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At least 469 records · Page 26
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

A new interstellar molecule - Tricarbon monoxide

The C3O molecule, whose pure rotational spectrum has only recently been studied in the laboratory, has been detected in the cold, dark interstellar Taurus Molecular Cloud 1. Since C3O is the first interstelar carbon chain molecule to contain oxygen, its existence places an important new constraint on chemical schemes for cold interstellar clouds. The abundance of C3O can be understood in terms of purely gas-phase ion-molecule chemistry.

Matthews, H. E.↗
NASA NTRS1984

IUE Observations of the Gaseous Component of the Local Interstellar Medium

Discovery of interstellar Ge, Ga, and Kr is reported. Several intercombination lines of Fe 2 are detected. The depletion is most pronounced in Ca, Ti, and V. The highly ionized gas C 4 and Si 4 is not co-extensive with the Si 2 and C 2 gas nor with the O 6 gas. The molecular gas (CO) shows very small velocity dispersion (b approximately 1 km/sec). HD 149404 has the richest interstellar spectrum (except molecules) of all the stars in this study. HD 147889, the heavily obscured star in the Rho Oph cloud, has the strongest interstellar CO spectrum. Noisy nature of the spectra precludes detection of other molecules.

Gilra, D. P.↗
NASA NTRS1986

Ultraviolet-pumped infrared fluorescent molecular hydrogen emission in reflection nebulae

Strong molecular hydrogen emission at 2.41 microns has been observed in three out of six reflection nebulae surveyed. A spectrum of one nebula, Parsamyan 18, shows several H2 lines whose intensity ratios have values agreeing with those predicted if the excitation is due to UV-pumped fluoresence and disagreeing with those predicted for shock and X-ray excitations.

Sellgren, K.↗
NASA NTRS1986

3 micron spectroscopy of comet Halley (1982i)

Near-infrared spectroscopy and photometry was obtained of comet Halley in December 1985 when its heliocentric distance was 1.19 AU. No water ice absorption or molecular band emission were observed. The interstellar 3.3-micron emission band was also not observed. The 3-micron spectrum of comet Halley consisted of scattered sunlight at wavelengths less than 3.1 microns and of thermal emission by dust at longer wavelengths.

Tokunaga, A. T.↗
NASA NTRS1988

Vaporization of ices containing S2 - Implications for comets

An effort is made to ascertain whether the S2 detected in Comet IRAS-Araki-Alcock 1983d can be stored in ices during warming, and is released during the vaporization of its water ice matrix, in view of data on the UV spectrum of S2 in Ar and Kr matrices and water ice in which the ratio of matrix or molecular ice to S2 is of the order of 500:1. The results obtained support the hypothesis that the S2:H2O ratio in the solid phase may not be a predictor of the gas phase ratio. It is concluded that similar vaporization from a cometary nucleus would not release most of the S2 contained in the ice.

Moore, M. H.↗
NASA NTRS1997

Quantitative spectroscopy for the analysis of GOME data

Accurate analysis of the global ozone monitoring experiment (GOME) data to obtain atmospheric constituents requires reliable, traceable spectroscopic parameters for atmospheric absorption and scattering. Results are summarized for research that includes: the re-determination of Rayleigh scattering cross sections and phase functions for the 200 nm to 1000 nm range; the analysis of solar spectra to obtain a high-resolution reference spectrum with excellent absolute vacuum wavelength calibration; Ring effect cross sections and phase functions determined directly from accurate molecular parameters of N2 and O2; O2 A band line intensities and pressure broadening coefficients; and the analysis of absolute accuracies for ultraviolet and visible absorption cross sections of O3 and other trace species measurable by GOME.

