Photoionisation of molecular wavepackets – the NaK(C1Σ+) case

The ultrafast photoionisation dynamics of NaK molecules in the C(3)1Σ+ state is investigated by pump–probe spectroscopy. The results are consistent with decreasing electronic transition dipole moment for photoionisation of the C state with increasing internuclear separation, due to increasing Na+K− ion pair character of the C state at the outer turning point of the wavepacket trajectory. Effects of a possible low-lying superexcited state cannot be ruled out, though, and in general future studies on ultrafast photoionisation processes need to address in more detail such effects.