The Electronic Spectrum of the Fulvenallenyl Radical

The fulvenallenyl radical was produced in 6 K neon matrices after mass-selective deposition of C7H5− and C7H5+ generated from organic precursors in a hot cathode ion source. Absorption bands commencing at λ=401.3 nm were detected as a result of photodetachment of electrons from the deposited C7H5− and also by neutralization of C7H5+ in the matrix. The absorption system is assigned to the 1 2B1←X 2B1 transition of the fulvenallenyl radical on the basis of electronic excitation energies calculated with the MS-CASPT2 method. The vibrational excitation bands detected in the spectrum concur with the structure of the fulvenallenyl radical. Employing DFT calculations, it is found that the fulvenallenyl anion and its radical are the global minima on the potential energy surface among plausible structures of C7H5.