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NASA NTRS2005

Correlations of (Delta)O-17 with Chemical Characteristics Among Chondrite Groups

Demonstration of mass-independent O isotopic variations in solar system materials was a seminal discovery of meteoritics. These variations were thought to reflect incomplete mixing of O from different nucleosynthesis sources. Since then, two non-nucleosynthetic causes have been suggested: (1) differential photodissociation of distinct isotopomers of CO, enriching nebular gas in chemically reactive heavy O, and (2) gas-phase molecular reactions producing mass-independent O isotopic exchange. Nebular processes caused chemical fractionations that are observed in chondrite bulk compositions. If nebular processes also produced mass-independent O isotopic variations, then these may correlate with chondrite bulk chemistry.

Mittlefehldt, D. W.↗
NASA NTRS1995

Pressure Dependence and Metastable State Formation in the Photolysis of Dichlorine Monoxide (Cl2O)

Physics%K photolysis, dichlorine monoxide, pressure%U http://techreports.jpl.nasa.gov/1995/95-0924.pdfThe photodissociation of dichlorine monoxide (Cl2O) was studied using broadband flash photolysis to investigate the influence of variations in the photolysis wavelength domain, bath gas pressure, and bath gas identity on the yield and temporal dependence of the ClO product. ClO yields were independent of bath gas pressure when the photolysis spectral band extended to 200 nm (quartz cutoff) but for photolysis restricted to wavelengths longer than about 250 nm, ClO yields decreased with increasing bath gas pressure and there was a pressure-dependent delay in the formation of ClO.!.

photolysis↗
NASA NTRS1995

Far-Infrared Spectroscopy of M82: Interstellar Properties of the Dual Nuclear Starbursts

We have measured [O I] 63 mm and [Si II] 35 mm in the central 44' (700 pc) of the starburst galaxy M82. The luminosities in these transitions are each ~0.1 percent of the bolometric luminosity. We model the [O I] in M82 as arising from warm neutral gas photodissociated by FUV flux from OB stars, while most of the [Si II] emission arises from associated H II regions.!.

spectroscopy starburst galaxy luminosity↗
NASA NTRS1994

Measurement of the V-T Energy Transfer Rates of Highly Excited (sup 2)A(sub 1) NO(sub 2)

Production of electronic ground state NO(sub 2) from 248 nm photolysis of HNO(sub 3) was detected by laser induced fluorescence (LIF). A growth in the LIF signal was observed following the photolysis and has been interpreted as the relaxation of NO(sub 2) through the higher vibrational levels of the X state; an energy region where the probe laser photodissociates the NO(sub 2) instead of inducing fluorescence.

laser induced fluorescence (LIF)↗
NASA NTRS2006

Vibrational and rotational quenching of CO by collisions with H, He, and H2

Collisional quenching of molecular species is an important process in a variety of astrophysical environments including interstellar clouds, photodissociation regions, and cool stellar/planetary atmospheres. In this work, quantum mechanical scattering calculations are presented for the rotational and vibrational relaxation of rotationally-excited CO due to collisions with H, He and H2 for collision energies between 10(exp -6) and approx.15000/cm. The calculations were performed using the close-coupling approach and the l-labeled form of the coupled-states approximation. Cross sections and rate coefficients for the quenching of the v=0-2, j=0-6 levels of CO are presented and comparisons with previous calculations and measurements, where available, are provided.

Yang, Benhui↗
NASA NTRS2006

Oscillator Strengths and Predissociation Widths for Rydberg Transitions in Carbon Monoxide

CO is used as a probe of astronomical environments ranging from planetary atmospheres and comets to interstellar clouds and the envelopes surrounding stars near the end of their lives. One of the processes controlling the CO abundance and the ratio of its isotopomers is photodissociation. Accurate oscillator strengths for Rydberg transitions are needed for modeling this process. Absorption bands were analyzed by synthesizing the profiles with codes developed independently in Meudon and Toledo. Each synthetic spectrum was adjusted to match the experimental one in a non-linear least-squares fitting procedure with the band oscillator strength, the line width (instrumental and predissociation.

Federman, Steven R.↗
NASA NTRS2007

Mesospheric Water Vapor Retrieved from SABER/TIMED Measurements

The SABER instrument on board the TIMED satellite is a limb scanning infrared radiometer designed to measure temperature and minor constituent vertical profiles and energetics parameters in the mesosphere and lower thermosphere (MLT) The H2O concentrations are retrieved from 6.3 micron band radiances. The interpretation of this radiance requires developing a non-LTE H2O model that includes energy exchange processes with the system of O3 and O2 vibrational levels populated at the daytime through a number of photoabsorption and photodissociation processes. We developed a research model base on an extended H2O non-LTE model of Manuilova coupled with the novel model of the electronic kinetics of the O2 and O3 photolysis products suggested by Yankosvky and Manuilova. The performed study of this model helped u to develop and test an optimized operational model for interpretation of SABER 6.3 micron band radiances. The sensitivity of retrievals to the parameters of the model is discussed. The H2O retrievals are compared to other measurements for different seasons and locations.

