Experimental and theoretical investigation of the charge-separation energies of hydrated zinc(II): redefinition of the critical size.

In the preceding article, the hydration energies of Zn(2+)(H(2)O)(n) complexes, where n = 6-10, were measured using threshold collision-induced dissociation (CID) in a guided ion beam tandem mass spectrometer (GIBMS) coupled with an electrospray ionization (ESI) source. The present investigation explores the charge-separation processes observed, Zn(2+)(H(2)O)(n) --> ZnOH(+)(H(2)O)(m) + H(+)(H(2)O)(n-m-1), and the competition between this process and the loss of water. Our results demonstrate that charge-separation processes occur at variable complex sizes of n = 6, 7, and 8, prompting a redefinition of the critical size for charge separation. Experimental kinetic energy-dependent cross sections are analyzed to yield 0 K threshold energies for the charge-separation products and the effects of competition with this channel on the energies for losing one and two water ligands after accounting for multiple collisions, kinetic shifts, and energy distributions. A complete reaction coordinate is calculated for the n = 7 complex dissociating into ZnOH(+)(H(2)O)(3) + H(+)(H(2)O)(3). Calculated rate-limiting transition states for n = 6-8 are also compared to experimental threshold measurements for the charge-separation processes.