Naphthyl radical: Negative ion photoelectron spectroscopy, Franck-Condon simulation, and thermochemistry

The naphthyl anion (C10H7-, naphthalenide) is prepared in a flow tube reactor by proton transfer between NH2- and naphthalene (C10H8). The photoelectron spectrum of this anion is measured at a fixed laser wavelength of 364 nm. A single electronic band is observed, corresponding to the neutral naphthyl radical (C10H7, naphthalenyl). The Franck-Condon profiles for both 1-naphthyl (alpha -naphthyl) and 2-naphthyl (beta -naphthyl) are simulated on the basis of density functional theory calculations of the vibrational frequencies and normal coordinates. Issues involving Franck-Condon simulations for large polyatomic molecules and Duschinsky rotation are discussed. and improved Franck-Condon simulation algorithms are presented. Comparison of the Franck-Condon simulations with the photoelectron spectrum shows that the observed band is predominantly due to the 1-naphthyl isomer, consistent with previous measurements showing the 1-naphthyl anion as more stable than the 2-naphthyl anion. The observed electron affinity of the 1-naphthyl radical is EA(0)(1-C10H7) = 1.403 +/- 0.015 eV. On the basis of an evaluation of literature data. the recommended gas-phase acidity of naphthalene is Delta H-acid(298)(1-C10H7-H) = 1649 +/- 14 kJ/mol and the recommended bond dissociation energy of naphthalene is DH298(1-C10H7-H) = 472 +/- 14 kJ/mol.