Reaction Operator in the Main Equation of Spin Chemistry

In our previous works, using an exactly solvable model as an example, we demonstrated the validity of the reaction operator in the basic equation of spin chemistry. However, in those works, only recombination from the singlet state was considered, although the general relations allowed us to consider the general case. In this paper, such a general case is analyzed. The radical pair comes into contact in a mixed singlet-triplet state, and recombination proceeds from both the singlet and triplet states. The result obtained fully corresponds to the basic equation of spin chemistry.