Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “TRIPLETS”

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 1,027 records · Page 57
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Solenoidal Fields from Permanent Magnets for a Polarized Electron Preinjector

This technical note describes the design of a compact focusing solenoid constructed from permanent bar magnets, intended for the low-energy section of a spin-polarized electron injector. Typically, quadrupole triplets provide appropriate focusing for the low-energy spin rotator section; however, their large footprint precludes the insertion of sufficient beam diagnostics. The primary motivation of this study is to provide beam focusing while preserving the vertical spin orientation of the electron beam. We propose a solenoidal field composed of multiple permanent magnets arranged to naturally yield a zero longitudinal magnetic field integral ($\int B_zdz = 0$). This design serves as a compact, passive, and non-coupling alternative to traditional quadrupole triplets. We present the magnet arrangement, field calculation methodology, spin tracking simulations using space charge codes, and calculations demonstrating that the required field strength is achievable.

43 PARTICLE ACCELERATORS↗
DOE OSTI2022

The Reaction of HO2 and CH3O2: CH3OOH Formed from the Singlet Electronic State Surface

High-level coupled-cluster calculations in combination with two-dimensional master equation simulations were used to study the HO2 + CH3O2 reaction, which plays an important role in the oxidation of methane and hydrocarbons in the Earth’s atmosphere and low-temperature combustion. The main reaction pathways taking place on the lowest-lying triplet and singlet potential energy surfaces (PES) were characterized. Interestingly, methyl hydroperoxide (CH3OOH), the sole product, could be produced from both the triplet and singlet PESs, with a ratio of roughly 9:1. Formaldehyde is not made as a primary product, but can be formed via secondary chemistry. The formation of methyl tetraoxide (MTO) from the singlet PES is unimportant. The calculated reaction rate coefficients were found to be practically pressure-independent for p ≤ 760 Torr and can be given by k(T)=2.75×10−13×e+1.75 kcal mol−1/RT (in cm3/s), an expression useful for kinetics modeling over the range T = 200–800 K. The rate constant has a slight negative Arrhenius energy dependence of about −1.75 kcal mol–1, falling about a factor of 30 from 200 K to 800 K.

2DME↗
DOE OSTI2016

Spectra, emission yields, cross sections, and kinetic energy distributions of hydrogen atoms from H{sub 2}X{sup 1}Σ{sub g}{sup +}–d{sup 3}Π{sub u} excitation by electron impact

Electron-impact excitation of H{sub 2} triplet states plays an important role in the heating of outer planet upper thermospheres. The d{sup 3}Π{sub u} state is the third ungerade triplet state, and the d{sup 3}Π{sub u}–a{sup 3}Σ{sub g}{sup +} emission is the largest cascade channel for the a{sup 3}Σ{sub g}{sup +} state. Accurate energies of the d{sup 3}Π{sub u}{sup −}(v, J) levels are calculated from an ab initio potential energy curve. Radiative lifetimes of the d{sup 3}Π{sub u}(v, J) levels are obtained by an accurate evaluation of the d{sup 3}Π{sub u}–a{sup 3}Σ{sub g}{sup +} transition probabilities. The emission yields are determined from experimental lifetimes and calculated radiative lifetimes and are further verified by comparing experimental and synthetic d{sup 3}Π{sub u}–a{sup 3}Σ{sub g}{sup +} spectra at 20 eV impact energy. Spectral analysis revealed that multipolar components beyond the dipolar term are required to model the X{sup 1}Σ{sub g}{sup +}–d{sup 3}Π{sub u} excitation, and significant cascade excitation occurs at the d{sup 3}Π{sub u}(v = 0,1) levels. Kinetic energy (E{sub k}) distributions of H atoms produced via predissociation of the d{sup 3}Π{sub u} state and the d{sup 3}Π{sub u}−a{sup 3}Σ{sub g}{sup +}−b{sup 3}Σ{sub u}{sup +} cascade dissociative emission are obtained. Predissociation of the d{sup 3}Π{sub u} state produces H atoms with an average E{sub k} of 2.3 ± 0.4 eV/atom, while the E{sub k} distribution of the d{sup 3}Π{sub u}−a{sup 3}Σ{sub g}{sup +}−b{sup 3}Σ{sub u}{sup +} channel is similar to that of the X{sup 1}Σ{sub g}{sup +}–a{sup 3}Σ{sub g}{sup +}−b{sup 3}Σ{sub u}{sup +} channel and produces H(1s) atoms with an average E{sub k} of 1.15 ± 0.05 eV/atom. On average, each H{sub 2} excited to the d{sup 3}Π{sub u} state in an H{sub 2}-dominated atmosphere deposits 3.3 ± 0.4 eV into the atmosphere, while each H{sub 2} directly excited to the a{sup 3}Σ{sub g}{sup +} state gives 2.2–2.3 eV to the atmosphere. The spectral distribution of the calculated a{sup 3}Σ{sub g}{sup +} –b{sup 3}Σ{sub u}{sup +} continuum emission due to the X{sup 1}Σ{sub g}{sup +}–d{sup 3}Π{sub u} excitation is significantly different from that of direct a{sup 3}Σ{sub g}{sup +} excitation.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2020

