Self‐broadening and self‐shifting of ammonia lines in the 2ν2 band around 16 μm

VIBRATIONAL DEPENDENCE OF LINE COUPLING AND LINE MIXING IN SELF-BROADENED PARALLEL BANDS OF NH3

Line coupling and line mixing effects have been calculated for several self-broadened NH₃ lines in parallel bands involving an excited v ₂ mode. It is well known that once the v ₂ mode is excited, the inversion splitting quickly increases as this quantum number increases. In the present study, we have shown that the v ₂ dependence of the inversion splitting plays a dominant role in the calculated line-shape parameters. For the v ₂ band with a 36 cm^-1 splitting, the intra-doublet couplings practically disappear and for the 2v ₂ and 2v ₂ - v ₂ bands with much higher splitting values, they are completely absent. With respect to the inter-doublet coupling, it becomes the most efficient coupling mechanism for the v ₂ band, but it is also completely absent for bands with higher v ₂ quantum numbers. Because line mixing is caused by line coupling, the above conclusions on line coupling are also applicable for line mixing. Concerning the check of our calculated line mixing effects, while the present formalism has well explained the line mixing signatures observed in the v ₁ band, there are large discrepancies between the measured Rosenkranz mixing parameters and our calculated results for the v ₂ and 2v ₂ bands. In order to clarify these discrepancies, we propose to make some new measurements. In addition, we have calculated self-broadened half-widths in the v ₂ and 2v ₂ bands and made comparisons with several measurements and with the values listed in HITRAN 2012. In general, the agreements with measurements are very good. In contrast, the agreement with HITRAN 2012 is poor, indicating that the empirical formula used to predict the HITRAN 2012 data has to be updated.

Low temperature hydrogen broadened linewidths of ammonia in the (0,1,0,0)?(0,0,0,0) band at 200 K

Fourier transform spectra of the (0,1,0,0)?(0,0,0,0) band of ammonia have been measured for values of the hydrogen broadened linewidth parameters at a temperature of 200 K. The halfwidths for >200 lines have been determined with an average RMS of 5% in the interval between 750 and 1250 cm(-1). No measurements of the widths in the (s)R branch, and only 12 widths in the (s)Q branch, were obtained because of severe lending of the J-K manifolds. The broadening coefficients vary between 0.06 and 0.14 cm(-1)/atm. for (J,K) < (12,12).

Ammonia spectrum as a test for two different pressure shift theories

Pressure shift calculations, based on the semiclassical ATC theory and on the quantum Fourier transform (QFT) theory, are compared wtih experimental results for seventy-two inversion, rotation, and vibration transitions of (14)NH(3) and (15)NH(3). ATC, even if not exact, allows a far better agreement than QFT. A possible reason for this is briefly discussed.