Ion Dissociation Dynamics of 1,2,3,4-Tetrahydronaphthalene: Tetralin as a Test Case For Hydrogenated Polycyclic Aromatic Hydrocarbons

The unimolecular dissociation of ionized tetralin was probed by tandem mass spectrometry, imaging photoelectron photoion coincidence (iPEPICO) spectroscopy, and theory. The major reactions observed were the loss of the hydrocarbons CH₃^•, C₂H₄, and C₃H₅^• together with H^•-atom loss. RRKM modeling of the iPEPICO data suggested a two-well potential energy surface. Ionized tetralin can lose all four neutrals via H-shift and ring-opening reactions or CH₃^• and C₂H₄ after interconversion to the 1-methylindane ion, a process similar to that found for ionized 1,2-dihydronaphthalene (isomerizing to form the 1-methylindene ion structure). This was confirmed at the B3LYP/6-31+G­(d,p) level of theory, and potential mechanisms for all reactions are described. The ionization energy of tetralin was established from the threshold photoelectron spectrum to be 8.46 ± 0.01 eV.