The photoabsorption spectra of HI and DI are computed using ab initio potential curves and transition dipole moments. Partial absorption cross-sections and quantum yields for the production of the ground state (P-2(3/2)) and the excited spin-orbit state (P-2(1/2)) of iodine are calculated using the time-dependent wave packet formalism as functions of the excitation energy. Very good overall agreement with experimental data is obtained for the band total absorption spectrum and for the I(P-2(1/2)) quantum yield. The spin-rotational coupling of the a(3)Pi (0) and A(1)Pi (1) states is estimated for the first time and is shown to play a negligible role in the HI photodissociation.