Thermal Kinetics of Aln- + O2 (n = 2-30): Measurable Reactivity of Al13.

Mass-selected aluminum anion clusters, Aln-, were reacted with O2. Rate constants (300 K) for 2 < n < 30 and product branching fractions for 2 < n < 17 are reported. Reactivity is strongly anticorrelated to Aln- electron binding energy (EBE). Al13- reacts more slowly than predicted by EBE but notably is not inert, reacting at a measurable 0.05% efficiency (2.5 ± 1.5 × 10-13 cm3 s-1). Al6- is also an outlier, reacting more slowly than expected after accounting for other factors, suggesting that high symmetry increases stability. Implications of observed Al13- reactivity, contributions of both electronic shell-closing and geometric homogeneity to Aln- resistance to O2 etching, and future directions to more fully unravel the reaction mechanisms are discussed.