Chance, K.↗
NASA NTRS2002

Microwave, Millimeter, Submillimeter, and Far Infrared Spectral Databases

The spectrum of most known astrophysical molecules is derived from transitions between a few hundred to a few hundred thousand energy levels populated at room temperature. In the microwave and millimeter wave regions. spectroscopy is almost always performed with traditional microwave techniques. In the submillimeter and far infrared microwave technique becomes progressively more technologically challenging and infrared techniques become more widely employed as the wavelength gets shorter. Infrared techniques are typically one to two orders of magnitude less precise but they do generate all the strong features in the spectrum. With microwave technique, it is generally impossible and rarely necessary to measure every single transition of a molecular species, so careful fitting of quantum mechanical Hamiltonians to the transitions measured are required to produce the complete spectral picture of the molecule required by astronomers. The fitting process produces the most precise data possible and is required in the interpret heterodyne observations. The drawback of traditional microwave technique is that precise knowledge of the band origins of low lying excited states is rarely gained. The fitting of data interpolates well for the range of quantum numbers where there is laboratory data, but extrapolation is almost never precise. The majority of high resolution spectroscopic data is millimeter or longer in wavelength and a very limited number of molecules have ever been studied with microwave techniques at wavelengths shorter than 0.3 millimeters. The situation with infrared technique is similarly dire in the submillimeter and far infrared because the black body sources used are competing with a very significant thermal background making the signal to noise poor. Regardless of the technique used the data must be archived in a way useful for the interpretation of observations.

Pearson, J. C.↗
NASA NTRS2012

Terabit Wireless Communication Challenges

This presentation briefly discusses a research effort on Terabit Wireless communication systems for possible space applications. Recently, terahertz (THz) technology (300-3000 GHz frequency) has attracted a great deal of interest from academia and industry. This is due to a number of interesting features of THz waves, including the nearly unlimited bandwidths available, and the non-ionizing radiation nature which does not damage human tissues and DNA with minimum health threat. Also, as millimeter-wave communication systems mature, the focus of research is, naturally, moving to the THz range. Many scientists regard THz as the last great frontier of the electromagnetic spectrum, but finding new applications outside the traditional niches of radio astronomy, Earth and planetary remote sensing, and molecular spectroscopy particularly in biomedical imaging and wireless communications has been relatively slow. Radiologists find this area of study so attractive because t-rays are non-ionizing, which suggests no harm is done to tissue or DNA. They also offer the possibility of performing spectroscopic measurements over a very wide frequency range, and can even capture signatures from liquids and solids. According to Shannon theory, the broad bandwidth of the THz frequency bands can be used for terabit-per-second (Tb/s) wireless communication systems. This enables several new applications, such as cell phones with 360 degrees autostereoscopic displays, optic-fiber replacement, and wireless Tb/s file transferring. Although THz technology could satisfy the demand for an extremely high data rate, a number of technical challenges need to be overcome before its development. This presentation provides an overview the state-of-the- art in THz wireless communication and the technical challenges for an emerging application in Terabit wireless systems. The main issue for THz wave propagation is the high atmospheric attenuation, which is dominated by water vapor absorption in the THz frequency band. The technical challenges in design such a system and the techniques to overcome the challenges will be discussed in this presentation.

Hwu, Shian U.↗
DOE OSTI2023

Longwave infrared (6.6–11.4 µm) dual-comb spectroscopy with 240,000 comb-mode-resolved data points at video rate

Using sub-3-cycle pulses from mode-locked Cr:ZnS lasers at λ ≈ 2.4 µm as a driving source, we performed high-resolution dual-frequency-comb spectroscopy in the longwave infrared (LWIR) range. A duo of highly coherent broadband (6.6–11.4 µm) frequency combs were produced via intrapulse difference frequency generation in zinc germanium phosphide (ZGP) crystals. Fast (up to 0.1 s per spectrum) acquisition of 240,000 comb-mode-resolved data points, spaced by 80 MHz and referenced to a Rb clock, was demonstrated, resulting in metrology grade molecular spectra of N 2 O (nitrous oxide) and CH 3 OH (methane). The key to high-speed massive spectral data acquisition was low intensity and phase noise of the LWIR combs and high (7.5%) downconversion efficiency, resulting in a LWIR power of 300 mW for each comb.

