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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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NASA NTRS2010

Atomic Data and Spectral Line Intensities for Ni XI

Electron impact collision strengths, energy levels, oscillator strengths and spontaneous radiative decay rates are calculated for Ni XI. We include in the calculations the 10 lowest configurations, corresponding to 164 fine structure levels: 3s(sup 2)3p(sup 6), 3s(sup 2)3p(sup 5)3d, 3s(sup 2)3p(sup 4)3d(sup 2), 3s3p(sup 6)3d, 3s(sup 2)3p(sup 5)4l and 3s3p6 4l with l =.s, p, d. Collision strengths are calculated at five incident energies for all transitions: 7.1, 16.8, 30.2, 48.7 and 74.1 Ry above the threshold of each transition. An additional energy, very close to the transition threshold, has been added, whose value is between 0.06 Ry and 0.25 Ry depending on the lower level. Calculations have been carried out using the Flexible Atomic Code and the distorted wave approximation. Excitation rate coefficients are calculated as a function of electron temperature by assuming a Maxwellian electron velocity distribution. Using the excitation rate coefficients and the radiative transition rates of the present work, combined with Close Coupling collision excitation rate coefficient available in the literature for the lowest 17 levels, statistical equilibrium equations for level populations are solved at electron densities covering the 10(exp 8)-10(exp 14) cu cm range and at an electron temperature of logT(sub c)(K)=6.1, corresponding to the maximum abundance of Ni XI. Spectral line intensities are calculated, and their diagnostic relevance is discussed. This dataset will be made available in the next version of the CHIANTI database.

Bhatia, A. K.↗
NASA NTRS1975

Vibration-translation energy transfer in anharmonic diatomic molecules. 2: The vibrational quantum number dependence

A semiclassical model of the inelastic collision between a vibrationally excited anharmonic oscillator and a structureless atom was used to predict the variation of thermally averaged vibration-translation rate coefficients with temperature and initial-state quantum number. Multiple oscillator states were included in a numerical solution for collinear encounters. The results are compared with CO-He experimental values for both ground and excited initial states using several simplified forms of the interaction potential. The numerical model was also used as a basis for evaluating several less complete but analytic models. Two computationally simple analytic approximations were found that successfully reproduced the numerical rate coefficients for a wide range of molecular properties and collision partners. Their limitations were also identified. The relative rates of multiple-quantum transitions from excited states were evaluated for several molecular types.

Mckenzie, R. L.↗
NASA NTRS1976

Vibration-translation energy transfer in anharmonic diatomic molecules. II - The vibrational quantum-number dependence

A semiclassical model of the inelastic collision between a vibrationally excited anharmonic oscillator and a structureless atom is used to predict the variation of thermally averaged vibrational-translational rate coefficients with temperature and initial-state quantum number. Multiple oscillator states are included in a numerical solution for collinear encounters. The results are compared with CO-He experimental values for both ground and excited initial states using several simplified forms of the interaction potential. The numerical model is also used as a basis for evaluating several less complete, but analytic, models. Two computationally simple analytic approximations are found that successfully reproduce the numerical rate coefficients for a wide range of molecular properties and collision partners. Their limitations are identified, and the relative rates of multiple-quantum transitions from excited states are evaluated for several molecular types.

Mckenzie, R. L.↗
NASA NTRS2003

Ultraviolet and Visible Emission Mechanisms in Astrophysics

The project involved the study of ultraviolet (UV) and visible emission mechanisms in astrophysical and atmospheric environments. In many situations, the emission is a direct consequence of a charge transferring collision of an ion with a neutral with capture of an electron to an excited state of the product ion. The process is also important in establishing the ionization and thermal balance of an astrophysical plasma. As little of the necessary collision data are available, the main thrust of the project was the calculation of total and state-selective charge transfer cross sections and rate coefficients for a very large number of collision systems. The data was computed using modern explicit techniques including the molecular-orbital close-coupling (MOCC), classical trajectory Monte Carlo (CTMC), and continuum distorted wave (CDW) methods. Estimates were also made in some instances using the multichannel Landau-Zener (MCLZ) and classical over-the-barrier (COB) models. Much of the data which has been computed has been formatted for inclusion in a charge transfer database on the World Wide Web (cfadc.phy.ornl.gov/astro/ps/data/). A considerable amount of data has been generated during the lifetime of the grant. Some of it has not been analyzed, but it will be as soon as possible, the data placed on our website, and papers ultimately written.

