H2O and O(3PJ) photodesorption from amorphous solid water deposited on a lunar mare basalt

DeSimone, Alice J.; Orlando, Thomas M.

doi:10.1016/j.icarus.2014.08.023

Cited by 14 publications

(13 citation statements)

References 18 publications

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“…VUV lasers offers a potentially higher flux monochromatic option. They have been used in ice photodesorption experiments to measure H 2 O and O( 3 P J ), and benzene photodesorption from water ice (mixtures), and their use could certainly be expanded to more ice photochemistry studies. , …”

Section: Experimental Methodsmentioning

confidence: 99%

“…VUV lasers offers a potentially higher flux monochromatic option. They have been used in ice photocdesorption experiments to measure H 2 O and O( 3 P J ), and benzene photodesorption from water ice (mixtures), and their use could certainly be expanded to more ice photochemistry studies 99,100. Finally, synchrotron beamlines in the VUV provides a monochromatic tunable source of UV photons ideal to study photochemical mechanisms in ices.…”

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confidence: 99%

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Photochemistry and Astrochemistry: Photochemical Pathways to Interstellar Complex Organic Molecules

2016

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The interstellar medium is characterized by a rich and diverse chemistry. Many of its complex organic molecules are proposed to form through radical chemistry in icy grain mantles.Radicals form readily when interstellar ices (composed of water and other volatiles) are exposed to UV photons and other sources of dissociative radiation, and if sufficiently mobile the radicals can react to form larger, more complex molecules. The resulting complex organic molecules (COMs) accompany star and planet formation, and may eventually seed the origins of life on nascent planets. Experiments of increasing sophistication have demonstrated that known interstellar COMs as well as the prebiotically interesting amino acids can form through ice photochemistry. We review these experiments and discuss the qualitative and quantitative kinetic and mechanistic constraints they have provided. We finally compare the effects of UV radiation with those of three other potential sources of radical production and chemistry in interstellar ices: electrons, ions and X-rays.

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Section: Experimental Methodsmentioning

confidence: 99%

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confidence: 99%

Photochemistry and Astrochemistry: Photochemical Pathways to Interstellar Complex Organic Molecules

2016

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“…For the adsorption rate of the hydroxyl radicals, we are assuming no energy barriers and no temperature variation in the sticking coefficient held constant at unity. Finally, an additional M ─ OH loss term ( k 8 ) is considered via photon‐stimulated desorption (DeSimone & Orlando, ). Here the M ─ OH complex can become electronically excited and desorb following relaxation along a repulsive surface (Knotek, ).…”

Section: Methodsmentioning

confidence: 99%

“…Similar to thermal induced RD, photoexcitation can cause OH radicals to combine resulting in gas‐phase water. The cross section for this process was taken as 6 × 10 −19 cm 2 (DeSimone & Orlando, ). Finally, water desorption ( k 9 ) was considered to follow standard Polany‐Wigner equation with a normal prefactor of 10 13 s −1 and desorption activation energy of 55 kJ/mole (Poston et al, ).…”

Section: Methodsmentioning

confidence: 99%

Solar Wind‐Induced Water Cycle on the Moon

Jones

Aleksandrov

Hibbitts

et al. 2018

Geophysical Research Letters

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The solar wind has been implicated as a source of water on airless bodies such as the Moon, asteroids, and possibly Mercury, yet a kinetic and mechanistic chemical model consistent with present-day observational data is still lacking. Utilizing available data sets on temperature-driven water formation and desorption from metal oxides (e.g., SiO 2 , TiO 2 , and Al 2 O 3 ) with surface hydroxyl defects (─OH) and experimental data from a lunar mare regolith Apollo sample (10084), the 2.8-μm optical signal on the Moon is modeled. Specifically, the presence and persistence of this band result from the balance of formation and loss mechanisms associated with solar wind production and thermal transformation of hydroxyls on and within the regolith. This cycle involves formation and release of molecular water via recombinative desorption of the chemically bound ─OH. Though this mechanism forms gas-phase H 2 O on the sunlit side, photodissociation and dissociative adsorption lead to rehydroxylation and very limited exospheric water over a lunation.Plain Language Summary The idea that water exists on the Moon has been around for many years, and its presence would provide a useful resource for human exploration. Lunar water is often observed by examining the 2.8-3 micron optical absorption feature seen in the reflecting sunlight. This feature is mainly associated with bound ─OH groups made from solar wind implantation and/or from molecular water dissociating upon adsorption onto the regolith. Molecular water can form when the Moon's surface reaches 50 K above room temperature. In this process, neighboring ─OH groups combine and react producing molecular water. This has been documented to occur at these relatively low temperatures for some metal oxides that are known constituents of the lunar regolith. The water will then leave following a ballistic trajectory and either molecularly adsorb or dissociate. We have modeled this process and show that the recent observations of the Moon's water may be mostly related to the presence of ─OH and only a small amount of exospheric water. This process can also happen on asteroids and Mercury or any other surface that is bombarded by the solar wind and can heat up above 350 K.

