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An undergraduate laboratory was developed as part of the Drugs for Neglected Diseases initiative's Open Synthesis Network. This activity aimed to develop new compounds efficacious against visceral leishmaniasis. Students successfully synthesized, purified, and characterized ten different benzoxazole amides that were sent for biological testing against several protozoan parasites. Although all the benzoxazole amides had poor activity against L. donovani, several (2, 4, and 9) showed moderate activity against T. cruzi, T. b. rhodesiense, and T. b. brucei paired with low cell cytotoxicity. This drug discovery laboratory activity made a measurable contribution to neglected tropical disease research and was an engaging and research-orientated experience for undergraduate students. Implementation of drug discovery laboratories across a range of student levels and backgrounds is highly achievable using existing laboratory equipment and a short investment in activity preparation and can be a sustainable course component.

The crystal structure of astromolecule propanal has been determined using powder X-ray diffraction (PXRD) where it is obsereved to crystallise in spacegroup P21/a, Z = 4 with a unit cell parameters a = 8.9833(6) Å, b = 4.2237(2) Å, c = 9.4733(6) Å and β = 97.508(6)°, resulting in a volume of 356.37(4) Å3 at 100 K.

Hydrogen-bonded organic frameworks (HOFs) are a promising class of porous crystalline materials for gas sorption and gas separation technologies that can be constructed under mild synthetic conditions. In forming three-dimensional networks of flexible hydrogen bonds between donor/acceptor subunits, these materials have displayed high stability at elevated temperature and under vacuum. Although the structural properties of HOFs are commonly characterized by diffraction techniques, new complimentary methods to elucidate phase behaviour and host-guest interactions at the molecular level are sought, particularly those that can be applied under changing physical conditions or solvent environment. To this end, this study has applied synchrotron far-IR and mid-IR spectroscopy to probe the properties of two known and one new HOF system assembled from tetrahedral amidinium and carboxylate building blocks. All three frameworks produce feature-rich and resolved infrared profiles from 30 to 4000 cm

The octol of a new rigid, tetraarylene-bridged cavitand was investigated for self-assembly behaviour in solution. 1H and DOSY NMR spectroscopic experiments show that the cavitand readily dimerizes through an unusual seam of interdigitated hydrogen-bonds that is resistant to disruption by polar co-solvents. The well-defined cavity encapsulates small cationic guests, but not their neutral counterparts, restricting the conformation of sequestered tetraethylammonium in solution and the solid state., A robust, dimeric capsule forms quantitatively in low-polarity solvents via a seam of 8 hydrogen bonds. The resulting electron-rich cavity selectively binds small organic cations over neutral counterparts.

As hydrogen bonded frameworks are held together by relatively weak interactions, they often form several different frameworks under slightly different synthesis conditions and respond dynamically to stimuli such as heat and vacuum. However, these dynamic restructuring processes are often poorly understood. In this work, three isoreticular hydrogen bonded organic frameworks assembled through charge-assisted amidinium⋅⋅⋅carboxylate hydrogen bonds (1

The use of well-defined synthons and rigid tectons has allowed for great advancement in the reticular synthesis of hydrogen-bonded organic frameworks. However, the use and influence of flexible tec...

A benzene/acetylene/hydrogen cyanide co-crystal has been predicted using a periodic density functional theory approach based on the empirical structure of the 1:1 benzene and acetylene co-crystal. This example of a stable ternary-phase systema three-component co-crystal comprising small neutral moleculesfinds relevance as a possible Titan aerosol composition formed by the condensation of abundant volatile photoproducts in the lower stratosphere. Calculated thermochemical data confirm the 2C6H6:C2H2:HCN co-crystal as a viable laboratory target, with free and cohesive energies competitive with those of binary-phase ices. Harmonic vibrational frequencies computed for the periodic system indicate that the co-crystal can be identified using low-frequency far-infrared or Raman spectroscopy, where distinctive intermolecular lattice signatures are predicted to lie. The geometry of the individual components within the unit cell appears optimal to promote ring-expansion chemistry upon ultraviolet or fast particle irradiation of the molecular co-crystal surface. Such co-crystal systems are unexplored in laboratory simulations of astrophysical ices and may have important implications for the solid-state formation of complex organic molecules in Titan’s atmosphere.

