              The id of the second of the three atoms that define the angle.\
               The second atom is taken to be the apex of the angle.\
\
               An atom with this id must exist in the component of the type\
               specified by _chem_comp_link.type_1 (or _chem_comp_link.type_2,\
               where the appropriate data item is indated by the value of\
               _chem_comp_link.atom_2_comp_id).