UCLCHEM uses notation, which differentiates between species types. Here, we'll give an overview of this notation and associated processes.
📄️ Gas Phase Reactions
Gas phase ODEs
📄️ Grain Surface Reactions
Whilst the basic treatment of gas phase chemistry is well established, grain surface chemistry is more complex. There are three possible ways to treat grain surface chemistry in UCLCHEM. In general we assume that:
📄️ Adsorption & Desorption Reactions
Coupling between the gas and the grain chemistry primarily comes from the freeze out of material from the gas phase onto the dust grains (adsorption) and the sublimation of material from the grains into the gas phase (desorption). The major processes considered by UCLCHEM are listed below. Note that we assume desorption and freeze out occur between the gas and the surface only, bulk material in three phase models does not directly desorb into the gas phase.
📄️ Bulk Ice Processes
For a three phase network, we must include reactions in the bulk and the process by which it is formed. To do this, MakeRates automatically duplicates all LH reactions so that a reaction on the surface and one in the bulk ice exists in the network. We then include two methods by which material can move between the bulk and the surface. First is the accumulation of the bulk as new surface layers are formed and second is the individual swapping of a particle from the bulk with one on the surface. Both of these processes are taken from Garrod & Pauly 2011