Eur. Phys. J. D (2017) 71: 2
https://doi.org/10.1140/epjd/e2016-70495-7

Regular Article

Tricationic metastability by symmetry restrictions: B₂ⁿ⁺, n = 3,4

IFISR – International Foundation for Independent Scientific Research, 576 Fifth Ave, Suite 903, New York, NY 10036, USA

^a e-mail: hogreve@ifisr.org

Received: 5 August 2016
Received in final form: 22 October 2016
Published online: 10 January 2017

Abstract

To explain the experimentally observed metastability of the trication B₂³⁺, we study this system by various ab-initio methods. Whereas the electronic ground state X²Σ_u⁺ of B₂³⁺ turns out to be unstable, the potential energy curves of the lowest excited state 1²Π_u and of the quartet state 1⁴Σ_g⁻ form barriers that support quasi-bound vibronic states. The lifetimes of these states are not only determined by the respective (dissociative) tunnelling rates, but also by possible radiative electronic transitions and predissociation via spin-orbit coupling, where the latter furnish the decisive decay mechanism for the low-lying vibronic levels. In case of the quadruply charged system B₂⁴⁺, our computations do not predict any metastable states in the low-lying electronic spectrum. The deviation from a purely Coulombic repulsive behaviour in B₂⁴⁺ is quantified by fitting the potential energy curves to a modified Murrell-Sorbie function.