Jan Bredehöft | University of Bremen (original) (raw)

Papers by Jan Bredehöft

Physical Chemistry Chemical Physics

A novel mechanism is proposed for the electron-induced production of methyl formate from CO and C... more A novel mechanism is proposed for the electron-induced production of methyl formate from CO and CH3OH which is relevant for interstellar ice chemistry. A key-step in this reaction is the formation of an intermediate CH3OCO radical.

ACS Earth and Space Chemistry

The Journal of Physical Chemistry A

Electron-induced reactions in condensed mixtures of ethylene (CH) and methanol (CHOH) lead to the... more Electron-induced reactions in condensed mixtures of ethylene (CH) and methanol (CHOH) lead to the formation of ethyl methyl ether (EME, CHOCH) as shown by post-irradiation thermal desorption spectrometry (TDS). In contrast to the electron-induced reaction between water (HO) and CH, product formation as a consequence of proton transfer following electron attachment (EA) to CH is not observed in the analogous reaction between CHOH and CH. However, a resonant process centered around 5.5 eV and a threshold-type increase of product yield starting at 9 eV is observed. Based on the presence and absence of particular side products after irradiation of the mixture as well as of the pure parent compounds, reaction mechanisms related to the two energy regimes are proposed. Below the ionization threshold of the reactants, dissociative electron attachment (DEA) to CHOH triggers the reaction sequence by producing reactive methoxy radicals, which attack neighboring CH molecules. The resulting adduct then abstracts a hydrogen atom to yield EME. Above but near the ionization threshold, electron impact ionization (EI) produces primarily intact molecular cations, which drive the reaction by converting the repulsive Coulomb force between the high electron densities at the reactive sites of the two neutral parent species into an attractive force. This again induces the formation of an adduct between the two reactants that rearranges to the product EME. Fragmentation of the molecular CHOH cation into CHO, however, may provide an additional reaction pathway toward EME. In this scenario, CHO attacks a neighboring CH molecule. The resulting adduct is then neutralized by a thermalized electron and abstracts a hydrogen atom from a nearby CHOH molecule to yield EME.

ACS Earth and Space Chemistry

The formation of the prebiotically relevant molecule formamide under electron exposure of ammonia... more The formation of the prebiotically relevant molecule formamide under electron exposure of ammonia and carbon monoxide was studied at cryogenic temperatures of 30−35 K. Postirradiation thermal desorption spectroscopy was used to study the energy dependence of the reaction. A resonant process centered around ∼9 eV and a threshold type increase of the yield above ∼12 eV were observed. On the basis of the absence of particular side products such as urea and ethanediamide and supported by quantum chemical calculations, reaction mechanisms related to the two observed energy regimes of formamide production are proposed. Below the ionization threshold, electron attachment to ammonia and the subsequent dissociation of the radical anion trigger the reaction sequence. At higher energies, electron impact ionization and addition of the formed radical cation to a neutral molecule ultimately lead to the formation of formamide.

The emission of [O I] lines in the coma of Comet 67P/Churyumov-Gerasimenko during the Rosetta mis... more The emission of [O I] lines in the coma of Comet 67P/Churyumov-Gerasimenko during the Rosetta mission have been explained by electron impact dissociation of water rather than the process of photodissociation. This is the direct evidence for the role of electron induced processing has been seen on such a body. Analysis of other emission features is handicapped by a lack of detailed knowledge of electron impact cross sections which highlights the need for a broad range of electron scattering data from the molecular systems detected on the comet. In this paper we present an overview of the needs for electron scattering data relevant for the understanding of observations in coma, the tenuous atmosphere and on the surface of 67P/Churyumov-Gerasimenko during the Rosetta mission. The relevant observations for elucidating the role of electrons come from optical spectra, particle analysis using the ion and electron sensors and mass spectrometry measurements. To model these processes electron...

