Reaction of niobium and tantalum neutral clusters with low pressure, unsaturated hydrocarbons in a pickup cell: From dehydrogenation to Met-Car formation

Abstract

Neutral niobium and tantalum clusters (Nbn and Tan) are generated by laser ablation and supersonic expansion into a vacuum and are reacted in a pickup cell with various low pressure (approximately 1 mTorr) unsaturated hydrocarbons (acetylene, ethylene, propylene, 1-butene, 1,3-butadiene, benzene, and toluene) under nearly single collision conditions. The bare metal clusters and their reaction products are ionized by a 193 nm laser and detected by a time of flight mass spectrometer. Partially and fully dehydrogenated products are observed for small (n<or=m) and large (n>or=m) neutral metal clusters, respectively, with m ranging from 2 to 5 depending on the particular hydrocarbon. In addition to primary, single collision products, sequential addition products that are usually fully dehydrogenated are also observed. With toluene used as the reactant gas, carbon loss products are observed, among which Nb8C12 and Ta8C12 are particularly abundant, indicating that the Met-Car molecule M8C12 can be formed from the neutral metal cluster upon two collisions with toluene molecules. The dehydrogenation results for low pressure reactions are compared with those available from previous studies employing flow tube (high pressure) reactors. Low pressure and high pressure cluster ion reactions are also compared with the present neutral metal cluster reactions. Reactions of unsaturated hydrocarbons and metal surfaces are discussed in terms of the present neutral cluster results.

Onset of carbon–carbon bonding in the Nb5Cy(y = 0–6) clusters: a threshold photo-ionisation and density functional theory study

“…Indeed, experiments in a low pressure pickup cell have shown that total dehydrogenation occurs for the first three C 2 H 2 molecules attached to the neutral Nb 5 cluster. 27 PIE spectra are recorded by monitoring the signal of each species as a function of photon energy. The shoulders present on the peaks due to oxide contamination were not included in the integration.…”

Reaction of carbon monoxide and hydrogen on neutral Nb8 clusters in the gas phase

“…There is no buffer gas to stabilize the intermediates in the pickup cell so M n A either directly dissociates ͑M n + A͒, undergoes further reactive dissociation ͑C + D , C and D A͒, or is detected in a metastable state. 20 Consequently, the chemistry in a pickup cell occurs at a much higher temperature ͑T ϳ 700 K͒ than that in a flow tube reactor ͑T ϳ 300 K͒.…”

Experimental vibrational spectra of gas-phase tantalum cluster cations

“…The reactivity of neutral Ta clusters with hydrocarbons and N 2 has been studied. [22][23][24] The ionization potentials of neutral Ta clusters are known from photoionization studies. 25 Raman spectra have been measured for Ta 2−4 in an argon matrix.…”