PHOTOLYSIS OF GROUP-III (AL, GA, IN) TRIMETHYL COMPOUNDS - DETECTION OF ORGANIC PHOTOFRAGMENTS CH3 AND C2H6 BY PICOSECOND LASER MASS-SPECTROSCOPY

The metal alkyls trimethylaluminum (TMA), trimethylgallium (TMG) and trimethylindium (TMI) were decomposed under collision-free conditions by tunable UV laser light in the range 190-310 nm and the photoproducts detected by laser mass spectroscopy using short and ultrashort laser pulses. At moderate laser fluences, these compounds decompose via a one-photon process. The simple separation of one or two methyl ligands leads to the metal-dimethyl radical (Al(CH3)2, Ga(CH3)2, In(CH3)2), and the metal-monomethyl radical (AlCH3, GaCH3, InCH3) as photoproducts. The vibronically excited metal-dimethyl radical can further decay - without the absorption of additional photons - into the metal atom plus ethane molecule. This has been proved for the first time by laser mass-spectroscopic detection of the ethane molecule as being a direct photoproduct of the investigated trialkyls. The quantum yields for the wavelength-dependent fragmentation are presented.