Theoretical investigation of the enhancement of positron affinity by the vibration and dimerization of non-polar carbon disulfide

Abstract

The positronic bound state for the non-polar carbon disulfide (CS₂) has been experimentally identified, although previous theoretical investigations, which were dedicated to studying the positronic CS₂ monomer, could not reasonably reproduce the experimentally measured positron affinity. In the present study, we performed analysis of the vibrational averaged positron affinity for the positronic CS₂ dimer, [C₂S₄; e⁺], using the Hartree–Fock and configuration interaction levels of the multi-component molecular orbital method combined with the self-consistent field level of the vibrational variational Monte Carlo method. We demonstrated that the equilibrium structure of the non-polar C₂S₄ can have the positronic bound state with a positron affinity of about 46.18 meV in the configuration interaction level, while this is 0 meV in the Hartree–Fock level. Furthermore, by taking into account the vibrational effect, we succeeded in reproducing the resonant positron kinetic energies lying close to the experimental value, where the vibrational averaged positron affinity becomes greater with an increased dipole moment and dipole polarizability. We also showed possible mechanisms to effectively enhance the resonant positron capture for [C₂S₄; e⁺], associated with both the infrared active and infrared inactive vibrational modes.