Angewandte Chemie (International ed. in English), Jan 27, 2015

Electron-induced reactions in condensed mixtures of ethylene and water lead to the synthesis of e... more Electron-induced reactions in condensed mixtures of ethylene and water lead to the synthesis of ethanol, as shown by post-irradiation thermal desorption spectrometry (TDS). Interestingly, this synthesis is not only induced by soft electron impact ionization similar to a previously observed electron-induced hydroamination but also, at low electron energy, by electron attachment to ethylene and a subsequent acid/base reaction with water.

Planetary and Space Science, 2014

ABSTRACT The comet rendezvous mission Rosetta will be the first mission to encounter and land on ... more ABSTRACT The comet rendezvous mission Rosetta will be the first mission to encounter and land on a comet nucleus. After a 10-year journey Rosetta is set for rendezvous with Comet 67P/Churyumov–Gerasimenko. The mission goal is: to study the origin of comets; the relationship between cometary and interstellar material and its implications for the origin of the solar system. The Rosetta spacecraft with an overall mass of about 3000 kg was launched in March 2004 and brought into cometary orbit towards comet 67P/Churyumov–Gerasimenko with 4 gravity assist maneuvers. On its way Rosetta passed and observed two asteroids, (2867) Šteins in 2008 and (21) Lutetia in 2010, respectively. In June 2011 Rosetta entered into hibernation and woke up – as planned – on January 20, 2014. In November 2014 Rosetta’s Philae lander and 10 science instruments will be deployed onto the surface of comet 67P/Churyumov–Gerasimenko. This will be followed by the first ever in situ investigation of a comet nucleus. Onboard Philae is the COmetary SAmpling and Composition experiment (COSAC), one of two evolved gas analysers that will investigate organic compounds within the material of the nucleus. Data from the COSAC instrument are expected to provide important insights into the early history of our solar system and contribute to our knowledge of small bodies that may have seeded the early Earth through impacts. In this paper we review recent developments in cometary science, including data on target comet 67P/Churyumov–Gerasimenko. We report on laboratory measurements and the calibration of the COSAC instrument as well as the preparation for operations on the nucleus of comet 67P/Churyumov–Gerasimenko.

Experimental Astronomy

The Triple F (Fresh From the Fridge) mission, a Comet Nucleus Sample Return, has been proposed to... more The Triple F (Fresh From the Fridge) mission, a Comet Nucleus Sample Return, has been proposed to ESA’s Cosmic Vision program. A sample return from a comet enables us to reach the ultimate goal of cometary research. Since comets are the least processed bodies in the solar system, the proposal goes far beyond cometary science topics (like the explanation of cometary activity) and delivers invaluable information about the formation of the solar system and the interstellar molecular cloud from which it formed. The proposed mission would extract three sample cores of the upper 50 cm from three locations on a cometary nucleus and return them cooled to Earth for analysis in the laboratory. The simple mission concept with a touch-and-go sampling by a single spacecraft was proposed as an M-class mission in collaboration with the Russian space agency ROSCOSMOS.

