The Chemical Modelling of Protoplanetary Disks in the Era of ALMA

Catherine Walsh

Protoplanetary disks are vital objects in star and planet formation.
They contain all the matter, gas and dust, which will go into forming a
planetary system surrounding the new star. Since much of the disk
consists of cold (~ 10 K) to warm (~ 100 K) molecular material, the
observation of molecules in disks are a vital tool in determining disk
physical conditions and chemical composition. This information, coupled
with detailed disk modelling, helps us unravel the conditions prior to,
and during, planet formation, which also aids our understanding of the
current configuration and composition of our Solar System. To date, only
a handful of molecules have been observed in disks around young stars,
usually small neutral molecules and molecular cations (and corresponding
isotopologues) which are relatively abundant and which possess simple
rotational and/or vibrational spectra e.g., CO, HCO+, HCN, CS, OH, and
H2O. The most complex molecule observed to date is formaldehyde, H2CO.
In this talk, I present the methods and tools used in modern chemical
models of protoplanetary disks, outlining what we know, what we don't
know and the impact ALMA is expected to have on our understanding of the
chemistry of protoplanetary disks. I present recent results of our
recent investigations into the importance of desorption, photochemistry,
X-ray ionisation and dust grains on the chemistry in disks and discuss
the level of chemical complexity which may be achieved in such
environments.