Knowledge Bank

Ammoniated ammonium ions are produced by electron impact of a continuous supersonic expansion of $NH3$ in argon. We have produced $NH4+(NH3)N$ with $N\le 60$. The $\nu 2$ mode (umbrella mode) of ammonia is excited with a cw $CO2$ laser to induce vibrational predissociation of a mass selected cluster ion. Infrared spectra have been measured for clusters with N up to 15. Our results are consistent with analogous experiments involving excitation of the $\nu 3$ (asymmetric NH stretch) mode of $ammonia1$ in which a first ``solvation'' shell of four ammonia molecules was confirmed. Peak absorption frequencies red shift from an $N=5$ value of $1077cm-1$ with increasing cluster size, converging to the bulk phase value of $-1050cm-1$. Comparison will be drawn to our previous studies of ammonia solvated alkali metal cations.2