Measurements with inelastic neutron scattering of the rotational spectra of the symmetric top molecule CH3D as substitutional impurities in crystalline argon and krypton are presented. The energy of the J = 1 doublet is shifted by 33% and 27% respectively, compared to the completely free rotor. Spin-rotational wave functions for the free CH3D rotor are constructed and used for the calculation of the dependence of the scattered intensities on momentum transfer In contrast to the CH4 molecule, the center of mass does not coincide with the position of the carbon atom in the case of the CH3D molecule. However, energies and intensities can only be explained if this fact is disregarded. The spin conversion behavior has been studied on a CH3D/argon sample within the temperature range 1.5 K less than or equal to T less than or equal to 5 K. Two different mechanisms for the conversion process (libron-phonon process and Raman process) are discussed.