The analysis of the complex rotational structures of the (2 \nu_{9}) parallel band and the (\nu_{8}) perpendicular band of (\mathrm{CH}{3} \mathrm{CCD}) is presented. All the levels of (2 \nu{9}\left(A_{1}\right)) and (\nu_{8}(E)) states are perturbed to varying degrees. A large number of off-diagonal perturbations connecting a quartet of interacting states, which include the (E) component of (2 \nu_{9}) and the (\left(A_{1}, A_{2}\right)) component of (\left(2 \nu_{10}+\nu_{9}\right)), account for the observed complex pattern. A few transitions of the type (\Delta K=+2) to the (2 \nu_{9}(E)) state and (\Delta K) (=0) to the (\left(2 \nu_{10}+\nu_{9}\right)\left(A_{1}, A_{2}\right)) state have also been identified. The major interactions are Fermi resonance between (2 \nu_{9}\left(A_{1}\right)) and the lower component of (\left(2 \nu_{10}+\nu_{9}\right)\left(A_{1}, A_{2}\right)). Fermi resonance between (2 \nu_{9}(E)) and (\nu_{8}(E), " \pm 2, \pm 2) " (\ell)-type resonance between (2 \nu_{9}\left(A_{1}\right)) and (2 \nu_{9}(E)), and (x y) Coriolis interaction between (2 \nu_{9}\left(A_{1}\right)) and (\nu_{8}(E)). Parameters of the four states and the interaction parameters have been determined. 1994 Academic Press, Inc.