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

Cobalt oxide clusters, ConOm+ (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 ConOn-2+ clusters decay via the loss of a Co atom, the photofragmentation behavior of ConOn-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.