ABSTRACT The complexity of molecules found in space varies widely. On one end of the scale of mol... more ABSTRACT The complexity of molecules found in space varies widely. On one end of the scale of molecular complexity is the hydrogen molecule H2 . Its formation from H atoms is if not understood than at least thoroughly investigated[1]. On the other side of said spectrum the precursors to biopolymers can be found, such as amino acids[2,3], sugars[4], lipids, cofactors[5], etc, and the kerogen-like organic polymer material in carbonaceous meteorites called "black stuff" [6]. These have also received broad attention in the last decades. Sitting in the middle between these two extremes are simple molecules that are observed by radio astronomy throughout the Universe. These are molecules like methane (CH4 ), methanol (CH3 OH), formaldehyde (CH2 O), hydrogen cyanide (HCN), and many many others. So far more than 40 such species have been identified.[7] They are often used in laboratory experiments to create larger complex molecules on the surface of simulated interstellar dust grains.[2,8] The mechanisms of formation of these observed starting materials for prebiotic chemistry is however not always clear. Also the exact mechanisms of formation of larger molecules in photochemical experiments are largely unclear. This is mostly due to the very complex chemistry going on which involves many different radicals and ions. The creation of radicals and ions can be studied in detail in laboratory simulations. They can be created in a setup mimicking interstellar grain chemistry using slow electrons. There is no free electron radiation in space. What can be found though is a lot of radiation of different sorts. There is electromagnetic radiation (UV light, X-Rays, rays, etc.) and there is particulate radiation as well in the form of high energy ions. This radiation can provide energy that drives chemical reactions in the ice mantles of interstellar dust grains. And while the multitude of different kinds of radiation might be a little confusing, they all have one thing in common: Upon hitting anything solid, they will create secondary electrons. These electrons are in fact the energy source needed to run interstellar chemistry. Slow electrons can in principle trigger three different primary processes in a molecule. The first is ionisation by electron impact (EI), which is used to create ions in mass spectrometry. In this process an electron hits a molecule M and knocks an outer shell electron to create a cation. This occurs whenever the electron energy is above the ionisation threshold of the target molecule. Another possibility is the attachment of a slow electron to a molecule to create an anion. This can occur at sharply defined resonance energies specific to the molecule M. A third possibility is to excite the molecule M to a neutral state M∗ .[9] M + e- -> M+ + 2 e- (Electron impact ionisation) M + e- -> M- (Electron attachment) M + e- -> M∗ + e- (Neutral excitation) The created states M+ , M- and M∗ are usually not stable states so they very often dissociate into ions and radicals, which can then further react with neighbouring molecules to form new chemical species. In these chemical reactions some products can be formed even at very low temperatures that would otherwise require a lot of thermal energy and/or special catalysts. The formation of ethylamine from ethylene and ammonia by hydroamination is one such example. The reaction is characterized by a high activation barrier caused by the electronic repulsion between the electron density rich C=C double bound and the lone pair electrons of ammo-nia. The reaction also has a highly negative entropy, so it becomes less favourable at higher temperatures, ruling out heat as a means to facilitate the reaction. In classical chemistry this problem is overcome by the use of catalysts. Unfortunately there still is no general catalyst for this kind of reaction. Recently it was shown that the reaction can efficiently be induced by low energy electron radiation.[10] One of the reaction partners is ionized and the reaction barrier is drastically lowered so that instant reaction between ethylene and ammonia occurs. This hydroamination reaction by means of low energy electrons or an analogous reaction mechanism could also help in clarifying the formation of the intermediate molecules observed in interstellar dust clouds. The formation for example of formamide from CO and NH3 could be facilitated by a very similar process. Formamide is a very interesting molecule in Astrochemistry as well as Astrobiology, since it is the smallest molecule with a peptide bond, the kind of bond that forms proteins from amino acids. Such ionisation-driven reactions leading to the formation of larger molecules appear to be more generally relevant than previously thought as will be discussed in this contribution. [1] Cazaux S., Caselli P., Tielens A.G.G.M., Le Bourlot J., Walmsley M: Molecular Hydrogen formation on grain surfaces. J of Phys. Conf. Series 6 (2005), 155-160 [2] Muñoz…

Angewandte Chemie, 2015

ABSTRACT Elektroneninduzierte Reaktionen in kondensierten Mischungen aus Ethen und Wasser führen ... more ABSTRACT Elektroneninduzierte Reaktionen in kondensierten Mischungen aus Ethen und Wasser führen zur Synthese von Ethanol, wie sich anhand von thermischer Desorptionsspektrometrie (TDS) nach Bestrahlung zeigen lässt. Diese Reaktion wird nicht nur durch Elektronenstoß-Ionisation nahe der Ionisationsschwelle ausgelöst, sondern auch durch Elektronenanlagerung an Ethen und eine nachfolgende Säure-Base-Reaktion mit Wasser.

