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At least 235 records · Page 13
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NASA NTRS1987

The bonding of FeN2, FeCO, and Fe2N2 - Model systems for side-on bonding of CO and N2

Qualitative calculations are performed to elucidate the nature of the side-on interaction of both N2 and CO with a single Fe atom. The systems are found to be quite similar, with bonding leading to an increase in the CO or N2 bond length and a decrease in the vibrational frequency. The CO or N2 stretching modes lead to a large dipole derivative along the metal-ligand bond axis. The populations show an almost identical, large donation from the Fe 3d orbitals into the CO or N2 Pi-asterisk. The larger system Fe2N2 is then considered, with the N2 bridging the Fe2, both parallel and perpendicular to the Fe2 bond axis for two different Fe-Fe distances. For FeN2, the shift in the observed N2 frequency is smaller than observed for the alpha state of N2/Fe(111). The shift in the N2 vibrational frequency increases when the N2 interacts with two Fe atoms, either at the Fe-Fe nearest neighbor distance or at the first layer Fe-Fe distance, when the side-on N2 axis is oriented perpendicular to an Fe-Fe bond.

Bauschlicher, Charles W., Jr.↗
NASA NTRS1988

Laboratory studies of the infrared spectral propertries of CO in astrophysical ices

The spectral properties of CO in various ices are presented. Included are peak positions, FWHMs, band profiles, and integrated absorbances of the CO fundamental at 2137/cm in different ices under various conditions. The results reveal that good quality moderate-resolution spectra of the interstellar CO feature can be used to unravel the composition, temperature, and thermal history of interstellar and cometary ices containing CO.

Sandford, S. A.↗
NASA NTRS1988

The photodissociation and chemistry of interstellar CO

Recent work on the vacuum UV absorption spectrum of CO to the description of the photodissociation of interstellar CO and its principal isotopic varieties is discussed. The effects of line broadening, self-shielding, shielding by H and H2, and isotope-selective shielding are examined as functions of depth into interstellar clouds. The photodissociation rates of the isotopic species are larger than that of (C-12)O inside the clouds by up to one to two orders of magnitude. A simple approximation to the attenuation by line absorption is given in tabular form. Computed abundances of CO and related species C and C+ are presented for a variety of interstellar clouds ranging from diffuse clouds to dense photodissociation regions. Several series of models of translucent clouds are presented which illustrate how the CO abundance increases rapidly with total cloud thickness. The variations of the isotopic abundances with depth and their sensitivity to temperature and total cloud thickness are explored in detail.

Van Dishoeck, Ewine F.↗
NASA NTRS1989

Theoretical studies of the transition metal-carbonyl systems MCO and M(CO)2, M = Ti, Sc, and V

Large Gaussian basis sets and an electron correlation treatment are used in ab initio calculations on the transition metal-carbonyl systems MCO and N(CO)2 for M = Ti, Sc, and V. The results show that high-spin ground states are favored for the monocarbonyl molecules, and that for the dicarbonyl molecules there is a competition between high, intermediate, and low spin states which are very close in energy. Dissociation energies of 0.62 eV for Ti-CO and 1.02 for Ti(CO)2 are found, relative to the ground state Ti atomic asymptote and CO 1Sigma(+). The binding energy per carbonyl for the three metal atoms is shown to be significantly lower for the dicarbonyl than for the the monocarbonyl molecules.

Barnes, Leslie A.↗
NASA NTRS1989

CO formation in the metal-rich ejecta of SN 1987A

A model for the formation of CO in the expanding ejecta of SN 1987A suggests that the 4.6-micron and 2.3 micron emissions noted in the SN spectrum may originate from the inner metal-rich regions of the ejecta. Also reported are the assignment of a 2.26-micron excess feature in the high-resolution IR spectra to the v = 2 to 0 overtone of CO(+) and the possible identification of a 2.95-micron feature with the v = 2 to 0 transition of electronically excited CO. The results suggest that the regions in which CO formation takes place must be ionized to a substantially lower degree than regions which dominate the line emission of heavier metals.

