Dynamics of I*(2P1/2) production from fluorinated alkyl iodides at 266, 280, and ∼305 nm

Abstract

In this paper, we present I*(2P1/2) 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(2P3/2) and spin–orbit excited I*(2P1/2) 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 α 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 Q03 state to the Q11 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.