Photodissociation of CH2ICH2I, CF2ICF2I, and CF2BrCF2I in solution

The photodissociation dynamics of CH2ICH2I, CF2ICF2I, and CF2BrCF2I have been studied in solution after excitation at 266 nm. Formation of I-2 is apparent within tens of picoseconds in solutions of CH2ICH2I and CF2ICF2I in acetonitrile. but not from CF2BrCF2I, More I-2 is formed from CH2ICH2I rather than from CF2-ICF2I, as expected if the 12 formation is a result of secondary dissociation of the haloethyl radicals followed by geminate combination. For CH2ICH2I, the 12 formation is ultrafast (<2 ps) in several different solvents. The quantum yields Of 12 formation (after a few microseconds) were found to be 1.0+/-0.1 for CH2ICH2I and 0.75-0.95 for CF2ICF2I in hexane, dichloromethane, and tetrachloromethane. The data on a nanosecond to microsecond time scale indicate that all haloethyl radicals decay within tens of nanoseconds. We suggest that the decay of haloethyl radicals can occur partially via abstraction.