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Molecular complexity in space (Originality)

Water in the Universe
With the launch of the Herschel observatory in 2007, the HIFI instrument will open up the submillimeter window to high resolution spectroscopic observations unobscured by telluric absorption. These observations from space will allow for the first time a systematic study of the multitude of water transitions expected in space. Water is a key ingredient in many environments, including young stellar objects, late type stars, planetary nebulae, dense molecular clouds, interstellar and circumstellar shocks, solar system objects such as comets, planets and satellites, and circumnuclear disks in Active Galactic Nuclei - essentially any dense and warm environment in space. Water is a cornerstone molecule in interstellar chemistry - influencing the abundances of many other species - and it can be a dominant reservoir of elemental oxygen in the gas phase. Because of its many levels, water is also an important coolant which can dominate the energy balance of the gas in such regions. This occurs in a very subtle way through a delicate balance between absorption of IR continuum radiation and rotational line emission; often in the same transition and, hence, requiring high spectral resolution. Of course, the many water levels with their different Einstein A values also provide a powerful diagnostic of the physical conditions in the emitting gas. HIFI has identified the study of water in space as one of its main goals. While water plays multiple roles on Earth, the prevailing low density and temperature of space make its excitation and chemistry in space unique. We have therefore selected this species for an in depth study of its molecular and physical characteristics under astrophysically relevant conditions.
Carbon chemistry
While some 10 years ago, molecular species were thought to be limited to highly shielded environments in space - so-called molecular clouds - where the conditions are fairly benign, it is now recognized that complex carbonaceous molecules are omnipresent, even in the harsh environment of the diffuse medium where they are exposed to strong photon fields. This has given new impetus to the study of carbon chemistry in space. For these large carbonaceous molecules, identification of specific molecules in space will have to be made through observations of their electronic transitions in the visible and ultraviolet or through their low ro-vibrational transitions in the submillimeter. Both of these types of transitions are unique tools for the identification of the specific molecules present in space. Astronomical observations have shown that two types of carbonaceous species are particularly relevant: large polycyclic aromatic hydrocarbons and long carbon chains. Both of these may be side-products or molecular intermediaries associated with carbon soot formed in the warm and dense ejecta of carbon-rich stars. Alternatively, they may also be efficiently formed in interstellar space, a possibility that the network will explore. Because of the multitude of isomers possible for large species, searches will have to target specific candidate species predicted to be highly abundant through the identification of the important chemical synthesis and fragmentation routes. This is a clear area of reseach where the power of the interdisciplinary nature of this network is imperative for further progress and we have selected it for an in depth study.
Deuterium: coming in from the cold
Ever since the detection of the first deuterated species some 30 years ago, deuterium fractionation has been recognized as an important diagnostic tool for astronomy. The deuterium abundance in space is five orders of magnitude less than that of hydrogen. Nevertheless, molecular species where one or more hydrogen atoms is replaced by a deuterium atom have much larger fractional abundances. Indeed, recently, deuterated methanol was measured to be as abundant as the fully hydrogenated methanol form around a low-mass solar-type protostar, while doubly deuterated methanol had an abundance of some 10% of that of the main isotope. These incredible deuterium fractionations reflect the small zero-point energy difference between the deuterated form and the main isotope. At the low temperatures of interstellar space, these small energy differences take on enormous importance and drive the chemistry towards transferring the deuterium from the main molecular (HD) reservoir to other species. The deuterium enhancement observed reflect the chemical routes involved, the actual energetic differences of the molecular species involved, and the local physical conditions. The latter become of course accessible through molecular observations themselves if molecular excitation rates are known. These simple chemical considerations show that deuterium fractionation provides a powerful tool for studying chemical routes in space. In order to tap this potential, a concerted research effort has to be directed towards identifying chemical routes, the spectroscopy of deuterated species and their excitation. Because the low temperatures are so unique to interstellar conditions and because of the low deuterium abundance, the physics and chemistry of deuterated species have received scant attention in the general physics and chemistry community.