Synchrotron Far-Infrared Spectroscopy Of The Two Lowest Fundamental Modes Of 1,1-Difluoroethane

The far-infrared (FIR) spectrum (50-600cm(-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 18(0)(1) and 17(0)(1) 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 18(0)(1) and 17(0)(1) 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 18(1)(2) 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 (18) = 2. The 18(0)(2) overtone was observed with 586 transitions assigned and fitted to give a band centre of 431.952763 (23) cm(-1) for (18) = 2. The difference in energy is attributed to a torsional splitting of 0.003740 (45) cm(-1) in the (18) = 2 state. Two hot bands originating from the (18) = 1 and (17) = 1 states were observed within the 17(1) (0) fundamental.