Planetary and Space Science, 2012

ABSTRACT On 10 July 2010 the Rosetta spacecraft flew-by asteroid Lutetia. At that time all the ma... more ABSTRACT On 10 July 2010 the Rosetta spacecraft flew-by asteroid Lutetia. At that time all the mass spectrometers in the payload of the Philae Lander capable of gas analysis were in operation. Among these, the COSAC (Cometary Sampling and Composition) experiment is a gas-chromatograph mass spectrometer which was switched on twice during the fly-by, once 3 h prior to Closest Approach for 126 s and 1 h afterwards for 126 s. The instrument performed well and two mass spectra were obtained from which the composition of the gas phase was evaluated. These spectra show no evidence of the presence of an exosphere at Lutetia. The most likely interpretation of the records is that traces of residual gas from Philae and from COSAC itself were recorded, with a slight change in composition between the two measurements. A mean upper pressure limit inside COSAC derived from the two measurements is of the order of 5×10-9 mbar. This is the highest limit quoted by the various onboard instruments but is explicable in the context that COSAC was designed to operate in environments characterized by relatively higher pressure. The COSAC results are in line with those of the other Rosetta instruments that made measurements during the fly-by (see other papers in this issue).

Macromolecular Materials and Engineering, 2012

ABSTRACT The crosslinking of thin liquid PDMS layers by three different technically relevant proc... more ABSTRACT The crosslinking of thin liquid PDMS layers by three different technically relevant processes, H2 radio-frequency plasma treatment, Xe2* excimer VUV irradiation, and low-energy electron beam processing is investigated. The modifications to the layers due to the processing are monitored by means of RAIRS. Plasma processing of liquid PDMS leads to a direct conversion to a SiOx-like material of the topmost layers, whereas a gradual transition from PDMS to the same product is observed upon VUV irradiation. Electron exposure does not induce oxidation. The initiating steps of the conversion induced by the interaction with VUV photons, low-energy electrons, or their combined effect with ions and H atoms in the plasma are discussed. The latter creates a high density of damage sites.

Experimental Astronomy, 2009

The Triple F (Fresh From the Fridge) mission, a Comet Nucleus Sample Return, has been proposed to... more The Triple F (Fresh From the Fridge) mission, a Comet Nucleus Sample Return, has been proposed to ESA's Cosmic Vision program. A sample return from a comet enables us to reach the ultimate goal of cometary research. Since comets are the least processed bodies in the solar system, the proposal goes far beyond cometary science topics (like the explanation of cometary activity) and delivers invaluable information about the formation of the solar system and the interstellar molecular cloud from which it formed.

The European Physical Journal D, 2012

ABSTRACT Thermal Desorption Spectrometry (TDS) and Electron Stimulated Desorption (ESD) are emplo... more ABSTRACT Thermal Desorption Spectrometry (TDS) and Electron Stimulated Desorption (ESD) are employed to investigate mechanisms responsible for the formation of C2H6 in electron irradiated multilayer films of acetonitrile (CH3CN) at 30 K. Using a high sensitivity time-of-flight mass spectrometer, we observe the ESD of anionic fragments H-, CH2-, CH3- and CN-. Desorption occurs following dissociative electron attachment (DEA) via several negative ion resonances in the 6 to 14 eV energy range and correlates well with a “resonant” structure seen in the TDS yield of C2H6 (i.e., at mass 30 amu). It is proposed that C2H6 is formed by the reactions of CH3 radicals generated following DEA to CH3CN which also yields CN-. Between 2 and 5 eV, a second resonant feature is seen in the C2H6 signal. While DEA is observed in the gas phase at these energies, no anion desorption occurs since anionic fragments likely have insufficient kinetic energy to desorb. Since the CH2- ion has not been observed in gas-phase measurements, we propose that it is formed, along with HCN (that is detected in TDS) when dissociation into CH3- and CN is hindered by adjacent molecules.

