The rotation–vibration spectrum of methyl fluoride from first principles

Abstract

Accurate ab initio calculations on the rotation-vibration spectrum of methyl fluoride (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 CH3F, vibrational transition moments, absolute line intensities of the ν6 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 CH3F to date.

The 2020 release of the ExoMol database: Molecular line lists for exoplanet and other hot atmospheres

“…The CLT line lists for LiH and LiH + due to Coppola et al [164] fall into the few-electron category and should be reliable. The other ab initio line lists provided, namely those for ScH [163] , CH 3 F [167] , AsH 3 [168] , P 2 H 2 [169] , PF 3 [170] , CH 3 [171] and YO [176] must be regarded as intrinsically less accurate than other line lists provided by the database. In the case of YO, work is in progress aimed at producing an empirical line list based on available experimental data.…”

Colloquium : Superheavy elements: Oganesson and beyond

“…Here, sophisticated electron correlation frameworks including quantum electrodynamic effects are required to correctly predict the dense valence-electron spectrum of superheavy elements, required for future experimental atom-at-a-time studies (Sewtz et al, 2003) in, e.g., cold traps. While such an accuracy has been already achieved for closed-shell atoms or for few-valence electron systems (Eliav et al, 2015;Pašteka et al, 2017;Schwerdtfeger et al, 2015), and even for small closed-shell molecules with lighter atoms (Owens et al, 2018(Owens et al, , 2015, this is not yet the case for complex multi-electron, open-shell systems where a very large multi-reference and configuration-interaction space within a relativistic and QED framework is required to correctly describe both static and dynamic electron correlation effects. Such calculations will give a deep insight into the electronic shell structure with the correct predition of groundstate symmetry (configuration) for the superheavy elements beyond oganesson, and into the regime of the critical nuclear charge Z crit .…”

Coupled-cluster techniques for computational chemistry: The CFOUR program package

“…The calculated DBOC has found most of its application in accurate prediction of thermochemical values, 235,[354][355][356] as well as in spectroscopy. [357][358][359][360][361][362][363][364] To demonstrate its importance, the DBOC contributions to the atomization energies of selected small molecules are given in Table X, as obtained by different methods. The table shows that the DBOC contribution can be as large as several tenth of kJ mol −1 , therefore non-negligible in certain applications.…”