Approaching the “Zundel” Limit: Tuning the Vibrational Coupling in N₂H⁺Ng, Ng = {He, Ne, Ar, Kr, Xe, and Rn}

Abstract

The diazenylium ion (N2H+) 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, νH+ . In this work, we have performed reduced-dimensional calculations to investigate the vibrational structure of N2H+Ng, Ng = {He, Ne, Ar, Kr, Xe, and Rn}. We demonstrate a few interesting things about this system. First, the vibrational coupling in N2H+ 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 N2H+He to N2H+Rn shows that the νH+ 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 N2H+Ng are also reported.