Details of the hydration and water exchange mechanism of Zn2+ have been studied using density functional calculations with a variety of different basis sets. The computed structures and hydration energies for complexes of the type [Zn(H2O) n ]2+ with n = 1−6 are in good agreement with previous results obtained from ab initio calculations and self-consistent reaction field methods. Extension of our investigations to the second coordination (first solvation) sphere and thus to complexes of the general type [Zn(H2O) n ]2+·mH2O with n = 5 and m = 1, 2 and n = 6 and m = 1 reveals two types of complexes having either one or two hydrogen bonds between first and second sphere water molecules. The water exchange mechanism of [Zn(H2O)6]2+ is analyzed on the basis of the structures and energies of these complexes. Within the variations due to the different basis sets employed, the Zn−O bond length for water molecules in the first coordination sphere is between 2.0 and 2.1 Å, water molecules in the second coordination sphere between 3.6 and 4.1 Å and at the frontier of both spheres between 2.7 and 3.0 Å. Within the limitations of the present model, in which bulk water, counterions, and more than one exchanging water molecule have not been considered, a limiting dissociative (D) mechanism for the water exchange reaction on [Zn(H2O)6]2+ is suggested. On the basis of the most reliable structures (i.e., those that could be verified with all levels of theory), the energy of activation for the water exchange is between 4.2 and 4.6 kcal/mol, depending on the basis set employed. A transition state for the interchange mechanism could not be localized. All optimizations invariably led to transition state structures that indicate a limiting D mechanism.

We investigate ultrafast multi-state nuclear dynamics in a triatomic cluster. In particular, we explore how the intracluster nuclear dynamics of the Ag 3 Ϫ /Ag 3 /Ag 3 ϩ system is reflected in the femtosecond pump-probe negative ion-to neutral-to positive ion ͑NENEPO͒ signals. The nuclear dynamics is based on classical trajectories on the ground electronic adiabatic state potential hypersurfaces obtained from accurate ab initio quantum chemistry calculations. The nuclear dynamics of Ag 3 initiated from the linear transition state involves distinct sequential processes of configurational relaxation to the triangular configuration, intracluster collisions, and the onset of IVR, resonant, and dissipative IVR, and vibrational equilibration. We determined the timescales for these processes and discussed their dependence on the initial cluster temperature. The Wigner representation of the density matrix was utilized to simulate the NENEPO-zero kinetic energy ͑NENEPO-ZEKE͒ signal and the total ͑integrated over the photoelectron energy͒ NENEPO signal. We show how geometrical change, completion of IVR and vibrational coherence effects can be identified in the NENEPO signals. A comparison of the calculated NENEPO signals with the available experimental data is presented.

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Based on two empirical studies of senior executives, this article examines key aspects of

The differential and total cross sections for kaon pair production in the pp → ppK + K − reaction have been measured at three beam energies of 2.65, 2.70, and 2.83 GeV using the ANKE magnetic spectrometer at the COSY-Jülich accelerator. These near-threshold data are separated into pairs arising from the decay of the φ-meson and the remainder. For the non-φ selection, the ratio of the differential cross sections in terms of the K − p and K + p invariant masses is strongly peaked towards low masses. This effect can be described quantitatively by using a simple ansatz for the K − p final state interaction, where it is seen that the data are sensitive to the magnitude of an effective K − p scattering length. When allowance is made for a small number of φ events where the K − rescatters from the proton, the φ region is equally well described at all three energies. A very similar phenomenon is discovered in the ratio of the cross sections as functions of the K − pp and K + pp invariant masses and the identical final state interaction model is also very successful here. The world data on the energy dependence of the non-φ total cross section is also reproduced, except possibly for the results closest to threshold.