[en] Identification of vapor-phase species and the kinetics of their reactions in simulated LWR nuclear accidents are important in predicting the ultimate fate of volatile fission products. Laser spectroscopic techniques such as laser Raman and laser-induced fluorescence (LIF) are valuable tools in determining molecular species and concentrations from these experiments. Equipment capable of vapor-phase measurements up to 1500⁰K is described. These techniques have been applied to molecular iodine and CsI vapors. The application of LIF to iodine vapor is reviewed and the problems associated with high-temperature concentration measurements (to 1200⁰K) are discussed. The characterization of the LIF spectrum of CsI vapor at 1100⁰K is presented