A theoretical study of the valence- and dipole-bound states of the nitromethane anion

The valence- and dipole-bound states of CH3NO2- are studied at the CCSD(T), HFDFT (B3LYP), and EA-EOMCC levels of theory. At both CCSD(T) and HFDFT levels, we have found a positive valence EA in nice agreement with the experimental data. The binding energy of the dipole-bound electron is about 13 meV according to the EA-EOMCC calculations. Interaction of the valence- and dipole-bound states (DBS) of CH3NO2- is complicated, since the dipole-bound state exists at the equilibrium geometry of the anion and corresponds to an excited state of the valence-bound anion. Hence, excitations of the valence anionic state could lead to both the detachment of an electron or formation of a DBS, whose geometry is similar to the geometry of the neutral parent. At the equilibrium geometry of the anion, the energies of the dipole-bound and valence states are close to each other. Since typical lifetimes of rovibrational excited states of a DBS are two orders of magnitude higher than the lifetimes of ordinary vibrationally excited states, it might be possible to transform the DBS into the valence ground state under certain experimental conditions. (C) 1996 American Institute of Physics.