Illustration of molecules depicting the various types of peripheral CH groups in PAHs in the Orion Bar. The counts of of solo, duo, trio, and quartet functional groups are denoted as s, d, t, and q, respectively. The numbers on the rings in each structure indicate the number of adjacent CH groups attached to each ring. Structure (a) satisfies the s/t CH group ratio, derived for the PDR. Structures (b) and (c), satisfy the s/t and d/q ratios derived for the atomic PDR and DF 3 of the Orion Bar, respectively.