Feofilov, Arte, G.↗
NASA NTRS2010

Complex Cometary Phenomena: The Distributed Source

Observations of H2CO toward comet Hale-Bopp demonstrate that this molecule has an extended distribution, which cannot be explained by direct sublimation from the nucleus or gas phase processes in the coma. A likely source of 142CO in comets may be coma grains composed of an organic-dominated silicate-organic matrix. These grains are released from the nucleus and are vaporized or thermally degraded by solar heating, ejecting organic molecules into the expanding coma. Hence, organic molecules with short photodissociation lifetimes (<10(exp 4) km) such as H2CO can be found much farther from the comet nucleus than their photodestruction rates would suggest. Distributed sources are also considered for other species such as CO, CN, and CS. We will present an overview of observations and experiments that can help decipher the origin of such species.

Milam, Stefanie N.↗
NASA NTRS2010

Detection of the 158 Micrometers[CII] Transition at z=1.3: Evidence for a Galaxy-Wide Starburst

We report the detection of 158 micrometer [C II] fine-structure line emission from MIPS J 142824.0+3526l9, a hyperluminous (L(sub IR) approx. 10(exp 13) Solar Luminosity starburst galaxy at z = 1.3. The line is bright, corresponding to a fraction L[C II]/L(sub FIR) approx. equals 2 x l0(exp -3) of the far-IR(FIR) continuum. The [C II], CO, and FIR continuum emission may be modeled as arising from photodissociation regions (PDRs) that have a characteristic gas density of n approx. 10(exp 4.2)/cu cm., and that are illuminated by a far-UV radiation field approx. 10(exp 3.2) times more intense than the local interstellar radiation field. The mass in these PDRs accounts for approximately half of the molecular gas mass in this galaxy. The L[C II]/L(sub F1R) ratio is higher than observed in local ultraluminous infrared galaxies or in the few high-redshift QSOs detected in [C II], but the L[CII]/L(sub FIR) and L(sub CO)/L(sub FIR) ratios are similar to the values seen in nearby starburst galaxies

Hailey-Dunsheath, S.↗
NASA NTRS2010

Detection of the 158 Micrometers[CII] Transition at z=1.3: Evidence for a Galaxy-Wide Starburst

We report the detection of 158 micron [C II] fine-structure line emission from MIPS J142824.0+352619, a hyperluminous ( L(sub IR) approximates 10(exp 13) L (sub solar)) starburst galaxy at z = 1.3. The line is bright, corresponding to a fraction L(sub [Cu II] L(sub Fir) approximates 2 x 10(exp -3) of the far-IR (FIR) continuum. The [C II], CO, and FIR continuum emission may be modeled as arising from photodissociation regions (PDRs) that have a characteristic gas density of n approximates 10(exp 4.2) /cm(exp 3) , and that are illuminated by a far-UV radiation field approximately 10(exp 3.2) times more intense than the local interstellar radiation field. The mass in these PDRs accounts for approximately half of the molecular gas mass in this galaxy. The L(sub [CII])/L(sub FIR) ratio is higher than observed in local ultralummous infrared galaxies or in the few high-redshift QSOs detected in [C II], but the L(sub [CII])/L(sub FIR) and L(sub CO)/L(sub FIR) ratios are similar to the values seen in nearby starburst galaxies. This suggests that MIPS J142824.0+352619 is a scaled-up version of a starburst nucleus, with the burst extended over several kiloparsecs.

Hailey-Dunsheath, S.↗
NASA NTRS2011

Multiwavelength Observations of Volatiles in Comets

Recently, there have been complimentary observations from multiple facilities to try to unravel the chemical complexity of comets. Incorporating results from various techniques, including: single-dish millimeter wavelength observations, interferometers, and/or IR spectroscopy, one can gain further insight into the abundances, production rates, distributions, and formation mechanisms of molecules in these objects [I]. Such studies have provided great detail towards molecules with a-typical chemistries, such as H2CO [2]. We report spectral observations of C/2006 M4 (SWAN), C/2007 N3 (Lulin), and C/2009 RI (McNaught) with the Arizona Radio Observatory's SMT and 12-m telescopes, as well as the NRAO Greenbank telescope and IRTFCSHELL. Multiple parent volatiles (HCN, CH3OH, CO, CH4, C2H6, and H2O) plus two photodissociation products (CS and OH) have been detected in these objects. We will present a comparison of molecular abundances in these comets to those observed in others, supporting a long-term effort of building a comet taxonomy based on composition. Previous work has revealed a range of abundances of parent species (from "organics-poor" to "organics-rich") with respect to water among comets [3,4,5], however the statistics are stiII poorly constrained and interpretations of the observed compositional diversity are uncertain.

