Photodissociation of partially fluorinated alkyl iodides in their A-band

Abstract

Photodissociation dynamics of partially substituted alkyl iodides with fluorine atoms at β and γ positions has been investigated. The iodine atoms in the ground I(²P_3/2) and spin-orbit excited I^∗(²P½) states produced in the ultraviolet photolysis of CF₃CH₂I, C₆F₁₃CH₂CH₂I, and C₈F₁₇CH₂CH₂I have been detected using a two photon laser induced fluorescence (TPLIF) scheme. The I^∗ quantum yield of the above iodides at 222, 236, 266, 280, and ~305 nm corresponding to the red and blue wings as well as the peak of their A-band absorption spectrum has been determined. The I^∗ yield from β and γ-substituted iodides is found to remain more or less unchanged as a function of excitation wavelength below 262 nm, which is the peak of their A-band. The observed dynamics at 222, 236, and 266 nm can be adequately described by the known Landau-Zener curve crossing model between the ³Q₀ and ¹Q₁ states. However, at wavelengths above 262 nm, the measured I quantum yield of β and γ-substituted alkyl iodides reflects that the ³Q₁ state has a significant contribution to the overall dynamics. The electronic effect exerted by fluorine on the dynamics appears to wither as the substitution moves further away from the C-I bond.