| Research Abstract |
In the laser ablation-molecular beam method developed by us, pulsed laser beam is focused on the surface of a metal substrate in vacuum. Laser ablation is utilized for the preparation of chemically reactive species, metal ions in this case. A molecular beam of organic or inorganic molecules, viz., benzene, ammonia or methanol, seeded in rare gas, is injected nearby. Ion-molecule reaction yields a variety of clustered complex ions such as M(C_6H_6)_n^+, M(CH_<>OH)_n^+, and M(NH_3)_n^+. For some metals, elimination of small neutrals like hydrogen or small hydrocarbon molecules is observed to give M(C_6H_6)(C_XH_Y) X*6, Y*4 and M(NH)_m(NH_3)_n, m=1, 2. Such a method, albeit very simple, is a versatile diagnosis for the study of reactions of metal ions with organic and inorganic molecules, especially with molecular clusters.
Taking the reactions of benzene clusters with metal ions as. an. example, a molecular beam of benzene in Ar(typ. C_6H_6 60 Torr/Ar 200 Torr)was used ; (C_6H_6)_n up to n=5 was found when probed by electron impact. With laser ablation of a metal substrate, reactions with M_+ ions gave clustered complex ions of the type M(C_6H_6)_n^+ (n=2-4)for most of metal ions used. Elimination of hydrogen occurred for Y^+, viz. the formation of Y(C_6H_4)^+. For Nb^+ and Ta^+, elimination of hydrogen or small hydrocarbon occurred to give fragment complex ions as Nb(C_<12>H_<10>)^+, Nb(C_<12>H_8)^+, Nb(C_<10>H_8)^+, Nb(C_<10>H_6)^+, Nb(C_8H_8)^+ and Nb(C_8H_6)_+.
In order to study reaction mechanisms in laser photo-CVD of organometallic compounds, photodissociation reactions of trimethylaluminum and trimethylgallium have been investigated both in the gas phase and on a solid substrate. Reaction intermediates such as Al, Al(CH_3)_n, Ga and Ga(CH_3)_n (n=1-2)have been probed either by laser-induced fluorescence or by multiphoton ionization followed by time-of-flight mass spectrometry.
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