High resolution spectroscopic study of CH₃D in the region 5900–6100 cm⁻¹

Abstract

The vibrational overtone band of monodeuterated methane (CH₃ in the region 5900–6100 cm⁻¹ was recorded by a high resolution Fourier transform spectrometer. Rotational analyses were performed separately for the parallel 2v ₄(A₁) and perpendicular 2v ₄(E) bands, whose origins were found to be 5980.41 cm⁻¹ and 6022.21 cm⁻¹, respectively. The A₁ band displays J-resolved rotational structure while the K structure is resolved only at higher J values. A resonance Hamiltonian with the polyad number P = 2n ₁ + 2n ₄ + n ₅ is derived using the fourth order Canonical Van Vleck Perturbation Theory (CVPT) to show that the 2v ₄(A₁ and 2v ₄(E) are vibrationally perturbed by Fermi and Darling—Dennison resonances. The observation of rotational l-resonance in the 2v ₄(E) band is a consequence and evidence of the mixing of the vibrational states with different l values.