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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
NASA NTRS2017

Externally Heated Protostellar Cores in the Ophiuchus Star-Forming Region

We present APEX 218 GHz observations of molecular emission in a complete sample of embedded protostars in the Ophiuchus star-forming region. To study the physical properties of the cores, we calculate H2CO and c-C3H2 rotational temperatures, both of which are good tracers of the kinetic temperature of the molecular gas. We find that the H2CO temperatures range between 16K and 124K, with the highest H2CO temperatures toward the hot corino source IRAS 16293-2422 (69-124 K) and the sources in the rho Oph A cloud (23-49 K) located close to the luminous Herbig Be star S1, which externally irradiates the rho Oph A cores. On the other hand, the c-C3H2 rotational temperature is consistently low (7-17 K) in all sources. Our results indicate that the c-C3H2 emission is primarily tracing more shielded parts of the envelope whereas the H2CO emission (at the angular scale of the APEX beam; 3600 au in Ophiuchus) mainly traces the outer irradiated envelopes, apart from in IRAS16293-2422, where the hot corino emission dominates. In some sources, a secondary velocity component is also seen, possibly tracing the molecular outflow.

CH3OH↗
NASA NTRS2005

Molecule Formation at High Extinction and Low Metallicity in the Magellanic Clouds

During 2005, our FUSE research group prepared two major FUSE surveys of interstellar molecular hydrogen: 1. Galactic Disk Sightlines. We measured N(H2) in rotational states J = 0 and 1 and in higher states, J = 2,3,4,5, sometimes up to J = l, for 139 sightlines to Galactic OB stars. 2. High-Latitude QSO sightlines. We surveyed 50 sightlines to high-latitude QSOs, finding H2 in most of them (44 of 50). 3 . Molecular Hydrogen in Infrared Cirrus. Related to the high-latitude H2 survey (#2), we examined the high-latitude infrared cirrus and its correlation with H2. In addition, we are accumulating H2 measurements for additional 0 stars in the Magellanic Clouds (LMC and SMC) to add to the previously published survey.

Shull, J. Michael↗
DOE OSTI2021

Collisional excitation of interstellar PN by H 2 : New interaction potential and scattering calculations

Here, rotational excitation of interstellar PN molecules induced by collisions with H 2 is investigated. We present the first ab initio four-dimensional potential energy surface (PES) for the PN–H 2 van der Waals system. The PES was obtained using an explicitly correlated coupled cluster approach with single, double, and perturbative triple excitations [CCSD(T)-F12b]. The method of interpolating moving least squares was used to construct an analytical PES from these data. The equilibrium structure of the complex was found to be linear, with H 2 aligned at the N end of the PN molecule, at an intermolecular separation of 4.2 Å. The corresponding well-depth is 224.3 cm -1 . The dissociation energies were found to be 40.19 cm -1 and 75.05 cm -1 for complexes of PN with ortho-H 2 and para-H 2 , respectively. Integral cross sections for rotational excitation in PN–H 2 collisions were calculated using the new PES and were found to be strongly dependent on the rotational level of the H 2 molecule. These new collisional data will be crucial to improve the estimation of PN abundance in the interstellar medium from observational spectra.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1994

