This paper provides results concerning the clustering and laser-assisted reactivity in constrained pulsed gas expansions of trimethylaluminum (TMA1) with and without ammonia. In these experiments, TMA1 is introduced with just an Ar buffer gas or co-expanded with ammonia into a high vacuum chamber through a dual-source pulsed nozzle assembly. Independent control of individual gas backing pressures is maintained, and the nozzle assembly can be cooled as well. The output of an ArF excimer laser (193 nm) is focused into the mixing and reaction region of the nozzle source, and a quadrupole mass spectrometer (QMS) is used to characterize the expansion products. Both pressure and laser power dependence studies are used to reveal the origins of individual mass spectral features. Under certain conditions, laser irradiation or expanding, neat TMAI results in the formation of (CH3)(4-x)H2-yAl2, where x = 0, 1 and y = 0, 1. During TMA1 expansion with NH3, the parent ion signal for the Lewis acid-base adduct (CH3)(3)Al:NH3 is observed in the gas phase by the QMS. Laser photolysis of the TMAl/NH3 gas mixture produces reactions involving both precursor and adduct molecules. Also, the formation of a new (CH3)(3)AlNH2 product as a result of NH2 radical reactivity with the (CH3)(3)Al:NH3 adduct, i.e., (CH3)(3)Al:NH3 + NH2 --> (CH3)(3)AlNH2 + NH3, is revealed. Diverse higher mass clusters with Al-N bonded nuclei, e.g., (CH3)(k)Al-l(NH2)(m)(NH)(n), have also been observed. Finally, a comparison of aluminum and gallium metal organic species reveals similar propensities for intermolecular association for the two metals.