Petuchowski, S. J.↗
NASA NTRS1990

Phillips CO-oxidation catalyts for long-lived CO2 lasers: Activity and initial characterization studies

Four different catalysts have been developed specifically for use in sealed carbon dioxide lasers. The catalysts have been designed to be low dusting, stable to shock and vibration, have high activity at low temperatures and have long active lifetimes. Measured global CO oxidation rates range from 1.4 to 2.2 cc CO converted per minute per gram of catalyst at ambient temperature. The catalysts also retain substantial activity at temperatures as low as -35 C. The Phillips laser catalysts are prepared in a variety of different shapes to meet the different pressure drop and gas flow profiles present in the many different styles of lasers. Each catalyst has been tested in sealed TEA lasers and has been shown to substantially increase the sealed life of the laser. Activity measurements made on the precious metal catalysts which were prepared with and without activity promoters showed that the promoter materials increase catalyst CO oxidation activity at least an order of magnitude at ambient temperature. Initial studies using H2 and CO chemisorption, X ray diffraction (XRD) and X ray photoelectron spectroscopy (XPS) have shown that the activity promoters do not significantly affect the precious metal crystallite size or the electronic structure around the precious metal. In addition, the formation or lack of formation of solid solutions between the precious metal and promoters has also been shown not to affect the activity of the promoted catalyst.

Kolts, J. H.↗
NASA NTRS1990

High resolution sub-millimetre mapping of starburst galaxies: Comparison with CO emission

Researchers present first results from a program of submillimeter continuum mapping of starburst galaxies, and comparison of their dust and CO emission. This project was prompted by surprising results from the first target, the nearby starburst M82, which shows in the dust continuum a morphology quite unlike that of its CO emission, in contrast to what might be expected if both CO and dust are accurately tracing the molecular hydrogen. Possible explanations for this striking difference are discussed. In the light of these results, the program has been extended to include sub-mm mapping of the nearby, vigorously star forming spirals, M83 and Maffei 2. The latter were also observed extensively in CO, in order to study excitation conditions in its central regions. The James Clerk Maxwell Telescope was used in these studies.

Smith, P. A.↗
NASA NTRS1990

Detection of CO emission in Hydra 1 cluster galaxies

A survey of bright Hydra cluster spiral galaxies for the CO(1-0) transition at 115 GHz was performed with the 15m Swedish-ESO submillimeter telescope (SEST). Five out of 15 galaxies observed have been detected in the CO(1-0) line. The largest spiral galaxy in the cluster, NGC 3312, got more CO than any spiral of the Virgo cluster. This Sa-type galaxy is optically largely distorted and disrupted on one side. It is a good candidate for ram pressure stripping while passing through the cluster's central region. A comparison with global CO properties of Virgo cluster spirals shows a relatively good agreement with the detected Hydra cluster galaxies.

Huchtmeier, W. K.↗
NASA NTRS1991

Discovery of a Doppler-limited CO line in the upper mesosphere of Venus - A new dynamical probe

The presence of CO in the upper atmosphere of Venus is a consequence of the photochemistry of CO2, the dominant atmospheric constituent. In December 1989 the J = 1-2 transition of CO was observed at 230 GHz. In addition to the broad absorption line first reported by Kakar et al. (1976), a narrow absorption feature at the center of the line due to upper mesospheric CO, where the temperature profile starts to exhibit diurnal variation with altitude. The narrow feature is approximately 600 kHz wide and is predominantly Doppler-broadened. The Doppler core provides a new means of measuring wind velocities at these altitudes in the atmosphere of Venus. Detection of small Doppler shifts in the line core can in principle be used to measure winds with an accuracy of 10 m/s. Results are presently limited by the 17 kHz uncertainty in the measured rest frequency, corresponding to a systematic error in wind velocity up to 22 m/s, and the absence of laboratory measurements of the pressure shift in CO by CO2.

Buhl, David↗
NASA NTRS1991

Venus imaged with the Hat Creek interferometer in the J = 1-0 CO line

Venus 2.7-mm continuum emission and CO J = 1-0 transition observations conducted in January 1987, when Venus was at western elongation, indicate a 10 percent brightness temperature increase from the day to the nightside. It is suggested that this brightness temperature variation, which is greater than anticipated on the basis of physical variations in temperature, may be associated with potentially cloud-related atmospheric opacity variations. Model fits to the CO spectra suggest that, while the CO at altitudes greater than 90 km decreases from night to day, low altitude CO may exhibit a general enhancement.

