Threshold Collision-Induced Dissociation of Hydrated Magnesium: Experimental and Theoretical Investigation of the Binding Energies for Mg2+(H2O)x Complexes (x=2–10)

Authors

  • Damon R. Carl,

    1. Department of Chemistry, University of Utah, 315 S. 1400 E. Room 2020, Salt Lake City, UT 84112 (USA)
    2. Current address: Heritage Research Group, 7901 W. Morris St., Indianapolis, IN 46231 (USA)
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  • Prof. Peter B. Armentrout

    Corresponding author
    1. Department of Chemistry, University of Utah, 315 S. 1400 E. Room 2020, Salt Lake City, UT 84112 (USA)
    • Department of Chemistry, University of Utah, 315 S. 1400 E. Room 2020, Salt Lake City, UT 84112 (USA)
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Abstract

The sequential bond energies of Mg2+(H2O)x complexes, in which x=2–10, are measured by threshold collision-induced dissociation in a guided ion beam tandem mass spectrometer. From an electrospray ionization source that produces an initial distribution of Mg2+(H2O)x complexes in which x=7–10, complexes down to x=3 are formed by using an in-source fragmentation technique. Complexes smaller than Mg2+(H2O)3 cannot be formed in this source because charge separation into MgOH+(H2O) and H3O+ is a lower-energy pathway than simple water loss from Mg2+(H2O)3. The kinetic energy dependent cross sections for dissociation of Mg2+(H2O)x complexes, in which x=3–10, are examined over a wide energy range to monitor all dissociation products and are modeled to obtain 0 and 298 K binding energies. Analysis of both primary and secondary water molecule losses from each sized complex provides thermochemistry for the sequential hydration energies of Mg2+ for x=2–10 and the first experimental values for x=2–4. Additionally, the thermodynamic onsets leading to the charge-separation products from Mg2+(H2O)3 and Mg2+(H2O)4 are determined for the first time. Our experimental results for x=3–7 agree well with quantum chemical calculations performed here and previously calculated binding enthalpies, as well as previous measurements for x=6. The present values for x=7–10 are slightly lower than previous experimental results and theory, but within experimental uncertainties.

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