Step-scan FTIR techniques for investigations of spectra and dynamics of transient species in gaseous chemical reactions

Infrared (IR) spectra have served as the molecular fingerprints for the identification and quantification of chemical species. For infrared spectral investigations of transient species, the step-scan Fourier-transform infrared (ss-FTIR) technique proves to be most successful if one considers all aspects including sensitivity, temporal and spectral resolutions, and applicability. In this chapter, we introduce fundamental principles of a ss-FTIR interferometer and cover the instrumentation for emission and absorption experiments and the key factors to be considered in experiments. For emission studies, dynamics of chemical reactions including molecular elimination of HX (X=F, Cl, Br) and CO, roaming reactions, and bimolecular reactions involving Cl or O(1D) or precursors of Criegee intermediates are discussed. For absorption studies, the transient IR absorption spectra of various reaction intermediates upon photolysis, including isomers of CH3SO2, peroxy radicals, Criegee intermediates and associated reaction intermediates and end products, are presented. Detailed reaction mechanism could be derived from these experimental results. Finally, we present some future perspective on research using the ss-FTIR technique.