The rotation-vibration spectrum of methyl fluoride from first principles

TL;DR

This paper presents highly accurate ab initio calculations of methyl fluoride's rotation-vibration spectrum using a new nine-dimensional potential energy surface and dipole moment surface, achieving the most precise theoretical results to date.

Contribution

The study introduces a comprehensive nine-dimensional PES and DMS for CH3F based on advanced electronic structure methods, enabling highly accurate rovibrational spectral predictions.

Findings

Root-mean-square error of 0.69 cm1 for six fundamental vibrational bands.

Excellent agreement with experimental data for energy levels and transition intensities.

Most accurate theoretical spectrum of CH3F to date.

Abstract

Accurate \textit{ab initio} calculations on the rotation-vibration spectrum of methyl fluoride (\ce{CH3F}) are reported. A new nine-dimensional potential energy surface (PES) and dipole moment surface (DMS) have been generated using high-level electronic structure methods. Notably, the PES was constructed from explicitly correlated coupled cluster calculations with extrapolation to the complete basis set limit and considered additional energy corrections to account for core-valence electron correlation, higher-order coupled cluster terms beyond perturbative triples, scalar relativistic effects, and the diagonal Born-Oppenheimer correction. The PES and DMS are evaluated through robust variational nuclear motion computations of pure rotational and vibrational energy levels, the equilibrium geometry of \ce{CH3F}, vibrational transition moments, absolute line intensities of the $\nu_6$ band, and the rotation-vibration spectrum up to $J=40$. The computed results show excellent agreement with a range of experimental sources, in particular the six fundamentals are reproduced with a root-mean-square error of 0.69~cm$^{-1}$. This work represents the most accurate theoretical treatment of the rovibrational spectrum of \ce{CH3F} to date.