The electronic spectrum of the C _s-C _(11)H _3 radical

摘要

The electronic gas-phase absorption spectrum of the bent carbon-chain radical, HC _4CHC _6H with C _s symmetry, is recorded in the 595 nm region by cavity ring-down spectroscopy through an expanding hydrogen plasma. An unambiguous spectroscopic identification becomes possible from a systematic deuterium labeling experiment. A comparison of the results with recently reported spectra of the nonlinear HC _4CHC _4H and HC _4C(C _2H)C _4H radicals with C _(2v) symmetry provides a more comprehensive understanding of the molecular behavior of -conjugated bent carbon-chain systems upon electronic excitation. We find that the electronic excitation in the bent carbon-chain HC _4CHC _(2n)H (n 1-4) series exhibits a similar trend as in the linear HC _(2n)1H (n 3-6) series, shifting optical absorptions towards longer wavelengths for increasing overall bent chain lengths. The -conjugation in bent HC _4CHC _(2n)H (n 1-4) chains is found to be generally smaller than in the linear HC _(2n)1H (n 3-6) case for equivalent numbers of C-atoms. The addition of an electron-donating group to the bent chain causes a slight decrease of the effective conjugation.