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High-resolution far-infrared synchrotron FTIR spectroscopy and analysis of the $ν_7$, $ν_{19}$ and $ν_{20}$ bands of trioxane

Rovibrational bands spectra of three $ν_{20}$, $ν_7$ and $ν_{19}$ bands of 1, 3, 5 -- trioxane (H$_2$CO)$_3$ were recorded in the 50--650 cm$^{-1}$ range using a long path absorption cell coupled to a high resolution Fourier transform spectrometer and synchrotron radiation at the AILES beamline of the SOLEIL synchrotron. More than 16000 lines were assigned with a dRMS better than $0.17\times10^{-3}$ cm$^{-1}$. Two different formalisms (tensorial and Watson) were used to derive accurate rotational and quartic parameters for the three bands and for the first time, a precise determination of Coriolis parameter and $q_+$ $l-$doubling constant for both $ν_{20}$ and $ν_{19}$ perpendicular bands was obtained. Last, each set of spectroscopic parameters is compared and discussed between both formalisms.