The crystal structure of propanal has been determined using powder X-ray diffraction (PXRD), where this common laboratory aldehyde is measured to crystallise in spacegroup

The structure and thermal expansion of the astronomical molecule propionitrile have been determined from 100 to 150 K using synchrotron powder X-ray diffraction. This temperature range correlates with the conditions of Titan's lower stratosphere, and near surface, where propionitrile is thought to accumulate and condense into pure and mixed-nitrile phases. Propionitrile was determined to crystallize in space group, Pnma (No. 62), with unit cell a = 7.56183 (16) Å, b = 6.59134 (14) Å, c = 7.23629 (14), volume = 360.675 (13) Å3 at 100 K. The thermal expansion was found to be highly anisotropic with an eightfold increase in expansion between the c and b axes. These data will prove crucial in the computational modelling of propionitrile–ice systems in outer Solar System environments, allowing us to simulate and assign vibrational peaks in the infrared spectra for future use in planetary astronomy.

Fourier transform infrared spectra of formic acid aerosol particles in situ generated in a collisional cooling cell at temperatures ranging between 90 and 210 K are recorded in the mid-infrared and THz/far-infrared regions. Infrared spectroscopic features are used to identify the formic acid dimer above 200 K, the crystalline β1 phase in the 110–200 K temperature range, and amorphous solid formic acid at ∼90 K. Density functional calculations of discrete clusters and the full periodic β1 crystalline structure help to assign the low wavenumber intermolecular modes by comparison with experimental far IR and Raman data from the literature. Refractive indices of the formic acid crystal in the mid-IR range are retrieved. These data are essential for radiative transfer modeling of solid formic acid condensed in the terrestrial atmosphere. THz/far IR spectra, in addition to the well documented mid-infrared spectra, may be useful for the identification of solid formic acid in astrophysical environments such as th...

Acetonitrile (CH3CN) and water (H2O) ice particles were generated within a collisional cooling cell coupled to the Australian Synchrotron light source. The evolution of the aerosols was tracked by infrared spectroscopy compiled over the 4000–50 cm–1 region. Gas pressure and temperature conditions were varied to replicate the lower altitudes of the Titan atmosphere allowing for comparison to far-infrared features detected by the Cassini–Huygens spacecraft. The experimental spectra show that CH3CN and H2O particles are microheterogeneous in composition and spherical in shape. CH3CN lattice bands display temperature-dependent shifts in frequency, implying that pure β-phase is present in the mixed particles. In addition, a red shift identified for the C≡N fundamental stretching mode indicates dipole–dipole and π-electron side-directed hydrogen bond coupling between segregated CH3CN and H2O phases exclusively at the grain interface. Discrete dipole approximation theory was implemented to evaluate various clust...

This combined laboratory and theoretical investigation focussed on a suite of crystalline phenethylamine-class molecules of forensic interest: amphetamine sulfate, levo- and dextro-methamphetamine hydrochloride, 3,4-methyl​enedioxy-methamphetamine (MDMA) hydrochloride, 3,4-methylenedioxy-​amphetamine (MDA) hydrochloride, and the hydrochloride salts of two substituted (4-fluoro and 4-methyl) methcathinones. Far-infrared (far-IR) spectra across the 30–600 cm−1 wavenumber range were recorded at the Australian Synchrotron light source. Resolved absorption profiles enabled vibrational features to be assigned via comparison to periodic density functional theory (p-DFT) performed at the B3LYP-D3/6-311 G(d) level. The calculations accurately reproduce the experimental spectra (frequencies and peak intensities) for ordered molecular crystal-type samples, such as methamphetamine stereoisomers and two substituted methcathinones. Significant band broadening for amphetamine sulfate was observed, likely due to crystal disorder, while MDMA and MDA showed convolved stretching modes from comparatively impure samples. For all seven molecular crystals investigated, previously unpublished peak assignments and relative band intensities have now been systematically compiled; completing the spectral region that lies between the more thoroughly studied terahertz and mid-IR regions. These results can be incorporated in spectral libraries and databases to enable far-IR statistical analyses to be performed on forensic samples of mixed or impure compounds.

