LOCAL MODE OVERTONE INTENSITIES OF C-H STRETCHING MODES IN ALKANES AND METHYL-SUBSTITUTED BENZENES

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. © 1979 American Institute of Physics.