Comparisons of theoretical and experimental mass spectra of two protonated pyrenes. All theoretical mass spectra were extracted from MD simulations at (a) and (b): Two theoretical mass spectra from [py + 5H]⁺ with different protonated sites. The isomer in (a) is 0.28 eV more stable than the isomer in (b). The color scheme of carbon and hydrogen atoms are as follows: gray (aromatic carbon), light yellow (aliphatic carbon), orange (protonated carbon), white (normal hydrogen), and green (proton). (c): the experimental mass spectrum of [py + 5H]⁺ recorded by collision-induced dissociation (CID). (d) and (e): two theoretical mass spectra from [py + 7H]⁺ with different protonated sites. The isomer in (d) is 0.08 eV more stable than the isomer in (e). (f): the experimental mass spectrum of [py + 7H]⁺ recorded by CID. See Fig. A.1 for the log-scaled mass spectra of (c) and (f) where peaks with lower intensities can be discerned.