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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Balloon borne LIDAR measurements of stratospheric hydroxyl radical

A balloon-borne laser radar (LIDAR) system for determining the stratospheric hydroxyl radical concentration constructed and flown by the Goddard Space Flight Center is discussed. The system measured hydroxyl in the altitude range of 34-37 km during an afternoon and early evening, producing the first post-sunset hydroxyl determination ever obtained. Daytime values (approximately 5 x 10 to the 6th/cu cm) are somewhat lower than previous measurements using in situ resonance fluorescence. Nighttime values (approximately 7 x 10 to the 5th/cu cm at 2100 CDT) are found to be higher than predicted by current one-dimensional models. Possible sources of these discrepancies, together with improvements possible in future systems, are outlined.

Heaps, W. S.↗
NASA NTRS1983

New technological developments for the remote detection of atmospheric hydroxyl radicals

New developments in the areas of narrowband tunable excimer lasers, high-resolution high-rejection optical filters, and wavelength measurement devices are considered for application to the remote sensing of atmospheric hydroxyl radicals. The conclusion is that an increase in the SNR of 10,000 could readily be gained through the use of these new devices. Also, considerable reductions in size and electrical energy consumption could be realized.

Mcdermid, I. S.↗
NASA NTRS1984

The role of surface generated radicals in catalytic combustion

The role of surface generated OH radicals in determining the catalytic ignition characteristics for propane oxidation on platinum were studied. The experiments were conducted in a stacked-plate, catalyst bed. Transient measurements, during catalytic ignition, of the catalyst's axial temperature profile were made and the effect of equivalence ratio, inlet temperature and inlet velocity was investigated. These measurements will provide insights which will be useful in planning and interpreting to OH measurements. Attempts to measure OH concentration in the catalyst bed using resonance absorption spectroscopy were unsuccessful, indicating that OH concentrations are below 10 to the 16th power/cc but still possibly above equilibrium values. Measurements are currently underway using forward scatter laser induced fluorescence which should extend the OH detection limits several orders of magnitude below the equilibrium concentrations.

Santavicca, D. A.↗
NASA NTRS1983

Laboratory detection of the C3N an C4H free radicals

The millimeter-wave spectra of the linear carbon chain free radicals C3N and C4H, first identified in IRC + 10216 and hitherto observed only in a few astronomical sources, have been detected with a Zeeman-modulated spectrometer in laboratory glow discharges through low pressure flowing mixtures of N2 + HC3N and He + HCCH, respectively. Four successive rotational transitions between 168 and 198 GHz have been measured for C3N, and five rotational transitions between 143 and 200 GHz for C4H; each is a well-resolved spin doublet owing to the unpaired electron present in both species. Precise values for the rotational, centrifugal distortion, and spin doubling constants have been obtained, which, with hyperfine constants derived from observations of the lower rotational transitions in the astronomical source TMC 1, allow all the rotational transitions of C3N and C4H at frequencies less than 300 GHz to be calculated to an absolute accuracy exceeding 1 ppm.

Gottlieb, C. A.↗
NASA NTRS1985

A measurement of the vibrational band strength for the upsilon sub 3 band of the HO2 radical

The HO2 radicals generated in a discharge-flow system were observed with tunable diode laser absorption in the P-branch of the nu(3) vibrationall band at 1080/cm. The observed line positions agree with those calculated from the molecular constants for the nu(3) bland obtained from a previous study using laser magnetic resonance spectroscopy. The band strength was determined by observing line center absoptions when HO2 is produced in the reaction F + H2O2 yields HO2 + HF (k1) with a measured concentration of atomic fluorine and excess hydrogen peroxide. F-atom concentrations are measured by diode laser absorption of the spin-orbit transition at 404/cm. The analysis accounts for HO2 losses due to the reactions of HO2 + HO2 yields H2O2 + O2 (k3) and F + HO2 yields HF + O2 (k4). The line strength for the 6(15) 7(16) F(1) transition is 2.9 x 10 to the 21st power sq cm/molecule/cm which corresponds to a nu(3) band strength of 34 +/- 9 sq/cm(STP atm). This value is a factor of 6 lower than previous ab initio calculations. These results will be useful in assessing the feasibility of atmospheric measurements of HO2 using infrared absorption techniques.

Zahniser, M. S.↗
NASA NTRS1984

The far-infrared laser magnetic resonance spectrum of the SiH radical and determination of ground state parameters

The far-infrared laser magnetic resonance spectrum of the SiH radical in the v = O level of its X2Pi state has been recorded. The signals are rather weak. The molecules were generated in the reaction between fluorine atoms and SiH4. Rotational transitions have been detected in both 2Pi1/2 and 2Pi3/2 spin components but no fine structure transitions between the spin components were observed. Proton hyperfine splittings were resolved on some lines. The measurements have been analyzed, subjected to a least-squares fit using an effective Hamiltonian, and the appropriate molecular parameters determined. The weakness of the spectrum and the failure of attempts to power saturate favorable lines are both consistent with a small value for the electric dipole moment for SiH.

