PHOTOFRAGMENTATION OF CF2I2 - COMPETITION BETWEEN RADICAL AND 3-BODY DISSOCIATION

The photodissociation of CF2I2 following excitation into the first UV absorption band system has been studied by photofragment translational spectroscopy. Time-of-flight and angular distributions of the dissociation products measured at the photolysis wavelengths 351, 337, 308, and 248 nm reveal the competition between a radical channel that forms the fragment pairs CF2I + I and a three-body dissociation that yields CF2 + I + I. These processes are found to occur via B1 <-- A1 type electronic transitions. For the iodine atoms produced in the radical channel the spin-orbit branching ratio I*(2P1/2)/I(2P3/2) increases from I*/I = 0.02 at 351 nm to I*/I = 0.2 at 337 nm and reaches I*/I = 2 at 308 nm. This wavelength-dependent selectivity of the I*/I ratio suggests that the absorption band system is composed of at least two overlapping B1 <-- A1 transitions. Although energetically accessible at 351 nm (where CF2I from the radical channel decays spontaneously to CF2 + I), the three-body dissociation is observed first at 308 nm as a minor decay mode and becomes the exclusive decay at 248 nm. The dissociation energy for the formation of CF2I + I(2P3/2) was determined to be D0I less-than-or-equal-to 51.3 +/- 2 kcal/mol; in the case of the reaction forming CF2 + I(2P3/2) + I(2P3/2) the dissociation energy is D0I + D0II less-than-or-equal-to 63.3 +/- 2 kcal/mol.