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.