Milam, Stefanie N.↗
NASA NTRS2001

The EUV Airglow of Titan: Production and Loss of N2 c'4(0) - X

The N(2) Carroll-Yoshino (CY) c'(4) X (0,0) and (0,1) Rydberg bands between 95 and 99 nm were reported to be the most prominent EUV emission features in Voyager 1 ultraviolet spectrometer (UVS) airglow spectra from Titan's atmosphere. Although c'(4) is strongly excited by photoelectron impact, the (0,0) band is optically thick near peak production, so a multiple-scattering model is employed to calculate (0,v) nadir-viewing intensities. The model accounts for all known loss processes and quantifies the redistribution of photons to (0,v is greater than 0). Results show 7.6 R of (0,1) intensity, in agreement with reported observations (5-10 R), and 0.2 R of (0,0), in spectacular disagreement with reported observations (6-10 R). Nadir-viewing intensities of all other expected NI multiplets and N2 bands in the brightest portion of the EUV airglow spectrum (92.0-101.5 nm) are also calculated using photodissociative ionization of N(2) and photoelectron impact on N(2). It is found that NI multiplets and N(2) bands near (0,0) and unresolved by the UVS combine to produce 8.3 R, consistent with that reported for (0,0) and indicating that it was misidentified in previous analyses. The Ultraviolet Imaging Spectrograph (UVIS) on Cassini should unambiguously distinguish any (0,0) intensity from the brightest features nearby.

EUV (EXTREME ULTRAVIOLET)↗
NASA NTRS2011

Signposts of Planet Formation in the Disk of GM Aur

Rice et al. noted that transitional disks hosting massive Jovian-mass planets should have suppressed accretion onto the star, while bringing about an absence of silicate emission. Their models also predict systems with less massive planets should permit small grain dust and some gas to filter into the cavity, leaving larger grains confined to the outer disk. Such systems are expected to have polarized light originating within the cavity, silicate emission, and small-grain reflection nebulosity detectable in FUV high-contrast imagery. A further consequence is that molecular gas should be less abundant in the inner disk due to photodissociation by the stellar FUV radiation field. GM Aur is a T-Tauri star/transitional disk system, where both silicate emission and a 24 AU cavity has been detected. We continue the analysis of GM Aur with FUV and optical HST imagery and report the presence of small-grain reflection nebulosity detected from 1400 - 2000 A in the cavity region, as well as a molecular outflow that has an inner radius corresponding to the cavity wall. These data, together with the presence of silicate emission, suggest that GM Aur hosts a planet with likely mass between 1 and 5 Mass of Jupiter

Hornbeck, Jeremy↗
NASA NTRS2011

The EUV Emission in Comet-Solar Corona Interactions

The Atmospheric Imaging Assembly (AlA) on the Solar Dynamics Observatory (SDO) viewed a comet as it passed through the solar corona on 2011 July 5. This was the first sighting of a comet by a EUV telescope. For 20 minutes, enhanced emission in several of the AlA wavelength bands marked the path of the comet. We explain this EUV emission by considering the evolution of the cometary atmosphere as it interacts with the ambient solar atmosphere. Water ice in the comet rapidly sublimates as it approaches the Sun. This water vapor is then photodissociated, primarily by Ly-alpha, by the solar radiation field to create atomic Hand O. Other molecules present in the comet also evaporate and dissociate to give atomic Fe and other metals. Subsequent ionization of these atoms can be achieved by a number of means, including photoionization, electron impact, and charge exchange with coronal protons and other highly-charged species. Finally, particles from the cometary atmosphere are thermalized to the background temperature of the corona. Each step could cause emission in the AlA bandpasses. We will report here on their relative contribution to the emission seen in the AlA telescopes.

