Sub-Doppler Infrared Spectra of the OH-Stretch Fundamental of 13C-Methanol

High-resolution infrared spectra of the ¹³C-methanol OH stretching band, ν₁, were obtained by slit-jet absorption spectroscopy at a rotational temperature of 12-15 K. Twenty-eight subbands were assigned within the range of upper state quantum numbers, K′ = 0 to 2 and J′ = 0 to 10. The upper state energy levels are heavily perturbed; about half of the assigned subbands were found to be split by perturbations with matrix elements in the range 1-3 cm^-1. The doubled lines were deperturbed and together with the "unperturbed" lines were fitted to a global torsion-rotation Hamiltonian with root-mean-square deviation of 0.41 cm^-1 to yield a torsional barrier height of ∼405 cm^-1 in the vibrationally excited state.