Rethinking the description of water product in polyatomic OH/OD + XH (X ≡ D, Br, NH2 and GeH3) reactions: theory/experimental comparison

Abstract

Davis’ group and Setser’s group using different experimental techniques measured water vibrational distribution for OH/OD + XH → H2O/HOD + X hydrogen abstraction reactions (X ≡ D, Br, NH2, GeH3). Theoretically, this issue has been studied by several groups: different potential energy surfaces (PESs) have been developed for each system, and quasi-classical trajectory (QCT) and quantum mechanics (QM) calculations have been performed. However, important experimental/theoretical controversies still exist. In the present work, we have revisited and performed new kinetics and dynamics calculations, comparing the theoretical and experimental results on the same footing. In general, theoretical results reproduce reasonably well experimental rate constants and total vibrational energy released to water, ~ 50–60%, although they underestimate water bending excitation. In the present work, we analyse different causes of this theory/experiment discrepancy and propose different mechanisms to explain the water bending excitation for diatom–diatom and polyatomic systems. Finally, we reflect on the ability of QCT and QM calculations to provide reasonable (although not quantitative) predictions for polyatomic reactions and observe that even using full-dimensional QM calculations on very accurate PESs, agreement with the experiment is far from that reached in the case of triatomic systems.