Observation of Continuum State Dissociation Enables the Determination of N2 Bond Dissociation Energy to Spectroscopic Accuracy.

Abstract

Nitrogen (N) is one of the most fundamental elements of life. Precise determination of the bond dissociation energy (BDE) of the corresponding homonuclear diatomic molecule N2 is not only important for calculating the enthalpies of formation for any N-containing molecules but also provides the best benchmark for evaluating theoretical computational methods. Thus, it has attracted many experimental and theoretical studies, while controversies still exist. Here, we report the observation of continuum state dissociation of N2 into the channel N(2D5/2,3/2)+N(2D5/2,3/2) for the first time by using the vacuum ultraviolet (VUV)-pump-VUV-probe time-sliced velocity-mapped imaging setup. The quantum-state-resolved images enable the direct visualization of the dissociation onsets corresponding to each of the correlated spin-orbit fine-structure channels within a few tenths of wavenumber. The BDEs of 14N2 and 15N2 are directly determined to be 78691.8 ± 0.3 cm-1 and 78731.5 ± 0.3 cm-1, respectively, which should represent the most accurate BDE of N2 thus far.