Thermochemistry of the Ir⁺ + SO₂ reaction using guided ion beam tandem mass spectrometry and theory

Kinetic energy dependences of the reactions of Ir⁺ (⁵F₅) with SO₂ were studied using a guided ion beam tandem mass spectrometer and theory. The observed cationic products are IrO⁺, IrS⁺, and IrSO⁺, formed in endothermic reactions. Bond dissociation energies (BDEs) of the products are determined by modeling the kinetic energy dependent product cross sections: D₀(Ir⁺-O) = 4.27 ± 0.11 eV, D₀(Ir⁺-S) = 4.03 ± 0.06 eV, and D₀(Ir⁺-SO) ≥ 2.95 ± 0.06 eV. The oxide BDE agrees well with literature values, whereas the two latter results are novel measurements. Quantum mechanical calculations are performed at the B3LYP level of theory using the def2-TZVPPD basis set for all product BDEs with additional calculations for IrS⁺, IrO₂ ⁺, and IrSO⁺ at the coupled cluster with single, double, and perturbative triple excitation levels with def2-QZVPPD and aug-cc-pVXZ (X = T and Q and for IrS⁺, also X = 5) basis sets and complete basis set extrapolations. These theoretical BDEs agree reasonably well with the experimental values. ¹A₁ (IrO₂ ⁺), ⁵Δ₄ (IrS⁺), and ³A″/¹A' (IrSO⁺) are found to be the ground states after including empirical spin-orbit corrections. The potential energy surfaces including intermediates and transition states for each reaction are also calculated at the B3LYP/def2-TZVPPD level. The formation of MO⁺ (M = Re, Os, and Ir) from M⁺ + SO₂ reactions is compared with those from the M⁺ + O₂ and M⁺ + CO reactions, where interesting trends in cross sections are observed. Overall, these studies suggest that the M⁺ + O₂ reactions had restrictions associated with reactions along A' and A″ surfaces.