Pore evolution in interstellar ice analogues

Cazaux, S.; Bossa, Jean-Baptiste; Linnartz, H.; Tielens, A. G. G. M.

doi:10.1051/0004-6361/201424466

Cited by 38 publications

(44 citation statements)

References 48 publications

(58 reference statements)

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“…One way to account for a SSA increase would be if pore clustering occurs in the ice, leading to larger (internal) pore surface areas in addition to the ice interface to the vacuum. Such a pore clustering was inferred by positron-annihilation spectroscopy [28] and recent kinetic Monte Carlo ice simulations [29]. Our c-ASW ice sample, however, exhibits no pore clustering-the pore shape, the radius (R G ), and periodic spacings between pores all remain constant.…”

supporting

confidence: 50%

Neutron Scattering Analysis of Water’s Glass Transition and Micropore Collapse in Amorphous Solid Water

et al. 2016

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The question of the nature of water's glass transition has continued to be disputed over many years. Here we use slow heating scans (0.4 K min^{-1}) of compact amorphous solid water deposited at 77 K and an analysis of the accompanying changes in the small-angle neutron scattering signal, to study mesoscale changes in the ice network topology. From the data we infer the onset of rotational diffusion at 115 K, a sudden switchover from nondiffusive motion and enthalpy relaxation of the network at <121 K to diffusive motion across sample grains and sudden pore collapse at >121 K, in excellent agreement with the glass transition onset deduced from heat capacity and dielectric measurements. This indicates that water's glass transition is linked with long-range transport of water molecules on the time scale of minutes and, thus, clarifies its nature. Furthermore, the slow heating rates combined with the high crystallization resistance of the amorphous sample allow us to identify the glass transition end point at 136 K, which is well separated from the crystallization onset at 144 K-in contrast to all earlier experiments in the field.

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confidence: 50%

Neutron Scattering Analysis of Water’s Glass Transition and Micropore Collapse in Amorphous Solid Water

et al. 2016

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“…However, it is unclear whether these cavities are closed inside the bulk ASW or interconnected and accessible from the vacuumice interface. In Figure 3 of Raut et al (2007b) and Figure 8 of Cazaux et al (2015), it was hinted that there are closed cavities, but there was no discussion about the connectivity of the cavities. In Figure 12 in this work, it is evident that after CO adsorption, the 3696 cm −1 band always drops to zero, regardless of the annealing temperature.…”

Section: Discussion and Astrophysical Implicationsmentioning

confidence: 99%

The Effective Surface Area of Amorphous Solid Water Measured by the Infrared Absorption of Carbon Monoxide

Clements

Emtiaz

et al. 2019

ApJ

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The need to characterize ices coating dust grains in dense interstellar clouds arises from the importance of ice morphology in facilitating the diffusion and storage of radicals and reaction products in ices, a well-known place for the formation of complex molecules. Yet, there is considerable uncertainty about the structure of ISM ices, their ability to store volatiles and under what conditions. We measured the infrared absorption spectra of CO on the pore surface of porous amorphous solid water (ASW), and quantified the effective pore surface area of ASW. Additionally, we present results obtained from a Monte Carlo model of ASW in which the morphology of the ice is directly visualized and quantified. We found that 200 ML of ASW annealed to 20 K has a total pore surface area that is equivalent to 46 ML. This surface area decreases linearly with temperature to about 120 K. We also found that (1) dangling OH bonds only exist on the surface of pores; (2) almost all of the pores in the ASW are connected to the vacuum-ice interface, and are accessible for adsorption of volatiles from the gas phase; there are few closed cavities inside ASW at least up to a thickness of 200 ML; (3) the total pore surface area is proportional to the total 3-coordinated water molecules in the ASW in the temperature range 60-120 K. We also discuss the implications on the structure of ASW and surface reactions in the ice mantle in dense clouds.

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“…In Table 2 we observe that these two photodissociation pathways yielding CH 3 and CH 2 radicals are among the slowest steps in the network (r0.1% of the fastest reactions) and therefore determine the rate at which the overall scheme proceeds. 36,45 Compared to photodissociation rates measured in the gas phase, photodissociation rates in the solid phase are in general substantially lower, most likely because of the fast reverse reactions between the dissociation fragments. Previous experimental studies on ices have demonstrated that the photodissociation rates of methane strongly depend on the environment.…”

Section: Discussionmentioning

confidence: 99%

Methane ice photochemistry and kinetic study using laser desorption time-of-flight mass spectrometry at 20 K

Bossa

Paardekooper

Isokoski

et al. 2015

Phys. Chem. Chem. Phys.

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The ice photochemistry of pure methane (CH4) is studied at 20 K upon VUV irradiation from a microwave discharge H2 flow lamp. Laser Desorption Post-Ionization Time-Of-Flight Mass Spectrometry (LDPI TOF-MS) is used for the first time to determine branching ratios of primary reactions leading to CH3, CH2, and CH radicals, typically for fluences as expected in space. This study is based on a stable end-products analysis and the mass spectra are interpreted using an appropriate set of coupled reactions and rate constants. This yields clearly different values from previous gas phase studies. The matrix environment as well as the higher efficiency of reverse reactions in the ice clearly favor CH3 radical formation as the main first generation photoproduct.

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Pore evolution in interstellar ice analogues

Cited by 38 publications

References 48 publications

Neutron Scattering Analysis of Water’s Glass Transition and Micropore Collapse in Amorphous Solid Water

Neutron Scattering Analysis of Water’s Glass Transition and Micropore Collapse in Amorphous Solid Water

The Effective Surface Area of Amorphous Solid Water Measured by the Infrared Absorption of Carbon Monoxide

Methane ice photochemistry and kinetic study using laser desorption time-of-flight mass spectrometry at 20 K

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