Over the past 6 years or so, our research group has demonstrated that the spectroscopic technique of resonant two-photon ionization spectroscopy is highly effective in locating the predissociation threshold in diatomic molecules that possess a high density of electronic states at the energy of the ground separated atom limit. These are molecules formed from an open d- or f-subshell metal atom in combination with a p-block element (e.g. B, C, N, O, Si, S, Cl, or Se). Further, because the large number of electronic states available in the vicinity of the ground separated atom limit leads to spin-orbit and nonadiabatic couplings that readily provide a pathway to dissociation, we have argued that predissociation sets in as soon as the ground separated atom limit is exceeded in these species. Thus, the predissociation threshold provides a direct measurement of the bond dissociation energy. Unfortunately, limitations of the OPO laser available in our group have prevented scanning to higher energies than ~5.8 eV, preventing the use of this technique to measure the most strongly bound molecules. In this presentation, it will be described how we have overcome this limitation through a new experimental technique based on resonant three-photon ionization (R3PI) spectroscopy. The application of the method to the bond dissociation energy of VO (6.545(2) eV), and possibly to other strongly bound diatomics, will be presented.

Employing resonant three-photon ionization spectroscopy for the measurement of molecular predissociation thresholds

ACS Spring 2022

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