- PAHs contain up to 10-20% of all the carbon in the ISM.
- PAHs (in both neutral and cation form) are thought to be the carriers of AIBs.
- Interstellar environments: low density, lack of collisions.
- Molecular hydrogen (H2) is the smallest and most abundant molecule in the universe.
- A symmetric and compact molecule which has great photostability against UV radiation.
[ ApJ 892, 11 (2020).]