Brown, J. M.↗
NASA NTRS1984

Temperature and pressure dependence of the absolute rate constant for the reactions of NH2 radicals with acetylene and ethylene

The absolute rate constants for the reaction between the NH2 free radical and acetylene and ethylene is measured experimentally using a flash photolysis technique. The constant is considered to be a function of temperature and pressure. At each temperature level of the experiment, the observed pseudo-first-order rate constants were assumed to be independent of flash intensity. The results of the experiment indicate that the bimolecular rate constant for the NH2 + C2H2 reaction increases with pressure at 373 K and 459 K but not at lower temperatures. Results near the pressure limit conform to an Arrhenius expression of 1.11 (+ or -) 0.36 x 10 to the -13th over the temperature range from 241 to 459 K. For the reaction NH2 + C2H4, a smaller rate of increase in the bimolecular rate constant was observed over the temperature range 250-465 K. The implications of these results for current theoretical models of NH2 + C2H2 (or H4) reactions in the atmospheres of Jupiter and Saturn are discussed.

Bosco, S. R.↗
NASA NTRS1984

The CN radical in diffuse interstellar clouds

A survey of 15 lines of sight for the CN B2Sigma(+) X2Sigma(+) interstellar absorption lines shows that the CN column density in diffuse interstellar clouds follows the relation log N(CN) is proportional to m log N(H2), where m is approximately equal to 3. This result is reproduced by a reaction network in which CN is produced primarily from C2 by the neutral-neutral reaction C2 + N yields CN + C, and photodissociation is the main destruction pathway for the neutral molecules CH, C2, and CN. The CN radical is the first molecular species observed in diffuse clouds that requires a neutral-neutral reaction for its formation in the gas phase. The network also reproduces the observed ratio N(CN)/N(H2).

Federman, S. R.↗
NASA NTRS1985

A potential-energy surface study of the 2A1 and low-lying dissociative states of the methoxy radical

Accurate, ab initio quantum chemical techniques are applied in the present study of low lying bound and dissociative states of the methoxy radical at C3nu conformations, using a double zeta quality basis set that is augmented with polarization and diffuse functions. Excitation energy estimates are obtained for vertical excitation, vertical deexcitation, and system origin. The rate of methoxy photolysis is estimated to be too small to warrant its inclusion in atmospheric models.

Jackels, C. F.↗
NASA NTRS1985

Observations of the SiC2 radical toward IRC + 10216 at 1.27 centimeters

The first centimeter-wave transition of the recently identified SiC2 radical has been observed in the envelope of the evolved carbon star IRC + 10216. The excellent agreement between the measured astronomical rest frequency and the predicted frequency, and the measured line intensity support the SiC2 identification. The high-resolution line profile and mapping data are used to estimate the size of the IRC + 10216 SiC2 envelope and the abundance of SiC2 relative to H2.

Snyder, L. E.↗
NASA NTRS1985

Direct measurement of the fundamental rotational transitions of the OH radical by laser sideband spectroscopy

The direct (zero-field) spectra of the fundamental rotational transitions of the OH radical in its Omega = 3/2 and 1/2 states at 2509.9 and 1834.7 GHz are obtained using a recently developed far-infrared laser sideband spectrometer. These measurements have verified and refined the predictions of previous laser magnetic resonance work, thereby confirming the far-infrared detection of interstellar OH. The increased accuracy of these direct measurements will be useful to future astronomical and atmospheric studies of these important transitions.

Farhoomand, J.↗
NASA NTRS1985

Free radicals in the stratosphere - A new observational technique

A new approach to in situ observations of trace reactive species in the stratosphere is described. A balloon-borne system, floating 40 kilometers above the earth's surface, successfully lowered and then retracted a cluster of instruments a distance of 12 kilometers on a filament of Kevlar. This instrument cluster is capable of detecting gas-phase free radicals at the part-per-trillion level. The suspended instrument array has excellent stability and has been used to measured atomic oxygen concentrations in the stratosphere.

