Local mode overtone intensities of C–H stretching modes in alkanes and methyl substituted benzenes

Abstract

A thermo‐optical spectrometer is used to resolve absorption peaks due to nonequivalent C–H local mode vibrations and combination bands in several molecules containing aromatic, primary, and secondary hydrogens. Although the bandwidths vary, a constant absorption cross section per C–H is observed for the transitions to the v=3,4,5, and 6 overtone levels. This result stands in contrast to the behavior of the fundamental transitions, where C–H stretching intensities are seen to vary by as much as a factor of four between aromatic and aliphatic C–H bonds.