Stancil, Phillip C.↗
NASA NTRS2006

Mestastable State Population in Laser Induced Plasmas

Laser induced plasma has been used as a source of neutrals and ions in the study of astrophysical plasmas. The purity of state of this source is essential in the determination of collision parameters such as the charge transfer rate coefficients between ions and neutrals. We will show that the temperature of the laser induced plasma is a rapidly decreasing function of time. The temperature is initially high but cools off rapidly through collisions with the expanding plasma electrons as the plasma recombines and streams into the vacuum. This rapid expansion of the plasma, similar to a supersonic jet, drastically lowers the internal energy of the neutrals and ions.

Kwong, V. H. S.↗
NASA NTRS2009

C02(nu2)-0 Quenching Rate Coefficient Derived from Coincidental Fort Collins Lidar and SABER Measurements

Among the processes governing the energy balance in the mesosphere and lower thermosphere (MLT), the quenching of CO2(V2) vibrational levels in collisions with oxygen atoms plays an important role. However, neither the rate coefficient of this process (k(CO2O)) nor the atomic oxygen concentrations ([O]) in the MLT are well known. The discrepancy between k(CO2O) measured in the lab and retrieved from atmospheric measurements is of about factor of 2.5. At the same time, the discrepancy between [O] in the MLT measured by different instruments is of the same order of magnitude. In this work we used a synergy of a ground based lidar and satellite infrared radiometer to make a further step in understanding of the physics of the region. In this study we apply the night- and daytime temperatures between 80 and 110 km measured by the Colorado State University narrow-band sodium (Na) lidar located at Fort Collins, Colorado for retrieving the product of k(CO2-O) x [O] from the limb radiances in the 15 micron channel measured by the SABER/TIMED instrument for nearly simultaneous common volume measurements of both instruments within +/-1 degree in latitude, +/-2 degrees in longitude and +/-10 minutes in time. We derive k(CO2-O) and its possible variation range from the retrieved product by utilizing the [O] values measured by the SABER and other instruments.

Feofilov, A. G.↗
NASA NTRS1998

Molecular Processes in Comets

The research focused on molecular hydrogen and its response to ultraviolet radiation, photoelectron impact excitation and X-ray radiation and on the interpretation of the ultraviolet spectra of the Jupiter dayglow and auroras. A systematic effort was made to obtain reliable rate coefficients for rovibrational energy transfer of H2, particularly in collisions with hydrogen atoms. We carried out elaborate quantum-mechanical calculations of the scattering of H and H2 on what had been characterized as a reliable potential energy surface of the H3 molecular system. These calculations took into account reactive channels and rate coefficients for ortho-para transitions were obtained. Quantal calculations are too complex to be applied to all the possible rovibrational transitions and we turned to a semi-classical method. With it we calculated rate coefficients for transitions, reactive and non-reactive, for all the rovibrational levels. We carried out the calculations for three of the available H3 potential energy surfaces. We discovered an unexpected sensitivity of the rate coefficients for the non-reactive channels to the potential energy surface. This discovery stimulated more thorough investigations of the potential energy surface elsewhere and to the construction of a new surface. We have used it in further semi-classical calculations in work that will shortly be 2 completed and which, together with new quantum-mechanical calculations should comprise a set of reliable rate coefficients that can be used in discussions of H2 on the Jovian planets. We carried out a detailed study of the Jovian ultraviolet dayglow. There has been a long-running argument about the dayglow on Jupiter. There are two sources of excitation: fluorescence and photoelectron impact excitation. It had been argued that a third source "the electron glow" was needed to bring theory and observation into agreement. We believe we have shown conclusively that the third source is unnecessary. We have achieved a close quantitative agreement between the predicted spectrum arising from fluorescence and photoelectrons and the measured spectrum. We also demonstrated a method by which the presence of HD could be established observationary. Similar calculations were carried out of the ultraviolet spectra of the Jovian auroras. We again found close agreement. Indeed, the agreement was so detailed we were able to derive the temperature of the atmosphere. We found, contrary to the standard model of the time, a high temperature between 400 K and 600 K and established the presence of a significant temperature gradient. A large temperature gradient was indeed found by direct sampling with the Jupiter probe.

