We present the kinetic energy dependence of reactions of the late third-row transition metal cation Ir+ with H-2, D-2, and HD measured using a guided ion beam tandem mass spectrometer. A flow tube ion source produces Ir+ ions in its electronic ground state term and primarily in the ground spin-orbit level. Corresponding state-specific reaction cross sections are obtained. The kinetic energy dependence of the cross sections for forming IrH+ and IrD+ are analyzed to give a 0 K bond dissociation energy of D-0(Ir+-H) = 3.12 ± 0.06 eV. Ab initio calculations at the B3LYP/HW+/6-311+G(3p), BHLYP/HW+/6-311+G(3p), and QCISD(T)/HW+/6-311+G(3p) levels performed here show reasonable agreement with the experimental bond energies and with the previous theoretical values available. Theory also provides the electronic structures of these species and the reactive potential energy surfaces. We also compare this third-row transition metal system with those of the first-row and second-row congeners Co+ and Rh+. We find that Ir+ has a stronger M+-H bond, which can be explained by the lanthanide contraction and relativistic effects that alter the relative size of the valence s and d orbitals. Results from reactions with HD provide insight into the reaction mechanisms and indicate that Ir+ reacts largely via an insertion mechanism, in contrast with the lighter group 9 metal ions Co+ and Rh+ which react via direct mechanisms.