Synchrotron far-infrared (far-IR) spectra were measured for a representative set of pharmaceutical-type molecular crystals: phenylethylamine hydrochloride salt, ephedrine base and its hydrochloride salt, and pseudoephedrine base and its hydrochloride salt. Resolved spectral profiles in the 30–600 cm−1 range allowed for comparison of absorption bands to simulated spectra obtained by periodic density function theory (DFT) code. The B3LYP-D3/6-311G(d) level of theory returned highly accurate predictions of the experimental far-IR spectra for well-ordered crystalline samples, including an agreement between relative peak intensities almost unprecedented for organic crystal systems of this size. Simulated far-IR spectra for the phenylethylamine hydrochloride and ephedrine base samples do not match to the same degree; potentially due to higher disorder within the solid-state. These comparisons to theory generally allowed for confident assignment of prominent absorption bands to low-lying vibrational modes. The experimental spectra (including those for related illicit drug compounds: amphetamine sulphate, methamphetamine hydrochloride, MDA hydrochloride, and MDMA hydrochloride), peak assignments, and relative band intensities are compiled and evaluated for their inclusion in spectral libraries and their application to chemometric analysis for mixed compounds of pharmaceutical and forensic interest.

Future spacecraft missions to planetary systems, Trans-Neptunian objects, and cometary bodies could implement far-infrared surveys to confirm the presence of condensed-phase species via their unique lattice features. For composite molecular ices of astrophysical significance, laboratory reference spectra are required to provide absorption coefficients used to quantify solid-state abundances. However, due to strong intermolecular interactions in polar ice systems, laboratory data of mixed-phase ices are difficult to interpret. In this study we have applied periodic density functional theory code to model bulk molecular crystals. This method allows for more accurate simulation of thin-film spectra than approaches simulating small clusters. For this proof-of-principle study on a series of pure nitrile ices of planetary interest, our simulated far-infrared spectra show excellent agreement to data from thin film studies performed at the Australian Synchrotron (crystalline acetonitrile and propionitrile) and to previously published spectra (hydrogen cyanide, acrylonitrile, cyanoacetylene, and cyanogen). The combined theoretical and experimental approach has provided a new explanation for the asymmetric profile of the hydrogen cyanide lattice feature and a more systematic assignment of nitrile ice absorption bands to low-frequency lattice modes. We nominate prominent absorption features for the detection of crystalline nitrile carriers located on planetary surfaces.

Experiments designed to simulate the low temperature surface chemistry occurring in interstellar clouds provide clear evidence of a reaction between oxygen atoms and propyne ice. The reactants are dosed onto a surface held at a fixed temperature between 14 and 100 K. After the dosing period, temperature programmed desorption (TPD), coupled with time-of-flight mass spectrometry, are used to identify two reaction products with molecular formulae C3H4O and C3H4O2. These products result from the addition of a single oxygen atom, or two oxygen atoms, to a propyne reactant. A simple model has been used to extract kinetic data from the measured yield of the single-addition (C3H4O) product at surface temperatures from 30–100 K. This modelling reveals that the barrier of the solid-state reaction between propyne and a single oxygen atom (160 ± 10 K) is an order of magnitude less than that reported for the gas-phase reaction. In addition, estimates for the desorption energy of propyne and reaction rate coefficient, as a function of temperature, are determined for the single addition process from the modelling. The yield of the single addition product falls as the surface temperature decreases from 50 K to 30K, but rises again as the surface temperature falls below 30 K. This increase in the rate of reaction at low surface temperatures is indicative of an alternative, perhaps barrierless, pathway to the single addition product which is only important at low surface temperatures. The kinetic model has been further developed to characterize the double addition reaction, which appears to involve the addition of a second oxygen atom to C3H4O. This modelling indicates that this second addition is a barrierless process. The kinetic parameters we extract from our experiments indicate that the reaction between atomic oxygen and propyne could occur under on interstellar dust grains on an astrophysical time scale.

