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Experimental and Theoretical Investigation of the Charge-Separation Energies of Hydrated Zinc(II): Redefinition of the Critical Size

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journal contribution
posted on 10.12.2009, 00:00 by Theresa E. Cooper, P. B. Armentrout
In the preceding article, the hydration energies of Zn2+(H2O)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, Zn2+(H2O)n → ZnOH+(H2O)m + H+(H2O)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+(H2O)3 + H+(H2O)3. Calculated rate-limiting transition states for n = 6−8 are also compared to experimental threshold measurements for the charge-separation processes.