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(X²Π1/2) → 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 ΔfH⁰(NO, 0 K), ΔfH⁰(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(C²Π) predissociation provides direct experimental confirmation of spin-orbit interaction with the NO(a⁴Π) continuum. These results establish definitive benchmarks for thermochemistry and ab initio quantum chemistry, potentially advancing kinetic modeling in atmospheric chemistry, combustion, and NOx research.