Nonadiabatic effects on the photodissociation of diatomic molecules to open-shell atoms

Photodissociation of diatomic molecules to open-shell atoms is shown to be very strongly affected by nonadiabatic interactions when the photon energy is just above the threshold for dissociation. The energy dependences of photodissociation cross sections and various anisotropy parameters exhibit a wealth of structure in conformity with our theoretical predictions that nonadiabatic interactions between molecular states, approaching the same atomic term limit, lead to the emergence of resonance features in the spectra. Some of these features are associated with Feshbach and shape resonances on states that carry no oscillator strength in zeroth order. As an example, we consider the photodissociation cross sections for the production of individual C⁺(²P_3/2,1/2) states from selected initial CH⁺ levels and the fragment angular distribution, orientation, and alignment. We discuss how totally oriented fragments can be produced by near-threshold photodissociation in a magnetic field.