Benchmarking State-of-the-Art ab Initio Thermochemical Predictions with Accurate Pulsed-Field Ionization Photoion−Photoelectron Measurements

This Account presents a comparison between highly precise thermochemical data, including ionization energies, 0 K dissociative photoionization thresholds, and 0 K bond dissociation energies, of selected radicals and molecules and their cations obtained by pulsed field ionization photoion-photoelectron measurements and state-of-the-art thermochemical predictions calculated by the wavefunction-based ab initio CCSD(T)/CBS procedures with high-level corrections. The CCSD(T)/CBS method combines the coupled cluster approach including single, double, and quasi-perturbative triple excitations [CCSD(T)] and the complete basis set (CBS) extrapolation approximation. This benchmarking effort indicates that the CCSD(T)/CBS procedures together with high-level corrections are capable of yielding reliable thermochemical predictions with error limits < or =10 meV for small radicals and molecules and their cations. The error limits increase to approximately 35 meV for larger molecular species, such as phenyl and benzyl radicals.