TUNNELING SPLITTINGS IN THE ROTATIONAL SPECTRUM OF C2H3+

The splitting of some rotational lines due to a predicted hydrogen ato m migration in protonated acetylene, C2H3+, was not observed in the fi rst pure rotational spectroscopy experiment in the vibrational ground state. An improvement of the spectral resolution of the spectrometer h as allowed the observation of some of these small splittings. They hav e been interpreted within the semi-rigid bender model. Numerical resul ts are presented for different values of the barrier height. Reasonabl e agreement between observed and calculated splittings is obtained wit h a barrier of about 1600 cm(-1), which is 15% higher than the most re cent ab initio value.