Surface-Aligned Ion--Molecule Reaction on the Surface of a Molecular Crystal CD3+ + CD3l → C2D5+ + Dl.

An ion-molecule reaction has been observed from a condensed molecular crystal of CD3I using the time-of-flight electron-stimulated desorption ion angular distribution technique. The CD3I multilayer is produced by growth on an ordered substrate. The reaction occurs between CD3+ ions produced by electron- stimulated desorption and neighbor CD3I molecules in the topmost layer of the molecular crystal of CD3I, forming product C2D5+ ions whose desorption dynamics have been measured. The normal momentum of the product ion is close to that of the reactant ion, suggesting that the reaction is dominated by a two-body collision, i.e., the momentum of the reactant CD3+ ion governs the momentum of the product C2D5+ ion. The ion-molecule reaction is of high cross section since the C2D5+ yield is comparable to the CD3+ yield. It is found that the yield and directionality of the emission of the C2D5+ product ion is governed by the molecular order that is characteristic of the molecular crystal of CD3I. Destroying or modifying this order by using a spacer layer of H2O diminishes the C2D5+ product ion yield relative to the reactant CD3+ yield and broadens the ion emission directions. [ABSTRACT FROM AUTHOR]