A local mode picture for H atom reaction with vibrationally excited H₂O: a full dimensional state-to-state quantum...

A local mode picture was postulated some time ago to explain the negligible OD product excitation from H reacting with D₂O in fundamental asymmetrical excitation: the D₂O asymmetric stretch state is best thought as a linear combination of local mode stretches with the H atom reacting preferentially with the excited OD bond, but has never been verified. Here we report the first full-dimensional state-to-state study for the title reaction with H₂O in the ground and the first symmetric and asymmetric stretching excited states. It is found that symmetric and asymmetric stretching excited states, which vibrate in very different ways in the normal mode picture, behave essentially identically in the reaction. More importantly, our calculations revealed that the reaction produces a small fraction of OH in the v = 1 state, with the population close to the relative reactivity between the ground and vibrationally excited states, and therefore it confirms the local mode picture for H₂O in symmetric or asymmetric stretch states when reacting with an H atom.