Bond Dissociation Energy of NO with Subwavenumber Precision via State-to-State Resolved Threshold Fragment Yield Spectroscopy

We report the bond dissociation energy (BDE) of nitric oxide (NO) with subwavenumber precision (±0.20 cm^-1), measured via state-to-state resolved threshold fragment yield spectroscopy. The ground-state dissociation limit, NO(<i>X</i>²Π_1/2) → N(⁴S) + O(³P₂), yields a BDE of 52396.92 ± 0.20 cm^-1 (6.496390 ± 0.000025 eV; 626.8064 ± 0.0024 kJ/mol), reducing the uncertainty of prior work by a factor of 50. Combining this result with equally precise BDEs for N₂, O₂, CO, NO₂, and CO₂, we derive spectroscopically accurate thermochemical benchmarks, including Δ_f<i>H</i>⁰(NO, 0 K), Δ_f<i>H</i>⁰(NO₂, 0 K), the atomization energy of NO₂, the ion-pair dissociation energy of NO, the bond dissociation energies of NO⁺, and the reaction energies for seven key processes. The O(³P₂) fragment angular distribution from NO(<i>C</i>²Π) predissociation provides direct experimental confirmation of spin-orbit interaction with the NO(<i>a</i>⁴Π) continuum. These results establish definitive benchmarks for thermochemistry and <i>ab initio</i> quantum chemistry, potentially advancing kinetic modeling in atmospheric chemistry, combustion, and NO_<i>x</i> research.