Photochemistry with Infrared Radiation

Abstract

The irradiation of polyatomic molecules with intense infrared radiation from pulsed laser light sources can induce photochemical reactions, which require the absorption of many (10 to 50) quanta. The experimental principles are outlined and the primary processes due to vibrational excitation in the electronic ground state are discussed. A method for determining quantitative rate parameters is presented and illustrated with some recent experimental results for CF₃I^- and C₂F₄S₂-IR photolysis. Simple theoretical correlations for absolute rate coefficients provide an understanding of the most important molecular parameters determining the rate of an IR-photochemical reaction. The relationship of IR-photochemical and thermal, collisional reactions is analyzed. Qualitative experimental effects and quantitative rates in IR-photochemistry can be rationalized with somewhat different success using various theoretical descriptions for the primary processes. A brief summary of the current status of experiments and theories concludes the article.