We expect that several regions of the spectrum should be indicative of the structural motifs in each cluster. For instance, the region of 3550 -3700 cm -1 is highly diagnostic for free OH groups. The region between 1500 -2500 cm -1 typically includes CO stretches that are expected to be sensitive to the precise molecular structure of each cluster. the seven-membered ring (B) is the most consistent match to the experimentally observed spectrum. We conclude that structure B is the most likely structure and hypothesize that the minimum-energy structure is not likely to be found due to the presence of a tight transition state for five-membered ring closing, requiring coordinated motions of the hydrocarbon backbone. OH stretch around 3400 cm -1 , a likely CH stretch around 3000 cm -1 , a stretch near 2300 cm -1 in a range that would most likely correspond to CO motion, and a peak near 1500 cm -1 that is not straightforwardly identified. The computed harmonic vibrational spectrum of the lowest energy structure (A) found is in relatively good agreement with three of these peaks, capturing the major OH, CO, and COH stretches.