Nonstatistical bond breaking in the multiphoton ionization/dissociation of [Fe(CO)5]mArn clusters

Photoionization of iron pentacarbonyl/argon clusters with 30 ps, 266 nm laser pulses results in the ultimate detection of iron ions solvated with argon atoms. Clusters such as Fem+Arn (m=1,2; n=1–26) are readily observed following the laser-induced decarbonylation of the [Fe(CO)5]mArn species formed in the supersonic jet. An interesting intensity alternation of the Fe+Arn ions is observed up to a magic number at n=6, after which a monotonically decreasing intensity pattern is noted. The pattern is similar to a more extensive spectrum (with additional magic numbers) observed in separate experiments where metallic iron is laser ablated into a supersonic flow of argon, krypton, or xenon, and the resulting cluster ions are detected in a reflectron mass spectrometer. In another experiment in the latter apparatus, the sputtering of iron into a mixture of carbon monoxide and argon shows the relative reactivity of Fe+ to form Fe+Arn and Fe+(CO)n ions. Mechanisms for the energy disposal during the ionization/dissociation process are discussed. Additionally, the intensity pattern of iron–rare gas clusters, Fe+(RG)n, is discussed in the context of structural arguments which have previously been applied successfully to a large number of metal–rare gas systems.