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NASA NTRS1973

Chemical evolution of cosmic clouds

Reaction rate characteristics of interstellar matter were studied by the reaction of hydrogen cyanide and molecular hydrogen at about 1000 K at an HCN to H2 ratio of 1 to 100 to simulate the large excess of cosmic hydrogen. It was found that HCN decays with a half life of about 20 hours and that a large surface increases the reaction rate as a function of temperature. Reaction rates may be considerable increased by energetic processes that produce free radicals and ions.

Down, B. D.↗
NASA NTRS1975

Photosynthesis of organic compounds in the atmosphere of Jupiter

An efficient conversion of CH4 to hydrocarbons and HCN takes place when NH3 is photolysed in the presence of CH4, H2, and He using a 184.9 nm light source. The extent of NH3 decomposition after a 1 hr exposure was determined spectrophotometrically; CH4, N2, and C2 and C3 hydrocarbons were detected and analyzed by mass spectrometry. Photolysis of one molar equivalent of NH3 results in the loss of 0.84 molar equivalent of CH4, which apparently reacts with hot hydrogen atoms produced by photolysis. The 8% of the NH3 which is not converted to N2 probably is converted to organic amines and nitrile derivatives. The results indicate that NH3 photolysis is a highly probable mechanism for the conversion of methane to more complex hydrocarbons in the upper atmosphere of Jupiter, and predict the occurrence of HCN, NH2NH2, and higher hydrocarbons in the Jovian atmosphere above the NH3 clouds.

Ferris, J. P.↗
NASA NTRS1976

Formation of amino acids by cobalt-60 irradiation of hydrogen cyanide solutions

Experiments were conducted to study the pathway for the prebiotic origin of amino acids from hydrogen cyanide (HCN) under the action of ionizing radiation considered as an effective source of energy on the primitive earth. The irradiations were performed in a cobalt-60 source with a dose rate of 200,000 rad/hr. Seven naturally occurring amino acids are identified among the products formed by the hydrolysis of gamma-irradiated solutions of HCN: glycine, alanine, valine, serine, threonine, aspartic acid, and glutamic acid. The identity of these amino acids is established by gas chromatography and mass spectrometry. Control experiments provided evidence that the amino acids are not the result of contamination.

Sweeney, M. A.↗
NASA NTRS1977

A review of available LC/50/ data

Several gaseous products of pyrolysis and combustion have been evaluated for LC/50/, defined as the concentration of toxic gas in the atmosphere being inhaled by test animals that will produce death in 50% of the animals within a given time period. The products tested included CO, HCl, HF, HCN, NO2, and SO2. It was found that HCN and NO2 were consistently the most toxic of the gases reviewed, and that mice were more susceptible than rats to HCl and HF, although less susceptible than rats to NO2. Extrapolation of LC/50/ data to humans indicates that metabolic rate may be a valid basis for extrapolation when the toxicity mechanism is interference with oxygen transport and utilization, or pulmonary edema, but not when it is irritation and damage to the upper respiratory tract.

Hilado, C. J.↗
NASA NTRS1978

C3 and infrared spectrophotometry of Y Canum Venaticorum

The 1.2- to 5.6-micron spectrum of the carbon star Y CVn is presented and discussed. The observations were made from the Kuiper Airborne Observatory at an altitude of 12.5 km, thereby avoiding most of the absorption due to terrestrial water vapor. Comparison of Y CVn near 5 microns with laboratory spectra provides possible evidence for the presence of the linear triatomic molecule C3. For the first time in a carbon star the clearly formed band heads of the CN red system between 1.2 and 2.3 microns are observed. Corroborative evidence for the presence of the molecules HCN and C2H2 is presented, and the relative contributions of C3, HCN, and C2H2 to the 3.1-micron absorption band are discussed. Spectra of two other carbon stars, TX Psc and S Cep, are presented for comparison.

