New measurements on water ice photodesorption and product formation under ultraviolet irradiation

Cruz-Díaz, G. A.; Martín-Doménech, R.; Moreno, Elena; Muñoz, G. M.; Chen, Yu-Jung

doi:10.1093/mnras/stx2966

Cited by 39 publications

(66 citation statements)

References 43 publications

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“…Additionally, the increased yield derived here may also be related to a higher temperature of the ice: 20 K in this work, compared to 8-12 K in the former study. A similar behavior was previously shown for H 2 O and CO ices (Westley et al 1995;Arasa et al 2010;Cruz-Diaz et al 2018;Öberg et al 2009a).…”

Section: Comparison With Other Studiessupporting

confidence: 86%

Novel approach to distinguish between vacuum UV-induced ice photodesorption and photoconversion

Bulak

Paardekooper

Fedoseev

et al. 2020

A&A

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Context. In cold regions of the interstellar medium with intense ultraviolet radiation fields, photodesorption has been suggested as a nonthermal desorption mechanism promoting the transition of molecules from the solid state to the gas phase. Laboratory experiments measuring photodesorption rates are crucial in attempting to explain high molecular gas phase abundances of species that are expected to form in the solid state, such as methane, methanol, and acetonitrile, and to aid astrochemical modeling. Due to the convoluted competition between photodesorption and photoconversion, it is far from trivial to derive accurate photodesorption rates. Aims. The aim of this study is to apply a new methodology to discriminate between the two processes. The method has been validated using the well-studied case of CO and extended to CH4, CH3OH, and CH3CN. Methods. Vacuum ultraviolet (VUV; photon energy of 7–10.2 eV) irradiated ices at 20 K are studied, first as a pure CH4, CH3OH, or CH3CN ice and subsequently with an Ar coating on top. The latter is transparent to the VUV photons (wavelength below 200 nm), but it quenches the photodesorption process. Comparing the laser desorption post ionization time-of-flight mass spectrometry of the ices with and without the Ar coating provides information on the different interactions of the VUV photons with the ice. Results. The newly developed experimental technique allowed for a derivation of photodesorption rates for ices at 20 K of: CO (3.1 ± 0.3)×10−3 mol. photon−1, CH4 (3.1 ± 0.5)×10−2 mol. photon−1, and upper limits for CH3OH (< 6 × 10−5 mol. photon−1) and CH3CN (< 7.4 × 10−4 mol. photon−1); in the latter case, no literature values have been reported yet. The newly introduced approach provides more insight into the photodesorption process, in particular, for commonly observed complex organic molecules (COMs). Photoconversion cross sections are presented in the 7–10.2 eV range. The possible role of photodesorption and photoconversion in the formation of interstellar COMs is discussed.

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Section: Comparison With Other Studiessupporting

confidence: 86%

Novel approach to distinguish between vacuum UV-induced ice photodesorption and photoconversion

Bulak

Paardekooper

Fedoseev

et al. 2020

A&A

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“…The observed temperature effects for desorbing O 2 and H 2 ( Table 1) are similar to those observed in the UV range [24], and are well explained by diffusion and thermal desorption processes. At 15 K O 2 is not mobile and thus its desorption yield is very low and confined to the molecules produced near the surface.…”

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confidence: 74%

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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“…NH3 molecules were found to photodesorb with an average yield of 2.1 +2.1 −1.0 x 10 −3 molecules incident photon , which is of the same order than the photodesorption measured for H2O molecules during irradiation of a pure water ice (Cruz-Díaz et al (2017)). N2 molecules are not expected to efficiently photodesorb from pure N2 ices (Y pd (N2) ≤ 2 × 10 −4 molecules incident photon…”

Section: Resultssupporting

confidence: 52%

“…This value is on the order of the observed H2O photodesorption during photoprocessing of pure H2O ices using the same UV lamp, (Cruz-Díaz et al (2017)), while it is one order of magnitude lower than the photodesorption yield of CO molecules during photoprocessing of a pure CO ice (Muñoz Caro et al (2010)), and one order of magnitude higher than that measured for CO2 (see Table 4) under similar conditions (Martín-Doménech et al (2015)). Photodesorption of NH3 molecules from an ice mixture dominated by water will be addressed in a forthcoming paper, and is expected to be lower than the value presented in this paper for segregated (pure) NH3 ice (Loeffler & Baragiola (2010)).…”

Section: Astrophysical Implicationsmentioning

confidence: 65%

UV photoprocessing of NH3 ice: photon-induced desorption mechanisms

Martín-Doménech

Cruz-Díaz

Muñoz

2017

Monthly Notices of the Royal Astronomical Society

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Ice mantles detected on the surface of dust grains toward the coldest regions of the interstellar medium can be photoprocessed by the secondary ultraviolet (UV) field present in dense cloud interiors. In this work, we present UV-irradiation experiments under astrophysically relevant conditions of pure NH 3 ice samples in an ultra-high vacuum chamber where solid samples were deposited onto a substrate at 8 K. The ice analogs were subsequently photoprocessed with a microwave-discharged hydrogen-flow lamp. The induced radiation and photochemistry led to the production of H 2 , N 2 and N 2 H 4 . In addition, photodesorption to the gas phase of the original ice component, NH 3 , and two of the three detected photoproducts, H 2 and N 2 , was observed thanks to a quadrupole mass spectrometer (QMS). Calibration of the QMS allowed quantification of the photodesorption yields, leading to Y pd (NH 3 ) = 2.1 +2.1 −1.0 x 10 −3 molecules incident photon , which remained constant during the whole experiments, while photodesorption of H 2 and N 2 increased with fluence, pointing toward an indirect photodesorption mechanism involving energy transfer for these species. Photodesorption yield of N 2 molecules after a fluence equivalent to that experienced by ice mantles in space was similar to that of the NH 3 molecules (Y pd (N 2 ) = 1.7 +1.7 −0.9 x 10 −3 molecules incident photon ).

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New measurements on water ice photodesorption and product formation under ultraviolet irradiation

Cited by 39 publications

References 43 publications

Novel approach to distinguish between vacuum UV-induced ice photodesorption and photoconversion

Novel approach to distinguish between vacuum UV-induced ice photodesorption and photoconversion

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

UV photoprocessing of NH3 ice: photon-induced desorption mechanisms

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