High resolution GHz and THz (FTIR) spectroscopy and theory of parity violation and tunneling for 1,2-dithiine (C4H4S2) as a candidate for measuring the parity violating energy difference between enantiomers of chiral molecules

Abstract

We report high resolution spectroscopic results of 1,2-dithiine-(1,2-dithia-3,5-cyclohexadiene, C₄H₄S₂) in the gigahertz and terahertz spectroscopic ranges and exploratory theoretical calculations of parity violation and tunneling processes in view of a possible experimental determination of the parity violating energy difference Δ_pvE in this chiral molecule. Theory predicts that the parity violating energy difference between the enantiomers in their ground state (Δ_pvE ≃ 1.1 × 10⁻¹¹(hc) cm⁻¹) is in principle measurable as it is much larger than the calculated tunneling splitting for the symmetrical potential ΔE_± < 10⁻²⁴ (hc) cm⁻¹. With a planar transition state for stereomutation at about 2500 cm⁻¹ tunneling splitting becomes appreciable above 2300 cm⁻¹. This makes levels of well-defined parity accessible to parity selection by the available powerful infrared lasers and thus useful for one of the existing experimental approaches towards molecular parity violation. The new GHz spectroscopy leads to greatly improved ground state rotational parameters for 1,2-dithiine. These are used as starting points for the first successful analyses of high resolution interferometric Fourier transform infrared (FTIR, THz) spectra of the fundamentals ν₁₇ (1308.873 cm⁻¹ or 39.23903 THz), ν₂₂ (623.094 cm⁻¹ or 18.67989 THz) and ν₃ (1544.900 cm⁻¹ or 46.314937 THz) for which highly accurate spectroscopic parameters are reported. The results are discussed in relation to current efforts to measure Δ_pvE.