Molecules as Tracers of PN Structure
  Molecular gas plays an important role in the structure of planetary nebulae: it is a major component of the equatorial tori of bipolar nebulae, it forms the cores of globules and related mircostructures, and is the likely origin of multiple arcs. It is also a key component during the early stages of formation where interactions with outflows or jets provide an important shaping mechanism. 
P. J. Huggins