Electronic spectra of the chains HC2nH (n=8–13) in the gas phase

The intense Σu+1←X1Σg+ electronic transition of the chains HC2nH (n=8–13) has been recorded in the gas phase using resonant two color two photon ionization spectroscopy. The gas phase frequencies lie ∼1300 cm−1 to the blue of the values in a neon matrix. These polyynes appear to be linear in both the ground and the excited state and, as for the polyynes, spectral and theoretical evidence for large bond alternation in the ground state is found indicating localized π orbitals on the C≡C units. These species are the longest carbon chains observed spectroscopically in the gas phase up to now.