Bryans, Paul↗
NASA NTRS2011

Highly Accurate Quartic Force Fields, Vibrational Frequencies, and Spectroscopic Constants for Cyclic and Linear C3H3(+)

High levels of theory have been used to compute quartic force fields (QFFs) for the cyclic and linear forms of the C H + molecular cation, referred to as c-C H + and I-C H +. Specifically the 33 3333 singles and doubles coupled-cluster method that includes a perturbational estimate of connected triple excitations, CCSD(T), has been used in conjunction with extrapolation to the one-particle basis set limit and corrections for scalar relativity and core correlation have been included. The QFFs have been used to compute highly accurate fundamental vibrational frequencies and other spectroscopic constants using both vibrational 2nd-order perturbation theory and variational methods to solve the nuclear Schroedinger equation. Agreement between our best computed fundamental vibrational frequencies and recent infrared photodissociation experiments is reasonable for most bands, but there are a few exceptions. Possible sources for the discrepancies are discussed. We determine the energy difference between the cyclic and linear forms of C H +, 33 obtaining 27.9 kcal/mol at 0 K, which should be the most reliable available. It is expected that the fundamental vibrational frequencies and spectroscopic constants presented here for c-C H + 33 and I-C H + are the most reliable available for the free gas-phase species and it is hoped that 33 these will be useful in the assignment of future high-resolution laboratory experiments or astronomical observations.

Huang, Xinchuan↗
NASA NTRS2011

Photolysis of Pure Solid O3 and O2 Films at 193nm

We studied quantitatively the photochemistry of solid O3 and O2 films at 193 nm and 22 K with infrared spectroscopy and microgravimetry. Photolysis of pure ozone destroyed O3, but a small amount of ozone remained in the film at high fluence. Photolysis of pure O2 produced O3 in an amount that increased with photon fluence to a stationary level. For both O2 and O3 films, the O3:O2 ratio at large fluences is ?0.07, about two orders of magnitude larger than those obtained in gas phase photolysis. This enhancement is attributed to the increased photodissociation of O2 due to photoabsorption by O2 dimers, a process significant at solid-state densities. We obtain initial quantum yield for ozone synthesis from solid oxygen, phi (O3) = 0.24 0.06, and quantum yields for destruction of O3 and O2 in their parent solids, phi(-O3) = 1.0 0.2 and phi(-O2) = 0.36 0.1. Combined with known photoabsorption cross sections, we estimate probabilities for geminate recombination of 0.5 0.1 for O3 fragments and 0.88 0.03 for oxygen atoms from O2 dissociation. Using a single parameter kinetic model, we deduce the ratio of reaction cross sections for an O atom with O2 vs. O3 to be 0.1 0.2. The general good agreement of the model with the data suggests the validity of the central assumption of efficient energy and spin relaxation of photofragments in the solid prior to their reactions with other species.

Raut, U.↗
NASA NTRS2012

Observations of Carbon Isotopic Fractionation in Interstellar Formaldehyde

Primitive Solar System materials (e.g. chondrites. IDPs, the Stardust sample) show large variations in isotopic composition of the major volatiles (H, C, N, and O ) even within samples, witnessing to various degrees of processing in the protosolar nebula. For ex~ ample. the very pronounced D enhancements observed in IDPs [I] . are only generated in the cold. dense component of the interstellar medium (ISM), or protoplanetary disks, through ion-molecule reactions in the presence of interstellar dust. If this isotopic anomaly has an interstellar origin, this leaves open the possibility for preservation of other isotopic signatures throughout the form ation of the Solar System. The most common form of carbon in the ISM is CO molecules, and there are two potential sources of C-13 fractionation in this reservoir: low temperature chemistry and selective photodissociation. While gas-phase chemistry in cold interstellar clouds preferentially incorporates C-13 into CO [2], the effect of self-shielding in the presence of UV radiation instead leads to a relative enhancement of the more abundant isotopologue, 12CO. Solar System organic material exhibit rather small fluctuations in delta C-13 as compared to delta N-15 and delta D [3][1], the reason for which is still unclear. However, the fact that both C-13 depleted and enhanced material exists could indicate an interstellar origin where the two fractionation processes have both played a part. Formaldehyde (H2CO) is observed in the gas-phase in a wide range of interstellar environments, as well as in cometary comae. It is proposed as an important reactant in the formation of more complex organic molecules in the heated environments around young stars, and formaldehyde polymers have been suggested as the common origin of chondritic insoluable organic matter (IOM) and cometary refractory organic solids [4]. The relatively high gas-phase abundance of H2CO observed in molecular clouds (10(exp- 9) - 10(exp- 8) relative to H2) makes it feasible to observe its less common isotopologues. As a step in our investigation of C-13 fractionation patterns in the ISM, we here present comparisons between observations of the C-13 fraction in formaldehyde, and chemical fractionation models.

Wirstrom, E. S.↗