Theoretical and Laboratory Studies on the Interaction of Cosmic‐Ray Particles with Interstellar Ices. I. Synthesis of Polycyclic Aromatic Hydrocarbons by a Cosmic‐Ray–induced Multicenter Mechanism

Kaiser, Ralf; Roessler, Κ.

doi:10.1086/303506

Cited by 74 publications

(49 citation statements)

References 27 publications

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“…Some of these effects are also found in experiments in which ices are bombarded with highly energetic charged particles, analogous to cosmic rays or X rays (e.g. Moore et al 1983, Strazzula & Baratta 1992, Kaiser & Roessler 1997. The thermal heating, photochemical, and irradiation processes are often referred to in the literature as energetic processing, without discrimination.…”

Section: Grain-surface Chemistrymentioning

confidence: 97%

Chemical Evolution of Star-Forming Regions

Dishoeck

Blake

1998

Annu. Rev. Astron. Astrophys.

452

241

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Recent advances in the understanding of the chemical processes that occur during all stages of the formation of stars, from the collapse of molecular clouds to the assemblage of icy planetesimals in protoplanetary accretion disks, are reviewed. Observational studies of the circumstellar material within 100-10,000 AU of the young star with (sub)millimeter single-dish telescopes, millimeter interferometers, and ground-based as well as space-borne infrared observatories have only become possible within the past few years. Results are compared with detailed chemical models that emphasize the coupling of gas-phase and grain-surface chemistry. Molecules that are particularly sensitive to different routes of formation and that may be useful in distinguishing between a variety of environments and histories are outlined. In the cold, low-density prestellar cores, radicals and long unsaturated carbon chains are enhanced. During the cold collapse phase, most species freeze out onto the grains in the high-density inner region. Once young stars ignite, their surroundings are heated through radiation and/or shocks, whereupon new chemical characteristics appear. Evaporation of ices drives a "hot core" chemistry rich in organic molecules, whereas shocks propagating through the dense envelope release both refractory and volatile grain material, resulting in prominent SiO, OH, and H 2 O emission. The role of future instrumentation in further developing these chemical and temporal diagnostics is discussed. 317

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Section: Grain-surface Chemistrymentioning

confidence: 97%

Chemical Evolution of Star-Forming Regions

Dishoeck

Blake

1998

Annu. Rev. Astron. Astrophys.

452

241

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“…The processing of methane ices has shown the facile production of the C2 hydrocarbons ethane, ethylene, and acetylene (Bennett et al 2006); the exposure of ethane ices to ionizing radiation depicts the production of methane, ethylene, and acetylene (Kim et al 2010). These C1 and C2 hydrocarbons are building blocks of aromatic systems from benzene (Zhou et al 2010) up to polycyclic aromatic hydrocarbons (PAHs) (Kaiser & Roessler 1997;Jones & Kaiser 2013). Therefore, an understanding of the chemistry of the C1 and C2 hydrocarbon species is crucial for a complete understanding of the formation of hydrocarbons in interstellar and planetary ices.…”

Section: Astrophysical Implicationsmentioning

confidence: 99%

“…The EI-QMS operating at 70-100 eV, where the ionization cross section of organic molecules is often at their maximum, readily ionizes molecules, but this ionization also causes substantial fragmentation (dissociative ionization) of the molecule; in the most unfavorable case, this results in a lack of the molecular parent ion altogether. Furthermore, the fragment ions of molecules, especially of structural isomers, often overlap making a confident assignment of structural isomers very difficult (Kaiser et al 1997aKaiser & Roessler 1997;Bennett et al 2005a;Bennett & Kaiser 2007). For example, a simple model ice mixture of carbon monoxide (CO) and methane (CH 4 ) would present a difficult detection of COMs such as acetaldehyde (CH 3 CHO; m/z = 44) via EI-QMS because of contributing ion counts from both carbon dioxide (CO 2 ; m/z = 44) and propane (C 3 H 8 ; m/z = 44), which are both principal products in processed carbon monoxide and methane ices ).…”

Section: Introductionmentioning

confidence: 99%

COMPLEX HYDROCARBON CHEMISTRY IN INTERSTELLAR AND SOLAR SYSTEM ICES REVEALED: A COMBINED INFRARED SPECTROSCOPY AND REFLECTRON TIME-OF-FLIGHT MASS SPECTROMETRY ANALYSIS OF ETHANE (C₂H₆) AND D6-ETHANE (C₂D₆) ICES EXPOSED TO IONIZING RADIATION

Abplanalp

Kaiser

2016

ApJ

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The irradiation of pure ethane (C 2 H 6 /C 2 D 6 ) ices at 5.5 K, under ultrahigh vacuum conditions was conducted to investigate the formation of complex hydrocarbons via interaction with energetic electrons simulating the secondary electrons produced in the track of galactic cosmic rays. The chemical modifications of the ices were monitored in situ using Fourier transform infrared spectroscopy (FTIR) and during temperature-programmed desorption via mass spectrometry exploiting a quadrupole mass spectrometer with electron impact ionization (EI-QMS) as well as a reflectron time-of-flight mass spectrometer coupled to a photoionization source (PI-ReTOF-MS). FTIR confirmed previous ethane studies by detecting six molecules: methane (CH 4 ), acetylene (C 2 H 2 ), ethylene (C 2 H 4 ), the ethyl radical (C 2 H 5 ), 1-butene (C 4 H 8 ), and n-butane (C 4 H 10 ). However, the TPD phase, along with EI-QMS, and most importantly, PI-ReTOF-MS, revealed the formation of at least 23 hydrocarbons, many for the first time in ethane ice, which can be arranged in four groups with an increasing carbon-to-hydrogen ratio: C n H 2n+2 (n = 3, 4, 6, 8, 10), C n H 2n (n = 3-10),2 2 (n = 3-10), andn n 2 4 (n = 4-6). The processing of simple ethane ices is relevant to the hydrocarbon chemistry in the interstellar medium, as ethane has been shown to be a major product of methane, as well as in the outer solar system. These data reveal that the processing of ethane ices can synthesize several key hydrocarbons such as C 3 H 4 and C 4 H 6 isomers, which have been found to synthesize polycyclic aromatic hydrocarbons like indene (C 9 H 8 ) and naphthalene (C 10 H 8 ) in the ISM and in hydrocarbon-rich atmospheres of planets and their moons such as Titan.