Four prominent features of Titan's haze are found within the '3.4-' absorption to be uniform with recent vertically resolved Cassini/VIMS spectra. These are absorptions at 2998 (3.34 ), 2968 (3.37 ), 2927 (3.42 ), and 2882 (3.47 ). A detailed fitting suggests that the 2998 feature could originate from amorphous acetonitrile () carrying about 25% of integrated optical depth; the remaining features, which account for 75% of the integrated optical depth, could arise from a distinct triplet (C-H stretching) structure of radiolyzed hydrocarbons. An additional feature was possibly evidenced at altitudes higher than 300 km and attributable to 'polymer-capped' methane (), significantly constraining the chemical composition of organic haze layers under Titan's active radiation field.

Pure, crystalline acetonitrile (CH3CN) and propionitrile (CH3CH2CN) particles were formed in a collisional cooling cell allowing for infrared (IR) signatures to be compiled from 50 to 5000 cm-1. The cell temperature and pressure conditions were controlled to simulate Titan's lower atmosphere (80-130 K and 1-100 mbar), allowing for the comparison of laboratory data to the spectra obtained from the Cassini-Huygens mission. The far-IR features confirmed the morphology of CH3CN aerosols as the metastable β-phase (monoclinic) ice, however, a specific crystalline phase for CH3CH2CN could not be verified. Mie theory and the literature complex refractive indices enabled of the experimental spectra to be modelled. The procedure yielded size distributions for CH3CN (55-140 nm) and CH3CH2CN (140-160 nm) particles. Effective kinetic profiles, tracing the evolution of aerosol band intensities, showed that condensation of CH3CH2CN proceeded at twice the rate of CH3CN aerosols. In addition, the rate of CH3CH2CN aerosol depletion via lateral diffusion of the particles from the interrogation volume was approximately 50% faster than that of CH3CN. The far-IR spectra recorded for both nitrile aerosols did not display absorption profiles that could be attributed to the unassigned 220 cm-1 feature, which has been observed to fluctuate seasonally in the spectra obtained from Titan's atmosphere.

Optical constants are important properties governing the response of a material to incident light. It follows that they are often extracted from spectra measured by absorbance, transmittance or reflectance. One convenient method to obtain optical constants is by curve fitting. Here, model curves should satisfy Kramer-Kronig relations, and preferably can be expressed in closed form or easily calculable. In this study we use dielectric constants of three different molecular ices in the infrared region to evaluate four different model curves that are generally used for fitting optical constants: (1) the classical damped harmonic oscillator, (2) Voigt line shape, (3) Fourier series, and (4) the Triangular basis. Among these, only the classical damped harmonic oscillator model strictly satisfies the Kramer-Kronig relation. If considering the trade-off between accuracy and speed, Fourier series fitting is the best option when spectral bands are broad while for narrow peaks the classical damped harmonic oscillator and the Triangular basis fitting model are the best choice.

