Photochemical Reactions of Organometallic Compounds

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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.