Photodissociation of Chromium Oxide Cluster Cations

Chromium oxide cluster cations, Cr_nO_m⁺, are produced by laser vaporization in a pulsed nozzle cluster source and detected with time-of-flight mass spectrometry. The mass spectrum exhibits a limited number of stoichiometries for each value of n, where m > n. The cluster cations are mass selected and photodissociated using the second (532 nm) or third (355 nm) harmonic output of a Nd:YAG laser. At either wavelength, multiphoton absorption is required to dissociate these clusters, which is consistent with their expected strong bonding. Cluster dissociation occurs via elimination of molecular oxygen, or by fission processes producing stable cation species and/or eliminating stable neutrals such as CrO₃, Cr₂O₅, or Cr₄O₁₀. Specific cation clusters identified to be stable because they are produced repeatedly in the decomposition of larger clusters include Cr₂O₄⁺, Cr₃O₆⁺, Cr₃O₇⁺, Cr₄O₉⁺, and Cr₄O₁₀⁺.