Dark state illuminated: Infrared spectrum and inverted torsional structureof 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 funda mentals remaining en route to full vibrational description of this prototyp e 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 fou nd to be inverted, the first such discovery for a bending state and an impo rtant pointer to potential generality of this phenomenon for the whole clas s of threefold internal rotor molecules. Level-crossing resonances giving t ransfer channels for intramolecular vibrational energy redistribution (IVR) have been found, and new insights are reported for far-infrared laser emis sion involving nu(11) levels.