ENERGIES OF DIPOLE-BOUND ANIONIC STATES

Dipole-bound anionic states of CH3CN, C3H2, and (HF)(2) were studied u sing highly correlated electronic structure methods and extended one-e lectron basis sets. The electron detachment energies were calculated u sing the coupled cluster method with single, double, and noniterative triple excitations. Geometrical relaxation of the molecular framework upon electron attachment and the difference in the harmonic zero-point vibrational energies between the neutral and the dipole-bound anionic species were calculated at the MP2 level of theory. We demonstrate th at the dispersion interaction between the loosely bound electron and t he electrons of the neutral molecule is an important component of the electron binding energy, comparable in magnitude to the electrostatic electron-dipole stabilization. The geometrical relaxation upon electro n attachment and the change in the zero-point vibrational energy is im portant for the weakly bound HF dimer. The predicted values of the ver tical electron detachment energies for the dipole bound states of CH3C N and C3H2 of 112 and 188 cm(-1) respectively, are in excellent agreem ent with the recent experimental results of 93 and 171 +/- 50 cm(-1), respectively. For (HF)(2)(-), the predicted value of adiabatic electro n detachment energy is 396 cm(-1), whereas the experimental vertical d etachment energy is 508 +/- 24 cm(-1). The possibility of formation of the neutral dimer in an excited vibrational state is considered. (C) 1997 John Wiley & Sons, Inc.