Reactions of alkaline earth metal ions with methanol clusters

The gas phase reactions between singly charged alkaline earth metal ions (Mg⁺, Ca⁺, Sr⁺ and Ba⁺) and methanol clusters are studied in a pick-up cluster source. In much the same way as for the alkaline earth metal ion - water cluster systems studied by Fuke et al. (J. Am. Chem. Soc. 1995, 177, 747), anomalous product distributions were observed that are characterized by two product switching regions. The first product switching from M⁺(CH₃OH)_n to MOCH₃⁺(CH₃OH)_n-1 occurs for n at around 5. The MOCH₃⁺(CH₃OH)_n-1 species switches back to Mg⁺(CH₃OH)_n for n at around 15 (second switching). The critical sizes for the first and the second switching were found to be affected by the metal and deuterium substitutions. Ab initio calculations on the structures and energetics of the reactants and products were carried out to facilitate the interpretation of the product switching behaviors.