Continuum state spectroscopy: A high resolution ion imaging study of IBr photolysis in the wavelength range 440-685 nm

The photodissociation of jet-cooled IBr molecules has been investigated at numerous excitation wavelengths in the range 440-685 nm using a state-of-ar t ion imaging spectrometer operating under optimal conditions for velocity mapping. Image analysis provides precise threshold energies for the ground, I(P-2(3/2)) + Br(P-2(3/2)), and first excited [I(P-2(3/2)) + Br(P-2(1/2))] dissociation asymptotes, the electronic branching into these two active pr oduct channels, and the recoil anisotropy of each set of products, as a fun ction of excitation wavelength. Such experimental data have allowed mapping of the partial cross-sections for parallel (i.e., Delta Omega = 0) and per pendicular (i.e., Delta Omega = +/-1) absorptions and thus deconvolution of the separately measured (room temperature) parent absorption spectrum into contributions associated with excitation to the A (3)Pi (1), B (3)Pi (0(+) ) and (1)Pi (1) excited states of IBr. Such analyses of the continuous abso rption spectrum of IBr, taken together with previous spectroscopic data for the bound levels supported by the A and B state potentials, has allowed de termination of the potential energy curves for, and (R independent) transit ion moments to, each of these excited states. Further wave packet calculati ons, which reproduce, quantitatively, the experimentally measured wavelengt h dependent product channel branching ratios and product recoil anisotropie s, serve to confirm the accuracy of the excited state potential energy func tions so derived and define the value (120 cm(-1)) of the strength of the c oupling between the bound (B) and dissociative (Y) diabatic states of 0(+) symmetry. (C) 2001 American Institute of Physics.