Synchrotron far-infrared spectroscopy of the two lowest fundamental modes of 1,1-difluoroethane

The far-infrared (FIR) spectrum (50–600 cm−1) of 1,1-difluoroethane was recorded using the high-resolution infrared AILES beamline at the Soleil synchrotron. A ro-vibrational assignment was performed on the lowest wavenumber, low intensity 181 0 and 171 0 modes, yielding band centres of 224.241903 (10) cm−1 and 384.252538 (13) cm−1, respectively. A total of 965 and 2031 FIR transitions were assigned to the 181 0 and 171 0 fundamentals, respectively. Previously measured pure rotational transitions from the upper states were included into the respective fits to yield improved rotational and centrifugal distortion constants. The 182 1 hot band was observed within the fundamental band, with 369 FIR transitions assigned and co-fitted with the fundamental to give a band centre of 431.956502 (39) cm−1 for ν 18 = 2. The 182 0 overtone was observed with 586 transitions assigned and fitted to give a band centre of 431.952763 (23) cm−1 for ν 18 = 2. The difference in energy is attributed to a torsional splitting of ...