Characterization of the relevant excited states in the photodissociation of CO-ligated hemoglobin and myoglobin.

The relevant excited states in the rapid photodissociation process of hemoglobin and myoglobin are examined by means of time-dependent density functional theory. Our calculations clearly show that the photodissociation is mediated by two repulsive states (5 A' ' and 3 A') which cross the lowest excited states (1 A' and 1 A' ') at an internuclear Fe-C distance of about 2 A. Electron detachment/attachment density plots nicely explain the repulsive nature of the 5 A' ' and 3 A' states.