Spectroscopy and dynamics of methanol: Fundamental and overtone spectra of the hydroxyl stretch in carbon-13 methanol

Rotationally resolved spectra of the OH stretch manifold at v₁ = 1, 4, and 5 in 13C-methanol are reported and compared with similar spectra of 12C-methanol. The spectra of both isotopomers in the 5ν₁ region have a strong vibrational splitting assigned to a resonance between 5ν₁ and 4ν₁ + ν ₂. Double-resonance spectra reveal the secondary structure of the first-order states resulting from this strong resonance. While the higher energy feature in the 12C-species is split by interactions with the remaining bath of dark states, the lower energy feature shows little fragmentation. The 13C-species, however, shows an equally complex pattern of couplings for both first-order states. The difference between the two isotopomers arises from the relative position of key background states. Despite a vibrational state density of 100 per cm−1, only a small number of states appear to determine the secondary structure.; In double-resonance spectra of the 4ν₁ band, the assigned A-symmetry transitions reached upper states with K = 0 and 1, and J from 0 to 5. For E-symmetry, the transitions reached levels with K in the range −3 to 2 and J from 1 to 7. The rotation torsional analysis resulted in the torsional tunneling splitting of 2.8 ± 0.4 cm−1 at v₁ = 4. This value is in quantitative agreement with the trend of monotonically decreasing tunneling splittings reported for 12CH₃OH and interpreted in terms of a linear increase in the torsional barrier height with OH stretch excitation (J. Chem. Phys. 110, 11359 (1999)).; High-resolution infrared spectra of the ν₁ band 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 of 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 at v₁ = 1.