Gas-Phase Ion-Neutral Reactions of Cerium Cluster Ions with Deuterium.

The gas-phase interactions of cerium cluster cations and deuterium neutrals have been investigated using a temperature-dependent reaction cell embedded between two quadrupole mass analyzers. Ce$_{\mathrm{m}}^{\mathrm{+}}$ (m $=$ 1 -- 20) have been generated with our instrumentation and evidence for reaction of these clusters with D$_{\mathrm{2\thinspace }}$to form cerium-deuterium adducts has been obtained. No evidence for fragmentation of cerium clusters via reaction with D$_{\mathrm{2}}$ was found. Accordingly, rate constants for the reaction of Ce$_{\mathrm{m}}^{\mathrm{+}}$ with D$_{\mathrm{2}}$ to form Ce$_{\mathrm{m}}$D$_{\mathrm{2m}}^{\mathrm{+}}$ (m $=$ 1 -- 3) products have been acquired as a function of temperatures ranging from approximately 235 -- 515 K. Arrhenius analysis of the data indicate activation energy barriers exists along the potential energy surfaces (PESs) for the reaction of Ce$_{\mathrm{2}}^{\mathrm{+}}$ and Ce$_{\mathrm{3}}^{\mathrm{+\thinspace }}$with D$_{\mathrm{2}}$, while a negative temperature dependence is observed for the rate constants of the Ce$^{\mathrm{+}}$/D$_{\mathrm{2}}$ reaction. Electronic structure calculations were performed using density functional theory (DFT) to characterize all reactant and product species. This combination of experimental and theoretical results suggest the cerium cluster ions dissociate the deuterium sigma bond to form Ce$^{\mathrm{+}}$-D bonds in an overall exothermic process. Preliminary data for extending these methods to larger cerium clusters is also presented.