Ultrafast Molecular Three-Electron Auger Decay

Abstract

Three-electron Auger decay is an exotic and elusive process, in which two outer-shell electrons simultaneously refill an inner-shell double vacancy with emission of a single Auger electron. Such transitions are forbidden by the many-electron selection rules, normally making their decay lifetimes orders of magnitude longer than the few-femtosecond lifetimes of normal (two-electron) Auger decay. Here we present theoretical predictions and direct experimental evidence for a few-femtosecond three-electron Auger decay of a double inner-valence-hole state in CH_{3}F. Our analysis shows that in contrast to double core holes, double inner-valence vacancies in molecules can decay exclusively by this ultrafast three-electron Auger process, and we predict that this phenomenon occurs widely.

Collective relaxation processes in atoms, molecules and clusters

“…Therefore, collective decay of the two initial vacancies represents the only accessible non-radiative relaxation pathway. Recent ab initio calculations [17] predicted a surprisingly short lifetime of about 3 fs, which is well within the range of typical two-electron Auger decay. Excellent agreement of the calculated and measured electron spectra provides experimental support for this rather astonishing result [17].…”

“…Therefore, CAD does not play a significant role in the relaxation of such highly excited states. It has been shown recently [17] that the situation can be radically different for doubly inner-valence ionized states of a variety of molecular species. Not only is CAD often the single possible radiationless decay channel for this class of metastable states, but it can proceed on the few-femtosecond time scale reminiscent of normal Auger transitions.…”

“…To confirm the theoretical results, coincidence experiments were carried out on the CH 3 F molecule [17]. The experimental setup was similar to that used to study CAD in Kr atom [85], i.e.…”

“…I in Ref. [17]) that for the studied doubly inner-valence ionized states, shake-up type configurations constitute up to 30-40% of the associated wavefunctions. Some of those configurations are coupled directly to the main configurations of the CAD final states.…”

“…To avoid these problems, Feifel et al [17] focused in their joint experimental and theoretical study of CAD on small molecules bearing relatively deep (e.g., F 2s…”