We present ab initio calculations of the repulsive Coulomb barrier for several geometrically stable isomers of the BeC4 2- dianion. We describe how the deformation of certain isomers can account for the experimental Coulomb explosion images of the dianion. For the most stable linear isomer, C2 -BeC2 - examined the electron tunneling process along the dissociation path to obtain C2 - plus BeC2 -. We found the crossing point for autodetachment to be Rdis C = 3.25 Å. Rdis is the bond length between C2 - and BeC2 - at this point, the electron tunneling energy is equal to the maximum of the repulsive Coulomb barrier. In the framework of the Wenzel-Kramer-Brioullin theory, the electron-loss lifetime of the metastable C2 -BeC2 - dianion at the equilibrium geometry, Rdis = 1.64 Å, was estimated to be about 5 ms. This lower limit is in agreement with the experimental results in which the BeC2 - dianion has a lifetime much longer than 5 μs.
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