Measuring the strongest chemical bond with spectroscopic accuracy: CO bond-dissociation energy via predissociation of superexcited states

The chemical bond of carbon monoxide (CO) is the strongest bond. It plays a crucial role in thermochemistry and serves as a benchmark for electronic structure calculations. The most accurate value to date has been obtained by analyzing its predissociation spectra related to the lowest energy dissociation channel, achieving an uncertainty of 60. 16em{0ex}cm^-1. In this work, we measured the bond-dissociation energy of CO by recording the CO rotationally resolved, sharp-rising the C (^1D₂) fragment yield spectrum related to the C (^1D₂) +O (^1D₂) threshold. The sharp rising steps at the thresholds in the fragment yield spectrum are caused by the predissociation of broad vibronic bands of superexcited states. The thresholds were validated by the velocity map images of the C (^1D₂). The determined bond-dissociation energy is 89 602. 80 (0. 10) cm^-1, representing an improvement in accuracy of over one order of magnitude compared to the previous values.