Dalgarno, A.↗
NASA NTRS1988

Two-temperature interpretation of dissociation rate data for N2 and O2

The existing experimental data on dissociation of nitrogen and oxygen obtained using shock-tubes during the 1960's and 1970's are reinterpreted using the two-temperature thermo-chemical model developed recently in order to determine the rate coefficients consistent with the model. In this model, the vibrational-electronic temperature is calculated by integrating a separate conservation equation accounting for the suppression of vibrational energy during dissociation due to preferential removal of high vibrational states. The rate coefficient is assumed to be a function of the geometrically-averaged temperature between the translational-rotational temperature and the vibrational-electronic temperature. By comparing the computed overall and species densities with the experimental data, the rate coefficient values most consistent with the model, and their ranges of uncertainty, are deduced for dissociation of N2 through collisions with N2 or N, and for O2 through collisions with O2, O or N2. It is seen that a single set of such rate coefficients fit all existing experimental data closely. According to the two-temperature model, density and species density are insensitive to the rate coefficients, and so the rate coefficients so determined are uncertain to within a factor of at least 1.5.

Park, Chul↗
NASA NTRS1969

Dielectronic recombination

Dielectronic recombination rate coefficient determined by quantum theory of resonance- collision processes, considering coupling, degeneracy and overlapping resonances

Shore, B. W.↗
NASA NTRS2006

Quenching of Excited Na due to He Collisions

The quenching and elastic scattering of excited Sodium by collisions with Helium have been investigated for energies between 10(exp -13) eV and 10 eV. With the ab initio adiabatic potentials and nonadiabatic radial and rotational couplings obtained from multireference single- and double-excitation configuration interaction approach, we carried out scattering calculations by the quantum-mechanical molecular-orbital close-coupling method. Cross sections for quenching reactions and elastic collisions are presented. Quenching and elastic collisional rate coefficients as a function of temperature between 1 micro-K and 10,000 K are also obtained. The results are relevant to modeling non-LTE effects on Na D absorption lines in extrasolar planets and brown dwarfs.

Lin, C. Y.↗
NASA NTRS2022

Design of Hypervelocity Flow Generator (HFG) and Its Diagnostics

Ground facilities for hypersonic research are a key element for successful development of aerodynamically proven hypervelocity vehicles. Design concepts and diagnostics of a hypervelocity flow generator (HFG) were made as a test platform for hypersonic/hypervelocity spacecraft models at the NASA Langley Research Center. The HFG is a hypersonic flow field generator using optically heated gas which is blown into an 80 cu m vacuum chamber. The vacuum chamber is kept at a stable vacuum pressure with a combination of three large vacuum pumps, while the HFG is in the test mode. The HFG provides a relatively small test section with approximately a 20 cm window. This facility was designed to generate 2.45 km/sec of flow speed, and potentially generate a continuous flow with the nozzle and vacuum system. The window in test section provides a direct view of the shock wave around a model in order to measure temperature, pressure, and density profile within the shock layer. One of the key test goals under this project is to understand why the emission spectra from the standing shockwave plasma predicted by Lora-Loran codes are significantly different from the measured emission spectra from the Flight Investigation Reentry Environment (FIRE II) Flight. The correct estimate of the thermal loading on the leading edge of hypersonic vehicles greatly affects the aerodynamic design, the material selection for the vehicle, and the cooling requirement and can be obtained by the precise modeling of emission spectra from shockwave plasma. However, the estimation of thermal loading is not an easy task due to complex non-equilibrium radiative process within high temperature shock layers that still falls into a category of cold plasma. Direct flight experiments are the most desirable, but not a cost-effective approach. Analysis by computational fluid dynamics (CFD) offers many test flexibilities. However, the CFD codes must be fully tested and validated with experimental data before the codes are effectively used for practical design. Large discrepancies between experiments and codes appear in hypersonic/hypervelocity flow regimes at high altitudes of 60 km ~ 90 km. This HFG facility offers some important parameters for CFD code validation, such as collision cross-sections, relaxation times, reaction rate coefficients and transportation coefficients. The HFG test facility is based on the ejection flow of high temperature gas heated over to 3500 K through a nozzle. The tungsten gas chamber of the HFG is heated up to a desired temperature by a 60 kW optical power beam source. This system consists of an optical power source, a thermal chamber, an expansion nozzle, a test section, and an 80 cu m vacuum tank. 60 kW optical input power is obtained from the 150 kW Vortek arc lamp system (by Vortek Industries, Vancouver, Canada). This optical beam is focused to heat the gas chamber within which a flow media is heated. The maximum achievable temperature of the flow medium reached approximately 3500 K or even higher but is limited by the melting point of the chamber material used. The exhaust velocity through the nozzle was determined by the stagnation temperature and the molecular weight of the working medium at the test section. To provide design parameters, a NASA Chemical Equilibrium with Application (CEA) computer program is used for the simulation of aerothermal data. This CEA program can calculate chemical equilibrium and properties of complex mixtures using shock tube parameters. For nitrogen gas at 2666 K stagnation temperature, the maximum achievable velocity at the test section is approximately 2.45 km/sec which is within the range of the thermal velocity of 8000 K shock layer. Based on the calculation through the CEA program, the design parameters of a HFG were determined and implemented for the test section that includes an expansion nozzle. The installed test section of the experimental facility can sustain a condition of a re-entry vehicle from the Space at an altitude of 60-90 km. After installation of the HFG, the system was fully tested and its operational parameters were measured. An 80 cu m vacuum chamber of HFG was set at 1 torr level to keep a stable downstream condition. The pumping time to reach the minimum vacuum pressure (~ 1 torr) at the test chamber from atmospheric pressure was approximately an hour using Kinney (MBV-14000/MB -1600/KT-300) and Stokes (Model 1772 and 412) pumps. Such a setup condition allowed a continued stable operation of the HFG experiment with flowrates through 1-, 3-, or 5-mm diameters of nozzle throat. The flow characteristics of the HFG for various operating conditions were performed using a focused Schlieren method. At 0.8 torr chamber pressure, a barrel shock was observed at the test section. With a sphere obstacle of 12 mm diameter in the flow, a bow shock (~ 2-mm thickness) was observed by a focused Schlieren visualization method.

