Microwave spectrum of acetylene-d2

Eight P-branch transitions from the $\text{ν}{}_5{}^1\text{-ν}{}_4{}^1$ difference band of C₂D₂ have been observed in the microwave region. Significant improvements in the spectroscopic constants for the two states involved in the difference band have been obtained by combining infrared and microwave data. The Stark shifts for the observed C₂D₂ lines are discussed in some detail. The vibrational transition moment is found to be μ_vib = 0.0358 ± 0.0020 D.