High resolution FTIR spectra of “NO X” (NO 2, N 2O 4) in supersonic jet expansions and their rovibrational analysis

Abstract

Over the last decade we have developed in our laboratory high resolution interferometric Fourier transform infrared spectroscopy of gases in supersonic jet expansions. In the present work we have investigated NO X atmospheric trace gases in view of a high resolution rovibrational analysis of NO 2 and N 2O 4 spectra under low temperature gas phase conditions, particularly important for the understanding of atmospheric infrared absorptions. The spectral range covered is 700 to 1800 cm −1 with an unapodized instrumental bandwidth of 0.0024 cm −1. Rotational temperatures are between 20 K in seeded and about 100 K in neat expansions. Approximate preliminary band centres for N 2O 4 are ν 11 = 1261.080 cm −1, ν 9 ≅ 1756.769 cm −1 and for a resonance doublet of ν 12 with ν 10 + ν 6 at 747.85 cm −1 and 755.37 cm −1. Our results are discussed in relation to the atmospheric trace gas absorptions, molecular structure of N 2O 4 relaxation phenomena in jets and ab initio calculations.