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.