Absorption Line Width in the Rotation Spectrum of Atmospheric Water Vapor

Grating measurements at oblique incidence are employed as a means of obtaining the narrow slits essential to the direct observation of line width. Correction for the finite width of slit is small. It is accomplished by empirical extrapolation to zero slit in one instance, and by numerical estimation of slit influence in another. The absorption coefficient half-width at half-height for the atmospheric water vapor lines at 18.64 mu and 15.99 mu is found to be 0.12 ${\mathrm{cm}}^{-1\mathrm{}}$ and 0.11 ${\mathrm{cm}}^{-1\mathrm{}}$, respectively.