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“…The grain-surface radicals necessary for further molecular synthesis are thought to be produced by dissociation via UV photons created by the interaction of cosmic rays with H 2 molecules. Dissociation and/or ionisation via energetic electrons, created along the impact track as a cosmic ray particle penetrates a dust grain, is an alternative scenario (see, e.g., Kaiser & Roessler 1997). Further warming to T 100 K allows the removal of these more complex species from the ice mantle via thermal desorption thus "seeding" the gas with gasphase COMs.…”

Section: Introductionmentioning

confidence: 99%

Complex organic molecules in protoplanetary disks

Walsh

Millar

Nomura

et al. 2014

A&A

220

356

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Context. Protoplanetary disks are vital objects in star and planet formation, possessing all the material, gas and dust, which may form a planetary system orbiting the new star. Small, simple molecules have traditionally been detected in protoplanetary disks; however, in the ALMA era, we expect the molecular inventory of protoplanetary disks to significantly increase. Aims. We investigate the synthesis of complex organic molecules (COMs) in protoplanetary disks to put constraints on the achievable chemical complexity and to predict species and transitions which may be observable with ALMA. Methods. We have coupled a 2D steady-state physical model of a protoplanetary disk around a typical T Tauri star with a large gas-grain chemical network including COMs. We compare the resulting column densities with those derived from observations and perform ray-tracing calculations to predict line spectra. We compare the synthesised line intensities with current observations and determine those COMs which may be observable in nearby objects. We also compare the predicted grain-surface abundances with those derived from cometary comae observations. Results. We find COMs are efficiently formed in the disk midplane via grain-surface chemical reactions, reaching peak grain-surface fractional abundances ∼10 −6 -10 −4 that of the H nuclei number density. COMs formed on grain surfaces are returned to the gas phase via non-thermal desorption; however, gas-phase species reach lower fractional abundances than their grain-surface equivalents, ∼10 −12 -10 −7 . Including the irradiation of grain mantle material helps build further complexity in the ice through the replenishment of grain-surface radicals which take part in further grain-surface reactions. There is reasonable agreement with several line transitions of H 2 CO observed towards T Tauri star-disk systems. There is poor agreement with HC 3 N lines observed towards LkCa 15 and GO Tau and we discuss possible explanations for these discrepancies. The synthesised line intensities for CH 3 OH are consistent with upper limits determined towards all sources. Our models suggest CH 3 OH should be readily observable in nearby protoplanetary disks with ALMA; however, detection of more complex species may prove challenging, even with ALMA "Full Science" capabilities. Our grain-surface abundances are consistent with those derived from cometary comae observations providing additional evidence for the hypothesis that comets (and other planetesimals) formed via the coagulation of icy grains in the Sun's natal disk.

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Theoretical and Laboratory Studies on the Interaction of Cosmic‐Ray Particles with Interstellar Ices. I. Synthesis of Polycyclic Aromatic Hydrocarbons by a Cosmic‐Ray–induced Multicenter Mechanism

Cited by 74 publications

References 27 publications

Chemical Evolution of Star-Forming Regions

Chemical Evolution of Star-Forming Regions

COMPLEX HYDROCARBON CHEMISTRY IN INTERSTELLAR AND SOLAR SYSTEM ICES REVEALED: A COMBINED INFRARED SPECTROSCOPY AND REFLECTRON TIME-OF-FLIGHT MASS SPECTROMETRY ANALYSIS OF ETHANE (C₂H₆) AND D6-ETHANE (C₂D₆) ICES EXPOSED TO IONIZING RADIATION

Complex organic molecules in protoplanetary disks

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Theoretical and Laboratory Studies on the Interaction of Cosmic‐Ray Particles with Interstellar Ices. I. Synthesis of Polycyclic Aromatic Hydrocarbons by a Cosmic‐Ray–induced Multicenter Mechanism

Cited by 74 publications

References 27 publications

Chemical Evolution of Star-Forming Regions

Chemical Evolution of Star-Forming Regions

COMPLEX HYDROCARBON CHEMISTRY IN INTERSTELLAR AND SOLAR SYSTEM ICES REVEALED: A COMBINED INFRARED SPECTROSCOPY AND REFLECTRON TIME-OF-FLIGHT MASS SPECTROMETRY ANALYSIS OF ETHANE (C2H6) AND D6-ETHANE (C2D6) ICES EXPOSED TO IONIZING RADIATION

Complex organic molecules in protoplanetary disks

Contact Info

Product

Resources

About

COMPLEX HYDROCARBON CHEMISTRY IN INTERSTELLAR AND SOLAR SYSTEM ICES REVEALED: A COMBINED INFRARED SPECTROSCOPY AND REFLECTRON TIME-OF-FLIGHT MASS SPECTROMETRY ANALYSIS OF ETHANE (C₂H₆) AND D6-ETHANE (C₂D₆) ICES EXPOSED TO IONIZING RADIATION