Vasilyev, Sergey (ORCID:0000000225203547)↗
DOE OSTI2023

Fine‐Tuning Alkyl Chains on Quinoxaline Nonfullerene Acceptors Enables High‐Efficiency Ternary Organic Solar Cells with Optimizing Molecular Stacking and Reducing Energy Loss

Abstract Material design of guest acceptor is always a big challenge for improving the efficiency of ternary organic solar cells (OSCs). Here, a pair of isomeric nonfullerene acceptors based on quinoxaline core, Qx–p‐C 7 H 8 O and Qx–m‐C 7 H 8 O, is designed and synthesized. By moving the alkoxy chain attached on side phenyl frommeta‐position topara‐position, both π–π stacking distance and crystallinity are enhanced simultaneously. They obtain the uplifted lowest unoccupied molecular orbital level. Compared to Qx–m‐C 7 H 8 O, Qx–p‐C 7 H 8 O exhibits wider absorption spectrum and higher extinction coefficient. Using D18‐Cl:N3 as host materials, the addition of guest acceptor Qx–p‐C 7 H 8 O significantly improves the power conversion efficiency (PCE) from 17.61% to 18.49% because of higher open‐circuit voltage (0.875 V) and short‐circuit current density (27.85 mA cm −2 ). This can be attributed to the faster exciton dissociation, more balanced carrier mobility, fine fiber morphology, and lower energy loss in the ternary devices. However, Qx–m‐C 7 H 8 O‐based ternary device achieves relatively low PCE of 17.17% because this device shows extremely low electron mobility. The results indicate that molecular stacking, film morphology, etc., can be effectively modulated by fine‐tuning the side chains of guest materials, which may be an effective design rule for further improving the PCE of OSCs.

Chemistry↗
NASA NTRS1984

The nature of AFGL 2591 and its associated molecular outflow: Infrared and millimeter-wave observations

The results of infrared photometry from 2 to 160 microns of AFGL and CO(12) observations of its associated molecular cloud and high velocity molecular outflow are presented and discussed. The observed solar luminosity is 6.7 x 10(4) at a distance of 2 kpc. The spectrum of AFGL 2591 is interpreted in the context of a model in which a single embedded object is the dominant source of the infrared luminosity. This object is determined to be surrounded by a compact, optically thick dust shell with a temperature in excess of several hundred degrees kelvin. The extinction to this source is estimated to be between 26 and 50 visual magnitudes. The absolute position of the infrared sources at 10 microns was determined to an accuracy of + or in. This indicates for the first time that the IR source and H2O source are not coincident. The CO(12) observations show the high-velocity molecular flow near AFGL 2591 to be extended, bipolar and roughly centered on the infrared emission. The observations suggest that the red-shifted flow component extends beyond the boundary of the ambient cloud within which AFGL 2591 is embedded. The CO(12) observations also show that AFGL 2591 is embedded in a molecular cloud with an LSR velocity of -5 km/s.

Lada, C. J.↗
NASA NTRS1984

The nature of AFGL 2591 and its associated molecular outflow Infrared and millimeter-wave observations

The results of infrared photometry from 2 to 160 microns of AFGL and CO(12) observations of its associated molecular cloud and high velocity molecular outflow are presented and discussed. The observed solar luminosity is 6.7 x 10(4) at a distance of 2 kpc. The spectrum of AFGL 2591 is interpreted in the context of a model in which a single embedded object is the dominant source of the infrared luminosity. This object is determined to be surrounded by a compact, optically thick dust shell with a temperature in excess of several hundred degrees kelvin. The extinction to this source is estimated to be between 26 and 50 visual magnitudes. The absolute position of the infrared sources at 10 microns was determined to an accuracy of + or - 1 in. This indicates for the first time that the IR source and H2O source are not coincident. The CO(12) observations show the high-velocity molecular flow near AFGL 2591 to be extended, bipolar and roughly centered on the infrared emission. The observations suggest that the red-shifted flow component extends beyond the boundary of the ambient cloud within which AFGL 2591 is embedded. The CO(12) observations also show that AFGL 2591 is embedded in a molecular cloud with an LSR velocity of -5 km/s.

