In order to understand much of the chemistry that underpins astronomical phenomena (e.g. star and planet formation) it is essential to probe the physico-chemistry of ice surfaces under astronomical conditions. The physical properties and chemical reactivity of such icy surfaces depends upon its morphology. Thus it is necessary to explore how the morphology of astrochemical ices is influenced by their local environment (e.g. temperature and pressure) and the mechanisms by which they are processed. In this paper we report the results of a series of experiments to explore the morphology of a variety of molecular ices using VUV spectroscopy. Spectral signatures are found that may allow the morphology of such ices to be identified.

This paper discusses the interaction of conditions in the liquid metal surrounding the keyhole which is formed when a laser is used as the source of power for welding, with conditions in the vapour itself. The transfer of power and matter across the interface is considered, and a simple model set up for the energy interchange and vapour flow in the keyhole itself. The principal processes are identified. The model is then used to calculate keyhole shapes, and the variation with depth of the related quantities is found.

The authors present the results of a morphological study of solid ammonia using both Fourier-transform infrared and vacuum ultraviolet (VUV) spectroscopy. Dramatic changes in the VUV and infrared spectra at temperatures between 65 and 85 K provide a deeper insight into the structure of ammonia ice particularly with the observation of an exciton transition at 194 nm (6.39 eV) in the VUV spectrum, revealing a structure that is composed of crystallites. A complementary structure is observed in the IR spectrum at 1100 cm(-1) which is assigned to the symmetric deformation of ammonia molecules at the surfaces of the crystallites. Such spectral signatures may be used to identify the environment within which the ammonia ice is formed and provide a new route for obtaining information on the physical and chemical conditions occurring within the interstellar medium, on the surfaces of planetary bodies, and in Kuiper belt objects.

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The keyhole formed during penetration welding with a laser is modelled so far as its thermal absorption characteristics are concerned by the combination of a point and a line source. In this way a representation of the broader surface section of the weld is obtained in addition to the lower section. A simple analytical form for the temperature distribution is obtained and possible weld profiles are found numerically from this. These are compared with examples of actual welds; it is possible in this way to estimate the proportion of the laser power absorbed in each section of the weld. Graphs and some simple approximations are given which allow it to be done easily for a given weld.