Figure 1: The quiescent object Barnard 68 viewed in the visible (left) and infrared (right). Visible light is scattered by dust in the object, but infrared light is transmitted. Image copyright European Southern Observatory (ESO).

However, we now recognise that these cold dusty regions are in fact the progenitors of evolution in the modern Universe. Rich in chemical complexity, they are known to be the sites of star and planet formation and even the host for molecules that are necessary for the development of life itself. The young interdisciplinary science of Astrochemistry, lying at the interface of Astronomy, Astrophysics, Physics and Chemistry has evolved in order to explore the products, mechanisms and rates of the chemistry that dominates the Universe. Such astrochemistry is distinct from the chemistry occurring in the terrestrial and industrial environments for the following reasons:

• Due to the low densities encountered in many astronomical regions, the time scale of the chemical evolution of astronomical objects may be tens of thousands (or even millions) of years.
• The chemistry often takes place at much lower temperatures than those commonly encountered on Earth, emphasizing so-called barrierless chemical reactions.
• Chemical species not commonly found on Earth play a key role in astrochemistry e.g. the molecular ions H3+ and HeH+, both of which are believed to have taken part in the first chemical reactions to occur in the Universe.

Thus astrochemical research requires a multidisciplinary approach, bringing together researchers from astronomy, quantum physics/chemistry, surface science, condensed matter physics, low temperature physics as well as physical chemistry and chemical physics. This in turn requires the training of interdisciplinary researchers capable of assimilating techniques, ideas and practices from a wide range of scientific disciplines. In an earlier FP6 Research Training Network The Molecular Universe (http://molecular-universe.obspm.fr/index.php?page=home) aspects of the gas phase chemistry in these regions were explored. However, such chemistry cannot explain the overabundance of small hydrogenrich species such as molecular hydrogen (H2) and water (H2O) or the presence of more complex organic molecules, including those of potential biological significance, such as glycolaldehyde (CH2(OH)CHO, a sugar precursor), acetamide (CH3CONH2) and polycyclic aromatic and heteroaromatic species, that recent observations have shown are present in large abundances in such regions.

It is now recognised that if we are to understand the complex chemical synthesis prevalent in these dusty regions of the universe we must understand the heterogeneous chemistry that takes place on the surface of the micrometre-sized grains. Indeed, while Gould and Salpeter first proposed atomic recombination on dust grain surfaces as the most efficient mechanism for H2 formation in the 1960s, the true role of such heterogeneous chemistry has only become apparent with the recent data recorded by the Hubble, ISO and Spitzer space telescopes. This data has opened up the study into the socalled Gas-Grain Interaction, which may ultimately explain the formation of the chemical progenitors of life (Figure 2).

Figure 2: A cartoon illustrating some of the complexity of the gas-grain interaction in the ISM.

Dust grains are thought to have many roles including:

• Acting as catalysts for the formation of small hydrogen-rich molecules, including H2 itself.
• Acting as a reservoir for volatile gases through the accretion of icy mantles that are formed both by reaction on the grain surface (e.g. H2O) and condensation from the gas phase (e.g. CO). These mantles are returned to the gas phase during star formation to radiatively cool a collapsing gas clump.
• The icy mantles act as chemical nanofactories driven by light, electrons and cosmic rays to convert small molecules into more complex chemical species e.g. CO and H2O react to give carbon dioxide (CO2), H2O and methane (CH4) react to form methanol (CH3OH) and ammonia (NH3) and CH4 form methylamine (CH3NH2), seeding the Universe with the potential for life.
• Grains and their icy mantles are the building blocks from which comets, planets and other rocky bodies in the universe are assembled.

The Scientific Programme of the LASSIE ITN therefore seeks to address the cyclic role of dust in the chemical evolution of the Universe, from its synthesis in aged and dying stars, through its roles in the gas-grain interaction in increasingly dense environments in the interstellar medium (ISM) through to grain-grain collisions and the first steps in the construction of new stars and planetary systems. A combination of state-of-the-art computational and experimental chemical physics and molecular astronomy and astrophysics will be used to address these issues. The network brings together leading theoretical and experimental surface scientists working to unlock the secrets of the gas-grain interaction with astronomers engaged in observing and understanding star and planet formation and the role of icy dust grains in these processes. The network also includes several industrial partners who are producing the necessary state-of-the-art equipment to allow such research to be pursued.

The research programme of the LASSIE ITN is organised around five interconnected interdisciplinary themes (Figure 3) which have been internationally agreed as being the most urgent research topics for current astrochemical research and that aim to understand

1. the formation and destruction of interstellar dust.
2. the formation of simple molecules, and hence icy mantles, on realistic models of (icy) dust grain surfaces.
3. the physical processes that result when an icy grain mantle is heated or irradiated with light, electrons or ions.
4. the chemical processes that result when an icy grain mantle is heated or irradiated with light, electrons or ions.
5. the role of these processes in observations of grains, ices and the molecules formed by the intermediary of grains and their icy mantles in the evolving Universe.

Figure 3: Scientific themes and their connectivity within the LASSIE ITN.