Line-mixing effects in N2O Q branches:: Model, laboratory, and atmospheric spectra

A model based on the energy corrected sudden approximation is used in order to account for line-mixing effects in N2O Q branches of Sigma <-> Pi bands. The performance of this theoretical approach is demonstrated by comparisons with many (about 70) N2O-N-2 and N2O-O-2 laboratory spectra recorded in the 5 and 17 mu m regions by three instrument setups; the Q branches of the 2 nu(2)(0e) - nu(2)(1f) (near 579.3 cm(-1)), nu(2) (near 588.8 cm(-1)), and nu(2) + nu(3) (near 2798.3 cm(-1)) bands are investigated for different pressures (0.1-2.0 atm) and temperatures (200-300 K). The model is used to generate a set of line-mixing parameters for the calculation of the absorption by the nu(2) Q branch under atmospheric conditions. These data are tested by comparisons between computed stratospheric emissions and values measured using a balloon-borne high resolution Fourier transform instrument. The results confirm the need to account for the effects of line mixing and demonstrate the capability of the model to represent the N2O absorption in a region which can be used for the retrieval of N2O5 mixing ratios. (C) 1999 American Institute of Physics. [S0021-9606(99)01304-5].