Physical Chemistry Chemical Physics

A novel mechanism is proposed for the electron-induced production of methyl formate from CO and C... more A novel mechanism is proposed for the electron-induced production of methyl formate from CO and CH3OH which is relevant for interstellar ice chemistry. A key-step in this reaction is the formation of an intermediate CH3OCO radical.

ACS Earth and Space Chemistry

The Journal of Physical Chemistry A

Electron-induced reactions in condensed mixtures of ethylene (CH) and methanol (CHOH) lead to the... more Electron-induced reactions in condensed mixtures of ethylene (CH) and methanol (CHOH) lead to the formation of ethyl methyl ether (EME, CHOCH) as shown by post-irradiation thermal desorption spectrometry (TDS). In contrast to the electron-induced reaction between water (HO) and CH, product formation as a consequence of proton transfer following electron attachment (EA) to CH is not observed in the analogous reaction between CHOH and CH. However, a resonant process centered around 5.5 eV and a threshold-type increase of product yield starting at 9 eV is observed. Based on the presence and absence of particular side products after irradiation of the mixture as well as of the pure parent compounds, reaction mechanisms related to the two energy regimes are proposed. Below the ionization threshold of the reactants, dissociative electron attachment (DEA) to CHOH triggers the reaction sequence by producing reactive methoxy radicals, which attack neighboring CH molecules. The resulting adduct then abstracts a hydrogen atom to yield EME. Above but near the ionization threshold, electron impact ionization (EI) produces primarily intact molecular cations, which drive the reaction by converting the repulsive Coulomb force between the high electron densities at the reactive sites of the two neutral parent species into an attractive force. This again induces the formation of an adduct between the two reactants that rearranges to the product EME. Fragmentation of the molecular CHOH cation into CHO, however, may provide an additional reaction pathway toward EME. In this scenario, CHO attacks a neighboring CH molecule. The resulting adduct is then neutralized by a thermalized electron and abstracts a hydrogen atom from a nearby CHOH molecule to yield EME.

ACS Earth and Space Chemistry

The formation of the prebiotically relevant molecule formamide under electron exposure of ammonia... more The formation of the prebiotically relevant molecule formamide under electron exposure of ammonia and carbon monoxide was studied at cryogenic temperatures of 30−35 K. Postirradiation thermal desorption spectroscopy was used to study the energy dependence of the reaction. A resonant process centered around ∼9 eV and a threshold type increase of the yield above ∼12 eV were observed. On the basis of the absence of particular side products such as urea and ethanediamide and supported by quantum chemical calculations, reaction mechanisms related to the two observed energy regimes of formamide production are proposed. Below the ionization threshold, electron attachment to ammonia and the subsequent dissociation of the radical anion trigger the reaction sequence. At higher energies, electron impact ionization and addition of the formed radical cation to a neutral molecule ultimately lead to the formation of formamide.

The emission of [O I] lines in the coma of Comet 67P/Churyumov-Gerasimenko during the Rosetta mis... more The emission of [O I] lines in the coma of Comet 67P/Churyumov-Gerasimenko during the Rosetta mission have been explained by electron impact dissociation of water rather than the process of photodissociation. This is the direct evidence for the role of electron induced processing has been seen on such a body. Analysis of other emission features is handicapped by a lack of detailed knowledge of electron impact cross sections which highlights the need for a broad range of electron scattering data from the molecular systems detected on the comet. In this paper we present an overview of the needs for electron scattering data relevant for the understanding of observations in coma, the tenuous atmosphere and on the surface of 67P/Churyumov-Gerasimenko during the Rosetta mission. The relevant observations for elucidating the role of electrons come from optical spectra, particle analysis using the ion and electron sensors and mass spectrometry measurements. To model these processes electron...

