Threefold Differential Electron-Stimulated Desorption Yields of D- Anions from Multilayer Films of D2O and ND3 Condensed on Platinum

Electron-induced hydroamination of ethane as compared to ethene: implications for the reaction mechanism

The properties of carbonaceous materials with respect to various applications are enhanced by incorporation of nitrogen-containing moieties like, for instance, amino groups. Therefore, processes that allow the introduction of such functional groups into hydrocarbon compounds are of utmost interest. Previous studies have demonstrated that hydroamination reactions which couple amines to unsaturated sites within hydrocarbon molecules do not only proceed in the presence of suitably tailored catalysts but can also be induced and controlled by electron irradiation. However, studies on electron-induced hydroaminations so far were guided by the hypothesis that unsaturated hydrocarbons are required for the reaction while the reaction would be much less efficient in the case of saturated hydrocarbons. The present work evaluates the validity of this hypothesis by post-irradiation thermal desorption experiments that monitor the electron energy-dependent yield of ethylamine after electron irradiation of mixed C2H4:NH3 and C2H6:NH3 ices with the same composition and thickness. The results reveal that, in contrast to the initial assumption, ethylamine is formed with similar efficiency in both mixed ices. From the dependence of the product yields on the electron energy, we conclude that the reaction in both cases is predominantly driven by electron ionization of NH3. Ethylamine is formed via alternative reaction mechanisms by which the resulting NH2˙ radicals add to C2H4 and C2H6, respectively. The similar efficiency of amine formation in unsaturated and saturated hydrocarbons demonstrates that electron irradiation in the presence of NH3 is a more versatile tool for introducing nitrogen into carbonaceous materials than previously anticipated.

Desorption of neutrals, cations, and anions from core-excited amorphous solid water

Core-excitation of water ice releases many different molecules and ions in the gas phase. Studying these desorbed species and the underlying desorption mechanisms can provide useful information on the effects of x-ray irradiation in ice. We report a detailed study of the x-ray induced desorption of a number of neutral, cationic, and anionic species from amorphous solid water. We discuss the desorption mechanisms and the relative contributions of Auger and secondary electrons (x-ray induced electron stimulated desorption) and initial excitation (direct desorption) as well as the role of photochemistry. Anions are shown to desorb not just through processes linked with secondary electrons but also through direct dissociation of the core-excited molecule. The desorption spectra of oxygen ions (O⁺, OH⁺, H₂O⁺, O^-, and OH^-) give a new perspective on their previously reported very low desorption yields for most types of irradiations of water, showing that they mostly originate from the dissociation of photoproducts such as H₂O₂.

Glycine formation in CO2:CH4:NH3 ices induced by 0-70 eV electrons

Glycine (Gly), the simplest amino-acid building-block of proteins, has been identified on icy dust grains in the interstellar medium, icy comets, and ice covered meteorites. These astrophysical ices contain simple molecules (e.g., CO₂, H₂O, CH₄, HCN, and NH₃) and are exposed to complex radiation fields, e.g., UV, γ, or X-rays, stellar/solar wind particles, or cosmic rays. While much current effort is focused on understanding the radiochemistry induced in these ices by high energy radiation, the effects of the abundant secondary low energy electrons (LEEs) it produces have been mostly assumed rather than studied. Here we present the results for the exposure of multilayer CO₂:CH₄:NH₃ ice mixtures to 0-70 eV electrons under simulated astrophysical conditions. Mass selected temperature programmed desorption (TPD) of our electron irradiated films reveals multiple products, most notably intact glycine, which is supported by control measurements of both irradiated or un-irradiated binary mixture films, and un-irradiated CO₂:CH₄:NH₃ ices spiked with Gly. The threshold of Gly formation by LEEs is near 9 eV, while the TPD analysis of Gly film growth allows us to determine the "quantum" yield for 70 eV electrons to be about 0.004 Gly per incident electron. Our results show that simple amino acids can be formed directly from simple molecular ingredients, none of which possess preformed C-C or C-N bonds, by the copious secondary LEEs that are generated by ionizing radiation in astrophysical ices.

Electron induced reactions in condensed mixtures of methane and ammonia

We demonstrate the efficient formation of carbon-nitrogen bonds starting from CH₄ and NH₃ on a metal surface at cryogenic temperatures. Electrons in the energy range of 1-90 eV are used to initiate chemical reactions in mixed molecular films of CH₄ and NH₃ at ∼15 K, and the products are detected by performing temperature programmed desorption (TPD). Extensive dehydrogenation occurs at all energies giving the products CH₂NH and HCN in preference to CH₃NH₂. This is likely to do with the energetics of the reactions and the subsequent stability of these species in the condensed film. Thermal processing of the irradiated mixture favours dehydrogenation as indicated by the results of using different desorption rates. Electron impact excitation and subsequent dissociation into radicals is the reaction-initiating step rather than ionization of CH₄ and NH₃, as inferred from the yield of products as a function of electron energy. This could give insight into the important catalytic process of the industrial scale synthesis of HCN from CH₄ and NH₃ over Pt. This may also be a relevant pathway in the astrochemical environment where CN and HCN are abundant and low-energy electrons are found ubiquitously.

Reactivity induced at 25 K by low-energy electron irradiation of condensed NH3-CH3COOD (1 : 1) mixture

Chemical reactivity is observed following electron irradiation of a binary mixture of ammonia (NH(3)) and acetic acid (CH(3)COOD) at 25 K, without any subsequent thermal activation, as evidenced by vibrational high resolution electron energy loss spectroscopy (HREELS). Analysis of the HREEL spectra and comparison with infrared and Raman data of different molecules are compatible with glycine formation in its zwitterionic form. The onset for electron induced reaction is found to be at about approximately 13 eV. The mechanisms may involve NH radicals interaction with CH(3)COOD molecules. Then glycine formation does not imply any displacement of reactants, so that it involves only NH(3) and CH(3)COOD neighboring molecules.