11.2/3.3 μm intensity ratio of 27 different PAHs with blue coronene family, green compact, and red non-compact PAHs. The average photon energy absorbed by the PAHs used is 6.5 eV (see Eq. (1)). The ratio of the C-H stretching mode (3.3 μm) over the solo out-of-plane bending mode (11.2 μm) is extracted from the theoretical spectra from the NASA Ames PAH database. The y-axis is linearly proportional to the adopted intrinsic band strength of the 11.2/3.3 μm ratio. The colored horizontal lines have the same color coding as used for the 11.2/3.3 μm ratio maps in Figs. 2 and 4.