When nuclei catch up with electrons
Attosecond measurements on ionization dynamics performed on molecules typically assume that the nuclei can be considered as "frozen in their original positions". However, even in the attosecond time regime, this is not always the case.
Abstract
For the first time, a clear signature of the coupling between electron and nuclear dynamics in H2 photoemission delays is demonstrated by performing state-of-the-art experiments and theoretical calculations. The impact of this work goes well beyond the simple H2 molecule because H atoms are present in most organic and biologically relevant molecules. Thus, understanding the effects and contributions from coupled electron and nuclear dynamics present in such systems is of fundamental importance in many fields of research
The interaction of an extreme ultraviolet attosecond pulse with a molecular system produces a sudden removal of an electron, which can lead to significant changes in the chemical bonding and hence to rearrangement of the residual molecular cation. The time scales of the induced electronic and the related nuclear dynamics are usually very different, ranging from attoseconds to few-femtoseconds for electrons and from tens to hundreds of femtoseconds for nuclear motion, thus allowing for a separate treatment of their motion. This is certainly the case for molecules containing heavy atoms. However, when light atoms are involved, in particular hydrogen, the space-time correlation between electronic and nuclear motions cannot be ignored.
For the first time, Cattaneo et al. unambiguously show that ionization delays can significantly depend on both photoelectron kinetic energy and the nuclear kinetic energy. Variations of ionization delays with nuclear kinetic energy can be as large as variations with electron kinetic energy, which implies that whenever light atoms are involved in the molecular ionization process, the outgoing electron wavepacket cannot be disentangled from the nuclear wave packet, significantly modifying the concept of ionization delay introduced for atomic systems.
News item on the D-PHYS website:
https://www.phys.ethz.ch/news-and-events/d-phys-news/2018/04/when-nuclei-catch-up-with-electrons.html
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