An Absorption Band in Ethylene Gas in the Near Infrared

The absorption spectra of gaseous ethane and ethylene have been investigated by photographic methods in the region $\lambda \lambda 6500-9500$. In the case of ethane no absorption was found. In ethylene a rather strong band was found at $\lambda 8720$ which has a structure resembling that predicted by H. H. Nielsen for the oscillation-rotation bands of a molecule with moments of inertia in the ratio 1.4:1:0.14. The following very provisional values for the moments of inertia of the ethylene molecule are given: $A_x=31\mathrm{}\times {10}^{-40\mathrm{}}$, $A_y=27\mathrm{}\times {10}^{-40\mathrm{}}$, $A_z=3.8\mathrm{}\times {10}^{-40\mathrm{}}$.