Employing Soft X-Rays in Experimental Astrochemistry

Pilling, S.; Andrade, D.A.

doi:10.5772/29591

Cited by 4 publications

(5 citation statements)

References 60 publications

(78 reference statements)

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“…The region where X-rays are dominant can extend to the whole midplane if the disk is shielded from cosmic rays, as suggested by [13].The goal of this study is to provide experimental constraints on X-ray photodesorption, which allows modellers to assess the relevance of this process to the physics and chemistry of disks and other regions. Previous experimental studies have mainly focused on ion desorption [15,16,17], and only a few have attempted to derive quantitative desorption yields [18]. We used synchrotron radiation from the SEXTANTS beamline (SOLEIL facility) to irradiate amorphous solid water at either 15 K or 90 K in an ultra-high vacuum chamber (see Methods).…”

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confidence: 99%

X-ray photodesorption from water ice in protoplanetary disks and X-ray-dominated regions

et al. 2018

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Water is the main constituent of interstellar ices, and it plays a key role in the evolution of many regions of the interstellar medium, from molecular clouds to planet-forming disks [1]. In cold regions of the ISM, water is expected to be completely frozen out onto the dust grains. Nonetheless, observations indicate the presence of cold water vapor, implying that non-thermal desorption mechanisms are at play. Photodesorption by UV photons has been proposed to explain these observations [2,3], with the support of extensive experimental and theoretical work on ice analogues [4,5,6]. In contrast, photodesorption by X-rays, another viable mechanism, has been little studied. The potential of this process to desorb key molecules, such as water, intact rather than fragmented or ionised, remains unexplored. We experimentally investigated X-ray photodesorption from water ice, monitoring all desorbing species. We find that desorption of neutral water is efficient, while ion desorption is minor. We derive for the first time yields that can be implemented in astrochemical models. These results open up the possibility of taking into account the X-ray photodesorption process in the modelling of protoplanetary disks or X-ray dominated re-Numerous studies have explored the effects of Xrays on the chemistry of various regions of the ISM [7,8,9,10], with a few taking into account solid phase processes [11,12]. In the example of protoplanetary disks, as sketched in figure 1, the X-ray dominated region corresponds to a thin layer. The extent of the X-ray layer will depend on the type of star, the degree of evolution of the disk (dust settling, etc) and the physical model of disk considered. In the T Tauri model of ref [11], the limit between the UV and X-ray dominated layers occurs around z/R ∼ 0.2. The location of ices is disk-dependent as well, with the horizontal onset varying between <1 and 10 AU. Beyond a few tens of AU dust temperatures are cold enough for water to freeze out throughout the whole disk, and the X-ray layer overlaps with the icy region (cf fig.1). The region where X-rays are dominant can extend to the whole midplane if the disk is shielded from cosmic rays, as suggested by [13].The goal of this study is to provide experimental constraints on X-ray photodesorption, which allows modellers to assess the relevance of this process to the physics and chemistry of disks and other regions. Previous experimental studies have mainly focused on ion desorption [15,16,17], and only a few have attempted to derive quantitative desorption yields [18]. We used synchrotron radiation from the SEXTANTS beamline (SOLEIL facility) to irradiate amorphous solid water at either 15 K or 90 K in an ultra-high vacuum chamber (see Methods). Our set-up allows us 1 arXiv:1807.03725v1 [astro-ph.GA] 10 Jul 2018 (External X-rays) Cosmic Rays (External UV) z R Figure 1: Schematic representation of a vertical slice of a protoplanetary disk showing the various sources of irradiation in the ice-containing regions.To the left is the central star, wi...

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confidence: 99%

X-ray photodesorption from water ice in protoplanetary disks and X-ray-dominated regions

et al. 2018

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“…Processing of astrophysical ice analogs by X-rays is a key question in understanding molecular formation, abundances, and desorption in interstellar medium and other space environments. Several experiments on X-ray irradiation showed how X-rays promote chemical evolution of astrophysical ices. − Experiments on X-ray irradiation of astrophysical ice analogs have also shown: the possible formation of S 2 on comets by X-ray irradiation of H 2 S and CH 3 CN formation by X-ray processing of water-rich astrophysical ice analogs (H 2 O/CO/NH 3 ) . The present study is one more step in understanding how X-rays affect chemical evolution of astrophysical ices not only in star forming regions but also in regions close to compact objects.…”

Section: Introductionmentioning

confidence: 59%

Photolysis of CH₃CN Ices by Soft X-rays: Implications for the Chemistry of Astrophysical Ices at the Surroundings of X-ray Sources

