Dark State Illuminated: Infrared Spectrum and Inverted Torsional Structure of the ν₁₁ Out-of-Plane CH₃-Rocking Mode of Methanol

The ν₁₁ out-of-plane CH₃-rocking band of methanol, one of the last fundamentals remaining en route to full vibrational description of this prototype internal rotor, has been identified in the Fourier transform spectrum of CH₃OH in the 1150 cm^-1 region. The ν₁₁ torsional energy pattern is found to be inverted, the first such discovery for a bending state and an important pointer to potential generality of this phenomenon for the whole class of threefold internal rotor molecules. Level-crossing resonances giving transfer channels for intramolecular vibrational energy redistribution (IVR) have been found, and new insights are reported for far-infrared laser emission involving ν₁₁ levels.