Electronic and geometrical structure of dipole-bound anions formed by polar molecules

The electronic and geometrical structures of fourteen polar molecules, which have sufficiently large dipole moments to form dipole-bound stationary states with an extra electron, are investigated with the Hartree-Fock (HF) method and second-order Moller-Plesset (MP2) perturbation theory. The molecules considered are as follow: formaldehyde, H₂CO; propanal, CH₃CH₂CHO; pivalaldehyde, (CH₃)₃CCHO; butanal, CH₃-CH₂CH₃CHO; acetaldehyde, CH₃CHO; 2-butanone, CH₃CH₂COCH₃; trifluorobenzene, C₇H₅F₃; cyclohexanone, C₆H₁₀O; acetone; CH₃COCH₃; cyclopentanone, C₅H₈O; cyclobutanone, C₄H₆O; methylacrylonitrile, CH₂-CCH₃CN; acrylonitrile, CH₂CHCN; acetonitrile, CH₃CN. The electron affinities corresponding to the formation of the dipole-bound states of the anions are calculated. For all the molecules considered, except formaldehyde, the molecules are found to be able to support dipole-bound states. Almost direct proportionality is found between the dipole moment and the electron affinity (EA) in the series.