The above derivations have been made under the assumption that NAC-induced transitions between manifolds 0, I, and II can be neglected on the timescale of interest. Once the internal conversion (IC) e(τ) → g is allowed, Eq. ( ) remains valid, but the window functions W int k defined per Eq. ( ) have to be replaced by the new window functions W int k,IC which are defined in terms of the original window functions as follows 115 :