Rotationally induced Penning ionization of ultracold photoassociated helium dimers

TL;DR

This study investigates how rotation influences Penning ionization in ultracold helium dimers, revealing the role of spin states and rotational coupling in ionization processes through experimental comparisons.

Contribution

It provides new insights into the rotational and spin dynamics affecting Penning ionization in ultracold helium dimers, highlighting the impact of spin conservation and weak rotational coupling.

Findings

Identification of four vibrational series with different rotational states.

Penning ionization is inhibited by spin conservation at small interatomic distances.

Weak rotational coupling causes detectable ionization signals in certain series.

Abstract

We have studied photoassociation of metastable \tripS helium atoms near the \tripS-\tripP asymptote by both ion detection in a magneto-optical trap and trap-loss measurements in a magnetic trap. A detailed comparison between the results of the two experiments gives insight into the mechanism of the Penning ionization process. We have identified four series of resonances corresponding to vibrational molecular levels belonging to different rotational states in two potentials. The corresponding spin states become quasi-purely quintet at small interatomic distance, and Penning ionization is inhibited by spin conservation rules. Only a weak rotational coupling is responsible for the contamination by singlet spin states leading to a detectable ion signal. However, for one of these series Bose statistics does not enable the rotational coupling and the series detected through trap-loss does not give rise to sufficient ionization for detection.