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“…More recently, the investigation of water photodesorption in the VUV using excimer lasers at 6.4 eV (193 nm) and 7.9 eV (157 nm) coupled to a direct probe of the ejected species by Resonance Enhanced Multiphoton Ionisation (REMPI) have provided much insights on the desorption mechanisms from amorphous solid water at 100 K. Yabushita et al (2013) have reviewed these experimental results. Similar experiments, with slightly different conclusions on the kinetic energy released, have also been performed on thick water ice (DeSimone et al 2013;DeSimone & Orlando 2014) and compared to photodesorption from thinner Amorphous Solid Water (ASW) layers deposited on lunar substrates (DeSimone et al 2013;DeSimone & Orlando 2015). All the above results could be faced to a valuable series of results from molecular dynamics simulations studying the desorption events from ASW at low (10 K) and high temperature (90-100 K), which originate from initial photodissociation in the 7-9 eV energy range (Andersson & van Dishoeck 2008;Arasa et al 2010;Andersson et al 2011).…”

Section: Introductionmentioning

confidence: 98%

Vacuum-UV photodesorption from compact Amorphous Solid Water : photon energy, isotopic and temperature effects

Fillion¹,

Dupuy²,

Féraud³

et al. 2021

Preprint

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Context. Vacuum-UV (VUV) photodesorption from water-rich ice mantles coating interstellar grains is known to play an important role on the gas-to-ice ratio in stars and planets formation regions. Quantitative photodesorption yields from water ice are crucial for astrochemical models. Aims. The aims is to provide the first quantitative photon-energy dependent photodesorption yields from water ices in the VUV. This information is important for the understanding of the photodesorption mechanisms and to account for the variation of the yields under interstellar irradiation conditions. Methods. Experiments have been performed on the DESIRS beamline at the SOLEIL synchrotron facility (St Aubin, France), delivering tunable VUV radiation, using the ultra-high SPICES (Surface Processes and ICES) vacuum chamber. Thick compact amorphous solid water ice (H 2 O and D 2 O) grown onto a cold Au substrate have been irradiated from 7 to 13.5 eV. Quantitative yields have been obtained by detection into the gas phase with mass-spectrometry for sample temperatures ranging from 15 K to 100 K. Results. Photodesorption spectra of H 2 O (D 2 O), OH (OD), H 2 (D 2 ) and O 2 peak around 9-10 eV and decrease at higher energies. Average photodesorption yields of intact water at 15 K are 5 × 10 −4 molecule/photon for H 2 O and 5 × 10 −5 molecule/photon for D 2 O over the 7-13.5 eV range. The strong isotopic effect can be explained by a differential chemical recombination between OH (OD) and H (D) photofragments originating from lower kinetic energy available for the OH photofragments upon direct water photodissociation and/or possibly by an electronic relaxation process. It is expected to contribute to water fractionation during the building-up of the ice grain mantles in molecular clouds and to favor OH-poor chemical environment in comet-formation regions of protoplanetary disks. The yields of all the detected species except OH (OD) are enhanced above (70 ±10) K, suggesting an ice restructuration at this threshold temperature.

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H2O and O(3PJ) photodesorption from amorphous solid water deposited on a lunar mare basalt

Cited by 14 publications

References 18 publications

Photochemistry and Astrochemistry: Photochemical Pathways to Interstellar Complex Organic Molecules

Photochemistry and Astrochemistry: Photochemical Pathways to Interstellar Complex Organic Molecules

Solar Wind‐Induced Water Cycle on the Moon

Vacuum-UV photodesorption from compact Amorphous Solid Water : photon energy, isotopic and temperature effects

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