Isotopic chirality and high-resolution gigahertz and terahertz spectroscopy of <i>trans</i> -2,3-dideutero-oxirane ( <i>tc</i> -CHDCHDO)

We report the observation and assignment of the rotational spectra of the isotopically chiral molecule, <i>trans</i>-2,3-dideutero-oxirane (<i>tc</i>-CHDCHDO) measured with the Zurich gigahertz (GHz) spectrometer (64 to 500 GHz and Δ<i>ν</i>/<i>ν</i> = 10^-11) and with our highest resolution Fourier transform infrared spectrometer at the Swiss synchrotron light source (SLS) (best instrumental resolution Δ<i>ṽ</i> = 0.00053 cm^-1) in the terahertz range (far infrared from 25 to 80 cm^-1). The combined GHz and THz spectra were analysed using an accurate effective Hamiltonian providing newly determined rotational parameters, which are crucial for the prediction of <i>trans</i>-2,3-dideutero-oxirane transitions to be observed by astrophysical spectroscopy. The recent detection of singly deuterated oxirane in the protostar IRAS 16 293-2422 B based on our previous predictions highlights the potential for the detection of doubly deuterated oxiranes including <i>trans</i>-2,3-dideutero-oxirane. These offer insights into deuterium fractionation in space and the formation mechanisms of complex and in particular chiral molecules. This study is also related to the new isotope effect in isotopically chiral molecules characterised by the parity violation energy differences of the ground states of the enantiomers and to biomolecular homochirality. In addition, we report the analysis of the pure rotational spectra of <i>cis</i>-2,3-dideutero-oxirane also present in our experimental spectra in the GHz range.