STRUCTURE OF PROTONATED SOLVATION COMPLEXES - AMMONIA TRIMETHYLAMINE CLUSTER IONS AND THEIR METASTABLE DECOMPOSITIONS

The stable structures and metastable decomposition processes of neat trimethylamine and mixed ammonia-trimethylamine cluster ions are studied by using a reflectron time-of-flight mass spectrometer in conjunction with multiphoton ionization. The kinetic energy release of neat trimethylamine cluster ions is measured, and the binding energies are determined by using Klots' and Engelking's models. Observations on the relative cluster ion intensity distributions of (NH3)n((CH3)3N)mH+ under various experimental conditions suggest that NH3((CH3)3N)4H+, (NH3)2((CH3)3N)6H+, (NH3)3((CH3)3N)8H+, (NH3)4-((CH3)3N)10H+, and (NH3)5((CH3)3)N)12H+ are particularly stable. The stable configurations of these ionic species have been proposed to have central species NH4+, N2H7+, N3H10+, N4H13+, and N5H16+ which provide 4, 6, 8, 10, and 12 hydrogen-bonding sites, respectively, for the surrounding (CH3)3N molecules. The pattern of magic numbers at m = 2(n + 1) begins to break down at n = 6. Experimental results of the metastable decomposition studies also support the proposed stable structures of mixed ammonia-trimethylamine cluster ions.