Investigation of the validity conditions of using an isolated-line approximation to the level-mixing model

This work elucidates the dynamics of a system in the presence of an external field by using the density matrix method. An isolated-line approximation (ILA) is also applied to the Bixon–Jortner model in which the bright states and the dark states are clearly distinguished. The approximate solutions are then compared with the exact ones to determine the validity conditions of the ILA.