Goebel, J. H.↗
NASA NTRS1980

Ion chemistry in interstellar space

The temperature dependence of the bimolecular reactions of Cl(+), HCl(+), CH(+), CH2(+), N(+), NH(+), and NH2(+) reacting with H2 have been investigated. For Cl(+) and HCl(+) rate constants have been determined over the temperature range of 150 to 400 K. Preliminary data have been obtained for the other systems. The Cl(+)/H2 system shows a weak, but significant positive temperature dependence that could be important in interstellar modeling studies. The HCl(+)/H2 system shows a substantial negative temperature dependence with the rate constant approaching the collision rate at low temperatures. The association reaction CH3(+) + HCN yields CH3 HCN(+) has been theoretically modeled using statistical phase space theory. Both radiative and collisional stabilization have been included. The results are compared with experiment with good agreement obtained over wide variations in T and p. This system is potentially important in the mechanism of large molecule synthesis in interstellar space.

Bowers, M. T.↗
NASA NTRS1980

Molecular line observations of AFGL sources

HCN and (with three exceptions) CH emission lines have been detected from 14 molecular clouds associated with AFGL sources and/or Sharpless regions. Eleven are molecular cloud-H II region complexes. The remaining three appear to be similar (perhaps younger) objects; they are strong in the far infrared, but have no visible H II regions. Enhancement of the lower satellite transition of CH is seen in most cases. CH was also detected in association with the Herbig B8-A2e star V380 Ori. This emission was the most intense of all the CH detections. An effort was made to find a maser transition for a carbon-bearing molecule in late-type stars. A search was made for rotational transitions in the HCN bending mode (first overtone at 89.1 GHz) and stretching mode (fundamental at 88.0 GHz) as well as the CH ground state lambda-doublet in carbon stars.

Dinger, A. S. C.↗
NASA NTRS1980

An ICR study of ion-molecule reactions in the C2H2/HCN system

Using the ICR technique, rate constants are obtained for the reaction of C2H2(+) with HCN and of HCN(+) with C2H2. They are, respectively, 3.6 x 10 to the -10 cu cm/molecule-s and 6.9 x 10 to the -10 cu cm/molecule-s. Discrepancies between these results and other measurements of the first reaction are discussed. The relevance of this reaction to the formation of HC3N in interstellar clouds is considered.

Mcewan, M. J.↗
NASA NTRS1980

An ICR study of an association reaction at low pressure

The reactions of the gaseous ion CH3+ with HCN are investigated, using the ion cyclotron resonance technique. The pressure range of the experiment was 1 x 10 to the -6 to 3 x 10 to the -4 Torr with a rate coefficient of 2 x 10 to the -10 cu cm/sec. Good agreement was found between rate coefficients determined in the trapping mode at the low end of the pressure range and the drift mode at the high end of the pressure range. It is shown that the association reaction of CH3 with HCN follows second order kinetics throughout the entire pressure range of the experiment. The reaction is interpreted in terms of both a saturated three-body and a radiative association mechanism. Some explanations for the disagreement of the rate coefficient with that reported previously are also given.

Mcewan, M. J.↗
NASA NTRS1982

Chemical evolution. XL - Clay-mediated oxidation of diaminomaleonitrile

The inhibition of the oligomerization of HCN by montmorillonite clays is shown to be caused by oxidation of diaminomaleonitrile (DAMN) by ferric ion in the clay lattice, with ferrous ion and oxalic acid the reaction products. It is demonstrated that diiminosuccinonitrile is the initial reaction product and is rapidly hydrolized to oxalic acid and HCN. The same oxidative transformations are effected by ferric ion bound to Dowex 50, ferric ion in solution, and Ni(NH3)6(2+). The rate of reaction of DAMN indicates no catalytic role for the clay in the oxidation of DAMN, and little reaction of the latter was observed with montmorillonite in which the bulk of the iron was in the divalent state. The possible significance of these redox reactions to chemical evolution is discussed.

Ferris, J. P.↗
NASA NTRS1983

Galactic cosmic rays and N2 dissociation on Titan

The electromagnetic and particle cascade resulting from the absorption of galactic cosmic rays in the atmosphere of Titan is shown to be an important mechanism for driving the photochemistry at pressures of 1 to 50 mbar in the atmosphere. In particular, the cosmic ray cascade dissociates N2, a process necessary for the synthesis of nitrogen organics such as HCN. The important interactions of the cosmic ray cascade with the atmosphere are discussed. The N2 excitation and dissociation rates and the ionization rates of the principal atmospheric consituents are computed for a Titan model atmosphere that is consistent with Voyager 1 observations. It is suggested that HCN may be formed efficiently in the lower atmosphere through the photodissociation of methylamine. It is also argued that models of nitrogen and hydrocarbon photochemistry in the lower atmosphere of Titan should include the absorption of galactic cosmic rays as an important energy source.

