THEORETICAL-STUDY OF THE DIPOLE-BOUND ANION (H2O...NH3)(-)

The adiabatic electron detachment energy for (H2O...NH3)(-) has been f ound to be 109 cm(-1) at the coupled-cluster level of theory with sing le, double, and noninteractive triple excitations (CCSD(T)), to be com pared with the recent experimental result of 123-129 cm(-1) obtained b y Abdoul-Carime et al. [Z. Phys. D 40, 55 (1997)]. The stationary poin ts on the potential energy surface of the neutral and anionic dimer ha ve been determined at the second-order Moller-Plesset level of theory. Our results indicate that the second-order dispersion interaction bet ween the loosely bound electron and electrons of the neutral dimer is as important as the electrostatic electron-dipole stabilization. The h igher-order electron correlation corrections are also very important a nd the CCSD(T) electron binding energy is approximately four times lar ger than the Koopmans theorem estimation. In addition, the hydrogen bo nd in H2O...NH3 is susceptible to a deformation upon attachment of an electron. This deformation enhances both the electrostatic and dispers ion components of the electron binding energy. The calculated Franck-C ondon factors indicate that neutral dimers formed in electron photodet achment experiments may be vibrationally excited in both soft intermol ecular and stiff intramolecular modes. The theoretical photoelectron s pectrum based on the calculated Franck-Condon factors is reported. (C) 1998 American Institute of Physics. [S0021-9606(98)01315-4].