Small metal cluster dianions such as Be32- and Mg32- lie higher in energy than their respective monoanions and can decay by loss of an electron. This instability to autodetachment implies that the dianions possess only short-lived resonance states described by a resonance position and width where the width is proportional to the inverse of the lifetime. Here we study short-lived states of Be32- and Mg32- with the regularized analytic continuation (RAC) approach combined with a wide variety of quantum chemistry methods including CCSD(T), EOM-CCSD, and NEVPT2. For both Be32– and Mg32–, four low-energy resonance states in the energy range of 2.3 to 4.3 eV above the ground states of the respective monoanions were identified. The four states correspond to different occupation patterns of the two excess electrons in the two lowest p-σ and p-π orbitals, and the for both Be32– and Mg32– the triplet state corresponds to the lowest energy. All resonances are found to show large widths between 1 and 1.5 eV translating into fs lifetimes. Additionally, model solvation of the two dianions in their (p-π)2 states by six and 12 water molecules was considered. Our results show a dramatic drop in the resonance position and width corresponding to a lifetime increase by two orders of magnitude. However, the solvated clusters are still resonances, and a more pronounced perturbation (more water molecules, solvent with larger dipole, … ) will be needed to fully stabilize the two excess charges.

Temporary states of Be32- and Mg32- cluster dianions

ACS Spring Meeting 2021

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