Doppler-free polarization spectroscopy of diatomic molecules in flame reactions

Gas phase reactions are used to produce radicals or other molecules which can hardly be evaporated. The conditions of this production method require a sensitive spectroscopic technique if sub-Doppler spectra are to be recorded. Different techniques are discussed and Doppler-free polarization spectroscopy is shown to offer the highest sensitivity for the study of these species. First polarization spectra of the A ¹∑?X ¹∑ (1, 0) transition of BaO and the B ²∑?X ²∑ (0,0) transition of CaCl are reported.