Initial hydration processes of magnesium chloride: size-selected anion photoelectron spectroscopy and ab initio calculations

To understand the initial hydration processes of MgCl2, we measured photoelectron spectra of MgCl2(H2O)n(-) (n = 0-6) and conducted ab initio calculations on MgCl2(H2O)(n)(-) and their neutral counterparts up to n = 7. A dramatic drop in the vertical detachment energy (VDE) was observed upon addition of the first water molecule to bare MgCl2 (-). This large variation in VDE can be associated with the charge-transferto-solvent (CTTS) effect occurring in the MgCl2(H2O)(n)(-) clusters, as hydration induces transfer of the excess electron of MgCl2- to the water molecules. Investigation of the separation of Cl- -Mg2+ ion pair shows that, in MgCl2(H2O)(n)(-) anions, breaking of the first Mg-Cl bond occurs at n = 4, while breaking of the second Mg-Cl bond takes place at n = 6. For neutral MgCl2MgCl2(H2O)(n) clusters, breaking of the first Mg-Cl bond starts at n = 7.National Natural Science Foundation of China [21403249, 21543007]; Beijing National Laboratory for Molecular SciencesSCI(E)ARTICLE2315562-155691