Dynamics of I^∗(²P_½) production from fluorinated alkyl iodides at 266,280,and ~305 nm

Abstract

In this paper, we present I^∗(²P_½) quantum yield, φ^∗ from the gas phase photodissociation of a series of perfluoroalkyl iodides at three different wavelengths 266, 280, and ~305 nm. The iodine atoms in the ground I(²P_3/2) and spin-orbit excited I^∗(₂P_½) states were monitored directly by a two photon laser induced fluorescence scheme. The I^∗ quantum yields for the fluorinated alkyl iodides are found to be much higher than their corresponding alkyl iodide analogs over the entire A band. However, Φ^∗ remains more or less unchanged as a function of photolysis wavelength for the perfluoroalkyl iodides with the exception of CF₃I in which it drops monotonically as a function of wavelength. Unlike in normal alkyl iodides, branching at the a position does not affect the φ^∗ in perfluoroalkyl iodides. The prediction of I^∗ yield using the one dimensional Landau-Zener soft-radical-impulse model is opposite to what is seen from our measurements. In all the fluorinated alkyl iodides, the CF₃ in-plane rocking mode which can take the initially excited ³Q₀ state to the ¹Q₁ state through the crossing region appears to be weakly coupled to the C-I stretch resulting in low yield of I atom in the dissociation process.