Atmospheric Absorption of Millimetre Waves

The attenuation of electromagnetic waves in the region of 5 mm. wavelength due to resonance in the oxygen molecule was measured over atmospheric paths up to 2 km. long, using a fixed transmitter and a mobile superheterodyne receiver. For ten wavelengths between 6.34 and 4.48 mm. values were obtained which, after reduction to standard dry atmospheric conditions, range up to a maximum of 15.7 db/km. at the peak of the absorption curve. They agree substantially with the theory of Van Vleck, and give a value of line-breadth constant Δ - ν of about 0.02 cm -1 , confirming estimates derived from other methods.