We look ahead from the frontiers of research on ice dynamics in its broadest sense; on the structures of ice, the patterns or morphologies it may assume, and the physical and chemical processes in which it is involved. We highlight open questions in the various fields of ice research in nature; ranging from terrestrial and oceanic ice on Earth, to ice in the atmosphere, to ice on other solar system bodies and in interstellar space.

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We present the Infrared Space Observatory/Short-Wavelength Spectrometer full grating resolution spectrum of IRC +10216, which is dominated by strong absorption/emission bands of C2H2 and HCN. All C2H2 bands and the strong near-infrared stretching bands of HCN are observed in absorption, whereas the fundamental, hot, and combination bands of HCN involving the nu2 bending mode around 14 µm are observed in emission. Particularly strong is the HCN nu2=20-->nu2=11 vibrational transition at 14.3 µm. The most plausible mechanism for such emission is the radiative pumping of molecules from the ground to the nu2=20 state (7.1 µm) followed by radiative decay: nu2=20-->nu2=11. We present detailed models for HCN that verify the efficiency of the mentioned effect. The HCN abundance inferred from these models is &parl0;1.5-3&parr0;x10-5.

Aims. We studied the interaction between CO 2 (guest) and H 2 O (host) molecular ices. Methods. Ices of CO 2 and H 2 O are prepared by four different deposition techniques: sequential deposition (amorphous water ice followed by addition of CO 2 ), co-deposition (both gases added simultaneously), inverse sequential deposition (carbon dioxide ice followed by addition of water) and crystalline sequential deposition (crystalline water ice is prepared first and CO 2 is added afterwards). Samples are deposited at 80 K and are studied by temperature programmed desorption and transmission infrared spectroscopy. Results. Two slightly different varieties of association of CO 2 and H 2 O are revealed from the different spectroscopic properties of the asymmetric stretching band of 12 CO 2 and 13 CO 2 . The two varieties are found to co-exist in some of the samples at 80 K, whereas only the so-called internal CO 2 remains after heating at 105 K. At 80 K carbon dioxide is able to adhere to a crystalline water ice surface. Activation energies for the desorption of CO 2 from amorphous (E d = 20.7 ± 2 kJ mol −1 ) and crystalline (E d = 19.9 ± 2 kJ mol −1 ) water ice are derived from measurements of the sticking of CO 2 as a function of ice temperature. Conclusions. These findings may have implications for the study of icy bodies of the Solar System.

The molecular complexes formed by nitric acid with one, two, and three water molecules have been investigated by high level ab initio calculations. The B3LYP/aug-cc-pVTZ method and basis set have been used to derive equilibrium geometries and binding energies and to predict the infrared spectra of these complexes. It has been found that the complexes become stable through the formation of several hydrogen bonds. The main one is established between the acid, which acts as a donor, and the first water molecule, but further bonds are created between successive water molecules, with a weaker bond making a closed structure between the last water unit and the acid. Films of nitric acid mono-, di-, and trihydrates (NAM, NAD, and NAT) have been prepared by deposition on a cold surface and annealing to induce crystallization. RAIR spectra have been taken of these films. The spectra are compared to previous investigations, and the assignments of the spectra and the structure of the crystals are discussed. A global good agreement is obtained with previous transmission and RAIR spectra of thin films and extinction spectra of aerosols.

The conversion from neutral to zwitterionic glycine is studied using infrared spectroscopy from the point of view of the interactions of this molecule with polar (water) and non-polar (CO 2 , CH 4 ) surroundings. Such environments could be found on astronomical or astrophysical matter. The samples are prepared by vapour-deposition on a cold substrate (25 K), and then heated up to sublimation temperatures of the co-deposited species. At 25 K, the neutral species is favoured over the zwitterionic form in non-polar environments, whereas for pure glycine, or in glycine/water mixtures, the dominant species is the latter. The conversion is easily followed by the weakening of two infrared bands in the mid-IR region, associated to the neutral structure. Theoretical calculations are performed on crystalline glycine and on molecular glycine, both isolated and surrounded by water. Spectra predicted from these calculations are in reasonable agreement with the experimental spectra, and provide a basis to the assignments. Different spectral features are suggested as probes for the presence of glycine in astrophysical media, depending on its form (neutral or zwitterionic), their temperature and composition.