In this article, we first explored the chemical dynamics of simple diatomic radicals (dicarbon, methylidyne) utilizing the crossed molecular beams method. This versatile experimental technique can be applied to study reactions relevant to the atmospheres of planets and their moons as long as intense and stable supersonic beam sources of the reactant species exist. By focusing on reactions of dicarbon with hydrogen cyanide, we untangled the contribution of dicarbon in its singlet ground and first excited triplet states. These results were applied to understand and re-analyze the data of crossed beam reactions of the isoelectronic dicarbon plus acetylene reaction. Further, we investigated the interaction of ionizing radiation in form of energetic electrons with organic molecules ethane and propane sequestered on Titan’s surface. These experiments presented compelling evidence that even at irradiation exposures equivalent to about 44 years on Titan’s surface, aliphatic like organic residues can be produced on Titan’s surface with thicknesses up to 1.5 m. Finally, we investigated how Titan’s nascent chemical inventory can be altered by an external influx of matter as supplied by (micro)meteorites and possibly comets. For this, we simulated the ablation process in Titan’s atmosphere, which can lead to ground and electronically excited atoms of, for instance, the principal constituents of silicates like iron, silicon, and magnesium, in laboratory experiments. By ablating silicon species and seeding the ablated species in acetylene carrier gas, which also acts as a reactant, we produced organo silicon species, which were then photoionized utilizing tunable VUV radiation from the Advanced Light Source. In combination with electronic structure calculations, the structures and ionization energies of distinct organo-silicon species were elucidated.

Mechanisms for the electron-induced degradation of poly(methyl methacrylate) (PMMA) and Kapton polyimide (PMDA-ODA), both of which are commonly used in aerospace applications, were examined over a temperature range of 10 K to 300 K under ultra high vacuum (∼10(-11) Torr). The experiments were designed to simulate the interaction between the polymer materials and secondary electrons produced by interaction with galactic cosmic ray particles in the near-Earth space environment. Chemical alterations of the samples were monitored on line and in situ by Fourier-transform infrared spectroscopy and mass spectrometry during irradiation with 5 keV electrons and also prior and after the irradiation exposure via UV-vis. The irradiation-induced degradation of PMMA resulted in the formation and unimolecular decomposition of methyl carboxylate radicals (CH(3)OCO) forming carbon monoxide (k = 4.60 × 10(-3) s(-1)) and carbon dioxide (k = 1.29 × 10(-3) s(-1)). Temperature dependent gas-phase abundances for carbon monoxide, carbon dioxide, and molecular hydrogen were also obtained for the PMMA and Kapton samples. The lower gas yields detected for irradiated Kapton were typically one or two orders of magnitude less than PMMA suggesting a higher degradation resistance to energetic electrons. In addition, UV-vis spectroscopy revealed the propagation of conjugated bonds induced by the irradiation of PMMA and indicated a decrease in the optical band gap by an increase in absorbance above 500 nm in irradiated Kapton.

Carbon dioxide (CO2) ices were irradiated with energetic D + ions to simulate the exposure of oxygen-bearing solar system ices to energetic protons from the solar wind and magnetospheric sources. The formation of species was observed online and in situ by exploiting FTIR spectroscopy. Molecular products include ozone (O3), carbon oxides (CO3(C2v, D3h), CO4 ,C O 5 ,C O 6), D2-water (D2O), and D2-carbonic acid (D2CO3). Species released into the gas phase were sampled via a quadrupole mass spectrometer, and possible minor contributions from D2-formaldehyde (D2CO), D4-methanol (CD3OD), and D2-formic acid (DCOOD) were additionally identified. The feasibility of several reaction networks was investigated by determining their ability to fit the observed temporal column densities of 10 key species that were quantified during the irradiation period. Directly relevant to the CO2-bearing ices of comets, icy satellites in the outer solar system, and the ice caps on Mars, this work illustrates for the first time that D2-water is formed as a product of the exposure of CO2 ices to D + ions. These findings provide strong support for water formation from oxygen-bearing materials via non-thermal hydrogen atoms, and predict reaction pathways that are likely to be unfolding on the surfaces of asteroids and the Moon.

The water amidogen radical complex (H(2)O-NH(2)) is a reactive intermediate in the atmospheric oxidation of ammonia by a hydroxyl radical. In the present study, we identify for the first time the H(2)O-NH(2) complex using matrix isolation infrared spectroscopy. We corroborate our experimental findings with high level coupled cluster ab initio calculations.

