Photofragmentation Patterns of Cobalt Oxide Cations Co n O m + ( n = 5-9, m = 4-13): From Oxygen-Deficient to Oxygen-Rich Species.

Cobalt oxide clusters, Co _n O _m ⁺ (5 ≤ n ≤ 9 and 4 ≤ m ≤ 13), are produced by laser vaporization and studied by time-of-flight mass spectrometry. Specific stoichiometries are mass separated and photofragmented using 355 nm laser light. The preferred fragmentation channels of m = n -1, m = n -2, and m ≥ n species are investigated. Loss of oxygen molecules is the favorable dissociation channel of m ≥ n clusters. While Co _n O _{n -2} ⁺ clusters decay via the loss of a Co atom, the photofragmentation behavior of Co _n O _{n -1} ⁺ species interestingly can be divided into two regimes: the n ≤ 6 clusters tend to lose an oxygen atom, but for n > 6 they favorably dissociate via the loss of a cobalt atom. The geometric structures of selected m = n - 2 species are studied using density functional theory calculations. Dissociation energies for different evaporation channels are calculated and thermodynamically favorable channels are found to correspond to the experimental observations.