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 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.