Measurements of D<sub>2</sub>Yields from Amorphous D<sub>2</sub>O Ice by Ultraviolet Irradiation at 12 K

Watanabe, Naoki; Horii, Toshikazu; Kouchi, Akira

doi:10.1086/309458

Cited by 73 publications

(59 citation statements)

References 34 publications

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“…However, none of these species are observed at low temperatures (less than 120 K), indicating that the major source of energetic hydrogen atoms is MA rather than water. Although UV irradiation can generate hydrogen atoms by the photodissociation of water molecules in ice (e.g., Watanabe et al 2000), this process appears to occur with much lower efficiency than the photodissociation of MA. The observation is consistent with the fact that the O-H bond in water is stronger than the C-H and N-H bonds in MA.…”

Section: Reaction Pathways To Glycine and Other Isomers In Uv Processmentioning

confidence: 99%

Formation of Glycine on Ultraviolet-Irradiated Interstellar Ice-Analog Films and Implications for Interstellar Amino Acids

Lee

Kim

Moon

et al. 2009

ApJ

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We report the synthesis of glycine on interstellar ice-analog films composed of water, methylamine (MA), and carbon dioxide under irradiation of ultraviolet (UV) photons. Analysis of the UV-irradiated ice films by in situ mass spectrometric methods revealed glycine and other isomers as photochemical products. Deuterium-labeling experiments were conducted to determine the structures of the photoproducts and to examine their formation pathways. The reactions occur via photocleavages of C-H and N-H bonds in MA, followed by subsequent reactions of the nascent H atom with CO 2 , leading to the formation of HOCO and then to glycine and carbamic acid. The photochemical synthesis of glycine occurs efficiently at the ice surfaces, and the competing photosynthesis and photodestruction processes can reach a steady-state kinetic balance at an extended UV exposure, maintaining a substantial population level of glycine. The observation suggests that interstellar amino acids can be created on ice grains, and that they can also be stored in the ices by maintaining a kinetic balance under interstellar UV irradiation. As such, the transport of amino acids in interstellar space may be possible without depleting the net abundance of amino acids in the ices but rather increasing the structural diversity of the molecules.

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Section: Reaction Pathways To Glycine and Other Isomers In Uv Processmentioning

confidence: 99%

Formation of Glycine on Ultraviolet-Irradiated Interstellar Ice-Analog Films and Implications for Interstellar Amino Acids

Lee

Kim

Moon

et al. 2009

ApJ

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“…Ghormley & Hochanadel (1971) observed H, OH, and H 2 O 2 following UV irradiation of crystalline ice at 263 K, while Gerakines et al (1996) found production of OH, HO 2 , and H 2 O 2 in the ice upon exposing amorphous ice at 10 K to UV light covering mainly the first and second electronic absorption bands of H 2 O. Watanabe et al (2000) irradiated amorphous D 2 O ice at 12 K with UV photons and observed substantial amounts of D 2 after irradiation at λ = 126 nm, but very little at λ = 172 nm. In the experiments by Yabushita et al (2006) H atoms were found to desorb from the ice after UV irradiation at λ = 157 nm and λ = 193 nm.…”

