Absolute Intensities of Characteristic Infra-Red Absorption Bands of Aliphatic Hydrocarbons

Abstract

Integrated intensities of the 2900, 1460, and 1370 cm⁻¹ infra‐red absorption bands have been measured for twelve aliphatic hydrocarbons. The results are interpreted on the basis that the hydrocarbon molecule behaves like a non‐interacting mixture of [Complex chemical formula] structural groups. The unit structural group intensities are 4.41×10⁻⁷, 3.81×10⁻⁷, and 1.39×10⁻⁷ cm²/(molecule second) for the CH₃, CH₂ and CH groups respectively in the 2900 cm⁻¹ band; 0.544×10⁻⁷ and 0.232×10⁻⁷ for the CH₃ and CH₂ groups in the 1460 cm⁻¹ band; and 0.394×10⁻⁷ for the CH₃ group in the 1370 cm⁻¹ band. Values calculated for the CH bond dipole moment divided by the equilibrium CH bond length vary from approximately 0.2×10⁻¹⁸ to 0.4×10⁻¹⁸ c.g.s. units. Values of approximately −0.75×10⁻¹⁰ are obtained for the change in CH bond dipole moment with change in CH bond length.