Fourier transform and multiplexed intrapulse quantum cascade laser spectrometer measurements of NO2 and its dimer N2O4

A quantitative comparison has been made between the spectra recorded using an infrared Fourier transform (FT) spectrometer, and those based upon the use of chirped pulse quantum cascade (QC) lasers. The system chosen for this comparison is the chemical equilibrium between NO2 and its dimer N2O4. It is studied by making spectroscopic measurements of the dimerization of nitrogen dioxide (NO2). The intrapulse QC laser spectrometer used long duration pulses of wavelengths near 7.84, 7.46, and 6.14 μm, and a path length of 62 m, and the Université libre de Bruxelles (Brussels, Belgium) FTspectrometer used a path length of 21.1 cm. In the direct comparison of pairs of spectral regions allowed by the dual pulse system, it was possible to compare the 7.84 μm region, where both the spectra of the monomer and dimer are observed, with the 7.46 and 6.14 μm regions in which only monomer lines are detected. In the 7.84 μm region the NO2 absorption lines could be detected only when the dimer N2O4 is formed in the monomer NO2 in the QC laser spectra.