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Although the torsional spectrum of the isotopic species of methanol with a symmetrical CH$3$ or CD$3$ methyl group has been studied in great details, almost no investigations have been carried out on partially deuterated species of methanol, like CH$2$DOH or CD$2$HOH, with an asymmetrical CH$2$D or CD$2$H methyl group. This stems from the fact that these partially deuterated species of methanol require a complicated theoretical treatment} {\bf 38,} 540 (1963).} in order to compute their rotation-torsion energy levels and that they display a dense far infrared torsional spectrum} (2002) and Mukhopadhyay, Perry, Lock, and Klee, 57th International Symposium on Molecular Spectroscopy, paper {\bf RH07} (2002).} difficult to assign. With a view toward understanding this spectrum, a theoretical calculation of the rotation-torsion energy levels of CH$2$DOH has been undertaken aided by {\em ab initio} calculations. This approach accounts for the complicated torsion-rotation interaction displayed by this molecule and for the fact that, due to the low symmetry of the CH$2$D methyl group, the inertia tensor is strongly dependent on the torsional angle of rotation. In the theoretical approach, this angle is treated as an active coordinate} {\bf 116,} 8560 (2002).} and matrix elements of the kinetic energy part of the Hamiltonian, involving the inertia tensor, are calculated using Gaussian quadrature.}i'c, {\em J.\ Chem.\ Phys.} {\bf 87,} 408 (1987).} Rotation-torsion energy levels are obtained using a potential energy function retrieved through {\em ab initio} calculations. In the paper, a calculated rotation-torsion spectrum will be presented and compared to the experimental one, recorded in Gie\ss en. It will be shown that this allows us to assign about 50 torsional bands.