High-Resolution spectroscopy and analysis of the fundamental modes of (SiF4)-Si-28. Accurate experimental determination of the Si-F bond length

Silicon tetrafluoride (SiF4) is a trace component of volcanic gases and is gaining industrial importance. However, a better knowledge of spectroscopic parameters is needed for this molecule in order to derive accurate concentrations. Following a previous reinvestigation of the nu(3) and nu(4) fundamentals (Richard et al. 2021), we have undertaken an extensive high-resolution study of its infrared absorption bands. We present here an update of this study. It features the recording of new far-infrared spectra, taking advantage of synchrotron radiation, and a global fit giving a consistent parameter set for the ground and fundamental states of (SiF4)-Si-28, now including the nu(1) = 1 and nu(2) = 1 states, by adding to the global analysis the newly measured nu(2), nu(1) -nu(4), and nu(4) -nu(2) bands near 264, 412, and 125 cm(-1), respectively. Nearly 20 000 assigned lines pertaining to seven distinct rovibrational bands were fitted with an excellent accuracy (global standard deviation of 0.296). This allows us to obtain an accurate experimental value for the Si-F bond length, r(e)(SiF4) = 1.5516985(30) angstrom. Some new band intensity estimates allow us to update our SiF4 calculated spectroscopic database.