The vibrational overtone band of monodeuterated methane (CH 3 D) in the region 5900-6100cm -1 was recorded by a high resolution Fourier transform spectrometer. Rotational analyses were performed separately for the parallel 2t 4 (A 1 ) and perpendicular 2t 4 (E) bands, whose origins were found to be 5980.41cm -1 and 6022.21cm -1 , respectively. The A 1 band displays J-resolved rotational structure while the K structure is resolved only at higher J values. A resonance Hamiltonian with the polyad

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... umber P = 2n 1 + 2n 4 + n 5 is derived using the fourth order Canonical Van Vleck Perturbation Theory (CVPT) to show that the 2t 4( A 1) and 2t 4 (E) are vibrationally perturbed by Fermi and Darling± Dennison resonances. The observation of rotational l-resonance in the 2t 4 (E) band is a consequence and evidence of the mixing of the vibrational states with di erent l values. Experimental details Our high resolution Fourier transform spectrum was recorded at room temperature on a Bruker IFS 120 HR Molecular Physics