Excitonic states in a (Ti6O12)3 nanotube.

The low-lying excited electronic states of a (Ti(6)O(12))(3) nanotube are investigated using ab initio self-consistent field configuration interaction theory. The transition energies and moments are calculated and the nature of the orbitals involved is discussed. Transitions correspond to an excitation from an O(2p) to a nearby Ti(3d) orbital and singlet-singlet transitions vary in excitation energy from 2.1 eV to 4.3 eV, depending on the oxygen site and environment of the titanium site. Two different structures for the three stacked Ti(6)O(12) rings are found. The occluded Ti structure is lower in energy than a staggered structure by 1.25 eV, only 0.02 eV/bond. Excited electronic states are found to correspond to highly localized holes on oxygen and a highly localized electron in a d orbital on a nearest neighbor titanium. The staggered structure has four absorptions that lie within the intense portion of the solar spectrum, at 585 nm, 472 nm, 471 nm, 423 nm; the occluded structure has one strong absorption, at 532 nm.

Silver as an electron source for photodissociation of hydronium.

The photochemistry of a solvated hydronium ion near a silver surface is investigated using ab initio self-consistent field and configuration interaction theory. Photoinduced electron attachment can occur at energies in the range of 1.1-1.2 eV depending upon the initial orientation of the hydronium relative to the silver surface. Rearrangement of solvating waters considerably reduces transition state barriers to dissociation on the excited-state potential energy surface, such that fast dissociation of the neutralized hydronium would occur with no barrier. Both the H and H(2) product channels are exothermic pathways on the excited state surface and in several instances exothermic compared to the energy of the initial structure.