Spectroscopic Evidence for a Triplet Ground State in the Naphthyl Cation

Run to ground: Infrared spectroscopy of the isolated naphthyl carbocation, C10H7+ (prepared from C10H7Br, see scheme) provides evidence for a triplet electronic ground state (3A′′), in which a π electron is promoted to the vacant σ orbital. Previous computational studies have been ambiguous as to the relative stabilities of the singlet and triplet states; DFT calculations predict both states to be practically isoenergetic.