Dark state illuminated: infrared spectrum and inverted torsional structure of the nu(11) out-of-plane CH3-rocking mode of methanol.

The nu(11) 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 nu(11) 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 nu(11) levels.