Angewandte Chemie (International ed. in English), Jan 27, 2015

Electron-induced reactions in condensed mixtures of ethylene and water lead to the synthesis of e... more Electron-induced reactions in condensed mixtures of ethylene and water lead to the synthesis of ethanol, as shown by post-irradiation thermal desorption spectrometry (TDS). Interestingly, this synthesis is not only induced by soft electron impact ionization similar to a previously observed electron-induced hydroamination but also, at low electron energy, by electron attachment to ethylene and a subsequent acid/base reaction with water.

Planetary and Space Science, 2014

ABSTRACT The comet rendezvous mission Rosetta will be the first mission to encounter and land on ... more ABSTRACT The comet rendezvous mission Rosetta will be the first mission to encounter and land on a comet nucleus. After a 10-year journey Rosetta is set for rendezvous with Comet 67P/Churyumov–Gerasimenko. The mission goal is: to study the origin of comets; the relationship between cometary and interstellar material and its implications for the origin of the solar system. The Rosetta spacecraft with an overall mass of about 3000 kg was launched in March 2004 and brought into cometary orbit towards comet 67P/Churyumov–Gerasimenko with 4 gravity assist maneuvers. On its way Rosetta passed and observed two asteroids, (2867) Šteins in 2008 and (21) Lutetia in 2010, respectively. In June 2011 Rosetta entered into hibernation and woke up – as planned – on January 20, 2014. In November 2014 Rosetta’s Philae lander and 10 science instruments will be deployed onto the surface of comet 67P/Churyumov–Gerasimenko. This will be followed by the first ever in situ investigation of a comet nucleus. Onboard Philae is the COmetary SAmpling and Composition experiment (COSAC), one of two evolved gas analysers that will investigate organic compounds within the material of the nucleus. Data from the COSAC instrument are expected to provide important insights into the early history of our solar system and contribute to our knowledge of small bodies that may have seeded the early Earth through impacts. In this paper we review recent developments in cometary science, including data on target comet 67P/Churyumov–Gerasimenko. We report on laboratory measurements and the calibration of the COSAC instrument as well as the preparation for operations on the nucleus of comet 67P/Churyumov–Gerasimenko.

Experimental Astronomy

The Triple F (Fresh From the Fridge) mission, a Comet Nucleus Sample Return, has been proposed to... more The Triple F (Fresh From the Fridge) mission, a Comet Nucleus Sample Return, has been proposed to ESA’s Cosmic Vision program. A sample return from a comet enables us to reach the ultimate goal of cometary research. Since comets are the least processed bodies in the solar system, the proposal goes far beyond cometary science topics (like the explanation of cometary activity) and delivers invaluable information about the formation of the solar system and the interstellar molecular cloud from which it formed. The proposed mission would extract three sample cores of the upper 50 cm from three locations on a cometary nucleus and return them cooled to Earth for analysis in the laboratory. The simple mission concept with a touch-and-go sampling by a single spacecraft was proposed as an M-class mission in collaboration with the Russian space agency ROSCOSMOS.

