Shape resonance of the ethylene anion stabilized in a molecular trap

The possibility of stabilizing an electronically metastable anion in a molecular trap is studied using ab initio electronic structure methods. The 2B2g C2H4− d-wave shape resonance state is used as the metastable anion solute, and a pair of inwardly oriented LiCN molecules (NCLi⋯LiCN) is used as a molecular trap. Although the global minimum of the C2H4+2LiCN+e system is the (LiCN)2− anion with a weakly (van der Waals) bound C2H4 molecule, it was found that for the (NCLi⋯LiCN) trap at its local minimum geometry, the 2B2g state becomes electronically stable and is the ground state of the system. It is also found that, in this model trap, three other (excited) anionic states are bound (2Ag, 2B1u, and 2B2u). Detailed numerical results are presented for the (NCLi⋯H2CCH2⋯LiCN)− species (i.e., the trapped ethylene anion) whose vertical electron detachment energy is 2.97 eV at the CCSD(T) level with the augcc-pVDZ basis sets.