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

It has long been assumed that electron correlation effects are relatively unimportant for describing dipolebound anionic states. It is shown here that this assumption is incorrect: high-level electronic structure calculations on the dipole-bound anion states of CH3CN, C3H2, and C5H2 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 CH3CN and C3H2, 108 and 173 cm , respectively, are in excellent agreement with the recent experimental results, 93 cm and 171650 cm, respectively. The predicted value for C5H2 is 614 cm . @S1050-2947~96!09208-6#