Spectroscopic and Thermochemical Consequences of Site-Specific H-Atom Addition to Naphthalene

Abstract

Vibronic spectra of doublet-doublet transitions of 1-hydronaphthyl (1HN), 2-hydronaphthyl (2HN), and 1,2,3-trihydronaphthyl (THN, tetralyl) radicals have been recorded under jet-cooled conditions. Transitions due to the two C(10)H(9) isomers were identified and assigned based on the choice of radical precursor, visible-visible hole-burning spectroscopy, comparison of observed vibronic transitions with calculation, and photoionization efficiency scans. The latter provided accurate ionization potentials for the three free radicals (IP(1HN) = 6.570 eV, IP(2HN) = 6.487 eV, IP(THN) = 6.620 eV, errors +/-0.002 eV). A thermochemical cycle is used to extract from these ionization potentials the C-H bond dissociation energy (BDE) of 1HN at the 1-position of 121.2 +/- 2 kJ/mol. Using proton affinities of 2HN and THN calculated at the G3(MP2, CC)//B3LYP/6-311G** level of theory, the corresponding C-H BDEs of 2HN at the 2-carbon (103.6 +/- 2 kJ/mol) and of THN at the 3-position (168 +/- 3 kJ/mol) are derived. The possible role played by these hydronaphthyl radicals in Titan's atmosphere, the interstellar medium, and combustion are briefly discussed.