This presentation has the following goals: (i) to explain, within a historical context, some of the difficulties in disentangling our Galaxy’s three-dimensional structure; (ii) to summarise in broad terms what we presently know of this structure, concentrating on those features inferred from accurate distance measurements; (iii) to illustrate selected aspects in a visually stimulating manner; and (iv) to give a foretaste of the exciting results that lie ahead with future space astrometric experiments.

Astrophysical processes in which grains play key roles are briefly reviewed.

Understanding the properties and the evolution of cosmic dust requires laboratory experiments for measuring basic physical and chemical data and simulating the interaction of dust grains with their cosmic environments. We give a short review of such laboratory experiments using analogue materials of cosmic dust.

Interplanetary dust particles (IDPs) are from asteroids and comets, and they are the smallest and most fine-grained meteoritic objects available for laboratory investigation. Cometary IDPs are of special significance because they are presently the only samples of comets, and comets are expected to be enriched in preserved solar nebula and presolar components. These components may include not only cosmically rare refractory circumstellar grains(e.g. SiC) that are recovered from meteorites but also cosmically abundant interstellar silicates and carbonaceous grains that were the fundamental building blocks of the Solar System. D/H ratios measured in IDPs are consistent with the survival of interstellar carbonaceous material, and some IDPs contain glassy grains with properties similar to those of interstellar “amorphous silicates”. Submicrometer forsterite and enstatite crystals in IDPs resemble circumstellar silicates detected by the Infrared Space Observatory (ISO). ISO also detected a broad ~ 23 µm feature around several stars, and a similar feature observed in IDP spectra is due to submicrometer FeNi sulfide grains, suggesting that sulfide grains may be a significant constituent of astronomical dust.

A brief overview of mid-infrared science and future ground- and space-based facilities at mid-infrared and submillimeter wavelengths is given.

A selection of recent highlights in the area of infrared observations of interstellar ices is presented. The essential role that laboratory astrophysics plays in the interpretation of the data, and current problems and expected future needs are discussed.

The exploitation of the recent observations (in particular by ISO) of the near infrared emission bands (UIBs) requires a good knowledge of the spectroscopic properties of the main proposed carriers, i.e. the Polycyclic Aromatic Hydrocarbons, which are expected to act as efficient UV/visible to infrared free-flying light converters.

The charge state of the interstellar PAHs strongly affects their spectroscopy. The laboratory study of the electronic transitions of PAH cations in the gas phase enables to address important questions, like their possible contribution to the Diffuse Interstellar Bands (visible and near-IR absorption), and the mechanism responsible for electronic to vibrational intramolecular energy conversion.

Microcanonical simulations based on hybrid quantum/classical theoretical methods reveal how strongly affected are the infrared intensities by both the charge state and the vibrational temperature.

An overview is given of the occurrence and properties of crystalline silicates in space. Crystalline silicates are found in circumstellar shells of both young and evolved stars, and are present in Solar System comets. These silicates are Mg-rich and Fe-poor, in contrast to amorphous silicates. We discuss the formation mechanism of crystalline silicates and the apparent lack of these grains in the interstellar medium.

Some recent observations of interstellar, circumstellar, and stellar atoms and molecules, with ground-based telescopes and ISO, are discussed. The advantages of observations with SIRTF and SOFIA, and needed laboratory work are mentioned more briefly.

It is impossible to explain the abundances of some gas-phase and most condensed-phase interstellar molecules without the use of grain chemistry. Nevertheless, grain-surface chemistry is relatively poorly understood for a variety of reasons. Our current knowledge of this chemistry and its use in interstellar models is discussed along with specific needs for future research.

Classical molecular dynamics (MD) computer simulations were performed to investigate the whole fundamental processes of the H2 formation reaction on the amorphous water ice as a model surface of icy mantles of dust grains. The product energy distribution and formation pumping mechanism of H2 for med on dust grains were also examined.

The experimental results that have been obtained in simulation experiments of grain surface- and photochemistry are reviewed, and ways to include these in models of dense cloud chemistry are indicated.

Molecular hydrogen may be excited by collisions with other particles (as in shock waves), by ultraviolet pumping (as in photon-dominated regions), through its formation on the surfaces of dust grains (in interstellar clouds), or by absorption of the cosmic background radiation (in the primordial gas). We consider the adequacy of our knowledge of H2, from the viewpoint of being able to reliably predict the spectrum arising from these excitation mechanisms.

This paper will review the importance of the water molecule in the various stages of the star formation process, addressing in particular how the recent observations obtained with the ISO and SWAS satellites have challenged the existing theoretical models.

Water is found in a wide variety of cool stars and substellar objects such as brown dwarfs. The detection of water vapor in such objects is reviewed.

Cometary water, the main constituent of nucleus ices, is difficult to observe directly. Breakthroughs were made recently using new ground based infrared instruments and space techniques (ISO and SWAS) on comets C/1996 B2 (Hyakutake), C/1995 01 (Hale-Bopp), 103P/Hartley 2, and C/1999 H1 (Lee): observations of water hot bands, of water rotational lines, and measurements of the [D]/[H] ratio and ortho-to-para ratio of water. We discuss the laboratory data necessary to model the water spectrum and to interpret these observations.