Carvalho

Pilling

2020

J. Phys. Chem. A

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In this work, broad-band soft X-ray (6–2000 eV) was employed to irradiate frozen acetonitrile CH3CN, at the temperature 13 K, with different photon fluences up to 1.5 × 1018 photons cm–2. Here, acetonitrile is considered as a representative complex organic molecule (COM) present in astrophysical water-rich ices. The experiments were conduced at the Brazilian synchrotron facility (LNLS/CNPEM) employing infrared spectroscopy (FTIR) to monitor chemical changes induced by radiation. The effective destruction cross section of acetonitrile and effective formation cross section for daughter species formed inside the ice were obtained. The identified radiation products were HCN, CH4, H2CCNH, and CH3NC showing that fragmentation and rearrangement contribute to acetonitrile destruction. Chemical equilibrium and molecular abundances at this stage were determined, which also includes the abundance estimates of unknown molecules, produced but not directly detected, in the ice. The chemical equilibrium was reached at fluence around 1.5 × 1018 photons cm–2. Time scales for ices, at hypothetical snow line distances, to reach chemical equilibrium around compact objects, young stellar objects, and O/B stars and inside solar system were given. Among the obtained results are the time scales for reaching chemical equilibrium around different astronomical strong X-ray emitters, e.g., 14 days (for the Sun at 5 AU), 41 and 82 days (for O/B stars at 5 AU), 109–1011 years (for white dwarfs at 1 LY), 450 years (for Crab pulsar at 2.25 LY), around 107 years (for Vela pulsar at 2.25 LY), and 7.5 × 106 years (for Sagittarius A* at 3 LY).

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“…Contributions of the natural isotopomers of Cl and Se natural are summed together. The estimated experimental error was 10%. , …”

Section: Resultsmentioning

confidence: 92%

“… a Peaks for the corresponding naturally occurring isotopomer were observed. b The estimated experimental error was 10%. , …”

Section: Resultsmentioning

confidence: 99%

Photoelectron Spectroscopy and Ionic Fragmentation of OSeCl₂ and Its Analogue OSCl₂ under VUV Irradiation

et al. 2015

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The electronic structure and the dissociative ionization of selenium oxychloride, OSeCl2, have been investigated in the valence region by using results from both photoelectron spectroscopy (PES) and synchrotron-based photoelectron photoion coincidence (PEPICO) spectra. The PES is assigned with the help of quantum chemical calculations at the outer-valence Green's function (OVGF) and symmetry adapted cluster/configuration interaction (SAC-CI) levels. The first energy ionization is observed at 11.47 eV assigned to the ionization of electrons formally delocalized over the Se, Cl, and O lone pair orbitals. Irradiation of OSeCl2 with photons in the valence region leads to the formation of OSeCl2(•+), OSeCl(+), SeCl2(•+), SeCl(+), and SeO(•+) ions. Furthermore, the inner shell Se 3p, Cl 2p, and Se 3s electronic regions of OSeCl2 together with S 2p, Cl 2p, and S 2s electronic regions of thionyl chloride, OSCl2, have been studied by using tunable synchrotron radiation. Thus, total ion yield spectra and the fragmentation patterns deduced from PEPICO spectra at the various excitation energies have been studied. Cl(+), O(•+), and Se(•+) ions appear as the most intense fragments in the OSeCl2 PEPICO spectra, like in the sulfur analogue OSCl2, whose photofragmentation is dominated by the Cl(+), O(•+), and S(•+) ions. Fragmentation processes in OSCl2 leading to the formation of the double coincidences involving atomic ions appear as the most intense in the PEPIPICO spectra.

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Employing Soft X-Rays in Experimental Astrochemistry

Cited by 4 publications

References 60 publications

X-ray photodesorption from water ice in protoplanetary disks and X-ray-dominated regions

X-ray photodesorption from water ice in protoplanetary disks and X-ray-dominated regions

Photolysis of CH₃CN Ices by Soft X-rays: Implications for the Chemistry of Astrophysical Ices at the Surroundings of X-ray Sources

Photoelectron Spectroscopy and Ionic Fragmentation of OSeCl₂ and Its Analogue OSCl₂ under VUV Irradiation

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Employing Soft X-Rays in Experimental Astrochemistry

Cited by 4 publications

References 60 publications

X-ray photodesorption from water ice in protoplanetary disks and X-ray-dominated regions

X-ray photodesorption from water ice in protoplanetary disks and X-ray-dominated regions

Photolysis of CH3CN Ices by Soft X-rays: Implications for the Chemistry of Astrophysical Ices at the Surroundings of X-ray Sources

Photoelectron Spectroscopy and Ionic Fragmentation of OSeCl2 and Its Analogue OSCl2 under VUV Irradiation

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Photolysis of CH₃CN Ices by Soft X-rays: Implications for the Chemistry of Astrophysical Ices at the Surroundings of X-ray Sources

Photoelectron Spectroscopy and Ionic Fragmentation of OSeCl₂ and Its Analogue OSCl₂ under VUV Irradiation