Velocity map imaging of the photodissociation of CF3I:: Vibrational energy dependence of the recoil anisotropy

The photodissociation of jet-cooled CF3I into CF3+I(P-2(3/2)) and CF3+I-*(P-2(1/2)) has been investigated between 304 and 277 nm by using velocity map ion imaging. The two-dimensional images provide detailed information on the partition of available energy into kinetic and internal energy of the photofragments. Vibrational structure with spacing of 695+/-100 cm(-1) is resolved in both I and I* images, indicating excitation of the umbrella mode nu(2) of the CF3 photofragment. The fragment recoil anisotropies beta(I) and beta(I-*) are determined as a function of the excitation wavelength and their variations are interpreted in terms of the crossing between the (3)Q(0) and (1)Q(1) dissociative electronic states. The high-resolution images allow the determination of the variation of the anisotropy parameter beta as a function of the vibrational level of CF3 fragment, and provide a complementary method for the determination of the C-I bond energy. The vibrational dependence of the anisotropy values is discussed in terms of final-state interactions between the CF3 umbrella motion and the C-I dissociation coordinate, as discussed previously by Hennig [J. Chem. Phys. 84, 544 (1986)]. (C) 2003 American Institute of Physics.