Hypervelocity flow↗
NASA NTRS2003

Iron catalyst chemistry in modeling a high-pressure carbon monoxide nanotube reactor

The high-pressure carbon monoxide (HiPco) technique for producing single-wall carbon nanotubes (SWNTs) is analyzed with the use of a chemical reaction model coupled with flow properties calculated along streamlines, calculated by the FLUENT code for pure carbon monoxide. Cold iron pentacarbonyl, diluted in CO at about 30 atmospheres, is injected into a conical mixing zone, where hot CO is also introduced via three jets at 30 degrees with respect to the axis. Hot CO decomposes the Fe(CO)5 to release atomic Fe. Then iron nucleates and forms clusters that catalyze the formation of SWNTs by a disproportionation reaction (Boudouard) of CO on Fe-containing clusters. Alternative nucleation rates are estimated from the theory of hard sphere collision dynamics with an activation energy barrier. The rate coefficient for carbon nanotube growth is estimated from activation energies in the literature. The calculated growth was found be about an order of magnitude greater than measured, regardless of the nucleation rate. A study of cluster formation in an incubation zone prior to injection into the reactor shows that direct dimer formation from Fe atoms is not as important as formation via an exchange reaction of Fe with CO in FeCO.

Evaluation Studies↗
NASA NTRS1991

Association reactions at low pressure. IV - The HC3N(+)/HC3N system

Ion cyclotron mass spectrometry is used here to study the reactions between HC3N(+) and HC3N and between HC5N(+) and HC3N at pressures from 1 x 10 to the -7th to 0.001 Torr. The former reaction has both a bimolecular reaction path and a termolecular reaction path. The overall bimolecular reaction rate coefficient is 1.3 x 10 to the -19 cu cm/s. The primary product HC5N(+) represents 90 percent of the product ions, while HC6N2(+) and H2C6N2(+) each represent 5 percent. The termolecular association rate coefficient is 3.7 x 10 to the -24th cm exp 6/s, with He as the third body. The mean lifetime of the collision is 180 microsec. HC5N(+) reacts with HC3N to form the adduct ion H2C8N2(+) through both bimolecular and termolecular reactions. The bimolecular rate coefficient is 5.0 x 10 to the -10th cu cm/s and the termolecular one is 1.2 x 10 to the -22nd cm exp 6/s, with HC3N as the third body.

Sen, Atish D.↗
NASA NTRS1985

Improved excitation rate coefficients for the n = 2 and n = 3 levels of Ca XIX and Fe XXV including fine structure

Reently calculated collision strengths, including relativistic and resonance effects, are employed to compute Maxwellian averaged collision strengths for 78 transitions involving states of principal quantum numbers 2-1 and 3-1 in Ca XIX and Fe XXV. These rate parameters are tabulated at temperatures of interest in astrophysical and labortory plasmas with radiation in the hard X-ray wavelength range. For some transitions, significant differences are found with the earlier calculations of Pradhan, Norcross, and Hummer (1981).

