The interactions of Mo(a S-7(3)) and Mo*(a S-5(2)) with methane, CH4, and ethane, C2H6, were studied under single collision conditions using the crossed molecular beams technique. Ground state Mo(a S-7(3)) atoms were found to be unreactive at all collision energies studied up to [E-coll] = 35.4 kcal/mol. Nonreactive scattering of Mo(a S-7(3)) with methane and ethane was studied and compared to collisions with Ne and Ar. A forward peaking center-of-mass angular distribution, T(Theta), was necessary to simulate the elastic collisions with inert gases as well as inelastic collisions with the alkanes. At a collision energy of 14.4 kcal/mol with CH4 and 21.0 kcal/mol with C2H6, inelastic collisions were found to transfer similar to 10% and similar to 19% of the initial kinetic energy into alkane internal energy, respectively. For collisions of Mo*(a S-5(2)) + CH4, the dehydrogenation product, MoCH2, was observed at all collision energies studied down to 2.1 kcal/mol. The reaction Mo*(a S-5(2)) + C2H6--> MoC2H4 + H-2 was observed down to [E-coll] = 4.5 kcal/mol. For a given total energy (electronic+translational), it was found that electronic energy is highly effective in promoting this reaction whereas translational energy is ineffective. (C) 2000 American Institute of Physics. [S0021-9606(00)00910-7].