| Description |
In spite of high utility and central import in chemical studies, the bond strengths of transition metal - main group diatomic molecules have not been widely studied to high levels of precision; in some cases, no known previous measurement exists. In this work, the bond dissociation energies of several transition metal carbides and silicides have been studied by observation of predissociation thresholds in quasicontinuous ionization action spectra. These thresholds may be confidently assigned as the bond dissociation energies as long as two conditions are met: the molecule can dissociate to ground atomic states while conserving electronic angular momentum about the internuclear axis, and that a high density of states exists near the ground separated atom limits, such that the molecule is able to couple to dissociative states and promptly separate when the bond energy is exceeded. In the worst case, a predissociation threshold is a reliable upper limit to the dissociation energy; with these conditions met, an observed threshold offers a highly precise measurement of the bond dissociation energy, often a 100-fold increase in precision over previous measurements. In total, presented here are 33 bond energies, which allow for the derivation of 15 molecular ionization energies, 12 cation or anion bond energies, and the enthalpies of formation for all molecules. Trends and bonding patterns are discussed. These new data are also expected to be valuable as part of a larger project compiling benchmarking values for computational studies. |
