Vacuum Ultraviolet Photodesorption and Photofragmentation of Formaldehyde-Containing Ices

Féraud, Géraldine; Bertin, M.; Romanzin, C.; Dupuy, Rémi; Petit, Franck; Roueff, E.; Philippe, L.; Michaut, X.; Jeseck, Pascal; Fillion, J.-H.

doi:10.1021/acsearthspacechem.9b00057

Cited by 17 publications

(9 citation statements)

References 125 publications

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“…Finally, for the specific case of CH 3 OH photodesorption, Bertin et al (2016) suggested that the UV photodesorption of methanol from pure methanol ice originates from the exothermic recombination of CH 3 O/CH 2 OH into CH 3 OH followed by its desorption (also suggested by Öberg 2016). An exothermic recombination was also proposed in similar experiments as a possible route for the UV photodesorption of H 2 CO from formaldehyde-containing ices (Féraud et al 2019). Bennett et al (2007) suggested that the main dissociation channels of CH 3 OH in condensed phase by 5 keV electrons lead to CH 2 OH, CH 3 O, and CH 4 formation.…”

Section: Mechanisms For the X-ray Photodesorption Of Neutrals From Pumentioning

confidence: 80%

Complex organic molecules in protoplanetary disks: X-ray photodesorption from methanol-containing ices

Basalgète

Dupuy

Féraud

et al. 2021

A&A

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Context. Astrophysical observations show complex organic molecules (COMs) in the gas phase of protoplanetary disks. X-rays emitted from the central young stellar object that irradiate interstellar ices in the disk, followed by the ejection of molecules in the gas phase, are a possible route to explain the abundances observed in the cold regions. This process, known as X-ray photodesorption, needs to be quantified for methanol-containing ices. This Paper I focuses on the case of X-ray photodesorption from pure methanol ices. Aims. We aim at experimentally measuring X-ray photodesorption yields (in molecule desorbed per incident photon, displayed as molecule/photon for more simplicity) of methanol and its photo-products from pure CH3OH ices, and to shed light on the mechanisms responsible for the desorption process. Methods. We irradiated methanol ices at 15 K with X-rays in the 525–570 eV range from the SEXTANTS beam line of the SOLEIL synchrotron facility. The release of species in the gas phase was monitored by quadrupole mass spectrometry, and photodesorption yields were derived. Results. Under our experimental conditions, the CH3OH X-ray photodesorption yield from pure methanol ice is ~10−2 molecule/photon at 564 eV. Photo-products such as CH4, H2CO, H2O, CO2, and CO also desorb at increasing efficiency. X-ray photodesorption of larger COMs, which can be attributed to either ethanol, dimethyl ether, and/or formic acid, is also detected. The physical mechanisms at play are discussed and must likely involve the thermalization of Auger electrons in the ice, thus indicating that its composition plays an important role. Finally, we provide desorption yields applicable to protoplanetary disk environments for astrochemical models. Conclusions. The X-rays are shown to be a potential candidate to explain gas-phase abundances of methanol in disks. However, more relevant desorption yields derived from experiments on mixed ices are mandatory to properly support the role played by X-rays in nonthermal desorption of methanol (see Paper II).

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Section: Mechanisms For the X-ray Photodesorption Of Neutrals From Pumentioning

confidence: 80%

Complex organic molecules in protoplanetary disks: X-ray photodesorption from methanol-containing ices

Basalgète

Dupuy

Féraud

et al. 2021

A&A

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“…where Y pd is the photodesorption yield (i.e., the fraction of molecules ejected over the total number of incident UV photons), G 0 is the strength of the UV photons relative to the standard interstellar radiation field. Y pd does vary on orders of magnitude from one molecule to the other (Féraud et al 2019). The timescales are shown in Figure 7.…”

Section: Ch3 Co Ohmentioning

confidence: 99%

“…The timescales are shown in Figure 7. One can see that the timescale of the rotational desorption is much shorter than that of the sublimation at T d ≤ 100 K. The thermal sublimation is dominant at T d ≥ 170 K. If we assume G 0 = U 0 = 10 5 , and adopt Y pd 7 × 10 −4 as for H 2 CO (i.e., 4-10 ×10 −4 , Féraud et al 2019), the rotational desorption mechanism is shorter than the UV photodesorption at n H < 5 × 10 6 cm −3 with 80 K ≤ T d ≤ 100 K. However, Bertin et al (2016) experimentally showed that the photodesorption yield is an order of 10 −5 for pure methanol ices, and even lower than 10 −6 when it mixes with CO molecules in the ice. In this case, the rotational desorption is dominant over the UV photodesorption.…”

