Line-mixing effect on NH3 line intensities

- Studied NH3 in the 1000-2000 cm−1 using broad-band high-resolution FTIR spectra.
- Measured line intensities and transition dipole moments squared for 462 transitions in the ν2, 2ν2 and ν4 bands.
- Considered line mixing effect, which was observed to produce intensities smaller by ∼6%.
- Discussed rotational quantum number, J and K, dependence of line intensities and transition dipole moments squared.
- Compared the measured line intensities to be lower than earlier work by up to ∼10%.

Line intensities belonging to nine branches of the ν2, 2ν2 and ν4 vibrational bands of ammonia have been measured between 1000 and 2000 cm−1. The laboratory spectra at room temperature (T=295 K) were recorded using a high-resolution Fourier transform spectrometer Bruker IFS 120 HR.More than 460 lines with J≤12 were analyzed using a non-linear least-squares multi-pressure fitting procedure. The fits were performed with and without including the line mixing effects using 11 experimental spectra recorded at different pressures of pure NH3. On average the line intensities uncertainty is estimated to be 2%. The dependence of the line intensities on the J and K quantum numbers is discussed. The effect of line mixing on the line intensities is analyzed as a function of the rotational quantum numbers, of the branches, and of the bands.On average the values of line intensities obtained in the ν4 band when taking into account line mixing have been found to be 6% smaller than those obtained using the Voigt profile.The transition dipole moments squared, determined for each line from the measured intensities, exhibit significant rotational dependencies which are mainly caused by vibration-rotation interactions. These moments are discussed as a function of vibrational and rotational states. Finally the measurements are compared with previous measurements and with values from spectroscopic databases.The whole set of line intensities and transition dipole moments are given as supplementary data for use in spectroscopic databases.