First Full-Dimensional Potential Energy and Dipole Moment Surfaces of SF₆

Abstract

A 15-dimensional analytical form for the potential energy and dipole moment surfaces of the SF6 molecule in the ground electronic state is obtained using ab initio methods. In order to calculate the equilibrium S-F distance, we applied coupled cluster CCSD(T) method and several versions of the correlation consistent basis sets -from valence triple-zeta (VTZ) and augmented valence triple-zeta (AVTZ) to core-valence quadruple-zeta (CVQZ) with Douglas-Kroll (DK) relativistic corrections that provided good agreement with empirical equilibrium value. Ab initio electronic energies on 15D grids of nuclear geometries are computed using CCSD(T) method with VTZ and CVQZ-DK basis sets. The analytical representation of the potential energy surface is determined through an expansion in symmetry adapted products of non-linear coordinates up to the 5-th order. The influence of additional redundant coordinates on the quality of the fit was investigated. Parameters of full dimensional dipole moment surfaces are determined up to the 4th order expansion in normal mode coordinates. For validation of ab initio results, the fundamental vibration frequencies and absorption cross-sections of the principal sulfur hexafluoride isotopolgue are calculated giving good agreement with cold (180 K) and room temperature ( 296 K) experimental spectra. Absorption cross-sections calculated from our preliminary line list agree much better with these observations than the simulations using SF6 line-by-line lists constructed from effective models included in currently available spectroscopic databases.

Vibrational levels of formaldehyde: Calculations from new high precision potential energy surfaces and comparison with experimental band origins

“…Theoretical line lists for ammonia [38] [27] and phosphine [39] [40] [41] are successful examples of this trend for four-atom species. New PESs and DMSs have been recently reported for five-atom [42] [43], six-atom molecules [44] [45], [46] and seven-atom [47] molecules.…”

The 2020 edition of the GEISA spectroscopic database

“…[170] and private communication), but the latter contains data at higher resolution (0.03 vs. 0.112 cm -1 ) and was retained in the Figure 12. As mentioned by Nikitin et al [169] it appears that ab initio cross sections agree much better with the observations than the simulations using SF6 line lists constructed from effective models as available in HITRAN2016, SheCaSDa and GEISA-2015 line parameters databases. The main reason relies on the fact that effective models, generally derived from cold spectra over a limited set of ground vibrational states, fail to extrapolate data at room temperature which requires an account of more significant contributions of hot bands involving higher vibrational states.…”

“…The main reason relies on the fact that effective models, generally derived from cold spectra over a limited set of ground vibrational states, fail to extrapolate data at room temperature which requires an account of more significant contributions of hot bands involving higher vibrational states. On the other hand, ab initio calculations succeed in giving a qualitative agreement with experimental data (Nikitin et al mentioned that their calculation should be extended [169]). For this reason, we plan to generalize in future GEISA releases the use of ab initio data both as a point of comparison with experimentally derived effective models but also to improve or complete existing data.…”

“….Contrary to the species describe in the section 2, SF6 has not been updated in the current version of GEISA, although new data were provided by Ke et al from the Dijon's database SheCaSDa [168]. Indeed, recent data from Nikitin et al [169] consisting of a complete line list based of extensive ab initio calculations (from TheoReTS database [170]) leads to significantly different results. The direct comparison of the different available databases with experimental absorption from GEISA-2015 cross-sections database [1] justify why we made the choice not to update the GEISA-2020 database with new data from Dijon.…”

“…Figure 12 shows a comparison of SF6 cross sections at room temperature (296K). The data from the GEISA-2015 cross-sections database are plotted along with simulated spectra derived from GEISA-2015 [1], HITRAN2016 [2], Dijon SheCaSDa [120] and TheoReTS [169] line list databases. Note that we also compared with the widely used PNNL spectra [83], which are similar than to GEISA-2015 cross-sections from Varanasi of et al (Ref.…”