Section: Introductionmentioning

confidence: 99%

Photodesorption of water ice

Andersson

Dishoeck²

2008

A&A

181

253

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Context. Absorption of ultraviolet radiation by water ice coating interstellar grains can lead to dissociation and desorption of the ice molecules. These processes are thought to be important in the gas-grain chemistry in molecular clouds and protoplanetary disks, but very few quantitative studies exist. Aims. We compute the photodesorption efficiencies of amorphous water ice and elucidate the mechanisms by which desorption occurs. Methods. Classical molecular dynamics calculations were performed for a compact amorphous ice surface at 10 K thought to be representative of interstellar ice. Dissociation and desorption of H 2 O molecules in the top six monolayers are considered following absorption into the first excited electronic state with photons in the 1300−1500 Å range. The trajectories of the H and OH photofragments are followed until they escape or become trapped in the ice. Results. The probability for H 2 O desorption per absorbed UV photon is 0.5−1% in the top three monolayers, then decreases to 0.03% in the next two monolayers, and is negligible deeper into the ice. The main H 2 O removal mechanism in the top two monolayers is through separate desorption of H and OH fragments. Removal of H 2 O molecules from the ice, either as H 2 O itself or its products, has a total probability of 2−3% per absorbed UV photon in the top two monolayers. In the third monolayer the probability is about 1% and deeper into the ice the probability of photodesorption falling to insignificant numbers. The probability of any removal of H 2 O per incident photon is estimated to be 3.7 × 10 −4 , with the probability for photodesorption of intact H 2 O molecules being 1.4 × 10 −4 per incident photon. When no desorption occurs, the H and OH products can travel up to 70 and 60 Å inside or on top of the surface, respectively, during which they can react with other species, such as CO, before they become trapped.

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“…In particular, the maximal value of Y 0 ∼ 8 × 10 −3 molecule photon −1 obtained at T = 100 K corresponded approximately to the probability of desorption from the topside molecular layer of the ice. Watanabe et al (2000) carried out mass -spectroscopy experiments on the formation of D 2 molecules from amorphous thin (thickness 4 and 12 nm) D 2 O ice samples by VUV irradiation (126 and 172 nm) at 12 K. According to their results, only a small fraction of the total D 2 photoproducts was released into gas-phase at the low temperature. Also they determined the cross section for the photodestruction of D 2 O which was found out to be close to the results gotten by Westley et al (1995a, b) for water ice.…”

Section: Introductionmentioning

confidence: 99%

Technical Note: VUV photodesorption rates from water ice in the 120–150 K temperature range – significance for Noctilucent Clouds

et al. 2011

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Abstract. Laboratory studies have been carried out with the aim to improve our understanding of physicochemical processes which take place at the water ice/air interface initiated by solar irradiation with a wavelength of 121.6 nm. It was intended to mimic the processes of ice particles characteristic of Noctilucent Clouds (NLCs). The experimental set-up used includes a high-vacuum chamber, a gas handling system, a cryostat with temperature controller, an FTIR spectrometer, a vacuum ultraviolet hydrogen lamp, and a microwave generator. We report the first results of measurements of the absolute photodesorption rate (loss of substance due to the escape of photoproducts into gas phase) from thin (20-100 nm) water ice samples kept in the temperature range of 120-150 K. The obtained results show that a flow of photoproducts into the gas phase is considerably lower than presumed in the recent study by Murray and Plane (2005). The experiments indicate that almost all photoproducts remain in the solid phase, and the principal chemical reaction between them is the recombination reaction H + OH → H 2 O which is evidently very fast. This means that direct photolysis of mesospheric ice particles seems to have no significant impact on the gas phase chemistry of the upper mesosphere.

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Measurements of D₂Yields from Amorphous D₂O Ice by Ultraviolet Irradiation at 12 K

Cited by 73 publications

References 34 publications

Formation of Glycine on Ultraviolet-Irradiated Interstellar Ice-Analog Films and Implications for Interstellar Amino Acids

Formation of Glycine on Ultraviolet-Irradiated Interstellar Ice-Analog Films and Implications for Interstellar Amino Acids

Photodesorption of water ice

Technical Note: VUV photodesorption rates from water ice in the 120–150 K temperature range – significance for Noctilucent Clouds

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Measurements of D2Yields from Amorphous D2O Ice by Ultraviolet Irradiation at 12 K

Cited by 73 publications

References 34 publications

Formation of Glycine on Ultraviolet-Irradiated Interstellar Ice-Analog Films and Implications for Interstellar Amino Acids

Formation of Glycine on Ultraviolet-Irradiated Interstellar Ice-Analog Films and Implications for Interstellar Amino Acids

Photodesorption of water ice

Technical Note: VUV photodesorption rates from water ice in the 120–150 K temperature range – significance for Noctilucent Clouds

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Measurements of D₂Yields from Amorphous D₂O Ice by Ultraviolet Irradiation at 12 K