Spectroscopic Determination of Stellar Parameters and Oxygen Abundances for Hyades/Field G–K Dwarfs

It has been suggested that Fe abundances of K dwarfs derived from Fe i and Fe ii lines show considerable discrepancies, and oxygen abundances determined from high-excitation O i 7771–5 triplet lines are appreciably overestimated (the problem becoming more serious toward lower T {sub eff}), which, however, has not yet been widely confirmed. With the aim of clarifying this issue, we spectroscopically determined the atmospheric parameters of 148 G–K dwarfs (Hyades cluster stars and field stars) by assuming the classical Fe i/Fe ii ionization equilibrium as usual, and determined their oxygen abundances by applying the non-local thermal equilibrium spectrum fitting analysis to O i 7771–5 lines. It turned out that the resulting parameters did not show any significant inconsistency with those determined by other methods (for example, the mean differences in T {sub eff} and logg from the well-determined solutions of Hyades dwarfs are mostly ≲100 K and ≲0.1 dex). Likewise, the oxygen abundances of Hyades stars are around [O/H] ∼ +0.2 dex (consistent with the metallicity of this cluster) without exhibiting any systematic T {sub eff}-dependence. Accordingly, we conclude that parameters can be spectroscopically evaluated to a sufficient precision in the conventional manner (based on the Saha–Boltzmann equation for Fe i/Fe ii) and oxygen abundances can be reliably determined from the O i 7771–5 triplet for K dwarfs as far as stars of T {sub eff} ≳ 4500 K are concerned. We suspect that previously reported strongly T {sub eff}-dependent discrepancies may have stemmed mainly from overestimation of weak-line strengths and/or improper T {sub eff} scale.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Nondetection of Helium in the Upper Atmospheres of Three Sub-Neptune Exoplanets

We present a search for helium in the upper atmospheres of three sub-Neptune-sized planets to investigate the origins of these ubiquitous objects. The detection of helium for a low-density planet would be strong evidence for the presence of a primary atmosphere accreted from the protoplanetary nebula because large amounts of helium are not expected in the secondary atmospheres of rocky planets. We used Keck+NIRSPEC to obtain high-resolution transit spectroscopy of the planets GJ 1214b, GJ 9827d, and HD 97658b around the 10833 Å He triplet feature. We did not detect helium absorption for any of the planets despite achieving a high level of sensitivity. We used the nondetections to set limits on the planets’ thermosphere temperatures and atmospheric loss rates by comparing grids of 1D models to the data. We also performed coupled interior structure and atmospheric loss calculations, which suggest that the bulk atmospheres (winds) of the planets would be at most modestly enhanced (depleted) in helium relative to their primordial composition. Our lack of detections of the helium triplet for GJ 1214b and GJ 9827d is highly inconsistent with the predictions of models for the present-day mass loss on these planets. Higher signal-to-noise data would be needed to detect the helium feature predicted for HD 97658b. We identify uncertainties in the extreme-ultraviolet fluxes of the host stars and the lack of detailed mass-loss models specifically for cool and metal-enhanced atmospheres as the main limitations to the interpretation of our results. Ultimately, our results suggest that the upper atmospheres of sub-Neptune planets are fundamentally different from those of gas giant planets.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1973

Electron impact excitation of H2O.

The authors (1971) detected a new triplet state of water at 9.81 eV energy, and assigned the low energy-loss feature to the excitation of low-lying triplet state(s) of water on the basis of the angular distribution of the scattered electrons. The results are discussed here in more detail, as well as relative differential cross sections for elastic scattering, and for the excitation of these and several other electronic and pure vibrational states of water at impact energies of 15, 20, and 53 eV and at scattering angles ranging from 0 to 90 deg.

Trajmar, S.↗
NASA NTRS1975

Relative and absolute level populations in beam-foil-excited neutral helium

Relative and absolute populations of 19 levels in beam-foil-excited neutral helium at 0.275 MeV have been measured. The singlet angular-momentum sequences show dependences on principal quantum number consistent with n to the -3rd power, but the triplet sequences do not. Singlet and triplet angular-momentum sequences show similar dependences on level excitation energy. Excitation functions for six representative levels were measured in the range from 0.160 to 0.500 MeV. The absolute level populations increase with energy, whereas the neutral fraction of the beam decreases with energy. Further, the P angular-momentum levels are found to be overpopulated with respect to the S and D levels. The overpopulation decreases with increasing principal quantum number.

