Approaching the "Zundel" Limit: Tuning the Vibrational Coupling in NHNg, Ng = {He, Ne, Ar, Kr, Xe, and Rn}.

The diazenylium ion (NH) is a ubiquitous ion in dense molecular clouds. This ion is often used as a dense gas tracer in outer space. Most of the previous works on diazenylium ion have focused on the shared-proton stretch band, ν. In this work, we have performed reduced-dimensional calculations to investigate the vibrational structure of NHNg, Ng = {He, Ne, Ar, Kr, Xe, and Rn}. We demonstrate a few interesting things about this system. First, the vibrational coupling in NH can be tuned to switch on interesting anharmonic effects such as Fermi resonance or combination bands by tagging it with different noble gases. Second, a comparison of the vibrational spectrum from NHHe to NHRn shows that the ν can be swept from an "Eigen-like" to a "Zundel-like" limiting case. Anharmonic calculations were performed using a multilevel approach, which utilized the MP2 and CCSD(T) levels of theories. Binding energies for the elimination of Ng in NHNg are also reported.