Capone, L. A.↗
NASA NTRS1984

Carbon and energy yields in prebiotic syntheses using atmospheres containing CH4, CO and CO2

Yields based on carbon are usually reported in prebiotic experiments, while energy yields (moles/cal) are more useful in estimating the yields of products that would have been obtained from the primitive atmosphere of the earth. Energy yields for the synthesis of HCN and H2CO from a spark discharge were determined for various mixtures of CH4, CO, CO2, H2, H2O, N2 an NH3. The maximum yields of HCN and H2CO from CH4, CO, and CO2 as carbon sources are about 4 x 10 to the -8th moles/cal.

Miller, S. L.↗
NASA NTRS1984

Laser measurements of the effects of vibrational energy on the reactions of CN

Pulsed laser photolysis of C2N2 at 193 nm has been used as a source of CN radicals in both the v-double-prime = 0 and v-double-prime = 1 levels. Individual rovibronic levels of these radicals were measured as a function of time with a tunable dye laser. From these measurements the rate constants for the reaction of each of these vibrational levels with H2, O2, CO, CO2, N2, HCN, C2N2, and CH4 have been determined. Some enhancement in the rate constant with vibrational energy which could not be ascribed to quenching was observed for O2, CH4, and H2. Only vibrational quenching was observed for HCN, N2, CO2, CO and C2N2. In the CO case the vibrational quenching rate appears to be significantly enhanced by complex formation during the quenching process.

Sayah, N.↗
NASA NTRS1985

The molecular core associated with DR 21

DR 21 has been observed in the J = 1-0 line of HCN with a resolution of 12.5 by 15.5 arcsec using the mm-wave interferometer at the Hat Creek Observatory. The HCN line is seen in both emission and absorption as an isolated clump immediately adjacent to the compact H II regions of DR 21. The full extent of the clump is about 30 arcsec in R.A. and 60 arcsec in decl. which corresponds to 0.3 by 0.6 pc for an assumed distance of 2 kpc. The mass of the clump is estimated to be about 200 solar masses. Two velocity components are present: the more intense one at -5 km/s is only seen in emission, and the other at -2.4 km/s is seen in emission in the northwest and mostly in absorption against the continuum source. The component at -5.0 km/s is identified to have higher excitation, and the one at -2.4 km/s to have greater column density.

Dickel, H. R.↗
NASA NTRS1984

Prebiotic syntheses of purines and pyrimidines

The results of experimental and theoretical investigations of the prebiotic synthesis of purines and pyramidines are surveyed. Topics examined include the synthesis of purines from HCN via 4,5-disubstituted imidazole derivatives in aqueous solutions or liquid NH3, simultaneous formation of amino acids and purines by electron irradiation of CH4-NH3-H2O mixtures, synthesis of pyrimadines from cynoacetylene, energetics, formation of bases under anhydrous or concentrated conditions, formation of bases under dilute conditions, Fischer-Tropsch-type reactions, and the role of activated intermediates. It is pointed out that the precursor compounds have been detected in the interstellar medium, on Titan, and in other solar-system bodies, and that solar-nebula HCN concentrations of the order of 1-10 mM have been estimated on the basis of meteorite measurements.