ABSTRACT The complexity of molecules found in space varies widely. On one end of the scale of mol... more ABSTRACT The complexity of molecules found in space varies widely. On one end of the scale of molecular complexity is the hydrogen molecule H2 . Its formation from H atoms is if not understood than at least thoroughly investigated[1]. On the other side of said spectrum the precursors to biopolymers can be found, such as amino acids[2,3], sugars[4], lipids, cofactors[5], etc, and the kerogen-like organic polymer material in carbonaceous meteorites called "black stuff" [6]. These have also received broad attention in the last decades. Sitting in the middle between these two extremes are simple molecules that are observed by radio astronomy throughout the Universe. These are molecules like methane (CH4 ), methanol (CH3 OH), formaldehyde (CH2 O), hydrogen cyanide (HCN), and many many others. So far more than 40 such species have been identified.[7] They are often used in laboratory experiments to create larger complex molecules on the surface of simulated interstellar dust grains.[2,8] The mechanisms of formation of these observed starting materials for prebiotic chemistry is however not always clear. Also the exact mechanisms of formation of larger molecules in photochemical experiments are largely unclear. This is mostly due to the very complex chemistry going on which involves many different radicals and ions. The creation of radicals and ions can be studied in detail in laboratory simulations. They can be created in a setup mimicking interstellar grain chemistry using slow electrons. There is no free electron radiation in space. What can be found though is a lot of radiation of different sorts. There is electromagnetic radiation (UV light, X-Rays, rays, etc.) and there is particulate radiation as well in the form of high energy ions. This radiation can provide energy that drives chemical reactions in the ice mantles of interstellar dust grains. And while the multitude of different kinds of radiation might be a little confusing, they all have one thing in common: Upon hitting anything solid, they will create secondary electrons. These electrons are in fact the energy source needed to run interstellar chemistry. Slow electrons can in principle trigger three different primary processes in a molecule. The first is ionisation by electron impact (EI), which is used to create ions in mass spectrometry. In this process an electron hits a molecule M and knocks an outer shell electron to create a cation. This occurs whenever the electron energy is above the ionisation threshold of the target molecule. Another possibility is the attachment of a slow electron to a molecule to create an anion. This can occur at sharply defined resonance energies specific to the molecule M. A third possibility is to excite the molecule M to a neutral state M∗ .[9] M + e- -> M+ + 2 e- (Electron impact ionisation) M + e- -> M- (Electron attachment) M + e- -> M∗ + e- (Neutral excitation) The created states M+ , M- and M∗ are usually not stable states so they very often dissociate into ions and radicals, which can then further react with neighbouring molecules to form new chemical species. In these chemical reactions some products can be formed even at very low temperatures that would otherwise require a lot of thermal energy and/or special catalysts. The formation of ethylamine from ethylene and ammonia by hydroamination is one such example. The reaction is characterized by a high activation barrier caused by the electronic repulsion between the electron density rich C=C double bound and the lone pair electrons of ammo-nia. The reaction also has a highly negative entropy, so it becomes less favourable at higher temperatures, ruling out heat as a means to facilitate the reaction. In classical chemistry this problem is overcome by the use of catalysts. Unfortunately there still is no general catalyst for this kind of reaction. Recently it was shown that the reaction can efficiently be induced by low energy electron radiation.[10] One of the reaction partners is ionized and the reaction barrier is drastically lowered so that instant reaction between ethylene and ammonia occurs. This hydroamination reaction by means of low energy electrons or an analogous reaction mechanism could also help in clarifying the formation of the intermediate molecules observed in interstellar dust clouds. The formation for example of formamide from CO and NH3 could be facilitated by a very similar process. Formamide is a very interesting molecule in Astrochemistry as well as Astrobiology, since it is the smallest molecule with a peptide bond, the kind of bond that forms proteins from amino acids. Such ionisation-driven reactions leading to the formation of larger molecules appear to be more generally relevant than previously thought as will be discussed in this contribution. [1] Cazaux S., Caselli P., Tielens A.G.G.M., Le Bourlot J., Walmsley M: Molecular Hydrogen formation on grain surfaces. J of Phys. Conf. Series 6 (2005), 155-160 [2] Muñoz…

Angewandte Chemie, 2015

ABSTRACT Elektroneninduzierte Reaktionen in kondensierten Mischungen aus Ethen und Wasser führen ... more ABSTRACT Elektroneninduzierte Reaktionen in kondensierten Mischungen aus Ethen und Wasser führen zur Synthese von Ethanol, wie sich anhand von thermischer Desorptionsspektrometrie (TDS) nach Bestrahlung zeigen lässt. Diese Reaktion wird nicht nur durch Elektronenstoß-Ionisation nahe der Ionisationsschwelle ausgelöst, sondern auch durch Elektronenanlagerung an Ethen und eine nachfolgende Säure-Base-Reaktion mit Wasser.

