Naphthyl Radical:  Negative Ion Photoelectron Spectroscopy, Franck−Condon Simulation, and Thermochemistry

The naphthyl anion (C 10 H 7 -, naphthalenide) is prepared in a flow tube reactor by proton transfer between NH 2 - and naphthalene (C 10 H 8 ). 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 (C 10 H 7, naphthalenyl). The Franck−Condon profiles for both 1-naphthyl (α-naphthyl) and 2-naphthyl (β-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-C 10 H 7 ) = 1.403 ± 0.015 eV. On the basis of an evaluation of literature data, the recommended gas-phase acidity of naphthalene is Δ acid H 298 (1-C 10 H 7 −H) = 1649 ± 14 kJ/mol and the recommended bond dissociation energy of naphthalene is DH 298 (1-C 10 H 7 −H) = 472 ± 14 kJ/mol.