Absorption in the troughs of the far infrared spectra of NH3 and mixtures of NH3 and H-2

The absorption coefficients in the troughs between the J-multiplets of the far infrared rotation-inversion spectrum of NH3 and NH3 broadened by H-2 we re measured at 296 K in the region from about 65-230 cm(-1). Wave numbers w ere selected in the troughs that are removed from nearby weak absorption li nes, and measurements of the absorption versus the density of NH3 and of H- 2 verified that the absorption was due to the wings of distant rather than nearby spectral lines. These measurements were compared with computations o f the absorption arising from binary collisions of NH3-NH3 and NH3-H-2 for uncoupled Lorentz lines. Except at the lowest and highest frequencies, the measured continuum absorption in the troughs was less than the computed abs orption, a discrepancy that increased with increasing frequency. An improve d representation of the measured absorption was obtained by fitting the Ros enkrantz line shape with the Ben-Reuven formulation of the line coupling co efficient of the inversion J-doublets. The application of these results to the spectrum of Jupiter shows clear differences between the spectrum of the above model and the Lorentz line shape, with the largest differences occur ring in the dearest troughs. (C) 1999 Elsevier Science Ltd. All rights rese rved.