De Pater, Imke↗
NASA NTRS1991

The CO luminosity function of galaxies

The CO luminosity function of galaxies derived previously by Verter (1983, 1987) is reevaluated with a larger sample drawn from the portion of the FCRAO Extragalactic CO Survey satisfying the optical-threshold (B super 0 sub T) = 12 mag condition. It is found that the newly derived CO luminosity function is consistent with previous galaxy luminosity functions in the blue and infrared, and with correlations between L(CO) and L(B) or L(IR).

Verter, Frances↗
NASA NTRS1991

Quantification of UV stimulated ice chemistry: CO and CO2

Recent laboratory experiments are presented that show that during photolysis of the pure ices there is evidence of the interconversion of CO to CO2 and CO2 to CO using Lyman alpha (1216A) radiation. In addition, there is a substantial amount of another substance being produced. This substance is evident by its infrared absorption peak at 2235 cm(-1). It is believed that this new peak is due to carbon suboxide, C3O2. CO and CO2 have already been detected in comets, and C3O2 has been suggested as a cometary from radiation of CO. Comparisons are made between our results at 1215A and proton radiation experiments and radiation at other wavelengths. The suggestion is that the processing of ices is energy dependent, i.e., dependent on the type of radiation. Several difficult problems have to be solved before these radiation conversions can be quantified. The steps that we are taking to quantify the kinetics are discussed.

Anicich, V. G.↗
NASA NTRS1991

Laboratory absorption spectra of molecules at interstellar cloud temperatures - First measurements on CO at about 97 nm

In the 91-100 nm spectral region, where absorption of photons by interstellar CO usually leads to dissociation, laboratory spectra obtained at 295 K show that most CO bands are both overlapped and perturbed. Reliable band oscillator strengths cannot be extracted from such spectra. As a consequence, synthetic extreme-ultraviolet absorption spectra for CO at the low temperatures that prevail in interstellar clouds are uncertain. A supersonic expansion technique has been used to cool CO to 30 K and three bands in the 97-nm region have been studied with high spectral resolution. The measured spectrum at 30 K is in reasonable agreement with some published modeled spectra, but the ratios of integrated cross sections are somewhat different from those determined from low resolution spectra obtained at 295 K, in which the bands are blended.

Smith, P. L.↗
NASA NTRS1992

Oriented Scintillation Spectrometer Experiment observations of Co-57 in SN 1987A

The Oriented Scintillation Spectrometer Experiment (OSSE) on the Compton Gamma Ray Observatory has observed SN 1987A for two 2 week periods during the first 9 months of the mission. Evidence for gamma-ray line and continuum emission from Co-57 is observed with an intensity of about 10 exp -4 gamma/sq cm/s. This photon flux between 50 and 136 keV is demonstrated by Monte Carlo calculations to be independent of the radial distribution of Co-57 for models of low optical depth, viz., models having photoelectric absorption losses of 122 keV photons no greater than several percent. For such models the observed Co-57 flux indicates that the ratio Ni-57/Ni-56 produced in the explosion was about 1.5 times the solar system ratio of Fe-57/Fe-56. When compared with nearly contemporaneous bolometric estimates of the luminosity for SN 1987A, our observations imply that Co-57 radioactivity does not account for most of the current luminosity of the supernova remnant in low optical depth models. We suggest alternatives, including a large optical depth model that is able to provide the SN 1987A luminosity and is consistent with the OSSE flux. It requires a 57/56 production ratio about twice solar.

Kurfess, J. D.↗
NASA NTRS1993

The H + OCS hot atom reaction - CO state distributions and translational energy from time-resolved infrared absorption spectroscopy

Time-resolved infrared diode laser spectroscopy has been used to probe CO internal and translational excitation from the reaction of hot H atoms with OCS. Product distributions should be strongly biased toward the maximum 1.4 eV collision energy obtained from 278 nm pulsed photolysis of HI. Rotations and vibrations are both colder than predicted by statistical density of states theory, as evidenced by large positive surprisal parameters. The bias against rotation is stronger than that against vibration, with measurable population as high as v = 4. The average CO internal excitation is 1920/cm, accounting for only 13 percent of the available energy. Of the energy balance, time-resolved sub-Doppler line shape measurements show that more than 38 percent appears as relative translation of the separating CO and SH fragments. Studies of the relaxation kinetics indicate that some rotational energy transfer occurs on the time scale of our measurements, but the distributions do not relax sufficiently to alter our conclusions. Vibrational distributions are nascent, though vibrational relaxation of excited CO is unusually fast in the OCS bath, with rates approaching 3 percent of gas kinetic for v = 1.

