The Experimental Determination of the Intensities of Infra-Red Absorption Bands. III. Carbon Dioxide, Methane, and Ethane

The absolute intensities of the chief infra-red absorption bands of carbon dioxide, methane, and ethane have been determined experimentally to be (in cycles per centimeter at N.T.P.): Carbon dioxideMethaneEthane670 cm−1 band:560×10101306 cm−1 band:450×1010 820 cm−1 band: 73×10102350 cm−1 band:8600×10103020 cm−1 band:900×10101450 cm−1 bands: 230×10102950 cm−1 bands:2200×1010These results are in satisfactory agreement with available data on infra-red dispersion and atomic polarization. They may be interpreted in terms of dipole moments, μ′, of bonds between vibrating atoms, and their rates of change with internuclear distance, ∂μ′/∂r. When this is done for the CH bond, however, unexpected variations in these quantities are found for the different vibrations and molecules studied. The average values are about μ′=0.4×10−18, ∂μ′/∂r=±0.6×10−10. For the CO bond the values are considerably larger.