Laboratory experiments on the radiation astrochemistry of water ice phases

Mifsud, Duncan V.; Hailey, Perry A.; Herczku, Péter; Juhász, Zoltán; Kovács, Sándor; Sulik, B.; Ioppolo, Sergio; Kaňuchová, Z.; McCullough, Robert; Paripás, Béla; Mason, Nigel J.

doi:10.1140/epjd/s10053-022-00416-4

Cited by 10 publications

(12 citation statements)

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“…Considering first the decay trends of the amorphous and crystalline H 2 S ices: it was noted that the rate of decay of the crystalline phase was significantly slower than that of the amorphous phase ( Figure 3 ). A similar trend was observed during the comparative electron irradiations of the amorphous and crystalline phases of CH 3 OH, N 2 O, and H 2 O ices ( Mifsud et al, 2022b ; Mifsud et al, 2022c ). This was attributed to the additional energy input required to disrupt the extensive intermolecular forces of attraction that characterise the crystalline solid before radiolytic chemistry as a result of molecular dissociation may proceed.…”

Section: Resultssupporting

confidence: 80%

“…3). A similar trend was observed during the comparative electron irradiations of the amorphous and crystalline phases of CH3OH, N2O, and H2O ices (Mifsud et al 2022b, Mifsud et al 2022c. This was attributed to the additional energy input required to disrupt the extensive intermolecular forces of attraction that characterise the crystalline solid before radiolytic chemistry as a result of molecular dissociation may proceed.…”

Section: Resultssupporting

confidence: 68%

“…Perhaps the most prominent of these is the significant broadening of the crystalline ice absorption bands, which also lose their resolved individual structures. This is due to radiation-induced amorphisation, which has been well documented in several ice species irradiated by ions, electrons, and ultraviolet photons; including H2O, CH3OH, N2O, and NH3 (e.g., Kouchi and Kuroda 1990, Moore et al 2007a, Famá et al 2010, Mifsud et al 2022b, Mifsud et al 2022c. It is interesting to note that, even at the end of the irradiation process once a fluence of >8×10 16 electrons cm -2 has been delivered to the crystalline ices, the appearances of their absorption bands are still not identical to those of the deposited amorphous ices.…”

Section: Resultsmentioning

confidence: 99%

“…It should be noted, however, that the extrapolation of radiation-induced amorphisation results acquired at low temperatures to higher ones may not be appropriate. For instance, although the amorphisation of crystalline H 2 O is known to occur efficiently as a result of its irradiation at 20 K, this process has never been reported at temperatures >70 K ( Mifsud et al, 2022c ). The efficiency of the radiation-induced crystalline SO 2 ice amorphisation process at various temperatures (including those relevant to the surface of Io) should therefore be tested in future experiments.…”

Section: Implications For Interstellar and Solar System Chemistrymentioning

confidence: 99%

“…Our recent work has also demonstrated that the solid phase of an irradiated ice plays a crucial role in determining the outcome of astrochemical reactions mediated by ionising radiation. Through a series of comparative electron irradiations, we have demonstrated that the radiolytic decay rate of an astrochemical ice is dependent upon the nature, strength, and extent of the intermolecular interactions that characterise its solid phase ( Mifsud et al, 2022b ; Mifsud et al, 2022c ). For instance, the decay rate of α-crystalline CH 3 OH was found to be significantly less rapid than that of the amorphous phase.…”

Section: Introductionmentioning

confidence: 99%

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Energetic electron irradiations of amorphous and crystalline sulphur-bearing astrochemical ices

et al. 2022

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Laboratory experiments have confirmed that the radiolytic decay rate of astrochemical ice analogues is dependent upon the solid phase of the target ice, with some crystalline molecular ices being more radio-resistant than their amorphous counterparts. The degree of radio-resistance exhibited by crystalline ice phases is dependent upon the nature, strength, and extent of the intermolecular interactions that characterise their solid structure. For example, it has been shown that crystalline CH3OH decays at a significantly slower rate when irradiated by 2 keV electrons at 20 K than does the amorphous phase due to the stabilising effect imparted by the presence of an extensive array of strong hydrogen bonds. These results have important consequences for the astrochemistry of interstellar ices and outer Solar System bodies, as they imply that the chemical products arising from the irradiation of amorphous ices (which may include prebiotic molecules relevant to biology) should be more abundant than those arising from similar irradiations of crystalline phases. In this present study, we have extended our work on this subject by performing comparative energetic electron irradiations of the amorphous and crystalline phases of the sulphur-bearing molecules H2S and SO2 at 20 K. We have found evidence for phase-dependent chemistry in both these species, with the radiation-induced exponential decay of amorphous H2S being more rapid than that of the crystalline phase, similar to the effect that has been previously observed for CH3OH. For SO2, two fluence regimes are apparent: a low-fluence regime in which the crystalline ice exhibits a rapid exponential decay while the amorphous ice possibly resists decay, and a high-fluence regime in which both phases undergo slow exponential-like decays. We have discussed our results in the contexts of interstellar and Solar System ice astrochemistry and the formation of sulphur allotropes and residues in these settings.

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Section: Resultssupporting

confidence: 80%

Section: Resultssupporting

confidence: 68%