High-resolution far-infrared synchrotron FTIR spectroscopy and analysis of the ${\nu }_7$, ${\nu }_{19}$ and ${\nu }_{20}$ bands of trioxane

Rovibrational bands spectra of three ${\nu }_{20}$, ${\nu }_7$ and ${\nu }_{19}$ 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 $0.17\times {10}^{-3}$ 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 ${\nu }_{20}$ and ${\nu }_{19}$ perpendicular bands was obtained. Last, each set of spectroscopic parameters is compared and discussed between both formalisms.