Proton transfer in malonaldehyde: From reaction path to Schrödinger’s Cat

Proton transfer in the chelated form of malonaldehyde is commonly supposed to occur between two tautomers, across a transition state involving changes of the chemical bonding. We show that this view is in conflict with rotational spectra. The molecule is better thought of as a superposition of indistinguishable and non-separable Cs tautomers and proton tunneling is totally decoupled from the other degrees of freedom. Double minimum potential functions are determined from experiments and ab initio calculations.