Molecular reorganization upon ionization and excitation: NH2, NH2+, and NH2− systems

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Abstract
The results of ab initio self-consistent field calculations on NH2+ (3B1 and 1A1), NH2 (2B1 and 2A1), and 1A1 NH2− reveal that the electron distribution in 2a1 and 1b2 bonding orbitals and in the in-plane 3a1 valence orbital is most affected by ionization or excitation. The formation of the cationic states is accompanied by a shift to the nitrogen atom of 0.35 electron for the 1A1 and 0.25 electron for the 3B1 state. In NH2− formation, electron density shifts to the hydrogens. These changes occur mainly in the bonding orbitals. Excitation of ground-state NH2 causes a shift of about 0.10 electron onto the nitrogen, whereas excitation of 3B1 NH2+ shifts charge density onto the hydrogens. These changes occur in the valence orbitals. The ionization potential calculated for 2B1 NH2 (11.6 eV) agrees well with experiment, but the photodetachment energy obtained for NH2− (0.30 eV) is less than half the experimental value. Polarization functions in the basis set made negligible contributions to the molecular orbitals with the exception of the 2a1 bonding orbital. Optimization of the nitrogen polarization functions for the 2B1 NH2 and the NH2− systems resulted in only a small improvement in the energy and a more marked change in the charge distribution in NH2−.