Absorption spectra of conjugated hydrocarbon cation chains in neon matrices Original Research Article

Absorption spectra for a series of mass selected Ck H2+ systems (k = 4–16) isolated in neon matrices at 5 K have been measured in the visible and near infrared region. Application of the free-electron molecular-orbital model reveals two homologous series corresponding to the deposition of systems containing even or odd numbers of carbon atoms. With the aid of previous gas-phase data, even-numbered carbon systems are identified as cations of polyacetylenic chains. Positions of the A2Π←X2Π origin bands as well as fundamental vibrational frequencies in the excited state for the systems H-(CC)n-H+(n = 4–8) have been obtained. For the deposition of ions containing an odd number of carbons, absorption transitions are tentatively assigned to HC2n+1H+ where n = 2–7.