Bond dissociation energy of N₂ measured by state-to-state resolved threshold fragment yield spectra

The precise determination of the bond dissociation energy of N-2 is crucial for thermochemistry database and theoretical calculations. However, there has been ongoing debate regarding its exact value. In this study, we used the velocity map imaging method combined with an extreme ultraviolet laser to measure the threshold fragment yield (TFY) spectra of N-2 in the N(D-2) + N(D-2) photodissociation channels. By integrating the signals within a small circular area on the fragment velocity map images, we were able to obtain TFY spectra at nine different dissociation thresholds. These spectra are rotational state-resolved for the N-2(J '') molecules and spin-orbit state-resolved for the dissociation channels involving N(D-2) fragments. By employing the Wigner threshold law to simulate the TFY spectra and conducting statistical analysis on the comprehensive dataset, we determined the N-2 bond dissociation energy to be 78 691.09 +/- 0.15 cm(-1). This work now places N-2 among the few diatomic molecules with bond dissociation energies measured at sub-wavenumber precision.