a route for converting from those microcanonical rates to accurate temperature- and pressure-dependent thermal rate constants. Here, we present the results of this conversion for the dissociation of two isopentyl β-QOOH isomers of relevance to isopentane oxidation. The results are compared with existing literature values, as well as with results obtained in a similar fashion for related •QOOH systems. Extrapolations from benchmark calculations of barrier properties for smaller systems to accurate predictions for larger systems and multidimensional hindered rotor treatments are both shown to be important components of the theoretical analysis. For completeness, we extend the theoretical analysis to a treatment of the full RO 2 /QOOH system for isopentyl (1,1-dimethyl-propyl) radical.

Ab initio kinetics↗
DOE OSTI2026

Bond Dissociation Energy, Ionization Energy, and Electronic Structure of Thorium Dimer

Diatomic thorium, Th 2 , has been investigated using a laser ablation, supersonic expansion source to produce the molecule and resonant two-photon ionization spectroscopy to measure its bond dissociation energy (BDE) and ionization energy (IE). The molecule has a high density of states in the vicinity of its bond dissociation energy, leading to rapid predissociation as soon as this energy is exceeded. The BDE is identified from this predissociation threshold as D 0 (Th 2 ) = 2.857(7) eV, where the assigned error limit is provided in parentheses in units of the last quoted digit. Similarly, the one-photon ionization threshold has been measured, providing the ionization energy IE(Th 2 ) = 5.042(4) eV. Together with a thermochemical cycle and the atomic ionization energy, these values provide the BDE of the cation, giving D 0 (Th 2 + ) = 4.122(8) eV. Computations show that Th 2 has three nearly degenerate low-lying electronic states (1 3 Σ u + , 1 1 Σ g + , and 1 3 Δ g ) with bonding dominated by 7s and 6d orbitals, indicating predominantly transition-metal-like behavior. The 1 3 Σ u + state exhibits a triple bond, whereas the 1 1 Σ g + and 1 3 Δ g states possess quadruple-bond character and correspondingly shorter bonds. Although 1 3 Σ u + is predicted to be the lowest state without spin–orbit coupling, the large spin–orbit stabilization of the 1 3 Δ g state makes its Ω = 1 g component the ground state. Furthermore, the calculated dissociation energy (2.840 eV) and ionization energy of Th 2 (5.098 eV) are both in excellent agreement with experiment.

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

Nature of molybdenum carbide surfaces for catalytic hydrogen dissociation using machine-learned potentials: an ensemble-averaged perspective

Molybdenum carbides with an electronic structure similar to noble metals have gained attention as a promising low-cost catalyst for biomass valorization and the hydrogen evolution reaction. However, our fundamental understanding of the catalyst surface and how different phases of these catalysts behave at varying reaction conditions is limited to ground state density functional theory calculations as ab initio molecular dynamics (AIMD) is computationally prohibitive at relevant length and time scales. Here, in this work, we train a multi-atomic cluster expansion (MACE) machine-learned interatomic potentials (MLIP) to study hydrogen dissociation and dynamics over Mo, δ-MoC, α-Mo 2 C, and β-Mo 2 C surfaces at varying temperatures and hydrogen partial pressures. Our simulations identify unique and different molecular and atomic hydrogen adsorption sites on different surfaces that do not depend on the temperature. At low hydrogen pressures, the surface coverage is monolayer, which transitions to two-layer adsorption at higher pressures. We find that atomic hydrogen diffusion and recombinations are preferred over molybdenum atom hollow sites, while the diffusion over carbon-terminated facets was negligible, signifying particularly strong C–H interactions. In contrast, molecular hydrogen adsorption occurs mostly atop Mo or the bridging sites. At a comparable hydrogen loading, β-Mo 2 C (001) is the most active surface for hydrogen dissociation reaction. This work provides insights into the dynamic nature of the hydrogen dissociation chemistry and the diversity of hydrogen adsorption sites on molybdenum carbides.

