Homogeneous and inhomogeneous structure in the vibrational overtone spectrum of tetramethyldioxetane

Vibrational overtone predissociation spectra of tetramethyldioxetane, obtained by monitoring the products of the vibrational overtone initiated unimolecular decomposition in both a room temperature sample and in a free jet, reveal the interactions that are likely to be responsible for the structure in the spectrum. The room temperature measurements provide spectra of the second, third, and fourth CH stretching overtone transitions (3νCH, 4νCH, and 5νCH ) and of combination bands in which a single quantum of methyl deformation is excited along with the stretching vibration. These spectra show the greatest complexity for the lowest energy transition (3νCH) and become simpler for higher levels of excitation. Two prominent maxima in the pure CH stretching overtone spectra come from hydrogen atoms in inequivalent environments in the molecule, but additional structure probably reflects a Fermi resonance between the stretching vibration and the methyl deformation.