Cross Sections for the Alkali-Metal–Halogen Molecule Reactions: Cs with I2

The reaction cross section of alkali-metal atoms with halogen molecules is obtained by a direct measurement of the alkali-atom decay rates. The alkali atoms are produced in the presence of a known amount of halogen molecules, by photodissociating an alkali halide salt with a short pulse of uv light. The alkali atoms react with the halogen molecules and the decay is monitored by observing the transmission of alkali-atom resonance light through the vapor. Since the halogen density is known, the reaction cross section can be computed from the decay rate. Using this method we studied the reaction Cs+I2→CsI+I. The cross section for this process is 180 ± 25 Å2.