Approaching the "Zundel" Limit: Tuning the Vibrational Coupling in N 2 H + Ng, Ng = {He, Ne, Ar, Kr, Xe, and Rn}.

The diazenylium ion (N 2 H + ) 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 H + . In this work, we have performed reduced-dimensional calculations to investigate the vibrational structure of N 2 H + Ng, Ng = {He, Ne, Ar, Kr, Xe, and Rn}. We demonstrate a few interesting things about this system. First, the vibrational coupling in N 2 H + 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 N 2 H + He to N 2 H + Rn shows that the ν H + 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 N 2 H + Ng are also reported.