Anderson, J. G.↗
NASA NTRS1985

Astronomical identification of the C3H radical

The C3H radical has been identified in the millimeter-wave spectra of IRC +10216 and TMC-1. In IRC +10216, four rotational transitions have been observed, three in the lower fine-structure ladder (2Pi1/2) and one in the upper (2Pi3/2), each a resolved or partially resolved lambda-doublet. In TMC-1, both lambda components of the lowest lying 3/2-1/2 transition of the 2Pi1/2 ladder have been observed, each with well-resolved hfs. In IRC +10216, the excitation of C3H is similar to that of SiCC: the rotational temperature Trot within the 2Pi1/2 ladder is low (8.5 K), because of rapid radiative decay, while Trot across the ladders is high (about 52 K), because interconnecting far-IR radiative transitions are only weakly permitted. The column density of C3H in IRC +10216 averaged over the estimated source diameter of 84 arcsec is 2.8 x 10 to the 13th/sq cm, an order of magnitude less than that of C2H and C4H.

Thaddeus, P.↗
NASA NTRS1985

Laboratory detection of the C3H radical

Millimeter-wave lines of the C3H radical, including six of the lines observed in space, were detected in a laboratory glow discharge through a flowing mixture of C2H2, He, and CO. Each of the 10 rotational transitions measured, five between 98 and 185 GHz in the 2Pi1/2 ladder and five between 80 and 194 GHz in the 2Pi3/2 ladder, is split by lambda-type doubling, and all but three possess resolved hyperfine structure. The excellent agreement between the fine-structure, rotation, lambda-doubling, and hyperfine constants derived from the laboratory data and from the astronomical observations conclusively confirms the identifications in IRC +10216 and TMC-1 by Thaddeus and colleagues (1985). An accurate set of spectroscopic constants, which allow calculation of the entire radio spectrum of C3H to a radial velocity of 0.1 km/s, was derived from a simulataneous fit to the laboratory frequencies and to the well-resolved hfs observed in the narrow-line astronomical source TMC-1.

Gottlieb, C. A.↗
NASA NTRS1985

Cometary atmospheres: Modeling the spatial distribution of observed neutral radicals

The analysis of observed brightness profiles for the C2 radical in comets with Haser's model implies that the parent scale length varies as the square of the heliocentric distance. The use of new Haser scale lengths for C2 and CN determined under this project appears to explain the apparent drop in the C2-to-CN ratio with increasing heliocentric distance.

Combi, M. R.↗
NASA NTRS1986

Cometary atmospheres: Modeling the spatial distribution of observed neutral radicals

New data for the spatial distribution of cometary C2 are presented. A recompilation of the Haser scale lengths for C2 and CN resolves the previously held anomalous drop of the C2/CN ratio for heliocentric distances larger than 1 AU. Clues to the source of cometary C2 have been found through fitting the sunward-antisunward brightness profiles with the Monte Carlo particle-trajectory model. A source (parent) lifetime of 3.1 x 10,000 seconds is found, and an ejection speed for C2 radicals upon dissociation of the parent(s) of approx. 0.5 km 1/5 is calculated.

Combi, M. R.↗
NASA NTRS1985

Infrared and far-infrared laser magnetic resonance spectroscopy of the GeH radical - Determination of ground state parameters

The GeH radical has been detected in its ground 2 Pi state in the gas phase reaction of fluorine atoms with GeH4 by laser magnetic resonance techniques. Rotational transitions within both 2 Pi 1/2 and 2 Pi 3/2 manifolds have been observed at far-infrared wavelengths and rotational transitions between the two fine structure components have been detected at infrared wavelengths (10 microns). Signals have been observed for all five naturally occurring isotopes of germanium. Nuclear hyperfine structure for H-1 and Ge-73 has also been observed. The data for the dominant isotope (/Ge-74/H) have been fitted to within experimental error by an effective Hamiltonian to give a set of molecular parameters for the X 2 Pi state which is very nearly complete. In addition, the dipole moment of GeH in its ground state has been estimated from the relative intensities of electric and magnetic dipole transitions in the 10 micron spectrum to be 1.24(+ or - 0.10) D.

Brown, J. M.↗
NASA NTRS1986

The microwave and far-infrared spectra of the O-(18)H radical

Far-infrared laser magnetic resonance (LMR) spectroscopy was used to calculate the frequencies, wavelengths, and line strengths for transitions of O-(18)H molecules at microwave and far-infrared frequencies. In this experiment, a molecular transition frequency is tuned into coincidence with that of a fixed frequency laser by the application of a variable magnetic field. The O-(18)H radicals, detected in natural abundance (0.20 percent), were produced by the reaction of hydrogen atoms with nitrogen dioxide. These data together with microwave frequencies ascertained by Gottlieb, Redford, and Smith (1974) were used to determine the parameters of an effective Hamiltonian. Rotational levels up to J = 5.5 were involved. Results are indicated schematically and the low-lying energy levels of O-(18)H are shown. It is concluded that the frequencies of transitions between levels studied directly in the LMR experiment are reliable.

Comben, E. R.↗