Energies of Dipole-Bound Anionic States

Ž . Dipole-bound anionic states of CH CN, C H , and HF were studied using highly 3 3 2 2 correlated electronic structure methods and extended one-electron basis sets. The electron detachment energies were calculated using 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 that the dispersion interaction between the loosely bound electron and the 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 electron attachment and the change in the zero-point vibrational energy is important for the weakly bound HF dimer. The predicted values of the vertical electron detachment energies for the dipole bound states of CH CN and C H of 112 and 188 cmy1, 3 3 2 respectively, are in excellent agreement with the recent experimental results of 93 and y1 Ž .y 171 " 50 cm , respectively. For HF , the predicted value of adiabatic electron 2 detachment energy is 396 cmy1, whereas the experimental vertical detachment energy is 508 " 24 cmy1. The possibility of formation of the neutral dimer in an excited vibrational state is considered. Q 1997 John Wiley & Sons, Inc. * Current address: High Performance Computational Chemistry Group, Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA, 99352. ( ) International Journal of Quantum Chemistry, Vol. 64, 183]191 1997 Q 1997 John Wiley & Sons, Inc. CCC 0020-7608 / 97 / 020183-09