Knowledge Bank

The $\mathrm{<mrow\; data-mjx-texclass="ORD">12,13</mrow>}C$ isotopic substitution method applied to IR absorption spectra has been successful in identifying the size and the geometry of many molecular systems, including carbon $clusters.a$ Using this method we obtained $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}C$-labeled IR spectra in the $v>2200cm-1$ region for linear carbon clusters isolated in an Ar matrix. By comparison to the calculated isotopomer frequencies at the $B3LYP/6-31G\ast$ level, the observed bands have been assigned to combination modes of $\mathrm{<mrow\; data-mjx-texclass="ORD">12,13</mrow>}Cn$ clusters. In addition, from these combination band frequencies the few symmetrical mode vibrations in the linear clusters have been deduced.