Vibration-rotation spectra of CD3CCH

Rotational structure in the perpendicular fundamentals ν₆, ν₇, and ν₈, and in the parallel component of 2ν₉ of CD₃CCH are fully analyzed at a resolution of 0.2–0.3 cm^?1. The A₁-E Coriolis resonances between ν₄ and ν₇, and ν₅ and ν₈ are analyzed by computer contour simulations. These permit accurate location of the parallel fundamentals, and determination of the associated Coriolis interaction constants. The fundamental vibrations ν₅ and ν₈ in CD₃CCH lie only 4 cm^?1 apart, and constitute the closest accidental Coriolis resonance yet studied by the simulation technique. The force field of methyl acetylene, constrained according to the hybrid orbital model, is calculated, using the recently determined molecular structure, and fitting all observed data, many of which have been revised in a number of recent studies.