The Production of IF(B³Π) in the 248 nm Laser Photolysis of Fluorine/Alkyl Iodide Mixtures

Sustained visible emission in the region 440–850 nm from the B → X system of IF is observed when a gas phase mixture (~0.5 mbar) of an alkyl iodide with F₂ in He is photolysed at 248 nm by a KrF laser. The total intensity and decay rate of the IF(B) emission is a strong function of the identity of the alkyl iodide and can be correlated with the 248 nm photon yields for the production of I*(²p_1/2). The half-lives for the IF(B) decays range from 5 μs for t-C₄H₉I to 770 μs for n-C₃F₇I. Decay curves for the I*(²p_1/2) concentrations are also measured by atomic fluorescence. The mechanism for IF(B) formation in these systems is discussed and it is suggested that IF(B) is produced either by a recombination process involving I* and F atoms or by multistep collisional excitation of ground state IF(X) by I*. The F atoms can be produced following the photolysis pulse by the reaction of the alkyl radical with molecular fluorine and IF(X) can result either from the reaction of F atoms with the alkyl iodide or from a dark reaction between molecular fluorine and the alkyl iodide.