Chapter 9 - Molecular Spectroscopy

Abstract

This chapter discusses that molecules play a dominant role in the behavior of most chemically reacting flow fields and their concentrations is measured accurately to describe the flow field. In combustion research, the more stable reactants and final products are usually measured using various analytical instruments. The spectroscopic detection of free radicals is complicated. There are many molecules of interest, and each of them has somewhat different spectroscopic behavior. Even among the diatomic molecules, it becomes important to collect a file on each particular molecule to be studied, so that individual attributes are accounted for. The analytical instrument often relies upon spectroscopy. This chapter presents the very basic ideas in molecular spectroscopy. It discusses where in the electromagnetic spectrum, signatures from atoms and molecules can be found. Even polyatomic molecules are significantly more complex, because they are three-dimensional. They are also much more difficult to detect optically because they have so many closely spaced energy levels; the Boltzmann fraction for an individual energy level that would be addressed by a narrow-band laser is thus, very low. Finally, because they are so reactive, these free radicals do not exist in large concentrations.