Cold, warm, and hot gas in the late-stage merger NGC 7252

We present the first observations of the neutral hydrogen distribution and x-ray emission in the prototypical merger remnant NGC 7252, the 'Atoms-for-Peace' galaxy. These data are supplemented by accurate B and R surface photometry, reaching a limit of mu(sub B) = 26.5 mag/sq arcsec, and images taken through a narrow-band H alpha filter. We find all of the 2 x 10(exp 9)/sq h solar mass of atomic gas to be restricted to the outer, tidal regions of this system (H(sub zero) = 100 h km/s/Mpc). By contrast, the molecular gas traced by the (12)CO(1 approaches zero) map of Wang et al. (1992) is confined to an inner rotating disk of radius 7 seconds and has an H alpha counterpart. The gap between the atomic and molecular gas distributions is filled in by diffuse H alpha emission and perhaps by x-ray emission. The velocity field of the atomic gas in the tidal tails indicates that they are swinging through space in the same sense as the rotation of the inner gas disk. The H I at the apparent base of the northwestern tail seems to be falling back toward the main body of the galaxy, yet there is no H I associated with this main stellar body: This suggests ongoing efficient conversion of the atomic gas into other phases in this region. The H alpha velocity anomalies previously found in the remnant body may be produced in part by the combination of tail-related, noncircular motions and the inner gas-disk rotation. Both tidal tails have bluer B-R colors than the main body of the remnant, with the bluest regions coinciding with peaks in the gas column density. Each tail contains one giant H II region near the end of its optical light distribution. These H II regions are associated with large concentrations of gas and stars that approach the sizes and gas contents of dwarf galaxies. The H I extends beyond the end of the optical tails and reaches projected distances of 62/h kpc east and 120/h kpc northwest from the center. We discuss the possible relevance of these data to : (1) the transformation of merged spirals into ellipticls; (2) the generation of ripples by returning tidal material; and (3) the formation of bound stellar systems from tidally torn material.

Hibbard, J. E.↗
DOE OSTI2023

Effects of MOF linker rotation and functionalization on methane uptake and diffusion

The flexible degrees of freedom in metal–organic frameworks (MOFs) can have significant effects on guest molecule behavior. However, in the majority of studies applying molecular simulations to MOFs, the framework is assumed to be rigid in order to minimize computational cost. Here, in this work, we assess the significance of this assumption on a representative example of methane uptake and diffusion in UiO-66. We introduce an open-source code to modify MOFs through functionalization and linker rotation and we perform Grand Canonical Monte Carlo and molecular dynamics simulations of methane in each of the functionalized and linker-rotated derivatives of UiO-66. We find that linker rotation moderately influences methane uptake and significantly influences methane diffusion. Our assessment provides ranges of property values that serve as measures of uncertainty of these two properties associated with linker rotation. We further determine that void volume fraction and minimum pore size are the features that govern methane uptake and diffusion, respectively. These findings illustrate the impact of linker rotation on MOFs and provide design principles to guide future investigations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2012

Submillimeter Measurements of Photolysis Products in Interstellar Ice Analogs: A New Experimental Technique

Over 150 molecular species have been confirmed in space, primarily by their rotational spectra at millimeter/submillimeter wavelengths, which yield an unambiguous identification. Many of the known interstellar organic molecules cannot be explained by gas-phase chemistry. It is now presumed that they are produced by surface reactions of the simple ices and/or grains observed and released into the gas phase by sublimation, sputtering, etc. Additionally, the chemical complexity found in meteorites and samples returned from comets far surpasses that of the remote detections for the interstellar medium (ISM), comets, and planetary atmospheres. Laboratory simulations of interstellar/cometary ices have found, from the analysis of the remnant residue of the warmed laboratory sample, that such molecules are readily formed; however, it has yet to be determined if they are formed during the warm phase or within the ice during processing. Most analysis of the ice during processing reveals molecular changes, though the exact quantities and species formed are highly uncertain with current techniques due to overwhelming features of simple ices. Remote sensing with high resolution spectroscopy is currently the only method to detect trace species in the ISM and the primary method for comets and icy bodies in the Solar System due to limitations of sample return. We have recently designed an experiment to simulate interstellar/cometary/planetary ices and detect trace species employing the same techniques used for remote observations. Preliminary results will be presented.

