ELECTRONIC-STRUCTURE OF DIPOLE-BOUND ANIONS

Dipole-bound anionic states of HCN, (HF)(2), CH3CN, C3H2, C4H2, C5H2, and stretched CH3F are studied using extended one-electron basis sets at thr coupled cluster level of theory with single, double, and nonite rative triple excitations (CCSD(T)). Orbital relaxation and electron c orrelation corrections to the Koopmans' theorem prediction of electron binding energy an analyzed, and a physical interpretation of low-orde r corrections is proposed. It is demonstrated that the second-order di spersion interaction between the loosely bound electron and the electr ons of the neutral host should be included into physical models of dip ole-bound anions. Higher-order electron correlation corrections are al so found to be important, and a slow convergence of the Moller-Plesset series for electron binding energies is documented. Modifications of the potential energy surfaces of the above polar molecules upon electr on attachment are studied at the second-order Moller-Plesset level, an d Franck-Condon factors for the anion/neutral pairs an calculated. It is predicted that photoelectron spectra of the dipole-bound anions of C4H2 and C5H2 should display vibrational structure.