Davidson, J.↗
NASA NTRS1975

Observations of helium and hydrogen emission in quiescent prominences

Observations of a number of helium triplet (10830, 4713, 4471, 3889, 4026 A) and hydrogen (H-gamma, delta, eta, and theta) emission-line intensities in six quiescent prominences are presented. The regions of prominence and neighboring corona were raster-scanned by the telescope, and all lines were measured concurrently at each point. The results are compared with previous observations and theory. In particular, the intensity of the 10830-A emission relative to the other triplets is found to differ strongly from the predictions of the recent detailed calculations of Heasley et al. (1974) for model quiescent prominences.

Illing, R. M. E.↗
NASA NTRS1976

Absorption cross sections of some atmospheric molecules for resonantly scattered O I 1304-A radiation

Absorption cross sections for O2, N2, CO2, CH4, N2O, and CO have been measured at each of the lines of the atomic oxygen triplet at 1302, 1305, and 1306 A. Radiation resonantly scattered from oxygen atoms at a temperature of about 300 K was used for the line source. Absorber temperatures were also near 300 K. Direct application of the Lambert-Beer absorption equation yielded pressure-dependent cross sections for carbon monoxide at each line of the O I triplet. Reasons for this apparent dependence are presented and discussed.

Starr, W. L.↗
NASA NTRS1976

Energy storage possibilities of atomic hydrogen

Several recent experiments designed to produce and store macroscopic quantities of atomic hydrogen are discussed. The bulk, ground state properties of atomic hydrogen, deuterium, and tritium systems are calculated assuming that all pair interactions occur via the atomic triplet potential. The conditions required to obtain this system, including inhibition of recombination through the energetically favorable singlet interaction, are discussed. The internal energy, pressure, and compressibility are calculated applying the Monte Carlo technique with a quantum mechanical variational wavefunction. The system studied consisted of 32 atoms in a box with periodic boundary conditions. Results show that atomic triplet hydrogen and deuterium remain gaseous at 0 K; i.e., the internal energy is positive at all molar volumes considered.

Etters, R. D.↗
NASA NTRS1978

A new channel for the formation of hydrogen cyanide in CH2-N2 systems

The reaction between N2 and either the singlet or the triplet electronic state of CH2 is investigated in order to shed light on the formation of NO in fuel-rich hydrocarbon flames. For the reaction of N2 and the triplet CH2, a rate constant less than or equal to 10 to the minus 16th power cu cm/molecule-sec is obtained. The time history of hydrogen cyanide production from the CH2-N2 systems is discussed as a basis for understanding the possible reaction routes from HCN to NO.

Laufer, A. H.↗
NASA NTRS1980

Zeeman degeneracy effects in collisional intense-field resonance fluorescence

Resonance fluorescence due to intense laser fields from a Zeeman degenerate atom being perturbed by collisional interactions is calculated in the impact regime by using the quantum-fluctuation-regression theorem. Various interesting effects are found. For example, the scattered intensity spectrum for a J = 0 to J = 1 transition for polarization parallel to the laser polarization is essentially an asymmetric triplet, whereas for a perpendicular polarization due to collisions the spectrum is essentially a doublet (whose frequencies do not correspond with any of those of the triplet). Further, the width of the fluorescent component (whose frequency is close to the unperturbed frequency) actually decreases with increasing laser power.

Cooper, J.↗
NASA NTRS1980

Photographic Combustion Characterization of LOX/Hydrocarbon Type Propellants

The advantages and limitations of using high speed photography to identify potential combustion anomalies (pops, fuel freezing, reactive stream separation (RSS), carbon formation) were demonstrated. Combustion evaluation criteria were developed for evaluating, characterizing, and screening promising low cost propellant combination(s) and injector element(s) for long life, reusable engine systems. Carbon formation and RSS mechanisms and trends were identified by using high speed color photography at speeds up to 6000 frames/sec. Single element injectors were tested with LOX/RP-1, LOX/Propane, LOX/Methane and LOX/Ammonia propellants. Tests were conducted using seven separate injector elements. Five different conventionally machined elements were tested: OFO Triplet; Rectangular Unlike Doublet (RUD); Unlike Doublet (UD); Like on Lke Doublet (LOL-EDM); and Slit Triplet.

