Bond Dissociation Energies in the Gas Phase for Large Molecular Ions by Threshold Collision-Induced Dissociation Experiments: Stretching the Limits

Accurate bond dissociation energies
for large molecules are difficult
to obtain by either experimental or computational methods. The former
methods are hampered by a range of physical and practical limitations
in gas-phase measurement techniques, while the latter require incorporation
of multiple approximations whose impact on accuracy may not always
be clear. When internal benchmarks are not available, one hopes that
experiment and theory can mutually support each other. A recent report
found, however, a large discrepancy between gas-phase bond dissociation
energies, measured mass spectrometrically, and the corresponding quantities
computed using density functional theory (DFT)-D3 and DLPNO-CCSD­(T)
methods. With the widespread application of these computational methods
to large molecular systems, the discrepancy needs to be resolved.
We report a series of experimental studies that validate the mass
spectrometric methods from small to large ions and find that bond
dissociation energies extracted from threshold collision-induced dissociation
experiments on large ions do indeed behave correctly. The implications
for the computational studies are discussed.