We report the first successful high-resolution analyses of the Fourier transform infrared (FTIR) spectrum of trisulfane. A band centered at 861.0292 cm⁻¹ can be assigned unambiguously to the chiral trans conformer by means of ground state combination differences in comparison with known rotational spectra. A second band near 864.698 cm⁻¹ is tentatively assigned to the cis conformer by comparison with theory. The results are discussed in relation to their importance for experimental attempts to measure the parity violating energy difference Δ_pvE between the ground states of enantiomers of chiral molecules.

Our results show that this molecule is a suitable candidate for a possible first determination of the parity violating energy difference Δ _pv E between enantiomers.

We report results on the dynamics of tunnelling switching based on a high-resolution spectroscopic investigation of meta-D-phenol in GHz and THz ranges. The pure rotational spectra were recorded in the range of 72–117 GHz and assigned to the localized syn- and anti-structures in the ground and the first excited torsional states. Specific torsional states were unambiguously assigned by comparison of the experimental rotational constants with theoretical results from quasiadiabatic channel reaction path Hamiltonian (RPH) calculations. The torsional fundamental ν_T at ≈ 309 cm⁻¹ and the first hot band (2ν_T – ν_T) at ≈ 277 cm⁻¹ were subsequently assigned in synchrotron based high-resolution Fourier transform infrared (FTIR, THz) spectra. The analyses provided accurate spectroscopic constants of all six states involved. It was found that the 2ν_T states are interacting through anharmonic resonances, indicating tunnelling switching as predicted by theory. Furthermore, tunnelling–rotation–vibration transitions were assigned and the tunnelling splitting in 2ν_T was determined as 1.72450(17) cm⁻¹. This key result allowed the assignment of two Q branches at 275.21303(9) and 277.67127(9) cm⁻¹ to vibration-tunnelling transitions of the (syn ← anti) type, hence confirming tunnelling switching dynamics in m-D-phenol. The ground-state energy difference of the syn- and anti-isotopomers is obtained experimentally as E₀ (syn) - E₀ (anti) = (hc)0.82 cm⁻¹ in satisfactory agreement with the theoretical ab initio predictions of (hc)1.5 cm⁻¹ given the small absolute values arising from the tiny zero point energy effects. The results are discussed in relation to further fundamental aspects of tunnelling in slightly asymmetric potentials including the effects of the parity violating electroweak interaction in chiral molecules.

The rotational spectrum of monodeutero-oxirane was analysed as measured using the Zurich Gigahertz (GHz) spectrometer and our highest resolution Fourier Transform Infrared (FTIR) spectrometer system coupled to synchrotron radiation at the Swiss Light Source (SLS). 112 distinct line frequencies have been newly assigned in the GHz range (extended to 120 GHz, compared to previous work extending to only 59 GHz) including rotational states up to J = 23. We have furthermore assigned 398 lines in the far infrared or Terahertz range (0.75–2.10 THz or 25–70 cm⁻¹) including transitions with rotational quantum numbers up to J = 59. The results are discussed in relation to the possible first astrophysical observation of an isotopically chiral molecule and in relation to molecular parity violation.

We report a comparison of the vibrational quantum dynamics based on the analysis of the low energy spectra of ¹³CHF₃ and ¹²CHF₃ from the THz (FIR) range to the ν₁ fundamental at high resolution ( or Doppler limited).