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Abstract:
We tested and applied a laser-induced oxidation method for identifying the IR-active stretching mode absorptions of linear C2n+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 C2n+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.