Planetary and Space Science, 2012

ABSTRACT On 10 July 2010 the Rosetta spacecraft flew-by asteroid Lutetia. At that time all the ma... more ABSTRACT On 10 July 2010 the Rosetta spacecraft flew-by asteroid Lutetia. At that time all the mass spectrometers in the payload of the Philae Lander capable of gas analysis were in operation. Among these, the COSAC (Cometary Sampling and Composition) experiment is a gas-chromatograph mass spectrometer which was switched on twice during the fly-by, once 3 h prior to Closest Approach for 126 s and 1 h afterwards for 126 s. The instrument performed well and two mass spectra were obtained from which the composition of the gas phase was evaluated. These spectra show no evidence of the presence of an exosphere at Lutetia. The most likely interpretation of the records is that traces of residual gas from Philae and from COSAC itself were recorded, with a slight change in composition between the two measurements. A mean upper pressure limit inside COSAC derived from the two measurements is of the order of 5×10-9 mbar. This is the highest limit quoted by the various onboard instruments but is explicable in the context that COSAC was designed to operate in environments characterized by relatively higher pressure. The COSAC results are in line with those of the other Rosetta instruments that made measurements during the fly-by (see other papers in this issue).

Macromolecular Materials and Engineering, 2012

ABSTRACT The crosslinking of thin liquid PDMS layers by three different technically relevant proc... more ABSTRACT The crosslinking of thin liquid PDMS layers by three different technically relevant processes, H2 radio-frequency plasma treatment, Xe2* excimer VUV irradiation, and low-energy electron beam processing is investigated. The modifications to the layers due to the processing are monitored by means of RAIRS. Plasma processing of liquid PDMS leads to a direct conversion to a SiOx-like material of the topmost layers, whereas a gradual transition from PDMS to the same product is observed upon VUV irradiation. Electron exposure does not induce oxidation. The initiating steps of the conversion induced by the interaction with VUV photons, low-energy electrons, or their combined effect with ions and H atoms in the plasma are discussed. The latter creates a high density of damage sites.

Experimental Astronomy, 2009

The Triple F (Fresh From the Fridge) mission, a Comet Nucleus Sample Return, has been proposed to... more The Triple F (Fresh From the Fridge) mission, a Comet Nucleus Sample Return, has been proposed to ESA's Cosmic Vision program. A sample return from a comet enables us to reach the ultimate goal of cometary research. Since comets are the least processed bodies in the solar system, the proposal goes far beyond cometary science topics (like the explanation of cometary activity) and delivers invaluable information about the formation of the solar system and the interstellar molecular cloud from which it formed.

The European Physical Journal D, 2012

ABSTRACT Thermal Desorption Spectrometry (TDS) and Electron Stimulated Desorption (ESD) are emplo... more ABSTRACT Thermal Desorption Spectrometry (TDS) and Electron Stimulated Desorption (ESD) are employed to investigate mechanisms responsible for the formation of C2H6 in electron irradiated multilayer films of acetonitrile (CH3CN) at 30 K. Using a high sensitivity time-of-flight mass spectrometer, we observe the ESD of anionic fragments H-, CH2-, CH3- and CN-. Desorption occurs following dissociative electron attachment (DEA) via several negative ion resonances in the 6 to 14 eV energy range and correlates well with a “resonant” structure seen in the TDS yield of C2H6 (i.e., at mass 30 amu). It is proposed that C2H6 is formed by the reactions of CH3 radicals generated following DEA to CH3CN which also yields CN-. Between 2 and 5 eV, a second resonant feature is seen in the C2H6 signal. While DEA is observed in the gas phase at these energies, no anion desorption occurs since anionic fragments likely have insufficient kinetic energy to desorb. Since the CH2- ion has not been observed in gas-phase measurements, we propose that it is formed, along with HCN (that is detected in TDS) when dissociation into CH3- and CN is hindered by adjacent molecules.