The formation of water (H2O) in the interstellar medium is intrinsically linked to grain-surface chemistry; thought to involve reactions between atomic (or molecular) hydrogen with atomic oxygen (O), molecular oxygen (O2), and ozone (O3). Laboratory precedent suggests that H2O is produced efficiently when O2 ices are exposed to H atoms (~100 K). This leads to the sequential generation of the hydroxyperoxyl radical (HO2), then hydrogen peroxide (H2O2), and finally H2O and a hydroxyl radical (OH); despite a barrier of ~2300 K for the last step. Recent detection of the four involved species toward ρ Oph A supports this general scenario; however, the precise formation mechanism remains undetermined. Here, solid O2 ice held at 12 K is exposed to a monoenergetic beam of 5 keV D+ ions. Products formed during the irradiation period are monitored through FTIR spectroscopy. O3 is observed through seven archetypal absorptions. Three additional bands found at 2583, 2707, and 1195 cm –1 correspond to matrix isolated DO2 (ν1) and D2O2 (ν1, ν5), and D2O (ν2), respectively. During subsequent warming, the O2 ice sublimates, revealing a broad band at 2472 cm–1 characteristic of amorphous D2O (ν1, ν3). Sublimating D2, D2O, D2O2, and O3 products were confirmed through their subsequent detection via quadrupole mass spectrometry. Reaction schemes based on both thermally accessible and suprathermally induced chemistries were developed to fit the observed temporal profiles are used to elucidate possible reaction pathways for the formation of D2-water. Several alternative schemes to the hydrogenation pathway (O2→HO2→H2O2→H2O) were identified; their astrophysical implications are briefly discussed.

Mimicking the bombardment of icy surfaces with heavy ions from solar system radiation fields, solid-phase molecular oxygen (32O2) and its isotope labeled analogue (36O2) were irradiated with monoenergetic carbon (C+), nitrogen (N+), and oxygen (O+) ions in laboratory experiments simulating the interaction of ions from the solar wind and those abundant in planetary magnetospheres. Online Fourier-transform infrared spectroscopy of the irradiated oxygen ices (12?K) showed that the yields of molecular ozone monomer (O3 ~ 2 ? 10?3 molecules eV?1 in 32O2) were independent of the mass of the implanted C+, N+, and O+ ions (?max?= 4.0?? 1014 ions cm?2). The production of oxygen atoms in the solid was observed in the mid-IR stabilized via the [O3...O] van der Waals complex. We expand on this inference by comparing the ozone yields induced by light particles (e ?, H+, and He+) to the heavy ions (C+, N+, and O+) to provide compelling evidence that the abundance of radiolytic products in an oxygen-bearing solid is primarily dependent on electronic stopping regimes, which supersedes the contribution of nuclear stopping processes irrespective of the mass of the particle irradiation in the kinetic energy regime of solar wind and magnetospheric particles.

Solid methane (CH(4)), ethane (C(2)H(6)), and ethylene (C(2)H(4)) ices (thickness: 120 ± 40 nm; 10 K), as well as high-density polyethylene (HDPE: [C(2)H(4)](n)) films (thickness: 130 ± 20 nm; 10, 100, and 300 K), were irradiated with mono-energetic oxygen ions (Φ ~ 6 × 10(15) cm(-2)) of a kinetic energy of 5 keV to simulate the exposure of Solar System hydrocarbon ices and aerospace polymers to oxygen ions sourced from the solar wind and planetary magnetospheres. On-line Fourier-transform infrared spectroscopy (FTIR) was used to identify the following O(+) induced reaction pathways in the solid-state: (i) ethane formation from methane ice via recombination of methyl (CH(3)) radicals, (ii) ethane conversion back to methane via methylene (CH(2)) retro-insertion, (iii) ethane decomposing to acetylene via ethylene through successive hydrogen elimination steps, and (iv) ethylene conversion to acetylene via hydrogen elimination. No changes were observed in the irradiated PE samples via infrared spectroscopy. In addition, mass spectrometry detected small abundances of methanol (CH(3)OH) sublimed from the irradiated methane and ethane condensates during controlled heating. The detection of methanol suggests an implantation and neutralization of the oxygen ions within the surface where atomic oxygen (O) then undergoes insertion into a C-H bond of methane. Atomic hydrogen (H) recombination in forming molecular hydrogen and recombination of implanted oxygen atoms to molecular oxygen (O(2)) are also inferred to proceed at high cross-sections. A comparison of the reaction rates and product yields to those obtained from experiments involving 5 keV electrons, suggests that the chemical alteration of the hydrocarbon ice samples is driven primarily by electronic stopping interactions and to a lesser extent by nuclear interactions.

