Giant $K$ Doubling in the Infrared Spectrum of C${\mathrm{H}}_3$OH: A Sensitive Probe for C${\mathrm{H}}_3$-Rock/CO-Stretch/OH-Bend Vibrational Coupling

The asymmetry splittings of $K$-doublet levels in excited vibrational state of methyl alcohol are found to be sensitive indicators of intermode interactions. Fourier transform spectra reveal giant $K$ doubling of the ${\left(n\tau K\right)}^V={\mathrm{}\left(122\right)\mathrm{}}^r$ C${\mathrm{H}}_3$-rocking levels due to a near resonance with the CO stretch. Several spectral anomalies are thereby explained, and a significant far-infrared laser transition system is reassigned. The $K$-doublet splittings will provide a useful tool for the study of torsion-mediated mode coupling and intramolecular energy transfer channels in methanol.