Nickolaisen, Scott L.↗
NASA NTRS1993

On origin of the olivine inclusions from the Kainsaz CO carbonaceous chondrite

Olivine inclusions and chondrules of Kainsaz were formed in a unique process of dust matter melting. The elemental abundances of four fractions of olivine (01) inclusions from Kainsaz were analyzed by INAA. The inclusions of fraction A (160 less than d less than 260 microns) have Fe-Ni grains, the inclusions of fractions B (100 less than d less than 160 microns), C (160 less than d less than 260 microns), and D (260 less than d less than 360 microns) do not. The average elemental enrichment factors relative to CI chondrite for each fraction and chondrules of Kainsaz is shown. The enrichment factors of siderophile Co, Ni, Ir, Au, and non-refractory Na in all fractions are less than 1. The factors of refractory Ca, Sc, La, Sm, and Yb are comparative with the corresponding values of O1 aggregates of Allende CV (average 4.76). For chondrules of Kainsaz these values are lower. Fraction A is enriched in Co, Ir, Au, and relative Ni and CI chondrites: Ir greater than Au greater than Co. The values of (Me/Ni)inc/(Me/Ni)CI are equal to 3.25 for Ir, 2.1 for Au, and 1.2 for Co. The superabundances in Ir and Au relative to Ni witness to formation of Fe-Ni grains of O1 inclusions by agglomeration of grains enriched in refractory metal with grains enriched in non-refractory metal (Au). The enrichments of fraction A in Ca, Sc, La, Sm, and Yb witness about presence of high-temperature phases in O1 inclusions.

Lavrukhina, A. K.↗
NASA NTRS1994

Search for CO absorption bands in IUE far-ultraviolet spectra of cool stars

Observations of the red supergiant (M2 Iab) alpha Ori with the Goddard High Resolution Spectrograph (GHRS) on board the Hubble Space Telescope (HST) have provided an unambiguous detection of a far-ultraviolet (far-UV) chromospheric continuum on which are superposed strong molecular absorption bands. The absorption bands have been identified by Carpenter et al. (1994) with the fourth-positive A-X system of CO and are likely formed in the circumstellar shell. Comparison of these GHRS data with archival International Ultraviolet Explorer (IUE) spectra of alpha Ori indicates that both the continuum and the CO absorption features can be seen with IUE, especially if multiple IUE spectra, reduced with the post-1981 IUESIPS extraction procedure (i.e., with an oversampling slit), are carefully coadded to increase the signal to noise over that obtainable with a single spectrum. We therefore initiated a program, utilizing both new and archival IUE Short Wavelength Prime (SWP) spectra, to survey 15 cool, low-gravity stars, including alpha Ori, for the presence of these two new chromospheric and circumstellar shell diagnostics. We establish positive detections of far-UV stellar continua, well above estimated IUE in-order scattered light levels, in spectra of all of the program stars. However, well-defined CO absorption features are seen only in the alpha Ori spectra, even though spectra of most of the program stars have sufficient signal to noise to allow the dectection of features of comparable magnitude to the absorptions seen in alpha Ori. Clearly if CO is present in the circumstellar environments of any of these stars, it is at much lower column densities.

Gessner, Susan E.↗
NASA NTRS1995

New insight in the solar T(sub MIN) region from the CO lines at 4.67 micron

We discuss recent observations of the fundamental vibration-rotation transitions of carbon monoxide (CO) in the solar infrared spectrum. Employing a new array detector at the McMath-Pierce facility on Kitt Peak we find that the CO lines sketch a rich picture of the dynamics of the solar temperature minimum region, the lower boundary of the chromosphere. In a spectra-spectroheliogram and a time-sequence of the slit-spectra obtained during exceptional seeing conditions we observe small-scale bright, ring shaped, blueshifted features. We speculate that they are the signature of granular overshoot into the convectively stable temperature minimum. The centers of the rings are among the coolest elements seen in strong CO-line heliograms on the disk, and may be instrumental to the low temperature observed in CO close to the solar limb.

Uitenbroek, Han↗