Spectroscopy and reactivity of size-selected Mg+–methanol clusters

Abstract

This work presents photodissociation spectra of ${\mathrm{Mg}}^{\mathrm{+}}{\mathrm{(CH}}_{\mathrm{3}}{\mathrm{OD)}}_n$ $\text{(n=1–5).}$ Mass spectrometry of the parent cluster ions shows that C–H bond cleavage occurs in the ground electronic state. The branching ratios for products of photodissociation show strong selectivity; methyl loss is the exclusive quenching channel in $\text{n=1,}$ while a unique pathway that eliminates ${\mathrm{CH}}_{\mathrm{3}}\mathrm{D}$ occurs in $\text{n=2.}$ Methyl loss does not occur for clusters with more than three solvent molecules. The maximum of spectral intensity shifts to the red with increasing cluster size until halting at $\text{n=3.}$ These data signal the formation of a solvent shell at a relatively small size. As the cluster size increases, ligand loss and D atom loss become overwhelmingly favored. We address the selectivity in the products in terms of the initial photoexcited state, nonadiabatic coupling to the ground state potential energy surface, and subsequent dissociation and product formation dictated by dynamics on the ground state surface.