Transitions 4p  5s were not observed due to the low transition probability since the transition does not follow the selection rule for two-photon excitation: ∆ l = 0,±2.
Færslur 4p  5s sáust ekki vegna lítilla færslulíkinda þar sem færslan fylgir ekki valreglunni fyrir tveggja-ljóseinda örvun: ∆ l = 0,±2.