We have employed molecular beam techniques to investigate the initial probability of direct dissociative chemisorption, P-d, and the intrinsic trapping probability, xi of C3H8, C3D8, and (CH3)(2)CD2 on Ir(110) as a function of beam translational energy, E(i), from 1.5 to 59 kcal/mol. For C3H8 and (CH3)(2)CD2, a measurable (greater than or equal to 0.02) initial probability of direct dissociative chemisorption is observed above a beam energy of approximately 7 kcal/mol. For C3D8 this energy is roughly 10 kcal/mol. Above these energies the initial probability of direct chemisorption of each of the isotopomers of propane increases nearly linearly with E(i), approaching a value of approximately P-d=0.48 at E(i)=52 kcal/mol for C3H8 and (CH3)(2)CD2, and P-d=0.44 at E(i)=59 kcal/mol for C3D8. This kinetic isotope effect for the direct chemisorption of C3D8 relative to C3H8 is smaller than that expected for a mechanism of H (or D) abstraction by tunneling through an Eckart barrier, suggesting a contribution of C-C bond cleavage to direct chemisorption. The lack of a kinetic isotope effect for the direct chemisorption of (CH3)(2)CD2 relative to C3H8 indicates that 1 degrees C-H bond cleavage dominates over 2 degrees C-H bond cleavage during the direct chemisorption of propane on Ir(110). The trapping behavior of each of these isotopomers of propane is approximately identical as a function of E(i), with xi>0.9 at E(i)=1.5 kcal/mol, xi=0.3 at E(i)=20 kcal/mol, and xi<0.1 above E(i)=40 kcal/mol.