Collision Broadening of the Ammonia Inversion Spectrum at High Pressures

Abstract

THE collision broadening of the inversion spectrum of ammonia has been studied by Bleaney and Penrose¹ at pressures up to 600 mm. mercury. The line-widths, measured at a pressure of 0·5 mm. mercury, give values for the collision diameters (for self-broadening) varying between 8·7 A. and 14·2 A., with a mean value (weighted according to the line strengths) of 13·2 A. Between 0·5 mm. and 100 mm. pressure, the shape of the absorption curve agrees closely with that calculated from the intensity and position of the individual lines, assuming that their widths vary linearly with the pressure. At 600 mm. pressure, however, the absorption maximum has shifted to less than 0·6 cm.^-1, and the curve shape is no longer consistent with that calculated from the structure factor of Van Vleck and Weisskopf², and Fröhlich³, using the extrapolated line-widths.