Pradhan, A. K.↗
NASA NTRS2012

Co2(nu2)-o Quenching Rate Coefficient Derived from Coincidental SABER-TIMED and Fort Collins Lidar Observations of the Mesosphere and Lower Thermosphere

Among the processes governing the energy balance in the mesosphere and lower thermosphere (MLT), the quenching of CO2(nu2) vibrational levels by collisions with O atoms plays an important role. However, there is a factor of 3-4 discrepancy between the laboratory measurements of the CO2-O quenching rate coefficient, k(sub VT),and its value estimated from the atmospheric observations. In this study, we retrieve k(sub VT) in the altitude region85-105 km from the coincident SABER/TIMED and Fort Collins sodium lidar observations by minimizing the difference between measured and simulated broadband limb 15 micron radiation. The averaged k(sub VT) value obtained in this work is 6.5 +/- 1.5 X 10(exp -12) cubic cm/s that is close to other estimates of this coefficient from the atmospheric observations.However, the retrieved k(sub VT) also shows altitude dependence and varies from 5.5 1 +/-1 10(exp -12) cubic cm/s at 90 km to 7.9 +/- 1.2 10(exp -12) cubic cm/s at 105 km. Obtained results demonstrate the deficiency in current non-LTE modeling of the atmospheric 15 micron radiation, based on the application of the CO2-O quenching and excitation rates, which are linked by the detailed balance relation. We discuss the possible model improvements, among them accounting for the interaction of the non-thermal oxygen atoms with CO2 molecules.

SABER/TIMED↗
NASA NTRS2016

Comparison of Quantum Mechanical and Empirical Potential Energy Surfaces and Computed Rate Coefficients for N2 Dissociation

Physics-based modeling of hypersonic flows is predicated on the availability of chemical reaction rate coefficients and cross sections for the collisional processes. This approach has been built around the use of quantum mechanical calculations to describe the interaction between the colliding particles. In this approach a potential energy surface (PES) is computed by solving the electronic Schrödinger equation and collision cross sections are determined for that PES using classical, semiclassical or quantum mechanical scattering methods. The rate coefficients are computed by integrating the thermally weighted cross sections. State-to-state rate coefficients are determined by only integrating over a thermal distribution of collisional energies. Finally, thermal rate coefficients are determined by summation of the state-to-state rate coefficients for reactions of molecules in all relevant ro-vibrational energy levels. If the flow is in thermal non-equilibrium, the translational, vibrational and rotational energy modes can be represented in different ways: three unique temperatures can be used to describe the distributions, the populations of individual ro-vibrational energy levels can be determined by solving the Master Equation, or through the use of direct simulation in particle-based Monte Carlo sampling. The PES-to-rate coefficient approach had been proposed and attempted in the early days of digital computing, but it is only in the last 15 years that computer hardware and software have been up to the task of calculating accurate interatomic and intermolecular potentials.

Jaffe, Richard L.↗
NASA NTRS1977

The influence of autoionization accompanied by excitation on dielectronic recombination and ionization equilibrium

In the process of dielectronic recombination, the doubly excited state formed by radiationless capture may autoionize preferentially into an excited state of the recombining ion. This additional autoionization process has not been discussed in previous treatments of dielectronic recombination. The dielectronic recombination rates for certain nonhydrogenic Fe ions, although still larger than the direct radiative recombination rates, are found to be substantially reduced by the inclusion of the additional autoionization rate in the branching ratio for the stabilizing radiative transition. Consequently, the temperatures of maximum equilibrium abundance are significantly lower than those predicted by recent calculations. Finally, the radiative energy loss rate coefficients are calculated for radiation processes involving electron Fe-ion collisions in high-temperature plasmas. Electron impact excitation of resonance line radiation is the dominant radiative cooling mechanism in steady-state plasmas at temperatures where ions with bound electrons are abundant. However, it is found that the radiation emitted during dielectronic recombination can be more important than direct recombination radiation and bremsstrahlung.

Jacobs, V. L.↗
NASA NTRS1987

Feasibility of hydroxyl concentration measurements by laser-saturated fluorescence in high-pressure flames

The effect of pressure on the laser-saturated fluorescence method for measuring OH concentration in high-pressure flames is studied using calculations for the burned-gas region of a stoichiometric H2-O2 flame at 2000 K. A numerical model of the excitation dynamics of OH is developed to explore the validity of the balanced cross-rate model at higher pressures. It is shown that depopulation of the laser-coupled levels is sensitive to collisions which depopulate v-double-prime (VDP) = 0 and to rate coefficients for rotational transfer in the ground state which are smaller than those in the excited state. In particular, it is shown that the depopulation of VDP = 0, and hence the laser-coupled levels, depends on the probability of electronic quenching to vibrational levels for which VDP is greater than 0 and vibrational relaxation to VDP = 0.

Carter, Campbell D.↗