Absolute infrared intensities in crystalline acetylene and ethane

Absolute infrared absorption intensities have been measured for three bands of crystalline acetylene and two bands (the hydrogen stretching motions) of crystalline ethane. The changes of intensity observed on condensation of the gases cannot be explained as a “dielectric effect”. In acetylene the large frequency shift and intensification of the hydrogen stretching mode are consistent with characterization of the intermolecular forces as hydrogen bonding to the acetylenic π-clouds.