Lada, C. J.↗
DOE OSTI2020

Cavity molecular dynamics simulations of liquid water under vibrational ultrastrong coupling

We simulate vibrational strong coupling (VSC) and vibrational ultrastrong coupling (V-USC) for liquid water with classical molecular dynamics simulations. When the cavity modes are resonantly coupled to the O–H stretch mode of liquid water, the infrared spectrum shows asymmetric Rabi splitting. The lower polariton (LP) may be suppressed or enhanced relative to the upper polariton (UP) depending on the frequency of the cavity mode. Furthermore, although the static properties and the translational diffusion of water are not changed under VSC or V-USC, we do find the modification of the orientational autocorrelation function of H 2 O molecules especially under V-USC, which could play a role in ground-state chemistry.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Nature of Hyperfine Interactions in TbPc 2 Single-Molecule Magnets: Multiconfigurational Ab Initio Study

Lanthanide-based single-ion magnetic molecules can have large magnetic hyperfine interactions as well as large magnetic anisotropy. Recent experimental studies reported tunability of these properties by changes of chemical environments or by application of external stimuli for device applications. In order to provide insight onto the origin and mechanism of such tunability, here we investigate the magnetic hyperfine and nuclear quadrupole interactions for a 159 Tb nucleus in TbPc 2 (Pc = phthalocyanine) single-molecule magnets using multiconfigurational ab initio methods including spin–orbit interaction. Since the electronic ground and first-excited (quasi)doublets are well separated in energy, the microscopic Hamiltonian can be mapped onto an effective Hamiltonian with an electronic pseudospin S = 1/2. From the ab initio calculated parameters, we find that the magnetic hyperfine coupling is dominated by the interaction of the Tb nuclear spin with electronic orbital angular momentum. The asymmetric 4f-like electronic charge distribution leads to a strong nuclear quadrupole interaction with significant transverse terms for the molecule with low symmetry. The ab initio calculated electronic–nuclear spectrum including the magnetic hyperfine and quadrupole interactions is in excellent agreement with the experiment. We further find that the transverse quadrupole interactions significantly influence the avoided level crossings in magnetization dynamics and that the molecular distortions affect mostly the Fermi contact terms as well as the transverse quadrupole interactions. Synopsis Hyperfine interactions for 159 Tb nucleus in TbPc 2 single-molecule magnets are investigated from first-principles using multiconfigurational calculations. Strong nuclear quadrupole and magnetic hyperfine coupling are found, with the latter being dominated by the paramagnetic spin-orbital mechanism. Furthermore, we construct an ab initio pseudospin Hamiltonian and obtain the electronic-nuclear spectrum that is in excellent agreement with experiment. The Zeeman diagram is calculated, and the magnetization dynamics is discussed. The effects of molecular distortions are researched.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1998

The Composition of Centaur 5145 Pholus

We present a new spectrum of the Centaur object 5145 Pholus between 1.15 and 2.4 micro meters. We model this, and the previously published (0.4- to 1.0- micrometer) spectrum, using Hapke scattering theory. Seen in absorption are the 2.04- micrometer band of H2O ice and a strong band at 2.27 micrometer, interpreted as frozen methanol and/or a photolytic product of methanol having small molecular weight. The presence of small molecules is indicative of a chemically primitive surface, since heating and other processes remove the light hydrocarbons in favor of macromolecular carbon of the kind found in carbonaceous meteorites. The unusually red slope of Pholus' spectrum is matched by fine grains of a refractory organic solid (tholin). Olivine (which we model with Fo 82) also appears to be present on Pholus. We present a five-component model for the composite spectrum of all spectroscopic and photometric data available for 5145 Pholus and conclude that this is a primitive object which has not yet been substantially processed by solar heat. The properties of Pholus are those of the nucleus of a large comet that has never been active.

Cruikshank, D. P.↗
NASA NTRS1976

Interstellar molecular hydrogen toward zeta Puppis

This paper reports the measurement of some 136 interstellar H2 absorption lines found in a continuous scan of the far-ultraviolet spectrum of zeta Pup at 0.05-A resolution with the Copernicus telescope. Absorptions from only the rotational levels 0 to 5 of the lowest vibrational state of the ground electronic state were observed. The total H2 column density is 2.8 by 10 to the 14th power molecules/sq cm; the ratio of H nuclei in H2 to the number in H I plus molecules is 6 by 10 to the -6th power; the population of the rotational levels can be represented by a single excitation temperature of 1120 (plus or minus 80) K. The radial velocities of all rotational levels were the same within 7 km/s and differed from most atoms and first ions by no more than 4.5 km/s on the average. The tables also list the best available data on wavelengths, oscillator strengths, and radiative damping constants for all the H2 lines with zero vibrational level likely to be observed in the interstellar gas.

