Thermal Kinetics of Al + O ( = 2-30): Measurable Reactivity of Al.

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