Reactive scattering of electronically excited alkali-metal atoms with molecules
Representative families of excited alkali-metal reactions have been studied using a crossed-beam apparatus. For those alkali-metal–molecule systems in which reactions are also known for ground-state alkali metal and involve an early electron-transfer step, no large differences are observed in the reactivity as Na is excited. More interesting are the reactions with hydrogen halides (HCl); it was found that adding electronic energy into Na changes the reaction mechanism. Early electron transfer is responsible for Na(5S, 4D) reactions, but not for Na(3P) reactions. Moreover, the NaCl product scattering is dominated by the HCl– repulsion in Na(5S, 4D) reactions, and by the NaCl–H repulsion in the case of Na(3P). The reaction of Na with O2 is of particular interest since it was found to be state-specific. Only Na(4D) reacts, and the reaction requires restrictive constraints on the impact parameter and the reactants' relative orientation. The reaction with NO2 is even more complex, since Na(4D) leads to the formation of NaO by two different pathways. However, the identification of NaO as product in these reactions has yet to be confirmed.