The microwave (MW) spectrum of forbidden Q-branch transitions of CH3D has been calculated for the first time. MW CH3D transitions of this type lie in the 3-4 cm-1 region, while the MW R-branch of CH3D, according to the HITRAN-2000 database, is spread above 7 cm-1. For the strongest MW CH3D transition (11, +1) - (11, -2) the absorption coefficient 0.0149 10-3 cm-1. These calculations of the forbidden CH3D spectrum show that it can be recorded by existing MW Stark modulation spectrometers or orotron spectrometers. The effective centrifugal distortion dipole moment model for molecules of trigonal symmetry is suggested on the basis of the limiting ordering scheme of an ultraspeed rotator. A possibility of construction of a Hamiltonian nonpolynomial model and the effective dipole moment based on the nonlinear transformation of a series with respect to rotational parameters is demonstrated.