Carbon dioxide (CO 2 ) is one of the most relevant and abundant species in astrophysical and atmospheric media. In particular, CO 2 ice is present in several solar system bodies, as well as in interstellar and circumstellar ice mantles. The amount of CO 2 in ice mantles and the presence of pure CO 2 ice are significant indicators of the temperature history of dust in protostars. It is therefore important to know if CO 2 is mixed with other molecules in the ice matrix or segregated and whether it is present in an amorphous or crystalline form. We apply a multidisciplinary approach involving IR spectroscopy in the laboratory, theoretical modeling of solid structures, and comparison with astronomical observations. We generate an unprecedented highly amorphous CO 2 ice and study its crystallization both by thermal annealing and by slow accumulation of monolayers from the gas phase under an ultrahigh vacuum. Structural changes are followed by IR spectroscopy. We also devise theoretical models to reproduce different CO 2 ice structures. We detect a preferential in-plane orientation of some vibrational modes of crystalline CO 2 . We identify the IR features of amorphous CO 2 ice, and, in particular, we provide a theoretical explanation for a band at 2,328 cm −1 that dominates the spectrum of the amorphous phase and disappears when the crystallization is complete. Our results allow us to rule out the presence of pure and amorphous CO 2 ice in space based on the observations available so far, supporting our current view of the evolution of CO 2 ice.astrochemistry | solid state morphology C arbon dioxide (CO 2 ) has come to play a fundamental role in several aspects of the Earth's geophysics (1, 2), but it is also a key element in astrophysical research (3, 4). In the interior of dense interstellar clouds, as well as in the envelopes around young stars, dust grains are covered by ice mantles formed by frozen volatile molecules, with water being the most abundant molecular species, followed by carbon monoxide (CO), CO 2 , methanol, methane, and others (5, 6). The structure of CO 2 in the icy phase of the interstellar grains is still an open question. Is CO 2 mixed up with other frozen components, or is it segregated in multilayer structures (7)? Has it attained a crystalline arrangement, or does it have an amorphous structure (8)? Because solid CO 2 is an indicator of the temperature history in the envelopes of young stars (9, 10), it is important to address these questions. Most of the available information on these systems comes from spectroscopic observations. Thus, many laboratory experiments have been performed on low-temperature CO 2 , both as a single species and mixed with other components, using IR spectroscopy as the main detection tool (11-15). In the context of solid-state physics, the existence of transverse optical (TO) and longitudinal optical (LO) modes in amorphous materials was questioned because the origin of this effect was linked to long-range order in crystals, but it was proved that longitudinal mode...

The effect of UV photon (120-200 nm) and electron (2 keV) irradiation of analogues of interstellar carbonaceous dust and of glycine were investigated by means of IR spectroscopy. Films of hydrogenated amorphous carbon (HAC), taken as dust analogues, were found to be stable under UV photon and electron bombardment. High fluences of photons and electrons, of the order of 10(19) cm(-2), were needed for a film depletion of a few percent. UV photons were energetically more effective than electrons for depletion and led to a certain dehydrogenation of the HAC samples, whereas electrons led seemingly to a gradual erosion with no appreciable changes in the hydrocarbon structure. The rates of change observed may be relevant over the lifetime of a diffuse cloud, but cannot account for the rapid changes in hydrocarbon IR bands during the evolution of some proto-planetary nebulae. Glycine samples under the same photon and electron fluxes decay at a much faster rate, but tend usually to an equilibrium value different from zero, especially at low temperatures. Reversible reactions re-forming glycine, or the build-up of less transparent products, could explain this behavior. CO2 and methylamine were identified as UV photoproducts. Electron irradiation led to a gradual disappearance of the glycine layers, also with formation of CO2. No other reaction products were clearly identified. The thicker glycine layers (a few hundred nm) were not wholly depleted, but a film of the order of the electron penetration depth (80 nm), was totally destroyed with an electron fluence of -1 x 10(18) cm(-2). A 60 nm ice layer on top of glycine provided only partial shielding from the 2 keV electrons. From an energetic point of view, 2 keV electrons are less efficient than UV photons and, according to literature data, much less efficient than MeV protons for the destruction of glycine. The use of keV electrons to simulate effects of cosmic rays on analogues of interstellar grains should be taken with care, due to the low penetration depths of electrons in many samples of interest.