High-resolution spectroscopy and analysis of the ν3, ν4 and 2ν4 bands of SiF4 in natural isotopic abundance

Abstract

Silicon tetrafluoride (SiF 4 ) is a trace component of volcanic gases. However, a better knowledge of spectroscopic parameters is needed for this molecule in order to derive accurate concentrations. This motivated FTIR measurements with high-spectral resolution (0.001 cm −1 ) and an extensive study of its infrared absorption bands, including the fundamentals and overtone and combinations. We present here a detailed analysis and modeling of the strongly absorbing ν 3 and ν 4 fundamental bands, for the three isotopologues in natural abundance: 28 SiF 4 (92.23 %), 29 SiF 4 (4.67 %) and 30 SiF 4 (3.10 %). It includes a global fit with consistent parameter sets for the ground and excited states. In particular, all existing rotational line data have been included. The 2ν 4 band of 28 SiF 4 could also be analyzed in detail. A first fit of the dipole moment derivative for the ν 3 band for 28 SiF 4 has been performed, along with two independent estimates of the integrated band intensity; the results are consistent with literature values, around 690 km/mol. The isotopic dependence of band centers and Coriolis parameters has also been studied. TFSiCaSDa, a new database of cross sections and calculated lines for the ν 3 band of SiF 4 , has been set up.

High-Resolution spectroscopy and analysis of the fundamental modes of 28SiF4. Accurate ex

“…As already mentioned in our previous work [15], silicon tetrafluoride is a tetrahedral spherical top molecule with T d point group symmetry at equilibrium and possesses four normal modes of vibration: ν 1 (non-degenerate, A 1 symmetry 800.7 cm −1 ), ν 2 (doubly degenerate, E symmetry, 264.2 cm −1 ), ν 3 and ν 4 (triply degenerate, F 2 symmetry, 1031.5 and 388.4 cm −1 , respectively). The wavenumbers of these modes are such that the molecule exhibits a nicely defined vibrational structure, with polyads every ca.…”

“…with one parameter, µ 2 ν 1 . In the case of the ν 3 −GS and ν 4 −GS transitions, their effective dipole moment operator is expanded exactly as described in Section 3.2 of our previous SiF 4 paper [15]. This allows to calculate absolute intensities of the ν 3 and ν 4 bands in order to update the TFSiCaSDa database, see Section 5 below.…”

“…If many low resolution IR and Raman studies have located all SiF 4 fundamentals [11], the knowledge of its rovibrational spectroscopy was however restricted until a recent date to a few IR diode high resolution (HR) studies on selected portions of the strong ν 3 band region [12,13], followed by double resonance experiment to obtain precious information on the ground state spectroscopic constants [14]. Lately, the other IR-active fundamental (the ν 4 bending mode near 388.4 cm −1 ) was observed at HR using synchrotron radiation (SR) [15].…”

A Decade with VAMDC: Results and Ambitions

“…Two new databases have been added recently: TFSiCaSDa [19] concerning the SiF 4 molecule with applications to volcanic gases and UHeCaSDa (UF 6 ) for applications for the nuclear industry. The latter database is an exception: no experimental data are publicly available for this peculiar radioactive molecule and calculations are only based on literature data [102,103].…”

“…The VAMDC project has directly stimulated the creation of new online databases such as TFSiCaSDa and UHeCaSDa [19], and the deployment of the theoretical PAH database within VAMDC [3,36], while motivating the development of an experimental databases for PAHs. The VAMDC infrastructure deployment also encouraged a similar strategy for experimental databases for solid-state data in SSHADE (Section 2.3.2).…”