If T is coordinated on its o(pen) side 10 (To), HAT from the preferred o(pen) conformation of TH (THo) in the THo-To complex can occur without major rearrangement of the molecular scaffolds. If another docking site of T is chosen by THo instead, HAT must be followed or preceded by torsion around the N-O bond to end up in an equivalent structure, thus widening the barrier. In the cold gas phase, fast HAT between degenerate structures manifests itself by spectral tunnelling splittings separating symmetric and antisymmetric wavefunctions for the H motion along the self-exchange reaction coordinate. In the vibrational ground state, these splittings are exceedingly small due to the large barrier. However, when the OH stretching vibration is excited by one quantum, a significant fraction of the barrier can be overcome because the OH stretching motion resembles the reaction coordinate, at least for a THo-To structure which requires no large amplitude heavy atom motion. Therefore, it is conceivable that the infrared OH stretching spectrum of 1:1 complexes combining TEMPO-H with TEMPO exhibits tunnelling splittings ∆ν reflecting this periodic HAT, where the full period T in ps is given by the inverse of the splitting ∆ν in THz. In this work, we show that two conformations of the TH-T complex are very close in energy. It represents a considerable challenge for quantum theory to correctly predict their energy order. Despite supportive vibrational excitation by 41 kJ mol -1 , we find no evidence for HAT on a 15 ps time scale in the vibrational line profile, suggesting that the barrier between equivalent structures is either very high or rather broad.