N${}_3^{+}$: Full-Dimensional Potential Energy Surface, Vibrational Energy Levels and Ground State Dynamics

Abstract

The fundamentals and higher vibrationally excited states for the N${}_3^{+}$ ion in its electronic ground state have been determined from quantum bound state calculations on 3-dimensional potential energy surfaces (PESs) at the CCSD(T)-F12 and MRCI+Q levels of theory. The vibrational fundamentals are at 1130 cm${}^{-1}$ (${\nu }_1$, symmetric stretch), 807 cm${}^{-1}$ (${\nu }_3$, asymmetric stretch), and 406 cm${}^{-1}$ (${\nu }_2$, bend) on the higher-quality CCSD(T)-F12 surface. For ${\nu }_1$, the calculations are close to the estimated frequency from experiment (1170 cm${}^{-1}$) and previous calculations\cite{rosmus.n3:1994} which find it at 1190 cm${}^{-1}$. Calculations of the vibrational states on the MRCI+Q PES are in qualitative agreement with those using the CCSD(T)-F12 PES. Analysis of the reference CASSCF wave function for the MRCI+Q calculations provides further insight into the shape of the PES and lends support for the reliability of Hartree-Fock as the reference wave function for the coupled cluster calculations. According to this, N${}_3^{+}$ has mainly single reference character in all low-energy regions of its electronic ground state (${}^3$A${}^{\prime \prime }$) 3d PES.

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