The millimetre-wave rotational spectrum of phenylacetylene

The room-temperature rotational spectrum of phenylacetylene (C6H5CCH), was studied at frequencies up to 340 GHz. Extensive new measurements, covering rotational transitions with quantum number values up to J=140 and Ka=59, allowed determination of precise spectroscopic constants for the ground state and for the lowest two excited vibrational states, v24=1 and v36=1. The two excited states belong to the lowest B1 and B2 symmetry normal modes and their rotational transitions are very strongly perturbed by a-axis Coriolis resonance. A successful fit of the resonance is reported, resulting in ζ24,36a=0.8403(3) and ΔE=E36-E24=15.38994(2)cm-1, in good agreement with results of ab initio computations.