The heat of formation of HNO

The heat of formation of HNO is determined from ab initio calculations to very high accuracy. Two independent approaches have been used to verify the reliability. The singles and doubles coupled-cluster approach that includes a perturbational estimate of the effects of connected triple excitations, denoted CCSD(T), has been used in conjunction with very large one-particle basis sets that include up to g functions. Correlation of the core electrons has also been investigated. The two approaches agree to within 0.4 kcal/mol, and our best estimate for ΔHf,0o (ΔHf,298o) is 26.7±0.8 kcal/mol (26.0±0.8 kcal/mol). This value is 2.2 kcal/mol larger than the currently accepted experimental value, indicating an error in the experimental determination.