The lowest-lying electronic singlet and triplet potential energy surfaces for the HNO–NOH system: Energetics, unimolecular rate constants, tunneling and kinetic isotope effects for the isomerization and dissociation reactions

The lowest-lying electronic singlet and triplet potential energy surfaces (PES) for the HNO–NOH system have been investigated employing high level ab initio quantum chemical methods. The reaction energies and barriers have been predicted for two isomerization and four dissociation reactions. Total energies are extrapolated to the complete basis set limit applying focal point analyses. Anharmonic zero-point vibrational energies, diagonal Born-Oppenheimer corrections, relativistic effects, and core correlation corrections are also taken into account. On the singlet PES, the 1HNO → 1NOH endothermicity including all corrections is predicted to be 42.23 ± 0.2 kcal mol−1. For the barrierless decomposition of 1HNO to H + NO, the dissociation energy is estimated to be 47.48 ±  0.2 kcal mol−1. For 1NOH → H + NO, the reaction endothermicity and barrier are 5.25 ±  0.2 and 7.88 ± 0.2 kcal mol−1. On the triplet PES the reaction energy and barrier including all corrections are predicted to be 7.73 ±  0.2 and 39.31 ± 0...