Chemical textbooks depict molecules as simple ball and stick models, which suggest that they have well defined geometrical structures in real space. This radical simplification of a many particle system is based on the Born-Oppenheimer approximation, which assumes that the electronic and nuclear part of the wave function can be separated. The nuclei slowly move within a binding potential produced by a cloud of fast electrons. The electronic wave function is calculated for a well defined spatial distribution of the nuclei. However, because of the Heisenberg uncertainty principle in reality the nuclei can not be localized without broadening their momentum distribution, which would immediately lead to fragmentation. Using the H_2~+ molecules we investigated whether it is possible to directly measure that spatial distribution.
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