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Exothermic reactions of transition-metal ions with alkanes have in many instances been shown to be facile in the gas phase.* 1 (14) At higher kinetic energies reaction cross-section data suggest that C-C bond insertion processes may become accessible.

Controlling the internal energy content of sizeselected cluster ions: An experimental comparison of the metastable decay rate and photofragmentation methods of quantifying the internal excitation of (H2O)− n J. Chem. Phys. 95, 7998 (1991); 10.1063/1.461330 Reply to the Comment on: Evaporation of covalent clusters: Unimolecular decay of energized size selected carbon clusters J. Chem. Phys. 94, 6934 (1991); 10.1063/1.460227 Comment on: Evaporation of covalent clusters: Unimolecular decay of energized sizeselected carbon cluster ions J. Chem. Phys. 94, 6933 (1991); 10.1063/1.460226 Infrared photodissociation of sizeselected methylamine clustersThe unimolecular decay of energized size-selected carbon clusters (C:,5 < n < 100) is investigated. The clusters are produced in a laser-generated plasma on the surface of a graphite rod. Directly extracted cations that decay on a ""S time scale are probed in a double-focusing, reverse-geometry mass spectrometer. The unimolecular decomposition rates are extracted from metastable fraction measurements. We observe a dramatic discontinuous increase in the decay rate constant as a function of cluster size around mass c 3 t (factor of 5 to 10). Additionally, low rate constants, relative to the neighbors, are found for cst, CJ;, and c 7 t. The results are rationalized by postulating a phase transition from small "rigid" clusters for n < 30 to larger "molten" entities for n > 30. In this model local deviations in rate constant reflect the thermodynamic stabilities of the clusters. A further consequence of this model is that "magic" numbers in the mass spectrum originate primarily from the intrinsic stability of the clusters with respect to evaporation and not from a kinetic growth mechanism.