Positron-attachment to acetonitrile, acetaldehyde, and acetone molecules: Vibrational enhancement of positron affinities with configuration interaction level of multi-component molecular orbital approach

To theoretically demonstrate the binding of a positron to acetonitrile, acetaldehyde, and acetone molecules, we have calculated the vibrational averaged positron affinity (PA) values along the local CN or CO vibrational contribution with the configuration interaction level of multi-component molecular orbital method. This method can take the electron-positron correlation contribution into account through single electronic - single positronic excitation configurations. The PA values are enhanced by including the local vibrational contribution from vertical PA values due to the anharmonicity of the potential. For acetonitrile, acetaldehyde, and acetone molecules, the PA values after averaging over the 1st vibrational state are 136, 55, and 96 meV, which can be compared with the corresponding experimental vlues of 180, 90, and 173 meV, respectively.