Synchrotron-Based Highest Resolution Terahertz Spectroscopy of the ν24 Band System of 1,2-Dithiine (C4H4S2): A Candidate for Measuring the Parity Violating Energy Difference between Enantiomers of Chiral Molecules

The chiral C2 symmetric molecule 1,2-dithiine (1,2-dithia-3,5-hexadiene, C4H4S2) has been identified as a possible candidate for measuring the parity violating energy difference between enantiomers. We report here the observation and analysis of the low-frequency fundamental ν24 using highest resolution synchrotron-based interferometric Fourier transform infrared (FTIR) spectroscopy in the terahertz range with a band center of ν0 = 6.95375559 THz (ν0 = 231.952319 (10) cm–1) and two related hot bands, the (ν13 + ν24) ← ν13 band at ν0 = 6.97256882 THz (ν0 = 232.579861 (33) cm–1) and the 2ν24 ← ν24 band at ν0 = 7.01400434 THz (ν0 = 233.962001 (14) cm–1). This success in the difficult analyses of the THz spectrum of a complex chiral molecule of importance for fundamental tests on molecular parity violation is enabled by the ideal setup of an FTIR experiment of currently unique resolution with the very stable and bright synchrotron radiation at the Swiss Light Source (SLS).