The four important geometries on the PES. Starting clockwise from the upper-left hand corner they are the vertical geometry [global minimum of ], the global minimum of , the transition state of , and the global minimum of .
The two-dimensional slice of the PES of the neutral , top, and ground state cation , bottom, as a function of the coordinates and . While these two coordinates are mostly uncoupled in the neutral dimer, they become strongly coupled in the cation. The minimum on each surface is indicated by an “X” on the figure.
The PES of the first excited state of the cation as a function of the coordinates and . While the minimum, indicated by an X, still corresponds to a proton-transferred geometry, there is a shelf in the Franck–Condon region, resulting in slow proton transfer in this state.
The calculated photoelectron spectrum of the water dimer corresponding to the ground state of the cation. There is a broad vibrational progression corresponding primarily to excited vibrational states of the coupled O–O and O–H stretches. The first feature has an onset of 11.1 eV and peaks at 11.7 eV, which are the adiabatic and VIEs, respectively. The second feature corresponds to the first excited state of the cation and has a single peak near the vertical ionization at 13.1 eV
Comparison of theoretical and experimental photoelectron spectra of the water dimer. The experimental spectrum is derived by taking the numeric derivative of averaged PIE curves, as fragment channels become energetically available, the PIE curve can decrease resulting in regions of negative slope.
Projection of the ground state cation wave packet on the two-dimensional subspace of the and coordinates. (a) Starting from the initial vertically ionized position, the wavepacket begins spreading along the coordinate in (b). Because the distance is still relatively unchanged, the wavepacket encounters a small barrier and the resulting transmission and reflection can be seen in (c) and (d).
The expectation values of the coordinates and as a function of wave packet propagation time. The hydrogen moves on a significantly faster time scale than the monomer and is able to complete approximately three oscillations in the same time required for the monomers to move closer. At about 50 fs, the wave packet has arrived at the product state of the complex.
Projection of the excited state cation wave packet on the two-dimensional subspace of the and coordinates. (a) The propagation of the wave packet is shown at several time steps after the initial vertical ionization. [(b)–(d)] Because of the flatness of the PES in the region of the vertical transition, the wavepacket remains relatively localized during the subsequent propagation.
The spectral evolution of the excited states of when the dynamics takes place on the ground state surface of the cation. The contours correspond to the intensities of individual electronic transitions. Excitation energies and transition dipole moments are evaluated at single point geometries along the path of the wave packet centroid.
The spectral evolution of the excited states of when the dynamics takes place on the excited state surface of the cation. The contours correspond to the intensities of individual electronic transitions. Excitation energies and transition dipole moments are evaluated at single point geometries along the path of the wave packet centroid.
Geometrical parameters and energies of the important geometries for in the ground and the first excited state. Lengths are given in Å and energies are given in kcal/mol.
Comparison of experimental frequencies from vibrational predissociation spectroscopy (Ref. 32), theoretical VCI frequencies, and the harmonic results from Ref. 31. Frequencies are given in .
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