A general method of accounting for non-steady-state unimolecular kinetics of reactive species in complex kinetic schemes is described. The method is based on dividing the overall population of affected species into virtual components corresponding to individual eigenvectors of the master equation matrix. It is shown that these individual virtual components are in their respective steady states and evolve independently of each other. The overall treatment is significantly simplified by the fact that only several of these virtual components need to be considered explicitly, and the contribution of the remainder can be described jointly as resulting in ordinary chemical branching. The described method reduces the problem of non-steady-state kinetics to a modest kinetic scheme which can be solved by standard techniques.