A three-dimensional quantum reactive scattering study of the I + di reaction and of the IDI^- photodetachment spectrum

In this paper are presented the results of a coupled-channel hyperspherical reactive scattering calculation of bimolecular reaction probabilities for the I + DI → ID + I reaction and of Franck-Condon factors for the photodetachment of IDI^-. The calculation is fully three-dimensional, but only the J = 0 partial wave is considered. The results show significant contributions of both resonances and direct scattering to the reaction dynamics. Very narrow resonances associated with transition-state quantum numbers (ν₁, ν₂, ν₃) = (000) and (100) are found and these are in excellent agreement with bound-state calculations by Clary and Connor. Much broader excited-state resonances labelled by the quantum numbers (002), (102), (202), (302), (004), (104), (204) and (304) have also been located. The calculated photodetachment spectra show that these broad resonances play a dominant role in determining two peaks that have recently been observed experimentally by Neumark and co-workers. The narrow resonances (000) and (100) are, by contrast, overwhelmed by direct scattering threshold contributions in determining a third peak in the photodetachment spectrum. An 'extra' peak also appears in the calculated photodetachment spectrum that is not seen in the experiments. This peak is due to the direct reaction threshold for the I + DI(v = 1) reaction, and presumably it arises because of inaccuracies in our potential surface. Its importance should therefore provide a useful diagnostic for improvements to the surface.