The CC stretching band ν6 of allene-d4

The infrared spectrum of C₃D₄ was measured in the region of the paralled band of the CC stretching vibration ν₆ centered at ν₀ = 1920.2332 cm^?1 on a high-resolution Fourier transform spectrometer and deconvolved to a linewidth of $\text{～}\text{1}\text{2}$ of the Doppler width (～0.0023 cm^?1). The high resolution reveals the presence of strong perturbations in the K = 4 and K = 8 to 12 levels of the ν₆ upper state. For a quantitative treatment of the observed transitions, a Hamiltonian matrix including six different perturbing states was constructed and used to refine the 6 spectroscopic constants of the ν₆ state and 20 of the constants for the perturbing states. Measurement of the hot band ν₆ + ν₁₁ ? ν₁₁ whose band center is at 1916.200 cm^?1 yielded the anharmonic constant x_6,11 = ?4.033 cm^?1.