The irradiation of pure molecular oxygen (O(2)) and carbon dioxide (CO(2)) ices with 5 keV H(+) and He(+) ions was investigated experimentally to simulate the chemical processing of oxygen rich planetary and interstellar surfaces by exposure to galactic cosmic ray (GCR), solar wind, and magnetospheric particles. Deposited at 12 K under ultra-high vacuum conditions (UHV), the irradiated condensates were monitored on-line and in situ in the solid-state by Fourier transform infrared spectroscopy (FTIR), revealing the formation of ozone (O(3)) in irradiated oxygen ice; and ozone, carbon monoxide (CO), and cyclic carbon trioxide (c-CO(3)) in irradiated carbon dioxide. In addition to these irradiation products, evolution of gas-phase molecular hydrogen (H(2)), atomic helium (He) and molecular oxygen (O(2)) were identified in the subliming oxygen and carbon dioxide condensates by quadrupole mass spectrometry (QMS). Temporal abundances of the oxygen and carbon dioxide precursors and the observed molecular products were compiled over the irradiation period to develop reaction schemes unfolding in the ices. These reactions were observed to be dependent on the generation of atomic oxygen (O) by the homolytic dissociation of molecular oxygen induced by electronic, S(e), and nuclear, S(n), interaction with the impinging ions. In addition, the destruction of the ozone and carbon trioxide products back to the molecular oxygen and carbon dioxide precursors was promoted over an extended period of ion bombardment. Finally, destruction and formation yields were calculated and compared between irradiation sources (including 5 keV electrons) which showed a surprising correlation between the molecular yields (∼10(-3)-10(-4) molecules eV(-1)) created by H(+) and He(+) impacts. However, energy transfer by isoenergetic, fast electrons typically generated ten times more product molecules per electron volt (∼10(-2)-10(-3) molecules eV(-1)) than exposure to the ions. Implications of these findings to Solar System chemistry are also discussed.

Mechanisms of the electron-induced degradation of three polymers utilized in aerospace applications (polyethylene (PE), polytetrafluoroethylene (PTFE), and polystyrene (PS)) were examined over a temperature range of 10 K to 300 K at ultra high vacuum conditions (∼10(-11) Torr). These processes simulate the interaction of secondary electrons generated in the track of galactic cosmic ray particles in the near-Earth space environment with polymer material. The chemical alterations at the macromolecular level were monitored on-line and in situ by Fourier-transform infrared spectroscopy and mass spectrometry. These data yielded important information on the temperature dependent kinetics on the formation of, for instance, trans-vinylene groups (-CH=CH-) in PE, benzene (C(6)H(6)) production in PS, fluorinated trans-vinylene (-CF=CF-) and terminal vinyl (-CF=CF(2)) groups in PTFE together with molecular hydrogen release in PE and PS. Additional data on the radiation-induced development of unsaturated, conjugated bonds were collected via UV-vis spectroscopy. Temperature dependent G-values for trans-vinylene formation (G(-CH=CH-) ≈ 25-2.5 × 10(-4) units (100 eV)(-1) from 10-300 K) and molecular hydrogen evolution (G(H(2)) ≈ 8-80 × 10(-5) molecules (100 eV)(-1) from 10-300 K) for irradiated PE were calculated to quantify the degree of polymer degradation following electron irradiation. These values are typically two to three orders of magnitude less than G-values previously published for the irradiation of polymers with energetic particles of higher mass.