ABSORPTION INTENSITIES, PRESSURE-BROADENING AND LINE MIXING PARAMETERS OF SOME LINES OF NH3 IN THE ν4 BAND

The intensities and foreign gas broadening coefficients of 57 selected lines of the ν₄ band of NH₃ have been measured in the region of 1550 cm^-1 using a high resolution Brucker Fourier transform spectrometer. The line intensities were obtained by using the methods of absorbance at the line center and by fitting Voigt profiles to the measured shapes of the lines. The latter method also provides the collisional widths of the lines. In addition, collision cross relaxation coefficients of O₂ and air foreign gases were measured for 9 doublets of NH₃ in the ν₄ band. The J and K quantum numbers dependencies of pressure-broadening coefficients and line intensities are discussed. The observed air broadening and cross relaxation coefficients were found to be in reasonable quantitative agreement with the concentration-weighted average of the N₂ and O₂ broadening coefficients. The comparison of our present and previous results obtained for the NH₃–H₂, NH₃–air, NH₃–N₂ and NH₃–CO₂ collisions shows an increase of the pressure broadening and cross relaxation coefficients with quadrupole moment of the foreign gas. The analysis of the line intensities was based on the third-order theory of line strengths and yields effective transition moments, vibrational band strengths and correction parameters of the symmetric and antisymmetric partial bands of the fundamental ν₄ band.