Calculations Electronic spectrum Polycyclic aromatic hydrocarbons Protonation article A transitions Ab initio calculations Aromatic compounds Atoms CARBON Carbon Charge transfer Charge transfer state Chromophores Electronic absorption Electronic spectroscopy Excited state ab initio calculations Excited states GASES Gases Hydrocarbon molecules Hydrocarbons INDOLES Indoles Isomers Lowest-energy isomers Molecules Naphthalene Nitrogen atom Photo-fragmentation spectrum