Judd, D. C.↗
NASA NTRS1982

The rotational spectra of HOCO/plus/, HOCN, HN3, and HNCO from quantum mechanical calculations

Ab initio molecular orbital theory has been used to determine the equilibrium geometries, rotational constants, and rotational spectra of four isoelectronic molecules. Two of these, HOCO(plus) and HOCN, are candidate interstellar molecules. The other two, HNCO and HN3, have known rotational constants. Theoretical rotational constants and spectra for the two unknown species were corrected with the mean experimental to theoretical ratios from the two known species. This procedure resulted in predicted frequencies of 83.75 plus or minus 0.2 GHz for the 4(04) to 3(03) transition in HOCN and 85.08 plus or minus 0.2 GHz for the same transition in HOCO(plus). These are the central lines of triplets whose other members are the 4(14) to 3(13) and 4(13) to 3(12) transitions. The triplet splittings were predicted to be 0.36 plus or minus 0.01 GHz for HOCN and 0.33 plus or minus 0.01 GHz for HOCO(plus). These results indicate that HOCO(plus) is a better candidate for the source of a series of lines reported by Thaddeus, Guelin, and Linke than is HOCN.

Defrees, D. J.↗
NASA NTRS1982

Rotational and vibrational spectra of ethynol from quantum-mechanical calculations

It is noted that ethynol (HCCOH), despite the theoretical prediction of its stability to tautomerization to ketene, has thus far not been observed. It is shown here that the identification of this unknown molecule, both in space and in the laboratory, can be aided by an ab initio calculation of spectroscopic parameters. At the HF/3-21G level, harmonic vibrational frequencies are computed by way of analytic second differentiation of the Hartee-Fock (HF) energy with respect to the nuclear coordinates. After applying an empirical scale factor, the resultant frequencies are (per cm) 473, 517, 773, 841, 1003, 1217, 2206, 3285, and 3418. The computed dipole moment at the CISD/DZ+P level is 1.79 D. At the CISD+Q/DZ+P level, the molecule's rotational constants are determined. After scaling by empirical correction factors, they are used in deriving the 4(04) - 3(03) frequency of 76.81 + or - 0.3 GHz with a triplet splitting of 0.30 + or - 0.01 GHz. The triplet splitting involves 4(14) - 3(13) and 4(13) - 3(12) relative to the 4(04) - 3(03) transition as the central line.

Defrees, D. J.↗
NASA NTRS1983

A theoretical study on the mechanism of electronic to vibrational energy transfer in Hg/3P/ + CO

The mechanism of electronic-to-vibrational (E-V) energy transfer in Hg(3P) + CO collisions has been studied theoretically. The configuration interaction (CI) method was employed to calculate potential energy surfaces of the collision system. A simplified theoretical model, based on the reaction coordinate concept and the calculated potential energy characteristics, was used to discuss the mechanism of the singlet-triplet transition and the energy disposal in the collision. The results obtained were that: (a) the quenching process processed via a collision complex mechanism; and that (b) the triplet-singlet transition occurs near the collinear geometry. A model classical trajectory calculation gives a product CO vibrational distribution in good agreement with the experimental result.

Kato, S.↗
NASA NTRS1986

Ab initio molecular orbital studies of low-energy, metastable isomers of the ubiquitous cyclopropenylidene

The discovery of cyclopropenylidene in space suggests that other C3H2 isomers may be present, and a tentative detection of one such isomer, propargylene (HCCCH), has been reported. Ab initio molecular orbital theory has been used to characterize five low-lying, metastable isomers of cyclopropenylidene. Extended calculations including the electron correlation energy, show that the lowest in energy is singlet propadienylidene, followed by propargylene; the singlet and triplet of the latter are too close in energy to allow an assignment of the ground state; triplet propadienylidene is at a significantly higher energy. Rotational frequencies computed to an expected accuracy of + or - 1 -2 percent do not confirm the tentative detection of propargylene in space, although the discrepancy between theory and the observation is not so great as to unequivocally rule out this possibility.

Defrees, D. J.↗
NASA NTRS1987

An ab initio study on (C5H5V)2C8H8

The bonding in the organometalic compound nu-(eta exp 5-(cyclooctatetraene) bis (eta exp 2 cyclopentadienyl) vanadium) involves a complex mixture of metal-metal and metal-ligand contributions. Although there is a direct V-V 3d interaction it is not as strong as a double bond with some triple bond character as has been suggested based upon experiment. The balance between metal-metal and metal-ligand bonding results in the appearance of a low-lying triplet state which retains the V-V 3d bonding. A small singlet-triplet separation is consistent with the change in magnetic properties with temperature.

Luthi, Hans P.↗