Milam, Stefanie N.↗
DOE OSTI2023

High-resolution vibrational predissociation spectroscopy of I - ·H 2 O by single-mode CW infrared excitation in a 3D cryogenic ion trap

We describe the integration of a tunable, single-mode, continuous wave infrared laser into a cryogenic ion spectroscopy experiment to measure the rovibrational spectrum of the I - ∙H 2 O complex in the OH stretching region. These upper levels lie about 300 cm -1 above the dissociation threshold. The measurements are carried out by loading the ions in a radiofrequency ion trap at 10 Hz and cooling them to 5 K with pulsed He buffer gas. IR photodissociation (PD) of the I - ∙H 2 O complex is monitored by recording the I - product yield by time-of-flight mass spectrometry as a function of laser wavelength. Very narrow (Δν~75 MHz) rotational lines are observed throughout the spectrum, indicating long (ca. 2 ns) lifetimes for the excited metastable rovibrational levels. Rotational analysis of the band arising from the K”=1 to K’=2 transition of the free OH stretching fundamental yields the structure of the complex for the first time. Over 50% of the trapped ion ensemble in the trap can be photodissociated upon excitation of a single rotational line. This enables very high signal-to-noise in the PD spectrum, and is traced to a mechanism in which the ground state rotational levels are rapidly equilibrated by collisions with the buffer gas.

74 ATOMIC AND MOLECULAR PHYSICS↗
NASA NTRS1987

Diatomic molecules in the solar infrared spectrum from ATMOS-SL 3 high resolution observations

The ATMOS Fourier Transform Spectrometer has observed, for the first time, the solar infrared spectrum, from 2 to 16 microns, free of any telluric absorption. A very large number of molecular lines are present on these high quality spectra: vibration-rotation lines of CO (Delta-v = 1 and 2; including the isotopic species C-13, O-18 and O-17), CH, NH, OH and pure rotation lines of OH. The analysis of these lines will allow to derive accurate values for the solar abundances of C, N and O and the isotopic ratios C-13/C-12, O-18/O-16, and O-17/O-16, to test the photospheric model from high to deep layers, to test the electric dipole moment functions of the different molecules and to derive much better molecular constants for CH.

Grevesse, Nicolas↗
NASA NTRS1980

Detection of CO J = 21-20 /124.2 microns/ and J = 22-21 /118.6 microns/ emission from the Orion nebula

The first observation of far-infrared molecular line emission from the interstellar medium is reported. Strong emission from the J = 21-20 and J = 22-21 rotational transitions of carbon monoxide was detected in the Kleinmann-Low/shocked H2 region of the Orion Molecular Cloud. The results imply that the region is optically thin in these lines and that much of the carbon is in the form of CO. This work also represents the first use of an antimony-doped germanium photoconductor in an astronomical application.

Watson, D. M.↗
NASA NTRS1994

Hydrogen and related materials at high density: Physics, chemistry and planetary implications

Recent studies of low-Z molecular materials including hydrogen to multimegabar pressures (less than 300 GPa) have uncovered a range of phenomena relevant to understanding the nature of the interiors of the outer planets and their satellites. Synchrotron x ray diffraction measurements (to 42 GPa) have been used to determine the crystal structure of the solid (hexagonal-close packed) and equation of state. Sound velocities in fluid and solid hydrogen (to 24 GPa) have been inverted to obtain elastic constants and aggregate bulk and shear moduli. In addition, an improved intermolecular potential has been determined which fits both static and shock-wave data. Use of the new potential for the molecular envelope of Jupiter suggests the need for major revisions of existing Jovian models or a reanalysis of reported free oscillations for the planet. Studies at higher pressures (greater than 100 GPa) reveal a sequence of pressure-induced symmetry-breaking transitions in molecular hydrogen, giving rise to three high-pressure phases (1, 2, and 3). Phase 1 is the rotationally disordered hcp phase which persists from low pressure to well above 100 GPa at high temperature (e.g., 300 K). Phase 2 is a low-temperature, high-pressure phase (transition at 100 GPa and 77 K in H2) with spectral features indicative of partial rotational ordering and crystallographic distortion. The transition to Phase 3 at 150 GPa is accompanied by a weakening of the molecular bond, gradual changes in orientational ordering, strong enhancement of the infrared intramolecular vibrational absorption, and strong intermolecular interactions similar to those of ambient-pressure network solids. Studies of the phase diagram reveal a triple point near 130 K and 160 GPa. Higher pressure measurements of vibrational spectra place a lower bound of approximately 250 GPa on the predicted transition pressure for dissociation of molecular hydrogen to form a monatomic metal.

