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.