Universal convergent scaling laws of high-n intercombination transitions in helium

A general expression for intercombination spontaneous transition probabilities A_int in neutral helium is proposed. Consideration of the wavefunction mixing for high n-states showed that interference effects between the upper and lower states lead to a drastic decrease of the transition probabilities for high angular momentum states. This allowed us to develop convergent expressions for A_int up to very high principal quantum numbers n. Spin-dependent atomic population kinetics demonstrate the particular influence of interference effects for the singlet/triplet population of high n-states and cascades driven by intercombination transitions.