Hemley, R. J.↗
NASA NTRS1983

The kinetic temperature and density of the Sagittarius B2 molecular cloud from observations of methyl cyanide

Observations of the K components of the CH3CN J = 4-to-3 rotational transition at 73.6 GHz, the 6-to-5 transition at 110.4 GHz, and the 7-to-6 transition at 128.7 GHz, yield a mean kinetic temperature value of 85 + or - 10 K and a mean H2 density of 110,000 + or - 50,000/cu cm for the central 2.0 arcmin of the Sgr B2 molecular cloud. Within the K = zero-to-4 ladders of CH3CN in Sgr B2, the populations of the radiatively coupled J levels are relaxed and exhibit a rotational temperature of about 16 K, which is similar to that of several linear molecules.

Cummins, S. E.↗
NASA NTRS2002

Optical Properties of Thin Film Molecular Mixtures

Thin films composed of molecular mixtures of metal and dielectric are being considered for use as solar selective coatings for a variety of space power applications. By controlling the degree of molecular mixing, the solar selective coatings can be tailored to have the combined properties of high solar absorptance, alpha, and low infrared emittance, epsilon. On orbit, these combined properties would simultaneously maximize the amount of solar energy captured by the coating and minimize the amount of thermal energy radiated. Mini-satellites equipped with solar collectors coated with these cermet coatings may utilize the captured heat energy to power a heat engine to generate electricity, or to power a thermal bus that directs heat to remote regions of the spacecraft. Early work in this area identified the theoretical boundary conditions needed to operate a Carnot cycle in space, including the need for a solar concentrator, a solar selective coating at the heat inlet of the engine, and a radiator. A solar concentrator that can concentrate sunlight by a factor of 100 is ideal. At lower values, the temperature of the solar absorbing surface becomes too low for efficient heat engine operation, and at higher values, cavity type heat receivers become attractive. In designing the solar selective coating, the wavelength region yielding high solar absorptance must be separated from the wavelength region yielding low infrared emittance by establishing a sharp transition in optical properties. In particular, a sharp transition in reflectance is desired in the infrared to achieve the desired optical performance. For a heat engine operating at 450C, a sharp transition at 1.8 micrometers is desired. The radiator completes the heat flow through the Carnot cycle. Additional work has been done supporting the use of molecular mixtures for terrestrial applications. Sputter deposition provides a means to apply coatings to the tubes that carry a working fluid at the focus of trough-style collectors. Sputtering offers considerable flexibility in coating conditions, including a wide variety of metal and dielectric targets. Coating designs range from simple two or three layer coatings to complex coatings that are purposely graded to be metal-rich at their base and oxide-rich at their surface in order to yield the desired solar selective properties. In these cermet coatings, molecular islands of metal are thought to be embedded in a three dimensional matrix of dielectric. Recent work has identified the use of custom made ion beam sputter deposition targets to produce coatings containing molecular mixtures of metal and dielectric. The targets are cylindrical and the surface consists of a gradually changing composition of metal and dielectric. Rotating the cylinder under the beam during ion beam sputter deposition yields a coating that is a molecular mixture of metal and dielectric, with the composition changing through the thickness of the coating. The optical properties of these coatings are not only dependent on their thickness and chemical composition, but are also dependent on the extent of the through thickness gradient established during deposition. This paper presents a summary of the optical properties of several thin film molecular mixtures designed as solar selective coatings. Optical performance is first identified as a function of wavelength, from the ultraviolet to the visible and infrared. Coating composition, thickness, and gradient from metal to dielectric also play an important role. Additional work for future activities is also identified.

