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 C(2)(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 O(2) and Ar-O(2) 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 C(9), C(11), C(13), C(15), and C(21). The data suggest that the strongest IR absorptions of the C(2)(n)(+1) (n > or = 4) chains form a regular pattern with increasing n. To obtain information about IR absorptions of carbon chain oxides, oxygen matrices with replaced (16)O --> ( 18)O isotopes were applied. Our data revise some of the IR assignments existing in the literature.