Structure, spectra, and mobility of low‐pressure ices: Ice I, amorphous solid water, and clathrate hydrates at T < 150 K

Abstract

Abstract. Recent advances in the study of low-pressure water ices, including clathrate hydrates, are examined, highlighting aspects of modern science possibly related to the behavior of water ices in extraterrestrial environments. An effort has been made to identify properties of ice that are likely to be important in the conditions that exist in such environments and to review advances in understanding these properties. The basic science of crystalline ice I is relatively mature, but attention is given to concepts, such as point defects, which continue to evolve and which relate in an important manner to the low-temperature behavior of ice ! as well as of amorphous ice and the clathrate hydrates. A concept of amorphous and microporous amorphous ice, developed in the early 1980s, is presented, but more recent characterizations are emphasized. Similarly, fundamental properties of clathrate hydrates are summarized and used in discussions of more recently appreciated characteristics that may be important in space science. Particular emphasis is placed on the formation, infrared spectroscopy, and behavior of clathrate hydrates in vacuo at temperatures below 150 K. The review closes with a section on the properties of ice nanoparticles, which have only recently emerged as a subject of molecular science. Modern experimental and theoretical studies of ice particles have focused on the infrared spectra and structure of the ice surface, and the interaction of the surface with molecular adsorbates. Since, with the exception of highenergy radiation, ice normally interacts with its environment through surface processes, such research may enlighten future studies.

Deposition and crystallization studies of thin amorphous solid water films on Ru(0001) and on CO-precovered Ru(0001)

“…Indeed, the surface of ASW has been characterized as such. 73 At coverages of D 2 O exceeding D 2 O ϳ 5 ML, the He intensity has reached plateaus and the shapes of the IRAS spectra are the same for all substrates. In what follows, we describe detailed adsorption features of D 2 O depending on the substrate observed from submonolayer to a few layers of D 2 O, i.e., the range depicted in Fig.…”

Communication: Distinguishing between bulk and interface-enhanced crystallization in nanoscale films of amorphous solid water

“…The use of HDO facilitates the observation and analysis of ASW crystallization because the O-D stretching frequency is decoupled from the OH stretch. 39,40 This is demonstrated in Figure 1 which shows that the initial broad amorphous spectrum (red curve) eventually transforms into a relatively sharp crystalline spectrum (blue curve) with a peak at ∼2426 cm 1 . The set of spectra have an isosbestic point, which is indicative of a transformation from one state (amorphous) to another (crystalline).…”

Ly-αphoton induced amorphization of Ic water ice at 16 Kelvin

“…When vapor is deposited at temperatures below ∼100 K the resulting ice is amorphous (P/ASW, Porous/Amorphous Solid Water). It is possible to obtain several forms of amorphous water ice (Boutron & Alben 1975;Hagen et al 1983;Jenniskens et al 1995); some of the sensible parameters are: substrate temperature and nature, deposition rate, deposition flow angle (Westley et al 1998;Devlin 2001). P/ASW once formed is unstable against temperature cycling: as T increases it is converted to crystalline ice on a time scale which depends exponentially on T (Schmitt et al 1989); at 150 K it is shorter than 10 s, at 20 K it is longer than the age of the Universe (Schmitt et al 1989).…”