Section: Ch3 Co Ohmentioning

confidence: 99%

Observational evidence for rotational desorption of Complex Molecules by radiative torques from Orion BN/KL

Tram,

Lee,

Hoang

et al. 2020

Preprint

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Complex Organic Molecules (COMs) are believed to form in the ice mantle of dust grains and are released to the gas by thermal sublimation when grain mantles are heated to temperatures of T d 100 K. However, some COMs are detected in regions with temperatures below 100 K. Recently, a new mechanism of rotational desorption due to centrifugal stress induced by radiative torques (RATs) is proposed by that can desorb COMs at low temperatures. In this paper, we report observational evidence for rotational desorption of COMs toward the nearest massive star-forming region Orion BN/KL. We compare the abundance of COMs computed using the rotational desorption mechanism with observations by ALMA, and demonstrate that the rotational desorption mechanism can explain the detection of COMs. We also analyze the polarization data from SOFIA/HAWC+ and JCMT/SCUBA-2 and find that the polarization degree at far-infrared/submm decreases with increasing the grain temperature for T d 71 K. This is consistent with the theoretical prediction using the Radiative Torque (RAT) alignment theory and Radiative Torque Disruption (RATD) mechanism. Such an anti-correlation between dust polarization and dust temperature supports the rotational disruption as well as rotational desorption mechanism of COMs induced by RATs.

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“…pure CH 3 CN ices. Several experimental studies regarding UV photodesorption of simple molecules such as CO, CO 2 , N 2 or CH 4 (Bertin et al 2013;Fillion et al 2014;Carrascosa et al 2019;Dupuy et al 2017) and more complex molecules such as CH 3 OH and H 2 CO (Bertin et al 2016;Martín-Doménech et al 2016;Féraud et al 2019) have shown that UV photodesorption yields are strongly dependent on the ice composition: e.g., when diluted in CO-dominated ices, CH 3 OH UV photodesorption is quenched whereas H 2 CO UV photodesorption is enhanced, compared to the case of pure CH 3 OH and H 2 CO ice respectively. This indicates that the UV photodesorption of complex molecules should be systematically studied as a function of the ice composition.…”

Section: Introductionmentioning

confidence: 99%

Photodesorption of acetonitrile CH3CN in UV-irradiated regions of the Interstellar Medium: an experimental evidence

Basalgète,

Ocaña,

Féraud

et al. 2021

Preprint

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Pure acetonitrile (CH 3 CN) and mixed CO:CH 3 CN and H 2 O:CH 3 CN ices have been irradiated at 15 K with Vacuum UltraViolet (VUV) photons in the 7-13.6 eV range using synchrotron radiation. VUV photodesorption yields of CH 3 CN and of photo-products have been derived as a function of the incident photon energy. The coadsorption of CH 3 CN with CO and H 2 O molecules, which are expected to be among the main constituents of interstellar ices, is found to have no significant influence on the VUV photodesorption spectra of CH 3 CN, CHCN•, HCN, CN• and CH 3 •. Contrary to what has generally been evidenced for most of the condensed molecules, these findings point toward a desorption process for which the CH 3 CN molecule that absorbs the VUV photon is the one desorbing. It can be ejected in the gas phase as intact CH 3 CN or in the form of its photo-dissociation fragments. Astrophysical VUV photodesorption yields, applicable to different locations, are derived and can be incorporated into astrochemical modeling. They vary from 0.67(±0.33) × 10 −5 to 2.0(±1.0) × 10 −5 molecule/photon for CH 3 CN depending on the region considered, which is high compared to other organic molecules such as methanol. These results could explain the multiple detections of gas phase CH 3 CN in different regions of the interstellar medium and are well-correlated to astrophysical observations of the Horsehead nebula and of protoplanetary disks (such as TW Hya and HD 163296).

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Vacuum Ultraviolet Photodesorption and Photofragmentation of Formaldehyde-Containing Ices

Cited by 17 publications

References 125 publications

Complex organic molecules in protoplanetary disks: X-ray photodesorption from methanol-containing ices

Complex organic molecules in protoplanetary disks: X-ray photodesorption from methanol-containing ices

Observational evidence for rotational desorption of Complex Molecules by radiative torques from Orion BN/KL

Photodesorption of acetonitrile CH3CN in UV-irradiated regions of the Interstellar Medium: an experimental evidence

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