Morton, D. C.↗
DOE OSTI2022

Density-matrix approach for sequential dissociative double ionization of molecules

Intense femtosecond infrared (IR) laser pulses have been used in recent years to study the breakup dynamics of molecules. However, observables such as kinetic energy release and branching ratios of molecular fragments are often difficult to predict by theory, making information of the molecular dynamics difficult to retrieve. In this work, we develop a simple model for sequential double ionization of molecules based on a density-matrix approach. The model describes tunneling ionization of the neutral and the ion as well as laser couplings between the ionic states simultaneously. Population of different doubly charged states can be obtained at a low computational cost. Furthermore, we applied our model to N 2 and obtained a good agreement on the kinetic energy release spectrum with a previous experiment. This theoretical development could open up the opportunities to use intense short IR laser pulses with coincidence measurement to probe molecular dynamics.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2023

Materials Design Directions for Solar Thermochemical Water Splitting

The sustainable, economical production of molecular hydrogen is a crucial component of a net zero-greenhouse-gas-emissions future. Solar thermochemical water splitting (STWS) offers a renewable route to hydrogen with the potential to help decarbonize several industries, including transportation, manufacturing, mining, metals processing, and electricity generation, as well as provide sustainable hydrogen as a chemical feedstock. STWS uses high temperatures generated from concentrated sunlight or other sustainable means for high-temperature heat to produce hydrogen and oxygen from steam. For example, in its simplest form of a two-step thermochemical cycle, a redox-active metal oxide is heated to ≈1700-2000 K, driving off molecular oxygen while producing oxygen vacancies in the material. The reduced metal oxide then cools (ideally with the extracted heat recuperated for re-use) and, in a separate step, comes into contact with steam, which reacts with oxygen vacancies to produce molecular hydrogen while recovering the original state of the metal oxide. Despite its promising use of the entire solar spectrum to split water thermochemically, the current estimated cost of hydrogen produced via STWS is ≈4-6× the U.S. Department of Energy (DOE) Hydrogen Shot target value of $1/kg. One contributing approach to bridging this cost gap is the design of new materials with improved thermodynamic properties to enable higher efficiencies. The state-of-the-art (SOA) redox-active metal oxide for STWS is ceria (CeO 2 ), due to its close to optimal, although too high, oxygen vacancy formation enthalpy and large configurational and electronic entropy of reduction. However, ceria requires high operating temperatures and its efficiency is insufficient. Therefore, efforts to increase the efficiency of STWS cycles have focused on further optimizing oxygen vacancy formation enthalpies and augmenting the reduction entropy via substitution or doping and materials discovery schemes. Examples of the latter include the perovskites BaCe 0.25 Mn 0.75 O 3 and (Ca,Ce)(Ti,Mn)O 3 . These efforts and others have revealed intuitive chemical principles for the efficient and systematic design of more effective materials, such as the strong correlation between the enthalpies of crystal bond dissociation and solid-state cation reduction with the enthalpy of oxygen vacancy formation, as well as configurational entropy augmentation via the coexistence of two or more redox-active cation sublattices. The purpose of this chapter is to prepare the reader with an up-to-date account of STWS redox-active materials, both the SOA and promising newcomers, as well as to provide chemically intuitive strategies for improving their cycle efficiencies through materials design – in conjunction with ongoing efforts in reactor engineering and gas separations – to reach the cost points for commercial viability. First, we will introduce the thermodynamics of STWS using a two-step, metal-oxide, thermochemical cycle with economics in mind. We also will compare the pros and cons of processes that do or do not involve phase changes. Second, we will describe the qualities that make ceria the SOA STWS redox-active material, as well as its limitations. Third, we will survey some of the most promising candidates to date in the search for materials to supplant ceria, emphasizing the post-ternary, metal-oxide-perovskite alloys. Lastly, we will enumerate and discuss the following materials design directions for STWS redox-active materials: crystal reduction potentials as a proxy for oxygen vacancy formation enthalpies, engineering the electronic and configurational entropy of reduction via f-shells and simultaneous redox, and vetting materials stability via temperature-dependent phase diagrams and melting-point prediction.

08 HYDROGEN↗