CH$_4\cdot$F$^-$ revisited: Full-dimensional ab initio potential energy surface and variational vibrational states

TL;DR

This paper develops a new high-accuracy potential energy surface for the CH₄·F⁻ complex, enabling detailed vibrational state calculations and revealing tunneling splittings related to molecular interconversion.

Contribution

It introduces a fully ab initio, full-dimensional PES for CH₄·F⁻ and demonstrates its use in variational vibrational calculations with new insights into tunneling phenomena.

Findings

The PES covers a broad configuration space including dissociation and isolated vibrations.

Variational calculations reveal tunneling splittings above 0.1 cm⁻¹.

The new PES improves upon previous models, especially at intermediate distances.

Abstract

The automated development of a new ab initio full-dimensional potential energy surface (PES) is reported for the CH$_4\cdot$F$^-$ complex using the ROBOSURFER program package. The new potential provides a near-spectroscopic quality description over a broad configuration range including the methane-ion dissociation, as well as isolated methane vibrations. In particular, it improves upon the earlier [Czak\'o, Braams, Bowman (2008)] PES over intermediate methane-fluoride distances. Full-dimensional (12D) variational vibrational computations using the new PES and the GENIUSH-Smolyak algorithm show that tunneling splittings larger than 0.1 cm$^{-1}$ appear below the top of the interconversion barrier of the four equivalent minima of the complex.