Jaworske, Donald A.↗
NASA NTRS2012

Modeling the Flow of Rarefied Gases at NASA

At modest temperatures, the thermal energy of atmospheric diatomic gases such as nitrogen is primarily distributed between only translational and rotational energy modes. Furthermore, these energy modes are fully excited such that the specific heat at constant volume is well approximated by the simple expression C(sub v) = 5/2 R. As a result, classical mechanics provides a suitable approximation at such temperatures of the true quantum mechanical behavior of the inter-molecular collisions of such molecules. Using classical mechanics, the transfer of energy between rotational and translation energy modes is studied. The approach of Lordi and Mates is adopted to compute the trajectories and time dependent rotational orientations and energies during the collision of two non-polar diatomic molecules. A Monte-Carlo analysis is performed collecting data from the results of many such simulations in order to estimate the rotational relaxation time. A Graphical Processing Unit (GPU) is employed to improve the performance of the Monte-Carlo analysis. A comparison of the performance of the GPU implementation to an implementation on traditional computer architecture is made. Effects of the assumed inter-molecular potential on the relaxation time are studied. The seminar will also present highlights of computational analyses performed at NASA Johnson Space Center of heat transfer in rarefied gases.

Forrest E. Lumpkin, III↗
DOE OSTI2024

Controlled molecule injector for cold, dense, and pure molecular beams at the European x-ray free-electron laser

A permanently available molecular-beam injection setup for controlled molecules (COMO) was installed and commissioned at the small quantum systems (SQS) instrument at the European x-ray free-electron laser (EuXFEL). A b-type electrostatic deflector allows for pure state-, size-, and isomer-selected samples of polar molecules and clusters. The source provides a rotationally cold (T ≈ 1 K) and dense (ρ ≈ 10 8 cm −3 ) molecular beam with pulse durations up to 100 µs generated by a new version of the Even-Lavie valve. Here, a performance overview of the COMO setup is presented along with characterization experiments performed both with an optical laser at the Center for Free-Electron-Laser Science and with x rays at EuXFEL under burst-mode operation. COMO was designed to be attached to different instruments at the EuXFEL, in particular, the SQS and single particles, clusters, and biomolecules (SPB) instruments. This advanced controlled-molecules injection setup enables x-ray free-electron laser studies using highly defined samples with soft and hard x-ray FEL radiation for applications ranging from atomic, molecular, and cluster physics to elementary processes in chemistry and biology.

He, Lanhai↗
NASA NTRS1990

The circumstellar environment of TMR-1 - A young, low-mass star in the Taurus molecular ring

Near-infrared camera and Owens Valley millimeter interferometer data are presented that reveal the circumstellar environment of TMR-1 on scales of roughly 1000 AU. TMR-1 is a deeply embedded, young, low-mass star located in a rotating ring of material in the TMC-1/Heiles Cloud 2 region of the Taurus molecular cloud. The stellar wind cavity, as outlined by the extended infrared continuum emission at 2.2 microns, overlaps with the redshifted outflow detected in the (C-12)O data. High-density circumstellar material is seen in (C-13)O in emission and at 2.2 microns in absorption. The morphology suggests the high-density gas may either be part of a 1000 AU disk or may represent infalling material from the molecular cloud core. TMR-1 appears to be in an early wind-clearing phase of protostar formation.

Terebey, S.↗
DOE OSTI2021

Characterization of a collimated neutron imager for low-rate fast neutron imaging

Spatial localization of special nuclear materials (SNM) via their neutron signatures amidst background requires knowledge of the background neutron environment or a means of separating a source from background based on low amounts of information. This requirement has created the need for characterizing the spatial distribution of the cosmogenic neutron background. Neutron scatter cameras have been developed and optimized for rapid detection of high activity sources, but have low imaging efficiency, making it difficult to use them to characterize low rate diffuse sources, such as the neutron background. The Low Intensity Neutron Imaging System (LINIS) is a collimated neutron imager that has been designed and optimized for imaging diffuse cosmogenic neutron background in the energy range of 0.5–15 MeV. LINIS operates using 16 liquid scintillation detectors shielded by ultra-high molecular weight polyethylene cylindrical collimators in a staggered orientation and rotates to 7 discrete positions, giving it roughly 2π sensitivity. Finally, LINIS has been characterized using (α, n) and fission neutron sources using two imaging techniques for neutron source localization, simple backprojection and Maximum Likelihood Expectation Maximization.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