Electron impact ionization and ion chemistry in trimethylaluminum and in trimethylgallium

Ionization of trimethylaluminum and trimethylgallium by electron impact fro m threshold to 70 eV and the gas-phase reactions of the resulting ions with their parent molecules are studied by using Fourier transform mass spectro metry. The total ionization cross sections rise from thresholds near 10 eV to 1.3 +/- 0.1 x 10(-15) and 1.2 +/- 0.1 x 10(-15) cm(2), respectively, at no eV. The most abundant product ions of dissociative ionization are M(CH3) (2)(+) (M = Al or Ga). Most of the ions generated by the electron impact io nization except M(CH3)(2)(+) and M+ react readily with the parent molecules yielding M(CH3)(2)(+) and M+ as the principal product ions, with rate coef ficients of (2-6) x 10(-10) cm(3) s(-1). Clusters with two metal atoms were observed with relatively small branching ratios or reaction rates. (Int J Mass Spectrom 202 (2000) 345-349) (C) 2000 Elsevier Science B.V.