From their recent laboratory kinetics studies, Parker and Nelson have proposed a monobridged molecular structure for the aluminum atom-trimethylatuminum system. Here molecular structures and energetics for the neutral aluminum atom-trimethylaluminum complex (AlTMA) are reported from theory. A second distinct minimum was located and characterized, corresponding to an unanticipated H3C-Al-Al(CH3)(2) geometry. In addition, the transition state between the two minima was located. The relative energies of these stationary points are also reported, predicting that the monobridged AlTMA structure recently reported is higher in energy than the methylaluminum. DMA discovered in this study by about 2 kcal mol(-1). (C) 2003 Elsevier B.V. All rights reserved.