Phys. Rev. A 107, 062824 (2023)

Fragmentation of and electron detachment from hot copper and silver dimer anions: A comparison

E. K. Anderson^1,2,*, A. F. Schmidt-May¹, P. K. Najeeb¹, G. Eklund¹, K. C. Chartkunchand³, S. Rosén¹, M. Kamińska¹, M. H. Stockett¹, R. Nascimento⁴, K. Hansen⁵, Å. Larson¹, H. Cederquist¹, H. Zettergren¹, and H. T. Schmidt^1,†

1 Department of Physics, Stockholm University, AlbaNova, SE-106 91 Stockholm, Sweden

2 Department of Physics and Astronomy, Aarhus University, DK-8000C Aarhus, Denmark

3 Atomic, Optical, and Molecular Physics Laboratory, RIKEN Cluster for Pioneering Research Wako-shi, Saitama 351-0198, Japan

4 Centro Federal de Educação Tecnológica Celso Suckow da Fonseca, Petrópolis, 25620-003, Rio de Janeiro, Brazil

5 Center for Joint Quantum Studies and Department of Physics, School of Science, Tianjin University, 92 Weijin Road, Tianjin 300072, China

* eemma.anderson@gmail.com
† schmidt@fysik.su.se

Abstract

We measured the spontaneous decays of internally hot copper and silver dimer anions, ${\mathrm{Cu}}_2^{-}$ and ${\mathrm{Ag}}_2^{-}$, stored in one of the two ion-beam storage rings of the Double Electrostatic Ion Ring Experiment (DESIREE) at Stockholm University. A coincidence detection technique was utilized enabling essentially background-free measurements of ${\mathrm{Cu}}_2^{-}\to$ Cu $+{\mathrm{Cu}}^{-}$ and ${\mathrm{Ag}}_2^{-}\to$ Ag $+{\mathrm{Ag}}^{-}$ fragmentation rates. Furthermore, the total rates of neutral decay products (monomers and dimers) were measured and the relative contributions of fragmentation and electron emission (${\mathrm{Cu}}_2^{-}\to {\mathrm{Cu}}_2+e^{-}$ and ${\mathrm{Ag}}_2^{-}\to {\mathrm{Ag}}_2+e^{-}$) were deduced as functions of storage time. Fragmentation is completely dominant at early times. However, after about 20 ms of storage, electron emission is observed and becomes the leading decay path after 100 ms for both dimer anions. The branching ratios between fragmentation and electron emission (vibrationally assisted autodetachment processes) are very nearly the same for ${\mathrm{Cu}}_2^{-}$ and ${\mathrm{Ag}}_2^{-}$ throughout the present storage cycle of 10 seconds. This is surprising considering the difference between the electron affinities of the neutral dimers, ${\mathrm{Cu}}_2$ and ${\mathrm{Ag}}_2$, and the difference between the ${\mathrm{Cu}}_2^{-}$ and the ${\mathrm{Ag}}_2^{-}$ dissociation energies.