Knowledge Bank

The $C5$ carbon cluster has been produced by trapping in Ar the products of the VUV-photolysis of 2-methyl-l,3-butadiene or by the high temperature evaporation of graphite. The $\nu 3(\sigma u$) stretching mode was earlier observed at $2164.3cm-1$ and a band at $1544cm-1$ was attributed to the $\nu 4(\sigma u$) vibration of $C5$, but was later assigned to the $\nu 3(\sigma u$ vibration of $C43$. In the present work, the second $C=C$ stretching mode, $\nu 4(\sigma u$ of $C5$, has been found at $1446.6cm-1$. Measurements have been made for all twenty $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}C$-substituted isotopomers of linear $C5$. Both the $\nu 4$ fundamental frequency and the isotopic shifts are in agreement with recent ab initio calculations done al the coupled electron pair approximation and MP2/DZP $levels.4,5$ Also produced in the high temperature evaporation of graphite was the $C6$ carbon cluster. The present work reports the continuation of the assignment of the $1197.3cm-1$ band, through extensive $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}C$ substitution, to the $\nu 4$ stretching mode of $C6$, The results of both the original assignment and the isotopic measurements agree well with recent ab initio calculations done at the $MP2/6-31G\ast$ $level.6$