The UMIST Database for Astrochemistry

The first release of the UMIST Database for Astrochemistry (UDfA) was made public in 1991 (Millar et al. 1991). It was, in main part, motivated by the various astrophysical applications - dark clouds, hot cores, circumstellar clouds, novae and supernovae - that were being studied by the UMIST Astrochemistry group at the time and the recognition that members of the group should have access to one set of reactions and rate coefficients that encompassed their various needs. Once we had done this, it became clear that releasing it to the wider community would encourage the spread of astrochemical modelling as a tool both to interpret and to test observations of molecules in space.

It has been known for some time that gas-phase synthesis of interstellar molecules has to be augmented through reactions in and on the icy mantles of interstellar dust grains. Gas-phase reactions do remain, however, the foundation on which such ice chemistry rests since it provides the feedstock for the grain mantle and can chemically process material that is removed from ices. The detections of around 100 new molecules in space in the last few years have led to the addition of many new reactions and species to gas-phase networks and reflects the importance of chemical networks in the interpretation of molecular line observations. This is particularly true in the current paradigm in which ‘bottom-up’ synthesis determines the abundances of larger species.

It is in this context that we present the sixth release of the database, Rate22 (previous releases: Rate91 – Millar et al. 1991; Rate95 – Millar et al. 1997; Rate99 – Le Teuff et al. 2000; Rate06 – Woodall et al. 2007; Rate12 – McElroy et al. 2013). Our fifth release (McElroy et al. 2013) contained 6173 reactions among 467 species and 13 elements and was developed in the context of the astronomical identification of around 150 molecular species at that time.

This version contains 8767 rate coefficients among 737 species involving 17 elements, making it around 50% bigger than Rate12.