IONIC REACTIVITY OF SMALL GAS PHASE MOLECULAR CLUSTERS

Author Institution: University of York, Department of Chemistry, Heslington, YO10 5DD, United KingdomThe study of ionised molecular clusters provides an insight into ion-molecule chemistry; ubiquitous in atmospheric, flame and plasma processes. The neutral fluorobenzene-ammonia system, essentially unreactive in the gas phase, will react in solution under high temperature and pressure conditions. However, fluorobenzene$^+$ will react, via nucleophilic substitution to form aniline$^+$ and HF. In combination with the aquisition of REMPI spectra, we have observed the following reactions, post-ionisation, of fluorobenzene$^+$-(NH$_3$)$_n$ (n=1,2) clusters: \vspace{1em} C$_6$H$_5$F$^+$.(NH$_3$)$_2$ $\longrightarrow$ C$_6$H$_5$NH$_2$$^+$ \vspace{1em} \vspace{1em} C$_6$H$_5$F$^+$.NH$_3$ $\longrightarrow$ NH$_3$$^+$ + C$_6$H$_5$F \vspace{1em} While nucleophilic substitution satisfactorily accounts for the formation of aniline$^+$, it is more difficult to rationalise the formation of NH$_3$$^+$ on thermodynamic grounds. By performing {\it ab initio} calculations we hope to be able to postulate a mechanism for this reaction