Reactions of Laser Ablated Metal Plasma with Molecular Alcohol Beams: Dependence of the Produced Cluster Ion Species on the Beam Condition

The gas phase reactions of metal plasma with alcohol clusters were studied by time of flight mass spectrometry (TOFMS) using laser ablation-molecular beam (LAMB) method. The significant dependence of the product cluster ions on the molecular beam conditions was observed. When the plasma acted on the low density parts of the pulsed molecular beam, the metal-alcohol complexes M⁺A_n (M=Cu, Al, Mg, Ni and A=C₂H₅OH, CH₃OH) were the dominant products, and the sizes of product ion clusters were smaller. While the plasma acted on the high density part of the beam, however, the main products turned to be protonated alcohol clusters H⁺A_n and, as the reactions of plasma with methanol were concerned, the protonated water-methanol complexes H₃O⁺(CH₃OH)_n with a larger size (n≦12 for ethanol and n≦24 for methanol). Similarly, as the pressure of the carrier helium gas was varied from 1×10⁵ to 5×10⁵ Pa, the main products were changed from M⁺A_n to H⁺A_n and the sizes of the clusters also increased. The changes in the product clusters were attributed to the different formation mechanism of the output ions, that is, the M⁺A_n ions came from the reaction of metal ion with alcohol clusters, while H⁺A_n mainly from collisional reaction of electron with alcohol clusters.