Imaging dynamics on the F + H2O -> HF + OH potential energy surfaces from wells to barriers.

The study of gas-phase reaction dynamics has advanced to a point where four-atom reactions are the proving ground for detailed comparisons between experiment and theory. Here, a combined experimental and theoretical study of the dissociation dynamics of the tetra-atomic FH2O system is presented, providing snapshots of the F + H2O → HF + OH reaction. Photoelectron-photofragment coincidence measurements of the dissociative photodetachment (DPD) of the F(-)(H2O) anion revealed various dissociation pathways along different electronic states. A distinct photoelectron spectrum of stable FH-OH complexes was also measured and attributed to long-lived Feshbach resonances. Comparison to full-dimensional quantum calculations confirms the sensitivity of the DPD measurements to the subtle dynamics on the low-lying FH2O potential energy surfaces over a wide range of nuclear configurations and energies.

Photodissociation studies of the electronic and vibrational spectroscopy of Ni(+)(H2O).

The electronic spectrum of Ni⁺(H2O) has been measured from 16200 to 18000 cm⁻¹ using photofragment spectroscopy. Transitions to two excited electronic states are observed; they are sufficiently long-lived that the spectrum is vibrationally and partially rotationally resolved. An extended progression in the metal-ligand stretch is observed, and the absolute vibrational quantum numbering is assigned by comparing isotopic shifts between 58Ni⁺(H2O) and 6°Ni⁺(H2O). Time-dependent density functional calculations aid in assigning the spectrum. Two electronic transitions are observed, from the ²A1 ground state (which correlates to the ²D, 3d9 ground state of Ni⁺) to the 3²A1 and 2²A2 excited states. These states are nearly degenerate and correlate to the ²F, 3d84s excited state of Ni⁺. Both transitions are quite weak, but surprisingly, the transition to the ²A2 state is stronger, although it is symmetry-forbidden. The 3d84s states of Ni⁺ interact less strongly with water than does the ground state; therefore, the excited states observed are less tightly bound and have a longer metal-ligand bond than the ground state. Calculations at the CCSD(T)/aug-cc-pVTZ level predict that binding to Ni⁺ increases the H-O-H angle in water from 104.2 to 107.5° as the metal removes electron density from the oxygen lone pairs. The photodissociation spectrum shows well-resolved rotational structure due to rotation about the Ni-O axis. This permits determination of the spin rotation constants ε(αα)'' = -12 cm⁻¹ and ε(αα)' = -3 cm⁻¹ and the excited state rotational constant A' = 14.5 cm⁻¹. This implies a H-O-H angle of 104 ± 1° in the 2²A2 excited state. The O-H stretching frequencies of the ground state of Ni⁺(H2O) were measured by combining IR excitation with visible photodissociation in a double resonance experiment. The O-H symmetric stretch is ν1'' = 3616.5 cm⁻¹; the antisymmetric stretch is ν5'' = 3688 cm⁻¹. These values are 40 and 68 cm⁻¹ lower, respectively, than those in bare H2O.