group-ID = user-assigned ID of an internally-created dynamic group that excludes reacting atoms, and can be used by a subsequent time integration fix such as nvt, npt, or nve (cannot be 'all')
{xmax} value = distance
distance = xmax value that is used by an internally created "nve/limit"_nve_limit.html integrator
distance = xmax value that is used by an internally created "nve/limit"_fix_nve_limit.html integrator
react = mandatory argument indicating new reaction specification
react-ID = user-assigned name for the reaction
react-group-ID = only atoms in this group are available for the reaction
