Hydroxyl radicals (OH) play a central role in the interstellar medium. Here, we observe highly rotationally excited OH radicals with energies above the bond dissociation energy, termed OH “super rotors”, from the vacuum ultraviolet photodissociation of water. The most highly excited OH(X) super rotors identified at 115.2 nm photolysis have an internal energy of 4.86 eV. A striking enhancement in the yield of vibrationally-excited OH super rotors is detected when exciting the bending vibration of the water molecule. Theoretical analysis shows that bending excitation enhances the probability of non-adiabatic coupling between the \(\tilde B\) and \(\tilde X\) states of water at collinear O–H–H geometries following fast internal conversion from the initially excited \(\tilde D\) state. The present study illustrates a route to produce extremely rotationally excited OH(X) radicals from vacuum ultraviolet water photolysis, which may be related to the production of the highly rotationally excited OH(X) radicals observed in the interstellar medium.

羟自由基（OH）在星际介质中起着核心作用。在这里，我们从水的真空紫外光解离中观察到高度旋转激发的OH自由基，其能量高于键解离能，被称为OH“超级转子”。在115.2 nm的光解作用下识别出的最高激发度的OH（X）超级转子的内部能量为4.86 eV。当激发水分子的弯曲振动时，会发现振动激发的OH超级转子的产量显着提高。理论分析表明，弯曲激励提高了\（\ tilde B \）与\（\ tilde X \）之间非绝热耦合的可能性从初始激发的\（\ tilde D \）状态进行快速内部转换后，水在共线O–H–H几何状态。本研究说明了从真空紫外水光解中产生极度旋转激发的OH（X）自由基的途径，这可能与星际介质中观察到的极度旋转激发的OH（X）自由基的产生有关。