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The CH5+ molecular ion is well-known for its large amplitude motions that lead to complete scrambling of the hydrogen atoms, even in the vibrational ground state. Experiments have been reported that probe the consequences of these large amplitude motions. We recently reported that quantum zero-point effects partially quench the scrambling when CH5+ is partially deuterated. Here, the consequences of this quantum localization are investigated through calculations of the low-resolution spectra of CH4D+, CHD4+, and CD5+. The spectra are obtained by convoluting stick spectra, evaluated for individual stationary points on an ab initio potential surface, multiplying them by Diffusion Monte Carlo ground state density at that stationary point, and taking the sum. The CH/D stretch regions of CH4D+ and CD5+ are red-shifted relative to CH5+, while the overall shape of the envelope remains unaffected. In contrast, for CHD4+, the shape of the spectral envelope in the CH/D stretch region differs from the other three isotopologs. These signatures of the quantum localization of the deuterium on the spectra are discussed.

We report a full-dimensional potential energy surface for H3O2-, based on fitting 66,965 ab initio electronic energies. A major feature of this potential is a barrier of roughly 200 cm-1 to internal rotation of the two hydroxyl groups about a line connecting the two oxygen atoms and the bridging hydrogen atom. The potential is used in calculations of vibrational energies, performed with the "Reaction Path" version of the code "MULTIMODE". The results are compared to recent infrared messenger experiments and are used to propose interpretations of the experimental results.