Pressure Broadening in the Microwave Spectrum of Ammonia

Half-widths of five pressure-broadened lines of the ammonia inversion spectrum have been measured as a function of total pressure. The perturbing gases were oxygen, helium, and nitrous oxide in various mix ratios. The results indicate a decrease in the collision diameters with increasing mix ratio of perturber to absorber. In the case of the nonpolar helium and oxygen the observed variation of collision diameter with quantum numbers of the lines can be compared with the predictions of the theory of collision broadening developed by P. W. Anderson. The general trend of the variation agrees with the theory, but its observed magnitude is considerably greater than predicted.