Contribution of electron correlation to the stability of dipole-bound anionic states

Abstract

It has long been assumed that electron correlation effects are relatively unimportant for describing dipole-bound anionic states. It is shown here that this assumption is incorrect: high-level electronic structure calculations on the dipole-bound anion states of ${\mathrm{CH}}_{3}$CN, ${\mathrm{C}}_{3}$${\mathrm{H}}_{2}$, and ${\mathrm{C}}_{5}$${\mathrm{H}}_{2}$ reveal that for these species a large fraction of the electron binding energy derives from the dispersion-type interaction between the loosely bound electron and the neutral molecule. The predicted values of the electron affinities of the dipole bound states of ${\mathrm{CH}}_{3}$CN and ${\mathrm{C}}_{3}$${\mathrm{H}}_{2}$, 108 and 173 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, respectively, are in excellent agreement with the recent experimental results, 93 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ and 171\ifmmode\pm\else\textpm\fi{}50 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, respectively. The predicted value for ${\mathrm{C}}_{5}$${\mathrm{H}}_{2}$ is 614 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. \textcopyright{} 1996 The American Physical Society.