MICROSOLVATION OF THE Mg2SO42+ CATION: CRYOGENIC VIBRATIONAL SPECTROSCOPY OF (Mg2+)2SO42_(H2O)n=4_11

Cryogenic ion vibrational predissociation (CIVP) spectroscopy was used to examine the onset of solvation upon the incremental addition of water molecules to the Mg$_{2}$SO$_{4}$$^{2+}$(H$_{2}$O)$_{n}$ cation (n = 4 � 11). D$_{2}$ predissociation spectra are reported for each cluster over the range 1000-3800 cm$^{-1}$. Initially, the Mg$^{2+}$ atoms each interact with two oxygen atoms on the sulfate anion in a bifurcated arrangement. The breaking of this motif occurs upon addition of the eighth water molecule as evidenced by splitting of the water bend, and broad absorption in the 3000-3400 cm$^{-1}$ range indicative of hydrogen bonding between the water molecules and sulfate ion