Assignment of Carbon Chain Molecules in Cryogenic Matrices by Selective Laser-Induced Oxidation

We tested and applied a laser-induced oxidation method for identifying the IR-active stretching mode absorptions of linear C2 n +1 molecules which have known strong UV−vis absorptions. For this purpose, we trapped the molecules of carbon vapor in non-inert matrices (pure O2 and Ar−O2 mixtures) at temperatures providing molecular growth. The matrix was exposed to laser light tuned to the wavelength of the UV−vis transition of a specific carbon species. We observed a bleaching of that UV−vis absorption and a correlated decrease of lines in the IR spectra for C9, C11, C13, C15, and C21. The data suggest that the strongest IR absorptions of the C2 n +1 (n ≥ 4) chains form a regular pattern with increasing n. To obtain information about IR absorptions of carbon chain oxides, oxygen matrices with replaced 16O → 18O isotopes were applied. Our data revise some of the IR assignments existing in the literature.