Basile, B.↗
NASA NTRS1986

Energy yields in the prebiotic synthesis of hydrogen cyanide and formaldehyde

Prebiotic experiments are usually reported in terms of carbon yields, i.e., the yield of product based on the total carbon in the system. These experiments usually involve a large input of energy and are designed to maximize the yields of product. However, large inputs of energy result in multiple activation of the reactants and products. A more realistic prebiotic experiment is to remove the products of the activation step so they are not exposed a second time to the energy source. This is equivalent to transporting the products synthesized in the primitive atmosphere to the ocean, and thereby protecting them from destruction by atmospheric energy sources. Experiments of this type, using lower inputs of energy, give energy yields (moles of products/joule) which can be used to estimate the relative importance of the different energy sources on the primitive earth. Simulated prebiotic atmospheres containing either CH4, CO or CO2 with N2, H2O and variable amounts of H2 were subjected to a high frequency Tesla coil. Samples of the aqueous phase were taken at various time intervals from 1 hr to 7 days, and the energy yields were obtained by extrapolation to zero time. The samples were analyzed for HCN with the cyanide electrode and for H2CO by chromotropic acid. The spark energy was estimated by calorimetry. The temperature rise in an insulated discharge flask was compared with the temperature rise from a resistance heater in the same flask. These results will be compared with calculated production rates of HCN and H2CO from lightning and a number of photochemical processes on the primitive Earth.

Stribling, R.↗
NASA NTRS1986

Radiative transfer in planetary atmospheres

The research effort was concentrated toward comet P/Halley, although observations of other comets including Giacobini-Zinner, Hartley-Good and Thiele were made as opportunities arise. In preparing for the apparition of P/Halley, detailed predictions for the emission in the 18 cm OH transitions were made in order to assist observers and to indicate what type of data would be particularly valuable. Likewise, since occultations by the comet of background radio sources can provide unique types of information, the tracks of P/Halley and P/Giacobini-Zinner were surveyed with the NRAO Very Large Array, background sources were mapped, and a catalogue of occulted sources published. Beginning in September, 1985, regular observations of the 18 cm OH lines have been made for P/Halley using the 43 m antenna of the NRAO in Greenbank, West Virginia. These data promise to provide the most accurate time sequence for the OH emission for any comet ever obtained at radio wavelengths. From the linewidth and shape, information is obtained on the kinetics of the gas in the cometary coma. An extensive series of observations have been undertaken with 14 m antenna to study emission from the HCN molecule in P/Halley. These data provide the first definitive detection of this component of the cometary ices. Interesting variations in the production of HCN were observed with time scales less than a day. Likewise, there appeared to be variations in the ratio of the hyperfine components of the J = 1-0 transition.

Irvine, W. M.↗
NASA NTRS1986

MM and subMM molecular line observations of the southwest lobe of L1551: Evidence of a shell structure

Observations have been made of the southwest outflow lobe of L1551 in several millimeter and submillimeter molecular lines. Maps have been made in the J=3-2 and J=2-1 transitions of CO over areas of 7.5 by 2.5 arc minutes and 5 by 5 arc minutes respectively at UKIRT. More detailed maps have also been made in the J=2-1 CO transition over an area of about 6 by 3.5 arc minutes at the NRAO 12m telescope. Additional observations of the J=4-3 transitions of HCN, HCO(+) abd H(13)CO(+) were made at selected positions. The HC(+) J=4-3 transition was detected at several positions along the outflow axis and at the position of IRS 5. Similarly the HCN J=4-3 transition was detected at the position of IRS 5 and also at a position close to HH29. However, the J=4-3 transition of H(13)CO(+) was bit detected at the position of IRS 5 even through it was observed at the position close to HH29 with a peak corrected antenna temperature of 0.23K at a V(LSR) of 1 km s(-1). The detection of the J=4-3 transitions of both HCO(+) and H(13)CO(+) close to the position of HH29 suggest the presence of very dense gas in this region. LVG analysis of the various molecular lines observed give a kinetic temperature between 10 and 15K and a density from 10(5) to 10(6) cm(-3) at the position of IRS 5 at the ambient cloud velocity. At the position close to HH29 LVG analysis of the CO observations gives a density between 10(3) and 10(4) cm(-3) at a kinetic temperature of 25k for a V(LSR) of 0 km s(-1). To the southwest of HH29 there is a large decrease in both the linewidth and intensity of CO emission. This may be due to the interaction between the outflow and a dense clump of gas which gives rise to HH29. The maps of the CO J=3-2 and CO J=2-1 emission integrated in 3.25 km s intervals show the shell structure postulated by Snell and Schloerb (1985).

Rainey, R.↗