A complete vibration-rotation analysis was made of the A 1 A 2 combination band ν 9 + ν 10 of CH 3CD 3 at 2582 cm −1. This band exhibits pseudoperpendicular structure due to the large effective Coriolis interaction constant (ζ ≈ 0.7), which couples the almost degenerate A 1 and A 2 vibrational components for all nonzero values of the rotational quantum number K, and gives a subband Q-branch spacing of 2.5 cm −1. The location of the band center is assisted through an interruption of the perpendicular-like structure, since both K = 0 Q branches are forbidden by the vibrational and rotational selection rules. The conventional A 1 parallel bands ν 3 + ν 4 at 2507 cm −1 and ν 5 (CC stretch) at 905 cm −1 were also analyzed. For ν 5, a combination of numerical analysis and band contour simulation was used to determine a set of upper-state rotation parameters. Combination of the present results with previous data for ν 9 and 2 ν 3 permits rotational parameters to be derived for the ν 4 and ν 10 fundamentals of CH 3CD 3. Neither of these fundamentals are amenable to straightforward analysis, both being very weak in the infrared and overlaid by the intense ν 11 fundamental.