Photodissociation of partially fluorinated alkyl iodides in their A-band

Photodissociation dynamics of partially substituted alkyl iodides with fluo rine atoms at beta and gamma positions has been investigated. The iodine at oms in the ground I(-P-3/2) and spin-orbit excited I*(P-2(1/2)) states prod uced in the ultraviolet photolysis of CF3CH2I, C6F13CH2CH2I, and C8F17CH2CH 2I 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 similar to 305 nm corresponding to the red and blue wings as well as th e peak of their A-band absorption spectrum has been determined. The I* yiel d from beta and gamma -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 betwee n the (3)Q(0) and (1)Q(1) states. However, at wavelengths above 262 nm, the measured I* quantum yield of beta and gamma -substituted alkyl iodides ref lects that the (3)Q(1) 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.