08 HYDROGEN↗
DOE OSTI2025

Competing ionization and dissociation: Extension of the energy-dependent frame transformation to the gerade symmetry of H 2

This article solves two major tasks that frequently arise in the theory of electron collisions with a target molecular cation. First, it extends the energy-dependent frame transformation (EDFT) treatment, which is needed to map fixed-nuclei electron-molecule scattering matrices into an energy-dependent laboratory-frame scattering matrix with vibrational channel indices. The EDFT mapping can now be carried out even when the target molecule possesses multiple low-energy potential curves, significantly transcending previous applications. Second, it implements a method to extract the rest of the full laboratory-frame scattering matrix, i.e., the columns and rows describing input and/or output dissociation channels. The treatment is benchmarked in this article against the essentially exact solution of a refined two-dimensional model of the singlet gerade Σ symmetry of H 2 . Our tests demonstrate that the theory accurately maps fixed-nuclei scattering information, of the type provided by existing electron-molecule computer codes, into a laboratory-frame scattering matrix that includes both ionization and dissociation. Furthermore, this treatment can provide a general framework applicable to a broad class of electron collision processes involving diatomic target ions, suitable for an accurate description of challenging processes such as dissociative recombination.

74 ATOMIC AND MOLECULAR PHYSICS↗
NASA NTRS2023

Effect of the Electrostatic Field due to the Surface Monolayer Metal Atoms on the Dissociation of Homonuclear Diatomic Gases in Gas-Metal Surface Reactions

The present paper examines the role of an electrostatic field generated by the outermost monolayer of metal ions prior to gas adsorption in aiding the dissociation of homonuclear diatomic gas molecules. The interaction of five homonuclear diatomic gases, Cl 2 , F 2 , H 2 , N 2 and O 2 , with several pure metals are examined using Coulomb’s law to calculate the attractive and repulsive forces between the electrons or ions in the gas molecule and the free surface metallic electrons or ions assuming a Bohr model. These calculations demonstrate that the total energy of the electrostatic fields from the metals can exceed the molecular binding energies of Cl 2 , F 2 , and O 2 at some distance from the metallic surface thereby suggesting that these gases interact primarily with the metallic surface in their atomic states after molecular bond dissociation prior to reaction. In contrast, H 2 and N 2 gases do not dissociate prior to reaching the metal surface due to the fact that the effective charge of the gas ions is less than the total electron charge at the outermost electronic shell. The present results correlate linearly with the electrochemical series standard reduction potential as well as with the Pauling electronegativity for several metals.

Gas-metal reactions↗
DOE OSTI2025

Design of facilitated dissociation enables timing of cytokine signalling

Protein design has focused on the design of ground states, ensuring that they are sufficiently low energy to be highly populated. Designing the kinetics and dynamics of a system requires, in addition, the design of excited states that are traversed in transitions from one low-lying state to another. This is a challenging task because such states must be sufficiently strained to be poorly populated, but not so strained that they are not populated at all, and because protein design methods have focused on generating near-ideal structures. Here we describe a general approach for designing systems that use an induced-fit power stroke to generate a structurally frustrated and strained excited state, allosterically driving protein complex dissociation. X-ray crystallography, double electron–electron resonance spectroscopy and kinetic binding measurements show that incorporating excited states enables the design of effector-induced increases in dissociation rates as high as 5,700-fold. We highlight the power of this approach by designing rapid biosensors, kinetically controlled circuits and cytokine mimics that can be dissociated from their receptors within seconds, enabling dissection of the temporal dynamics of interleukin-2 signalling.

deformation dynamics↗
DOE OSTI2026

Strong field ionization and dissociation dynamics of vinyl bromide (C 2 H 3 Br) initiated by few-cycle pulses

Photoelectron-photoion (PEPICO) and photoion-photoion (PIPICO) coincidence measurements, coupled with a few-cycle intense laser field, were employed to investigate strong field ionization/dissociation dynamics of vinyl bromide (C₂H₃Br). The angular streaking technique was used to map the recoil-frame angle-dependent ionization rates to identify ionizing orbitals. Dissociative single ionization was mainly attributed to ionizing the lower lying molecular orbitals, suggesting that direct ionization dominates with few-cycle pulses. Three dissociative double ionization channels, both prompt and delayed fragmentation, were identified. Theoretical analysis using time-dependent configuration interaction with complex absorbing potential (TDCI-CAP) and high-level electronic structure methods was performed to elucidate the underlying ionization and dissociation mechanisms.

Olowolafe, Temitayo A. [Wayne State University, De↗