Spectral Signatures of Protonated Noble Gas Clusters of Ne, Ar, Kr, and Xe: From Monomers to Trimers.

The structures and spectral features of protonated noble gas clusters are examined using a first principles approach. Protonated noble gas monomers (NgH + ) and dimers (NgH + Ng) have a linear structure, while the protonated noble gas trimers (Ng 3 H + ) can have a T-shaped or linear structure. Successive binding energies for these complexes are calculated at the CCSD(T)/CBS level of theory. Anharmonic simulations for the dimers and trimers unveil interesting spectral features. The symmetric NgH + Ng are charactized by a set of progression bands, which involves one quantum of the asymmetric Ng-H + stretch with multiple quanta of the symmetric Ng-H + stretch. Such a spectral signature is very robust and is predicted to be observed in both T-shaped and linear isomers of Ng 3 H + . Meanwhile, for selected asymmetric NgH + Ng', a Fermi resonance interaction involving the first overtone of the proton bend with the proton stretch is predicted to occur in ArH + Kr and XeH + Kr.