Line-Breadth Study of the 1.64-mm Absorption in Water Vapor

The 2₊₂→3₋₂ rotational transition in water vapor has been carefully studied by using both a simple video and a double modulation millimeter wave spectrometer. The line center remeasured is ν₀ = 183 310.12±0.10 Mc/sec. Self‐broadening and foreign‐gas broadening were investigated over the pressure range of 5 to 400 μ of Hg with the following results: $$\begin{array}{cc}\mathrm{Perturbing\; gas}& \mathrm{\Delta \nu /p\hspace{0.17em}(}\mathrm{Mc}/\sec ·\mathrm{mm})\\ & \\ {\mathrm{H}}_2\mathrm{O}& \text{19.06}\\ {\mathrm{CO}}_2& \text{6.09}\\ {\mathrm{N}}_2& \text{3.76}\\ {\mathrm{O}}_2& \text{2.72}\\ \mathrm{Ar}& \text{1.97.}\end{array}$$ These results, obtained by the double modulation spectrometer, have been compared with other line broadening studies, and for the first time linewidth calculations on asymmetric molecules appear to be valid.